diff --git a/.gitignore b/.gitignore
index 5d32289664..83cf1b7532 100644
--- a/.gitignore
+++ b/.gitignore
@@ -108,6 +108,10 @@
 /git-relink
 /git-remote
 /git-remote-curl
+/git-remote-http
+/git-remote-https
+/git-remote-ftp
+/git-remote-ftps
 /git-repack
 /git-replace
 /git-repo-config
@@ -158,6 +162,7 @@
 /test-delta
 /test-dump-cache-tree
 /test-genrandom
+/test-index-version
 /test-match-trees
 /test-parse-options
 /test-path-utils
diff --git a/Documentation/config.txt b/Documentation/config.txt
index 9f40955f8e..8acb613ec3 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -502,6 +502,10 @@ notes should be printed.
 This setting defaults to "refs/notes/commits", and can be overridden by
 the `GIT_NOTES_REF` environment variable.
 
+core.sparseCheckout::
+	Enable "sparse checkout" feature. See section "Sparse checkout" in
+	linkgit:git-read-tree[1] for more information.
+
 add.ignore-errors::
 	Tells 'git-add' to continue adding files when some files cannot be
 	added due to indexing errors. Equivalent to the '--ignore-errors'
diff --git a/Documentation/git-ls-files.txt b/Documentation/git-ls-files.txt
index 625723e41f..98f3b9e758 100644
--- a/Documentation/git-ls-files.txt
+++ b/Documentation/git-ls-files.txt
@@ -109,6 +109,7 @@ OPTIONS
 	Identify the file status with the following tags (followed by
 	a space) at the start of each line:
 	H::	cached
+	S::	skip-worktree
 	M::	unmerged
 	R::	removed/deleted
 	C::	modified/changed
diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index a10ce4ba40..d6faa14149 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 'git read-tree' [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>]
 		[-u [--exclude-per-directory=<gitignore>] | -i]]
-		[--index-output=<file>]
+		[--index-output=<file>] [--no-sparse-checkout]
 		<tree-ish1> [<tree-ish2> [<tree-ish3>]]
 
 
@@ -110,6 +110,10 @@ OPTIONS
 	directories the index file and index output file are
 	located in.
 
+--no-sparse-checkout::
+	Disable sparse checkout support even if `core.sparseCheckout`
+	is true.
+
 <tree-ish#>::
 	The id of the tree object(s) to be read/merged.
 
@@ -360,6 +364,52 @@ middle of doing, and when your working tree is ready (i.e. you
 have finished your work-in-progress), attempt the merge again.
 
 
+Sparse checkout
+---------------
+
+"Sparse checkout" allows to sparsely populate working directory.
+It uses skip-worktree bit (see linkgit:git-update-index[1]) to tell
+Git whether a file on working directory is worth looking at.
+
+"git read-tree" and other merge-based commands ("git merge", "git
+checkout"...) can help maintaining skip-worktree bitmap and working
+directory update. `$GIT_DIR/info/sparse-checkout` is used to
+define the skip-worktree reference bitmap. When "git read-tree" needs
+to update working directory, it will reset skip-worktree bit in index
+based on this file, which uses the same syntax as .gitignore files.
+If an entry matches a pattern in this file, skip-worktree will be
+set on that entry. Otherwise, skip-worktree will be unset.
+
+Then it compares the new skip-worktree value with the previous one. If
+skip-worktree turns from unset to set, it will add the corresponding
+file back. If it turns from set to unset, that file will be removed.
+
+While `$GIT_DIR/info/sparse-checkout` is usually used to specify what
+files are in. You can also specify what files are _not_ in, using
+negate patterns. For example, to remove file "unwanted":
+
+----------------
+*
+!unwanted
+----------------
+
+Another tricky thing is fully repopulating working directory when you
+no longer want sparse checkout. You cannot just disable "sparse
+checkout" because skip-worktree are still in the index and you working
+directory is still sparsely populated. You should re-populate working
+directory with the `$GIT_DIR/info/sparse-checkout` file content as
+follows:
+
+----------------
+*
+----------------
+
+Then you can disable sparse checkout. Sparse checkout support in "git
+read-tree" and similar commands is disabled by default. You need to
+turn `core.sparseCheckout` on in order to have sparse checkout
+support.
+
+
 SEE ALSO
 --------
 linkgit:git-write-tree[1]; linkgit:git-ls-files[1];
diff --git a/Documentation/git-remote-helpers.txt b/Documentation/git-remote-helpers.txt
index 5cfdc0cfc5..4685a898f1 100644
--- a/Documentation/git-remote-helpers.txt
+++ b/Documentation/git-remote-helpers.txt
@@ -25,7 +25,10 @@ Commands are given by the caller on the helper's standard input, one per line.
 
 'capabilities'::
 	Lists the capabilities of the helper, one per line, ending
-	with a blank line.
+	with a blank line. Each capability may be preceeded with '*'.
+	This marks them mandatory for git version using the remote
+	helper to understand (unknown mandatory capability is fatal
+	error).
 
 'list'::
 	Lists the refs, one per line, in the format "<value> <name>
@@ -90,6 +93,20 @@ Supported if the helper has the "push" capability.
 +
 Supported if the helper has the "import" capability.
 
+'connect' <service>::
+	Connects to given service. Standard input and standard output
+	of helper are connected to specified service (git prefix is
+	included in service name so e.g. fetching uses 'git-upload-pack'
+	as service) on remote side. Valid replies to this command are
+	empty line (connection established), 'fallback' (no smart
+	transport support, fall back to dumb transports) and just
+	exiting with error message printed (can't connect, don't
+	bother trying to fall back). After line feed terminating the
+	positive (empty) response, the output of service starts. After
+	the connection ends, the remote helper exits.
++
+Supported if the helper has the "connect" capability.
+
 If a fatal error occurs, the program writes the error message to
 stderr and exits. The caller should expect that a suitable error
 message has been printed if the child closes the connection without
@@ -123,6 +140,9 @@ CAPABILITIES
 	all, it must cover all refs reported by the list command; if
 	it is not used, it is effectively "*:*"
 
+'connect'::
+	This helper supports the 'connect' command.
+
 REF LIST ATTRIBUTES
 -------------------
 
@@ -165,9 +185,15 @@ OPTIONS
 	but don't actually change any repository data.	For most
 	helpers this only applies to the 'push', if supported.
 
+'option servpath <c-style-quoted-path>'::
+	Set service path (--upload-pack, --receive-pack etc.) for
+	next connect. Remote helper MAY support this option. Remote
+	helper MUST NOT rely on this option being set before
+	connect request occurs.
+
 Documentation
 -------------
-Documentation by Daniel Barkalow.
+Documentation by Daniel Barkalow and Ilari Liusvaara
 
 GIT
 ---
diff --git a/Documentation/git-reset.txt b/Documentation/git-reset.txt
index 9df6de2e7d..c7aa444317 100644
--- a/Documentation/git-reset.txt
+++ b/Documentation/git-reset.txt
@@ -68,6 +68,95 @@ linkgit:git-add[1]).
 <commit>::
 	Commit to make the current HEAD. If not given defaults to HEAD.
 
+DISCUSSION
+----------
+
+The tables below show what happens when running:
+
+----------
+git reset --option target
+----------
+
+to reset the HEAD to another commit (`target`) with the different
+reset options depending on the state of the files.
+
+In these tables, A, B, C and D are some different states of a
+file. For example, the first line of the first table means that if a
+file is in state A in the working tree, in state B in the index, in
+state C in HEAD and in state D in the target, then "git reset --soft
+target" will put the file in state A in the working tree, in state B
+in the index and in state D in HEAD.
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       A       B     C    D     --soft   A       B     D
+				--mixed  A       D     D
+				--hard   D       D     D
+				--merge (disallowed)
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       A       B     C    C     --soft   A       B     C
+				--mixed  A       C     C
+				--hard   C       C     C
+				--merge (disallowed)
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       B       B     C    D     --soft   B       B     D
+				--mixed  B       D     D
+				--hard   D       D     D
+				--merge  D       D     D
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       B       B     C    C     --soft   B       B     C
+				--mixed  B       C     C
+				--hard   C       C     C
+				--merge  C       C     C
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       B       C     C    D     --soft   B       C     D
+				--mixed  B       D     D
+				--hard   D       D     D
+				--merge (disallowed)
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       B       C     C    C     --soft   B       C     C
+				--mixed  B       C     C
+				--hard   C       C     C
+				--merge  B       C     C
+
+"reset --merge" is meant to be used when resetting out of a conflicted
+merge. Any mergy operation guarantees that the work tree file that is
+involved in the merge does not have local change wrt the index before
+it starts, and that it writes the result out to the work tree. So if
+we see some difference between the index and the target and also
+between the index and the work tree, then it means that we are not
+resetting out from a state that a mergy operation left after failing
+with a conflict. That is why we disallow --merge option in this case.
+
+The following tables show what happens when there are unmerged
+entries:
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       X       U     A    B     --soft  (disallowed)
+				--mixed  X       B     B
+				--hard   B       B     B
+				--merge  B       B     B
+
+      working index HEAD target         working index HEAD
+      ----------------------------------------------------
+       X       U     A    A     --soft  (disallowed)
+				--mixed  X       A     A
+				--hard   A       A     A
+				--merge  A       A     A
+
+X means any state and U means an unmerged index.
+
 Examples
 --------
 
diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index 6052484ab9..8d88018eed 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -15,6 +15,7 @@ SYNOPSIS
 	     [--cacheinfo <mode> <object> <file>]\*
 	     [--chmod=(+|-)x]
 	     [--assume-unchanged | --no-assume-unchanged]
+	     [--skip-worktree | --no-skip-worktree]
 	     [--ignore-submodules]
 	     [--really-refresh] [--unresolve] [--again | -g]
 	     [--info-only] [--index-info]
@@ -103,6 +104,13 @@ you will need to handle the situation manually.
 	Like '--refresh', but checks stat information unconditionally,
 	without regard to the "assume unchanged" setting.
 
+--skip-worktree::
+--no-skip-worktree::
+	When one of these flags is specified, the object name recorded
+	for the paths are not updated. Instead, these options
+	set and unset the "skip-worktree" bit for the paths. See
+	section "Skip-worktree bit" below for more information.
+
 -g::
 --again::
 	Runs 'git-update-index' itself on the paths whose index
@@ -308,6 +316,27 @@ M foo.c
 <9> now it checks with lstat(2) and finds it has been changed.
 
 
+Skip-worktree bit
+-----------------
+
+Skip-worktree bit can be defined in one (long) sentence: When reading
+an entry, if it is marked as skip-worktree, then Git pretends its
+working directory version is up to date and read the index version
+instead.
+
+To elaborate, "reading" means checking for file existence, reading
+file attributes or file content. The working directory version may be
+present or absent. If present, its content may match against the index
+version or not. Writing is not affected by this bit, content safety
+is still first priority. Note that Git _can_ update working directory
+file, that is marked skip-worktree, if it is safe to do so (i.e.
+working directory version matches index version)
+
+Although this bit looks similar to assume-unchanged bit, its goal is
+different from assume-unchanged bit's. Skip-worktree also takes
+precedence over assume-unchanged bit when both are set.
+
+
 Configuration
 -------------
 
diff --git a/Documentation/technical/api-directory-listing.txt b/Documentation/technical/api-directory-listing.txt
index 5bbd18f020..add6f435b5 100644
--- a/Documentation/technical/api-directory-listing.txt
+++ b/Documentation/technical/api-directory-listing.txt
@@ -58,6 +58,9 @@ The result of the enumeration is left in these fields::
 Calling sequence
 ----------------
 
+Note: index may be looked at for .gitignore files that are CE_SKIP_WORKTREE
+marked. If you to exclude files, make sure you have loaded index first.
+
 * Prepare `struct dir_struct dir` and clear it with `memset(&dir, 0,
   sizeof(dir))`.
 
diff --git a/Makefile b/Makefile
index be18389534..57045dee89 100644
--- a/Makefile
+++ b/Makefile
@@ -424,6 +424,16 @@ BUILT_INS += git-stage$X
 BUILT_INS += git-status$X
 BUILT_INS += git-whatchanged$X
 
+ifdef NO_CURL
+REMOTE_CURL_PRIMARY =
+REMOTE_CURL_ALIASES =
+REMOTE_CURL_NAMES =
+else
+REMOTE_CURL_PRIMARY = git-remote-http$X
+REMOTE_CURL_ALIASES = git-remote-https$X git-remote-ftp$X git-remote-ftps$X
+REMOTE_CURL_NAMES = $(REMOTE_CURL_PRIMARY) $(REMOTE_CURL_ALIASES)
+endif
+
 # what 'all' will build and 'install' will install in gitexecdir,
 # excluding programs for built-in commands
 ALL_PROGRAMS = $(PROGRAMS) $(SCRIPTS)
@@ -1107,7 +1117,7 @@ else
 	else
 		CURL_LIBCURL = -lcurl
 	endif
-	PROGRAMS += git-remote-curl$X git-http-fetch$X
+	PROGRAMS += $(REMOTE_CURL_NAMES) git-http-fetch$X
 	curl_check := $(shell (echo 070908; curl-config --vernum) | sort -r | sed -ne 2p)
 	ifeq "$(curl_check)" "070908"
 		ifndef NO_EXPAT
@@ -1686,7 +1696,13 @@ git-http-push$X: revision.o http.o http-push.o $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
 		$(LIBS) $(CURL_LIBCURL) $(EXPAT_LIBEXPAT)
 
-git-remote-curl$X: remote-curl.o http.o http-walker.o $(GITLIBS)
+$(REMOTE_CURL_ALIASES): $(REMOTE_CURL_PRIMARY)
+	$(QUIET_LNCP)$(RM) $@ && \
+	ln $< $@ 2>/dev/null || \
+	ln -s $< $@ 2>/dev/null || \
+	cp $< $@
+
+$(REMOTE_CURL_PRIMARY): remote-curl.o http.o http-walker.o $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
 		$(LIBS) $(CURL_LIBCURL) $(EXPAT_LIBEXPAT)
 
@@ -1782,6 +1798,7 @@ TEST_PROGRAMS_NEED_X += test-parse-options
 TEST_PROGRAMS_NEED_X += test-path-utils
 TEST_PROGRAMS_NEED_X += test-sha1
 TEST_PROGRAMS_NEED_X += test-sigchain
+TEST_PROGRAMS_NEED_X += test-index-version
 
 TEST_PROGRAMS = $(patsubst %,%$X,$(TEST_PROGRAMS_NEED_X))
 
@@ -1876,6 +1893,7 @@ endif
 ifneq (,$X)
 	$(foreach p,$(patsubst %$X,%,$(filter %$X,$(ALL_PROGRAMS) $(BUILT_INS) git$X)), test '$(DESTDIR_SQ)$(gitexec_instdir_SQ)/$p' -ef '$(DESTDIR_SQ)$(gitexec_instdir_SQ)/$p$X' || $(RM) '$(DESTDIR_SQ)$(gitexec_instdir_SQ)/$p';)
 endif
+
 	bindir=$$(cd '$(DESTDIR_SQ)$(bindir_SQ)' && pwd) && \
 	execdir=$$(cd '$(DESTDIR_SQ)$(gitexec_instdir_SQ)' && pwd) && \
 	{ test "$$bindir/" = "$$execdir/" || \
@@ -1889,6 +1907,12 @@ endif
 		ln -s "git$X" "$$execdir/$$p" 2>/dev/null || \
 		cp "$$execdir/git$X" "$$execdir/$$p" || exit; \
 	  done; } && \
+	{ for p in $(REMOTE_CURL_ALIASES); do \
+		$(RM) "$$execdir/$$p" && \
+		ln "$$execdir/git-remote-http$X" "$$execdir/$$p" 2>/dev/null || \
+		ln -s "git-remote-http$X" "$$execdir/$$p" 2>/dev/null || \
+		cp "$$execdir/git-remote-http$X" "$$execdir/$$p" || exit; \
+	  done; } && \
 	./check_bindir "z$$bindir" "z$$execdir" "$$bindir/git-add$X"
 
 install-doc:
diff --git a/archive.c b/archive.c
index 55b273246e..5b88507374 100644
--- a/archive.c
+++ b/archive.c
@@ -211,10 +211,33 @@ static const struct archiver *lookup_archiver(const char *name)
 	return NULL;
 }
 
+static int reject_entry(const unsigned char *sha1, const char *base,
+			int baselen, const char *filename, unsigned mode,
+			int stage, void *context)
+{
+	return -1;
+}
+
+static int path_exists(struct tree *tree, const char *path)
+{
+	const char *pathspec[] = { path, NULL };
+
+	if (read_tree_recursive(tree, "", 0, 0, pathspec, reject_entry, NULL))
+		return 1;
+	return 0;
+}
+
 static void parse_pathspec_arg(const char **pathspec,
 		struct archiver_args *ar_args)
 {
-	ar_args->pathspec = get_pathspec("", pathspec);
+	ar_args->pathspec = pathspec = get_pathspec("", pathspec);
+	if (pathspec) {
+		while (*pathspec) {
+			if (!path_exists(ar_args->tree, *pathspec))
+				die("path not found: %s", *pathspec);
+			pathspec++;
+		}
+	}
 }
 
 static void parse_treeish_arg(const char **argv,
diff --git a/builtin-apply.c b/builtin-apply.c
index 36e2f9dda5..541493e1ba 100644
--- a/builtin-apply.c
+++ b/builtin-apply.c
@@ -2666,7 +2666,7 @@ static int verify_index_match(struct cache_entry *ce, struct stat *st)
 			return -1;
 		return 0;
 	}
-	return ce_match_stat(ce, st, CE_MATCH_IGNORE_VALID);
+	return ce_match_stat(ce, st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
 }
 
 static int check_preimage(struct patch *patch, struct cache_entry **ce, struct stat *st)
diff --git a/builtin-archive.c b/builtin-archive.c
index 446d6bff30..3fb41364a5 100644
--- a/builtin-archive.c
+++ b/builtin-archive.c
@@ -5,6 +5,7 @@
 #include "cache.h"
 #include "builtin.h"
 #include "archive.h"
+#include "transport.h"
 #include "parse-options.h"
 #include "pkt-line.h"
 #include "sideband.h"
@@ -25,12 +26,16 @@ static void create_output_file(const char *output_file)
 static int run_remote_archiver(int argc, const char **argv,
 			       const char *remote, const char *exec)
 {
-	char *url, buf[LARGE_PACKET_MAX];
+	char buf[LARGE_PACKET_MAX];
 	int fd[2], i, len, rv;
-	struct child_process *conn;
+	struct transport *transport;
+	struct remote *_remote;
 
-	url = xstrdup(remote);
-	conn = git_connect(fd, url, exec, 0);
+	_remote = remote_get(remote);
+	if (!_remote->url[0])
+		die("git archive: Remote with no URL");
+	transport = transport_get(_remote, _remote->url[0]);
+	transport_connect(transport, "git-upload-archive", exec, fd);
 
 	for (i = 1; i < argc; i++)
 		packet_write(fd[1], "argument %s\n", argv[i]);
@@ -53,9 +58,7 @@ static int run_remote_archiver(int argc, const char **argv,
 
 	/* Now, start reading from fd[0] and spit it out to stdout */
 	rv = recv_sideband("archive", fd[0], 1);
-	close(fd[0]);
-	close(fd[1]);
-	rv |= finish_connect(conn);
+	rv |= transport_disconnect(transport);
 
 	return !!rv;
 }
diff --git a/builtin-checkout.c b/builtin-checkout.c
index 2708669383..793542eb06 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -696,7 +696,10 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	 * case 3: git checkout <something> [<paths>]
 	 *
 	 *   With no paths, if <something> is a commit, that is to
-	 *   switch to the branch or detach HEAD at it.
+	 *   switch to the branch or detach HEAD at it.  As a special case,
+	 *   if <something> is A...B (missing A or B means HEAD but you can
+	 *   omit at most one side), and if there is a unique merge base
+	 *   between A and B, A...B names that merge base.
 	 *
 	 *   With no paths, if <something> is _not_ a commit, no -t nor -b
 	 *   was given, and there is a tracking branch whose name is
@@ -722,7 +725,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		if (!strcmp(arg, "-"))
 			arg = "@{-1}";
 
-		if (get_sha1(arg, rev)) {
+		if (get_sha1_mb(arg, rev)) {
 			if (has_dash_dash)          /* case (1) */
 				die("invalid reference: %s", arg);
 			if (!patch_mode &&
diff --git a/builtin-clean.c b/builtin-clean.c
index 28cdcd0274..3a70fa81bd 100644
--- a/builtin-clean.c
+++ b/builtin-clean.c
@@ -75,11 +75,13 @@ int cmd_clean(int argc, const char **argv, const char *prefix)
 
 	dir.flags |= DIR_SHOW_OTHER_DIRECTORIES;
 
+	if (read_cache() < 0)
+		die("index file corrupt");
+
 	if (!ignored)
 		setup_standard_excludes(&dir);
 
 	pathspec = get_pathspec(prefix, argv);
-	read_cache();
 
 	fill_directory(&dir, pathspec);
 
diff --git a/builtin-commit.c b/builtin-commit.c
index 073fe90ba1..592b10396d 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -183,11 +183,15 @@ static int list_paths(struct string_list *list, const char *with_tree,
 
 	for (i = 0; i < active_nr; i++) {
 		struct cache_entry *ce = active_cache[i];
+		struct string_list_item *item;
+
 		if (ce->ce_flags & CE_UPDATE)
 			continue;
 		if (!match_pathspec(pattern, ce->name, ce_namelen(ce), 0, m))
 			continue;
-		string_list_insert(ce->name, list);
+		item = string_list_insert(ce->name, list);
+		if (ce_skip_worktree(ce))
+			item->util = item; /* better a valid pointer than a fake one */
 	}
 
 	return report_path_error(m, pattern, prefix ? strlen(prefix) : 0);
@@ -200,6 +204,10 @@ static void add_remove_files(struct string_list *list)
 		struct stat st;
 		struct string_list_item *p = &(list->items[i]);
 
+		/* p->util is skip-worktree */
+		if (p->util)
+			continue;
+
 		if (!lstat(p->string, &st)) {
 			if (add_to_cache(p->string, &st, 0))
 				die("updating files failed");
diff --git a/builtin-grep.c b/builtin-grep.c
index a5b6719a1a..529461fb8f 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -191,8 +191,6 @@ static int grep_file(struct grep_opt *opt, const char *filename)
 			error("'%s': %s", filename, strerror(errno));
 		return 0;
 	}
-	if (!st.st_size)
-		return 0; /* empty file -- no grep hit */
 	if (!S_ISREG(st.st_mode))
 		return 0;
 	sz = xsize_t(st.st_size);
@@ -222,6 +220,7 @@ static int exec_grep(int argc, const char **argv)
 	int status;
 
 	argv[argc] = NULL;
+	trace_argv_printf(argv, "trace: grep:");
 	pid = fork();
 	if (pid < 0)
 		return pid;
@@ -347,6 +346,21 @@ static void grep_add_color(struct strbuf *sb, const char *escape_seq)
 		strbuf_setlen(sb, sb->len - 1);
 }
 
+static int has_skip_worktree_entry(struct grep_opt *opt, const char **paths)
+{
+	int nr;
+	for (nr = 0; nr < active_nr; nr++) {
+		struct cache_entry *ce = active_cache[nr];
+		if (!S_ISREG(ce->ce_mode))
+			continue;
+		if (!pathspec_matches(paths, ce->name, opt->max_depth))
+			continue;
+		if (ce_skip_worktree(ce))
+			return 1;
+	}
+	return 0;
+}
+
 static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 {
 	int i, nr, argc, hit, len, status;
@@ -355,7 +369,8 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 	char *argptr = randarg;
 	struct grep_pat *p;
 
-	if (opt->extended || (opt->relative && opt->prefix_length))
+	if (opt->extended || (opt->relative && opt->prefix_length)
+	    || has_skip_worktree_entry(opt, paths))
 		return -1;
 	len = nr = 0;
 	push_arg("grep");
@@ -512,7 +527,7 @@ static int grep_cache(struct grep_opt *opt, const char **paths, int cached,
 		 * are identical, even if worktree file has been modified, so use
 		 * cache version instead
 		 */
-		if (cached || (ce->ce_flags & CE_VALID)) {
+		if (cached || (ce->ce_flags & CE_VALID) || ce_skip_worktree(ce)) {
 			if (ce_stage(ce))
 				continue;
 			hit |= grep_sha1(opt, ce->sha1, ce->name, 0);
diff --git a/builtin-ls-files.c b/builtin-ls-files.c
index c9a03e5427..738215768e 100644
--- a/builtin-ls-files.c
+++ b/builtin-ls-files.c
@@ -37,6 +37,7 @@ static const char *tag_removed = "";
 static const char *tag_other = "";
 static const char *tag_killed = "";
 static const char *tag_modified = "";
+static const char *tag_skip_worktree = "";
 
 static void show_dir_entry(const char *tag, struct dir_entry *ent)
 {
@@ -178,7 +179,8 @@ static void show_files(struct dir_struct *dir, const char *prefix)
 				continue;
 			if (ce->ce_flags & CE_UPDATE)
 				continue;
-			show_ce_entry(ce_stage(ce) ? tag_unmerged : tag_cached, ce);
+			show_ce_entry(ce_stage(ce) ? tag_unmerged :
+				(ce_skip_worktree(ce) ? tag_skip_worktree : tag_cached), ce);
 		}
 	}
 	if (show_deleted | show_modified) {
@@ -192,6 +194,8 @@ static void show_files(struct dir_struct *dir, const char *prefix)
 				continue;
 			if (ce->ce_flags & CE_UPDATE)
 				continue;
+			if (ce_skip_worktree(ce))
+				continue;
 			err = lstat(ce->name, &st);
 			if (show_deleted && err)
 				show_ce_entry(tag_removed, ce);
@@ -481,6 +485,9 @@ int cmd_ls_files(int argc, const char **argv, const char *prefix)
 		prefix_offset = strlen(prefix);
 	git_config(git_default_config, NULL);
 
+	if (read_cache() < 0)
+		die("index file corrupt");
+
 	argc = parse_options(argc, argv, prefix, builtin_ls_files_options,
 			ls_files_usage, 0);
 	if (show_tag || show_valid_bit) {
@@ -490,6 +497,7 @@ int cmd_ls_files(int argc, const char **argv, const char *prefix)
 		tag_modified = "C ";
 		tag_other = "? ";
 		tag_killed = "K ";
+		tag_skip_worktree = "S ";
 	}
 	if (show_modified || show_others || show_deleted || (dir.flags & DIR_SHOW_IGNORED) || show_killed)
 		require_work_tree = 1;
@@ -508,7 +516,6 @@ int cmd_ls_files(int argc, const char **argv, const char *prefix)
 	pathspec = get_pathspec(prefix, argv);
 
 	/* be nice with submodule paths ending in a slash */
-	read_cache();
 	if (pathspec)
 		strip_trailing_slash_from_submodules();
 
diff --git a/builtin-push.c b/builtin-push.c
index f7661d245e..28a26e7db2 100644
--- a/builtin-push.c
+++ b/builtin-push.c
@@ -125,8 +125,8 @@ static int push_with_options(struct transport *transport, int flags)
 
 	if (nonfastforward && advice_push_nonfastforward) {
 		printf("To prevent you from losing history, non-fast-forward updates were rejected\n"
-		       "Merge the remote changes before pushing again.  See the 'non-fast-forward'\n"
-		       "section of 'git push --help' for details.\n");
+		       "Merge the remote changes before pushing again.  See the 'Note about\n"
+		       "fast-forwards' section of 'git push --help' for details.\n");
 	}
 
 	return 1;
diff --git a/builtin-read-tree.c b/builtin-read-tree.c
index 2a3a32cbfe..50413ca17d 100644
--- a/builtin-read-tree.c
+++ b/builtin-read-tree.c
@@ -31,7 +31,7 @@ static int list_tree(unsigned char *sha1)
 }
 
 static const char * const read_tree_usage[] = {
-	"git read-tree [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] [-u [--exclude-per-directory=<gitignore>] | -i]]  [--index-output=<file>] <tree-ish1> [<tree-ish2> [<tree-ish3>]]",
+	"git read-tree [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] [-u [--exclude-per-directory=<gitignore>] | -i]] [--no-sparse-checkout] [--index-output=<file>] <tree-ish1> [<tree-ish2> [<tree-ish3>]]",
 	NULL
 };
 
@@ -98,6 +98,8 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 		  PARSE_OPT_NONEG, exclude_per_directory_cb },
 		OPT_SET_INT('i', NULL, &opts.index_only,
 			    "don't check the working tree after merging", 1),
+		OPT_SET_INT(0, "no-sparse-checkout", &opts.skip_sparse_checkout,
+			    "skip applying sparse checkout filter", 1),
 		OPT_END()
 	};
 
diff --git a/builtin-reset.c b/builtin-reset.c
index 5b647422d6..0f5022eed2 100644
--- a/builtin-reset.c
+++ b/builtin-reset.c
@@ -18,6 +18,8 @@
 #include "tree.h"
 #include "branch.h"
 #include "parse-options.h"
+#include "unpack-trees.h"
+#include "cache-tree.h"
 
 static const char * const git_reset_usage[] = {
 	"git reset [--mixed | --soft | --hard | --merge] [-q] [<commit>]",
@@ -54,27 +56,44 @@ static inline int is_merge(void)
 
 static int reset_index_file(const unsigned char *sha1, int reset_type, int quiet)
 {
-	int i = 0;
-	const char *args[6];
+	int nr = 1;
+	int newfd;
+	struct tree_desc desc[2];
+	struct unpack_trees_options opts;
+	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
 
-	args[i++] = "read-tree";
+	memset(&opts, 0, sizeof(opts));
+	opts.head_idx = 1;
+	opts.src_index = &the_index;
+	opts.dst_index = &the_index;
+	opts.fn = oneway_merge;
+	opts.merge = 1;
 	if (!quiet)
-		args[i++] = "-v";
+		opts.verbose_update = 1;
 	switch (reset_type) {
 	case MERGE:
-		args[i++] = "-u";
-		args[i++] = "-m";
+		opts.update = 1;
 		break;
 	case HARD:
-		args[i++] = "-u";
+		opts.update = 1;
 		/* fallthrough */
 	default:
-		args[i++] = "--reset";
+		opts.reset = 1;
 	}
-	args[i++] = sha1_to_hex(sha1);
-	args[i] = NULL;
 
-	return run_command_v_opt(args, RUN_GIT_CMD);
+	newfd = hold_locked_index(lock, 1);
+
+	read_cache_unmerged();
+
+	if (!fill_tree_descriptor(desc + nr - 1, sha1))
+		return error("Failed to find tree of %s.", sha1_to_hex(sha1));
+	if (unpack_trees(nr, desc, &opts))
+		return -1;
+	if (write_cache(newfd, active_cache, active_nr) ||
+	    commit_locked_index(lock))
+		return error("Could not write new index file.");
+
+	return 0;
 }
 
 static void print_new_head_line(struct commit *commit)
@@ -288,6 +307,10 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 	if (reset_type == HARD || reset_type == MERGE)
 		setup_work_tree();
 
+	if (reset_type == MIXED && is_bare_repository())
+		die("%s reset is not allowed in a bare repository",
+		    reset_type_names[reset_type]);
+
 	/* Soft reset does not touch the index file nor the working tree
 	 * at all, but requires them in a good order.  Other resets reset
 	 * the index file to the tree object we are switching to. */
diff --git a/builtin-update-index.c b/builtin-update-index.c
index a6b7f2d636..a64a752990 100644
--- a/builtin-update-index.c
+++ b/builtin-update-index.c
@@ -24,8 +24,9 @@ static int info_only;
 static int force_remove;
 static int verbose;
 static int mark_valid_only;
-#define MARK_VALID 1
-#define UNMARK_VALID 2
+static int mark_skip_worktree_only;
+#define MARK_FLAG 1
+#define UNMARK_FLAG 2
 
 __attribute__((format (printf, 1, 2)))
 static void report(const char *fmt, ...)
@@ -41,19 +42,15 @@ static void report(const char *fmt, ...)
 	va_end(vp);
 }
 
-static int mark_valid(const char *path)
+static int mark_ce_flags(const char *path, int flag, int mark)
 {
 	int namelen = strlen(path);
 	int pos = cache_name_pos(path, namelen);
 	if (0 <= pos) {
-		switch (mark_valid_only) {
-		case MARK_VALID:
-			active_cache[pos]->ce_flags |= CE_VALID;
-			break;
-		case UNMARK_VALID:
-			active_cache[pos]->ce_flags &= ~CE_VALID;
-			break;
-		}
+		if (mark)
+			active_cache[pos]->ce_flags |= flag;
+		else
+			active_cache[pos]->ce_flags &= ~flag;
 		cache_tree_invalidate_path(active_cache_tree, path);
 		active_cache_changed = 1;
 		return 0;
@@ -176,29 +173,29 @@ static int process_directory(const char *path, int len, struct stat *st)
 	return error("%s: is a directory - add files inside instead", path);
 }
 
-/*
- * Process a regular file
- */
-static int process_file(const char *path, int len, struct stat *st)
-{
-	int pos = cache_name_pos(path, len);
-	struct cache_entry *ce = pos < 0 ? NULL : active_cache[pos];
-
-	if (ce && S_ISGITLINK(ce->ce_mode))
-		return error("%s is already a gitlink, not replacing", path);
-
-	return add_one_path(ce, path, len, st);
-}
-
 static int process_path(const char *path)
 {
-	int len;
+	int pos, len;
 	struct stat st;
+	struct cache_entry *ce;
 
 	len = strlen(path);
 	if (has_symlink_leading_path(path, len))
 		return error("'%s' is beyond a symbolic link", path);
 
+	pos = cache_name_pos(path, len);
+	ce = pos < 0 ? NULL : active_cache[pos];
+	if (ce && ce_skip_worktree(ce)) {
+		/*
+		 * working directory version is assumed "good"
+		 * so updating it does not make sense.
+		 * On the other hand, removing it from index should work
+		 */
+		if (allow_remove && remove_file_from_cache(path))
+			return error("%s: cannot remove from the index", path);
+		return 0;
+	}
+
 	/*
 	 * First things first: get the stat information, to decide
 	 * what to do about the pathname!
@@ -209,7 +206,13 @@ static int process_path(const char *path)
 	if (S_ISDIR(st.st_mode))
 		return process_directory(path, len, &st);
 
-	return process_file(path, len, &st);
+	/*
+	 * Process a regular file
+	 */
+	if (ce && S_ISGITLINK(ce->ce_mode))
+		return error("%s is already a gitlink, not replacing", path);
+
+	return add_one_path(ce, path, len, &st);
 }
 
 static int add_cacheinfo(unsigned int mode, const unsigned char *sha1,
@@ -277,7 +280,12 @@ static void update_one(const char *path, const char *prefix, int prefix_length)
 		goto free_return;
 	}
 	if (mark_valid_only) {
-		if (mark_valid(p))
+		if (mark_ce_flags(p, CE_VALID, mark_valid_only == MARK_FLAG))
+			die("Unable to mark file %s", path);
+		goto free_return;
+	}
+	if (mark_skip_worktree_only) {
+		if (mark_ce_flags(p, CE_SKIP_WORKTREE, mark_skip_worktree_only == MARK_FLAG))
 			die("Unable to mark file %s", path);
 		goto free_return;
 	}
@@ -389,7 +397,7 @@ static void read_index_info(int line_termination)
 }
 
 static const char update_index_usage[] =
-"git update-index [-q] [--add] [--replace] [--remove] [--unmerged] [--refresh] [--really-refresh] [--cacheinfo] [--chmod=(+|-)x] [--assume-unchanged] [--info-only] [--force-remove] [--stdin] [--index-info] [--unresolve] [--again | -g] [--ignore-missing] [-z] [--verbose] [--] <file>...";
+"git update-index [-q] [--add] [--replace] [--remove] [--unmerged] [--refresh] [--really-refresh] [--cacheinfo] [--chmod=(+|-)x] [--assume-unchanged] [--skip-worktree|--no-skip-worktree] [--info-only] [--force-remove] [--stdin] [--index-info] [--unresolve] [--again | -g] [--ignore-missing] [-z] [--verbose] [--] <file>...";
 
 static unsigned char head_sha1[20];
 static unsigned char merge_head_sha1[20];
@@ -648,11 +656,19 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 				continue;
 			}
 			if (!strcmp(path, "--assume-unchanged")) {
-				mark_valid_only = MARK_VALID;
+				mark_valid_only = MARK_FLAG;
 				continue;
 			}
 			if (!strcmp(path, "--no-assume-unchanged")) {
-				mark_valid_only = UNMARK_VALID;
+				mark_valid_only = UNMARK_FLAG;
+				continue;
+			}
+			if (!strcmp(path, "--no-skip-worktree")) {
+				mark_skip_worktree_only = UNMARK_FLAG;
+				continue;
+			}
+			if (!strcmp(path, "--skip-worktree")) {
+				mark_skip_worktree_only = MARK_FLAG;
 				continue;
 			}
 			if (!strcmp(path, "--info-only")) {
diff --git a/cache.h b/cache.h
index 3f9ee86147..cf36c8160e 100644
--- a/cache.h
+++ b/cache.h
@@ -177,15 +177,20 @@ struct cache_entry {
 
 #define CE_HASHED    (0x100000)
 #define CE_UNHASHED  (0x200000)
+#define CE_CONFLICTED (0x800000)
+
+/* Only remove in work directory, not index */
+#define CE_WT_REMOVE (0x400000)
 
 /*
  * Extended on-disk flags
  */
 #define CE_INTENT_TO_ADD 0x20000000
+#define CE_SKIP_WORKTREE 0x40000000
 /* CE_EXTENDED2 is for future extension */
 #define CE_EXTENDED2 0x80000000
 
-#define CE_EXTENDED_FLAGS (CE_INTENT_TO_ADD)
+#define CE_EXTENDED_FLAGS (CE_INTENT_TO_ADD | CE_SKIP_WORKTREE)
 
 /*
  * Safeguard to avoid saving wrong flags:
@@ -234,6 +239,7 @@ static inline size_t ce_namelen(const struct cache_entry *ce)
 			    ondisk_cache_entry_size(ce_namelen(ce)))
 #define ce_stage(ce) ((CE_STAGEMASK & (ce)->ce_flags) >> CE_STAGESHIFT)
 #define ce_uptodate(ce) ((ce)->ce_flags & CE_UPTODATE)
+#define ce_skip_worktree(ce) ((ce)->ce_flags & CE_SKIP_WORKTREE)
 #define ce_mark_uptodate(ce) ((ce)->ce_flags |= CE_UPTODATE)
 
 #define ce_permissions(mode) (((mode) & 0100) ? 0755 : 0644)
@@ -464,7 +470,9 @@ extern int index_name_is_other(const struct index_state *, const char *, int);
 /* do stat comparison even if CE_VALID is true */
 #define CE_MATCH_IGNORE_VALID		01
 /* do not check the contents but report dirty on racily-clean entries */
-#define CE_MATCH_RACY_IS_DIRTY	02
+#define CE_MATCH_RACY_IS_DIRTY		02
+/* do stat comparison even if CE_SKIP_WORKTREE is true */
+#define CE_MATCH_IGNORE_SKIP_WORKTREE	04
 extern int ie_match_stat(const struct index_state *, struct cache_entry *, struct stat *, unsigned int);
 extern int ie_modified(const struct index_state *, struct cache_entry *, struct stat *, unsigned int);
 
@@ -529,6 +537,7 @@ extern int auto_crlf;
 extern int read_replace_refs;
 extern int fsync_object_files;
 extern int core_preload_index;
+extern int core_apply_sparse_checkout;
 
 enum safe_crlf {
 	SAFE_CRLF_FALSE = 0,
@@ -714,6 +723,7 @@ extern const char *resolve_ref(const char *path, unsigned char *sha1, int, int *
 extern int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref);
 extern int dwim_log(const char *str, int len, unsigned char *sha1, char **ref);
 extern int interpret_branch_name(const char *str, struct strbuf *);
+extern int get_sha1_mb(const char *str, unsigned char *sha1);
 
 extern int refname_match(const char *abbrev_name, const char *full_name, const char **rules);
 extern const char *ref_rev_parse_rules[];
diff --git a/config.c b/config.c
index 37385ce9d3..f4f2c59a34 100644
--- a/config.c
+++ b/config.c
@@ -518,6 +518,11 @@ static int git_default_core_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.sparsecheckout")) {
+		core_apply_sparse_checkout = git_config_bool(var, value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;
 }
diff --git a/contrib/hg-to-git/hg-to-git.py b/contrib/hg-to-git/hg-to-git.py
index 2a6839d81e..854cd94ba5 100755
--- a/contrib/hg-to-git/hg-to-git.py
+++ b/contrib/hg-to-git/hg-to-git.py
@@ -59,14 +59,14 @@ def getgitenv(user, date):
     elems = re.compile('(.*?)\s+<(.*)>').match(user)
     if elems:
         env += 'export GIT_AUTHOR_NAME="%s" ;' % elems.group(1)
-        env += 'export GIT_COMMITER_NAME="%s" ;' % elems.group(1)
+        env += 'export GIT_COMMITTER_NAME="%s" ;' % elems.group(1)
         env += 'export GIT_AUTHOR_EMAIL="%s" ;' % elems.group(2)
-        env += 'export GIT_COMMITER_EMAIL="%s" ;' % elems.group(2)
+        env += 'export GIT_COMMITTER_EMAIL="%s" ;' % elems.group(2)
     else:
         env += 'export GIT_AUTHOR_NAME="%s" ;' % user
-        env += 'export GIT_COMMITER_NAME="%s" ;' % user
+        env += 'export GIT_COMMITTER_NAME="%s" ;' % user
         env += 'export GIT_AUTHOR_EMAIL= ;'
-        env += 'export GIT_COMMITER_EMAIL= ;'
+        env += 'export GIT_COMMITTER_EMAIL= ;'
 
     env += 'export GIT_AUTHOR_DATE="%s" ;' % date
     env += 'export GIT_COMMITTER_DATE="%s" ;' % date
diff --git a/diff-lib.c b/diff-lib.c
index 349f612b61..1c7e652a80 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -159,7 +159,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 				continue;
 		}
 
-		if (ce_uptodate(ce))
+		if (ce_uptodate(ce) || ce_skip_worktree(ce))
 			continue;
 
 		/* If CE_VALID is set, don't look at workdir for file removal */
@@ -323,7 +323,8 @@ static void do_oneway_diff(struct unpack_trees_options *o,
 	int match_missing, cached;
 
 	/* if the entry is not checked out, don't examine work tree */
-	cached = o->index_only || (idx && (idx->ce_flags & CE_VALID));
+	cached = o->index_only ||
+		(idx && ((idx->ce_flags & CE_VALID) || ce_skip_worktree(idx)));
 	/*
 	 * Backward compatibility wart - "diff-index -m" does
 	 * not mean "do not ignore merges", but "match_missing".
diff --git a/diff.c b/diff.c
index aad4b3977a..04beb26a6a 100644
--- a/diff.c
+++ b/diff.c
@@ -1997,7 +1997,7 @@ static int reuse_worktree_file(const char *name, const unsigned char *sha1, int
 	 * If ce is marked as "assume unchanged", there is no
 	 * guarantee that work tree matches what we are looking for.
 	 */
-	if (ce->ce_flags & CE_VALID)
+	if ((ce->ce_flags & CE_VALID) || ce_skip_worktree(ce))
 		return 0;
 
 	/*
diff --git a/dir.c b/dir.c
index d0999ba055..3a8d3e67a5 100644
--- a/dir.c
+++ b/dir.c
@@ -200,11 +200,35 @@ void add_exclude(const char *string, const char *base,
 	which->excludes[which->nr++] = x;
 }
 
-static int add_excludes_from_file_1(const char *fname,
-				    const char *base,
-				    int baselen,
-				    char **buf_p,
-				    struct exclude_list *which)
+static void *read_skip_worktree_file_from_index(const char *path, size_t *size)
+{
+	int pos, len;
+	unsigned long sz;
+	enum object_type type;
+	void *data;
+	struct index_state *istate = &the_index;
+
+	len = strlen(path);
+	pos = index_name_pos(istate, path, len);
+	if (pos < 0)
+		return NULL;
+	if (!ce_skip_worktree(istate->cache[pos]))
+		return NULL;
+	data = read_sha1_file(istate->cache[pos]->sha1, &type, &sz);
+	if (!data || type != OBJ_BLOB) {
+		free(data);
+		return NULL;
+	}
+	*size = xsize_t(sz);
+	return data;
+}
+
+int add_excludes_from_file_to_list(const char *fname,
+				   const char *base,
+				   int baselen,
+				   char **buf_p,
+				   struct exclude_list *which,
+				   int check_index)
 {
 	struct stat st;
 	int fd, i;
@@ -212,27 +236,32 @@ static int add_excludes_from_file_1(const char *fname,
 	char *buf, *entry;
 
 	fd = open(fname, O_RDONLY);
-	if (fd < 0 || fstat(fd, &st) < 0)
-		goto err;
-	size = xsize_t(st.st_size);
-	if (size == 0) {
+	if (fd < 0 || fstat(fd, &st) < 0) {
+		if (0 <= fd)
+			close(fd);
+		if (!check_index ||
+		    (buf = read_skip_worktree_file_from_index(fname, &size)) == NULL)
+			return -1;
+	}
+	else {
+		size = xsize_t(st.st_size);
+		if (size == 0) {
+			close(fd);
+			return 0;
+		}
+		buf = xmalloc(size);
+		if (read_in_full(fd, buf, size) != size) {
+			close(fd);
+			return -1;
+		}
 		close(fd);
-		return 0;
 	}
-	buf = xmalloc(size+1);
-	if (read_in_full(fd, buf, size) != size)
-	{
-		free(buf);
-		goto err;
-	}
-	close(fd);
 
 	if (buf_p)
 		*buf_p = buf;
-	buf[size++] = '\n';
 	entry = buf;
-	for (i = 0; i < size; i++) {
-		if (buf[i] == '\n') {
+	for (i = 0; i <= size; i++) {
+		if (i == size || buf[i] == '\n') {
 			if (entry != buf + i && entry[0] != '#') {
 				buf[i - (i && buf[i-1] == '\r')] = 0;
 				add_exclude(entry, base, baselen, which);
@@ -241,17 +270,12 @@ static int add_excludes_from_file_1(const char *fname,
 		}
 	}
 	return 0;
-
- err:
-	if (0 <= fd)
-		close(fd);
-	return -1;
 }
 
 void add_excludes_from_file(struct dir_struct *dir, const char *fname)
 {
-	if (add_excludes_from_file_1(fname, "", 0, NULL,
-				     &dir->exclude_list[EXC_FILE]) < 0)
+	if (add_excludes_from_file_to_list(fname, "", 0, NULL,
+					   &dir->exclude_list[EXC_FILE], 0) < 0)
 		die("cannot use %s as an exclude file", fname);
 }
 
@@ -300,9 +324,9 @@ static void prep_exclude(struct dir_struct *dir, const char *base, int baselen)
 		memcpy(dir->basebuf + current, base + current,
 		       stk->baselen - current);
 		strcpy(dir->basebuf + stk->baselen, dir->exclude_per_dir);
-		add_excludes_from_file_1(dir->basebuf,
-					 dir->basebuf, stk->baselen,
-					 &stk->filebuf, el);
+		add_excludes_from_file_to_list(dir->basebuf,
+					       dir->basebuf, stk->baselen,
+					       &stk->filebuf, el, 1);
 		dir->exclude_stack = stk;
 		current = stk->baselen;
 	}
@@ -312,9 +336,9 @@ static void prep_exclude(struct dir_struct *dir, const char *base, int baselen)
 /* Scan the list and let the last match determine the fate.
  * Return 1 for exclude, 0 for include and -1 for undecided.
  */
-static int excluded_1(const char *pathname,
-		      int pathlen, const char *basename, int *dtype,
-		      struct exclude_list *el)
+int excluded_from_list(const char *pathname,
+		       int pathlen, const char *basename, int *dtype,
+		       struct exclude_list *el)
 {
 	int i;
 
@@ -325,6 +349,12 @@ static int excluded_1(const char *pathname,
 			int to_exclude = x->to_exclude;
 
 			if (x->flags & EXC_FLAG_MUSTBEDIR) {
+				if (!dtype) {
+					if (!prefixcmp(pathname, exclude))
+						return to_exclude;
+					else
+						continue;
+				}
 				if (*dtype == DT_UNKNOWN)
 					*dtype = get_dtype(NULL, pathname, pathlen);
 				if (*dtype != DT_DIR)
@@ -382,8 +412,8 @@ int excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
 
 	prep_exclude(dir, pathname, basename-pathname);
 	for (st = EXC_CMDL; st <= EXC_FILE; st++) {
-		switch (excluded_1(pathname, pathlen, basename,
-				   dtype_p, &dir->exclude_list[st])) {
+		switch (excluded_from_list(pathname, pathlen, basename,
+					   dtype_p, &dir->exclude_list[st])) {
 		case 0:
 			return 0;
 		case 1:
diff --git a/dir.h b/dir.h
index 320b6a2f38..3bead5f0e2 100644
--- a/dir.h
+++ b/dir.h
@@ -69,7 +69,11 @@ extern int match_pathspec(const char **pathspec, const char *name, int namelen,
 extern int fill_directory(struct dir_struct *dir, const char **pathspec);
 extern int read_directory(struct dir_struct *, const char *path, int len, const char **pathspec);
 
+extern int excluded_from_list(const char *pathname, int pathlen, const char *basename,
+			      int *dtype, struct exclude_list *el);
 extern int excluded(struct dir_struct *, const char *, int *);
+extern int add_excludes_from_file_to_list(const char *fname, const char *base, int baselen,
+					  char **buf_p, struct exclude_list *which, int check_index);
 extern void add_excludes_from_file(struct dir_struct *, const char *fname);
 extern void add_exclude(const char *string, const char *base,
 			int baselen, struct exclude_list *which);
diff --git a/entry.c b/entry.c
index 06d24f14c6..9d5b232781 100644
--- a/entry.c
+++ b/entry.c
@@ -206,7 +206,7 @@ int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *t
 	len += ce_namelen(ce);
 
 	if (!check_path(path, len, &st, state->base_dir_len)) {
-		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID);
+		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
 		if (!changed)
 			return 0;
 		if (!state->force) {
diff --git a/environment.c b/environment.c
index 5171d9f9a4..739ec27040 100644
--- a/environment.c
+++ b/environment.c
@@ -51,6 +51,7 @@ enum push_default_type push_default = PUSH_DEFAULT_MATCHING;
 enum object_creation_mode object_creation_mode = OBJECT_CREATION_MODE;
 char *notes_ref_name;
 int grafts_replace_parents = 1;
+int core_apply_sparse_checkout;
 
 /* Parallel index stat data preload? */
 int core_preload_index = 0;
diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index d52932878c..1560e84bd5 100755
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -322,7 +322,7 @@ make_squash_message () {
 }
 
 peek_next_command () {
-	sed -n "1s/ .*$//p" < "$TODO"
+	sed -n -e "/^#/d" -e "/^$/d" -e "s/ .*//p" -e "q" < "$TODO"
 }
 
 do_next () {
@@ -495,6 +495,25 @@ get_saved_options () {
 	test -f "$DOTEST"/rebase-root && REBASE_ROOT=t
 }
 
+LF='
+'
+parse_onto () {
+	case "$1" in
+	*...*)
+		if	left=${1%...*} right=${1#*...} &&
+			onto=$(git merge-base --all ${left:-HEAD} ${right:-HEAD})
+		then
+			case "$onto" in
+			?*"$LF"?* | '')
+				exit 1 ;;
+			esac
+			echo "$onto"
+			exit 0
+		fi
+	esac
+	git rev-parse --verify "$1^0"
+}
+
 while test $# != 0
 do
 	case "$1" in
@@ -602,7 +621,7 @@ first and then run 'git rebase --continue' again."
 		;;
 	--onto)
 		shift
-		ONTO=$(git rev-parse --verify "$1") ||
+		ONTO=$(parse_onto "$1") ||
 			die "Does not point to a valid commit: $1"
 		;;
 	--)
diff --git a/git-rebase.sh b/git-rebase.sh
index b121f4537c..3de0942c0f 100755
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -34,6 +34,8 @@ set_reflog_action rebase
 require_work_tree
 cd_to_toplevel
 
+LF='
+'
 OK_TO_SKIP_PRE_REBASE=
 RESOLVEMSG="
 When you have resolved this problem run \"git rebase --continue\".
@@ -417,7 +419,27 @@ fi
 
 # Make sure the branch to rebase onto is valid.
 onto_name=${newbase-"$upstream_name"}
-onto=$(git rev-parse --verify "${onto_name}^0") || exit
+case "$onto_name" in
+*...*)
+	if	left=${onto_name%...*} right=${onto_name#*...} &&
+		onto=$(git merge-base --all ${left:-HEAD} ${right:-HEAD})
+	then
+		case "$onto" in
+		?*"$LF"?*)
+			die "$onto_name: there are more than one merge bases"
+			;;
+		'')
+			die "$onto_name: there is no merge base"
+			;;
+		esac
+	else
+		die "$onto_name: there is no merge base"
+	fi
+	;;
+*)
+	onto=$(git rev-parse --verify "${onto_name}^0") || exit
+	;;
+esac
 
 # If a hook exists, give it a chance to interrupt
 run_pre_rebase_hook "$upstream_arg" "$@"
diff --git a/lockfile.c b/lockfile.c
index 6851fa55a5..b0d74cddde 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -164,9 +164,10 @@ static char *unable_to_lock_message(const char *path, int err)
 		    "If no other git process is currently running, this probably means a\n"
 		    "git process crashed in this repository earlier. Make sure no other git\n"
 		    "process is running and remove the file manually to continue.",
-		    path, strerror(err));
+			    make_nonrelative_path(path), strerror(err));
 	} else
-		strbuf_addf(&buf, "Unable to create '%s.lock': %s", path, strerror(err));
+		strbuf_addf(&buf, "Unable to create '%s.lock': %s",
+			    make_nonrelative_path(path), strerror(err));
 	return strbuf_detach(&buf, NULL);
 }
 
diff --git a/read-cache.c b/read-cache.c
index 9033dd3ab9..d214abab16 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -259,12 +259,17 @@ int ie_match_stat(const struct index_state *istate,
 {
 	unsigned int changed;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
+	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
 	int assume_racy_is_modified = options & CE_MATCH_RACY_IS_DIRTY;
 
 	/*
 	 * If it's marked as always valid in the index, it's
 	 * valid whatever the checked-out copy says.
+	 *
+	 * skip-worktree has the same effect with higher precedence
 	 */
+	if (!ignore_skip_worktree && ce_skip_worktree(ce))
+		return 0;
 	if (!ignore_valid && (ce->ce_flags & CE_VALID))
 		return 0;
 
@@ -564,7 +569,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 	int size, namelen, was_same;
 	mode_t st_mode = st->st_mode;
 	struct cache_entry *ce, *alias;
-	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_RACY_IS_DIRTY;
+	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
 	int verbose = flags & (ADD_CACHE_VERBOSE | ADD_CACHE_PRETEND);
 	int pretend = flags & ADD_CACHE_PRETEND;
 	int intent_only = flags & ADD_CACHE_INTENT;
@@ -1000,14 +1005,20 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 	struct cache_entry *updated;
 	int changed, size;
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
+	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
 
 	if (ce_uptodate(ce))
 		return ce;
 
 	/*
-	 * CE_VALID means the user promised us that the change to
-	 * the work tree does not matter and told us not to worry.
+	 * CE_VALID or CE_SKIP_WORKTREE means the user promised us
+	 * that the change to the work tree does not matter and told
+	 * us not to worry.
 	 */
+	if (!ignore_skip_worktree && ce_skip_worktree(ce)) {
+		ce_mark_uptodate(ce);
+		return ce;
+	}
 	if (!ignore_valid && (ce->ce_flags & CE_VALID)) {
 		ce_mark_uptodate(ce);
 		return ce;
@@ -1606,9 +1617,8 @@ int read_index_unmerged(struct index_state *istate)
 		len = strlen(ce->name);
 		size = cache_entry_size(len);
 		new_ce = xcalloc(1, size);
-		hashcpy(new_ce->sha1, ce->sha1);
 		memcpy(new_ce->name, ce->name, len);
-		new_ce->ce_flags = create_ce_flags(len, 0);
+		new_ce->ce_flags = create_ce_flags(len, 0) | CE_CONFLICTED;
 		new_ce->ce_mode = ce->ce_mode;
 		if (add_index_entry(istate, new_ce, 0))
 			return error("%s: cannot drop to stage #0",
diff --git a/remote-curl.c b/remote-curl.c
index 28b2a316d3..70fdceade5 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -510,7 +510,7 @@ static int rpc_service(struct rpc_state *rpc, struct discovery *heads)
 	strbuf_addf(&buf, "Content-Type: application/x-%s-request", svc);
 	rpc->hdr_content_type = strbuf_detach(&buf, NULL);
 
-	strbuf_addf(&buf, "Accept: application/x-%s-response", svc);
+	strbuf_addf(&buf, "Accept: application/x-%s-result", svc);
 	rpc->hdr_accept = strbuf_detach(&buf, NULL);
 
 	while (!err) {
diff --git a/sha1_name.c b/sha1_name.c
index ca8f9dba94..1739e9e612 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -794,6 +794,48 @@ release_return:
 	return retval;
 }
 
+int get_sha1_mb(const char *name, unsigned char *sha1)
+{
+	struct commit *one, *two;
+	struct commit_list *mbs;
+	unsigned char sha1_tmp[20];
+	const char *dots;
+	int st;
+
+	dots = strstr(name, "...");
+	if (!dots)
+		return get_sha1(name, sha1);
+	if (dots == name)
+		st = get_sha1("HEAD", sha1_tmp);
+	else {
+		struct strbuf sb;
+		strbuf_init(&sb, dots - name);
+		strbuf_add(&sb, name, dots - name);
+		st = get_sha1(sb.buf, sha1_tmp);
+		strbuf_release(&sb);
+	}
+	if (st)
+		return st;
+	one = lookup_commit_reference_gently(sha1_tmp, 0);
+	if (!one)
+		return -1;
+
+	if (get_sha1(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
+		return -1;
+	two = lookup_commit_reference_gently(sha1_tmp, 0);
+	if (!two)
+		return -1;
+	mbs = get_merge_bases(one, two, 1);
+	if (!mbs || mbs->next)
+		st = -1;
+	else {
+		st = 0;
+		hashcpy(sha1, mbs->item->object.sha1);
+	}
+	free_commit_list(mbs);
+	return st;
+}
+
 /*
  * This is like "get_sha1_basic()", except it allows "sha1 expressions",
  * notably "xyz^" for "parent of xyz"
diff --git a/t/t1011-read-tree-sparse-checkout.sh b/t/t1011-read-tree-sparse-checkout.sh
new file mode 100755
index 0000000000..62246dbf95
--- /dev/null
+++ b/t/t1011-read-tree-sparse-checkout.sh
@@ -0,0 +1,150 @@
+#!/bin/sh
+
+test_description='sparse checkout tests'
+
+. ./test-lib.sh
+
+cat >expected <<EOF
+100644 77f0ba1734ed79d12881f81b36ee134de6a3327b 0	init.t
+100644 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 0	sub/added
+EOF
+test_expect_success 'setup' '
+	test_commit init &&
+	echo modified >> init.t &&
+	mkdir sub &&
+	touch sub/added &&
+	git add init.t sub/added &&
+	git commit -m "modified and added" &&
+	git tag top &&
+	git rm sub/added &&
+	git commit -m removed &&
+	git tag removed &&
+	git checkout top &&
+	git ls-files --stage > result &&
+	test_cmp expected result
+'
+
+cat >expected.swt <<EOF
+H init.t
+H sub/added
+EOF
+test_expect_success 'read-tree without .git/info/sparse-checkout' '
+	git read-tree -m -u HEAD &&
+	git ls-files --stage > result &&
+	test_cmp expected result &&
+	git ls-files -t > result &&
+	test_cmp expected.swt result
+'
+
+test_expect_success 'read-tree with .git/info/sparse-checkout but disabled' '
+	echo > .git/info/sparse-checkout
+	git read-tree -m -u HEAD &&
+	git ls-files -t > result &&
+	test_cmp expected.swt result &&
+	test -f init.t &&
+	test -f sub/added
+'
+
+test_expect_success 'read-tree --no-sparse-checkout with empty .git/info/sparse-checkout and enabled' '
+	git config core.sparsecheckout true &&
+	echo > .git/info/sparse-checkout &&
+	git read-tree --no-sparse-checkout -m -u HEAD &&
+	git ls-files -t > result &&
+	test_cmp expected.swt result &&
+	test -f init.t &&
+	test -f sub/added
+'
+
+test_expect_success 'read-tree with empty .git/info/sparse-checkout' '
+	git config core.sparsecheckout true &&
+	echo > .git/info/sparse-checkout &&
+	test_must_fail git read-tree -m -u HEAD &&
+	git ls-files --stage > result &&
+	test_cmp expected result &&
+	git ls-files -t > result &&
+	test_cmp expected.swt result &&
+	test -f init.t &&
+	test -f sub/added
+'
+
+cat >expected.swt <<EOF
+S init.t
+H sub/added
+EOF
+test_expect_success 'match directories with trailing slash' '
+	echo sub/ > .git/info/sparse-checkout &&
+	git read-tree -m -u HEAD &&
+	git ls-files -t > result &&
+	test_cmp expected.swt result &&
+	test ! -f init.t &&
+	test -f sub/added
+'
+
+cat >expected.swt <<EOF
+H init.t
+H sub/added
+EOF
+test_expect_failure 'match directories without trailing slash' '
+	echo init.t > .git/info/sparse-checkout &&
+	echo sub >> .git/info/sparse-checkout &&
+	git read-tree -m -u HEAD &&
+	git ls-files -t > result &&
+	test_cmp expected.swt result &&
+	test ! -f init.t &&
+	test -f sub/added
+'
+
+cat >expected.swt <<EOF
+H init.t
+S sub/added
+EOF
+test_expect_success 'checkout area changes' '
+	echo init.t > .git/info/sparse-checkout &&
+	git read-tree -m -u HEAD &&
+	git ls-files -t > result &&
+	test_cmp expected.swt result &&
+	test -f init.t &&
+	test ! -f sub/added
+'
+
+test_expect_success 'read-tree updates worktree, absent case' '
+	echo sub/added > .git/info/sparse-checkout &&
+	git checkout -f top &&
+	git read-tree -m -u HEAD^ &&
+	test ! -f init.t
+'
+
+test_expect_success 'read-tree updates worktree, dirty case' '
+	echo sub/added > .git/info/sparse-checkout &&
+	git checkout -f top &&
+	echo dirty > init.t &&
+	git read-tree -m -u HEAD^ &&
+	grep -q dirty init.t &&
+	rm init.t
+'
+
+test_expect_success 'read-tree removes worktree, dirty case' '
+	echo init.t > .git/info/sparse-checkout &&
+	git checkout -f top &&
+	echo dirty > added &&
+	git read-tree -m -u HEAD^ &&
+	grep -q dirty added
+'
+
+test_expect_success 'read-tree adds to worktree, absent case' '
+	echo init.t > .git/info/sparse-checkout &&
+	git checkout -f removed &&
+	git read-tree -u -m HEAD^ &&
+	test ! -f sub/added
+'
+
+test_expect_success 'read-tree adds to worktree, dirty case' '
+	echo init.t > .git/info/sparse-checkout &&
+	git checkout -f removed &&
+	mkdir sub &&
+	echo dirty > sub/added &&
+	git read-tree -u -m HEAD^ &&
+	grep -q dirty sub/added
+'
+
+test_done
diff --git a/t/t2012-checkout-last.sh b/t/t2012-checkout-last.sh
index 87b30a268c..b44de9dc62 100755
--- a/t/t2012-checkout-last.sh
+++ b/t/t2012-checkout-last.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-test_description='checkout can switch to last branch'
+test_description='checkout can switch to last branch and merge base'
 
 . ./test-lib.sh
 
@@ -91,4 +91,29 @@ test_expect_success 'switch to twelfth from the last' '
 	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/branch13"
 '
 
+test_expect_success 'merge base test setup' '
+	git checkout -b another other &&
+	echo "hello again" >>world &&
+	git add world &&
+	git commit -m third
+'
+
+test_expect_success 'another...master' '
+	git checkout another &&
+	git checkout another...master &&
+	test "z$(git rev-parse --verify HEAD)" = "z$(git rev-parse --verify master^)"
+'
+
+test_expect_success '...master' '
+	git checkout another &&
+	git checkout ...master &&
+	test "z$(git rev-parse --verify HEAD)" = "z$(git rev-parse --verify master^)"
+'
+
+test_expect_success 'master...' '
+	git checkout another &&
+	git checkout master... &&
+	test "z$(git rev-parse --verify HEAD)" = "z$(git rev-parse --verify master^)"
+'
+
 test_done
diff --git a/t/t2104-update-index-skip-worktree.sh b/t/t2104-update-index-skip-worktree.sh
new file mode 100755
index 0000000000..1d0879be06
--- /dev/null
+++ b/t/t2104-update-index-skip-worktree.sh
@@ -0,0 +1,57 @@
+#!/bin/sh
+#
+# Copyright (c) 2008 Nguyễn Thái Ngọc Duy
+#
+
+test_description='skip-worktree bit test'
+
+. ./test-lib.sh
+
+cat >expect.full <<EOF
+H 1
+H 2
+H sub/1
+H sub/2
+EOF
+
+cat >expect.skip <<EOF
+S 1
+H 2
+S sub/1
+H sub/2
+EOF
+
+test_expect_success 'setup' '
+	mkdir sub &&
+	touch ./1 ./2 sub/1 sub/2 &&
+	git add 1 2 sub/1 sub/2 &&
+	git ls-files -t | test_cmp expect.full -
+'
+
+test_expect_success 'index is at version 2' '
+	test "$(test-index-version < .git/index)" = 2
+'
+
+test_expect_success 'update-index --skip-worktree' '
+	git update-index --skip-worktree 1 sub/1 &&
+	git ls-files -t | test_cmp expect.skip -
+'
+
+test_expect_success 'index is at version 3 after having some skip-worktree entries' '
+	test "$(test-index-version < .git/index)" = 3
+'
+
+test_expect_success 'ls-files -t' '
+	git ls-files -t | test_cmp expect.skip -
+'
+
+test_expect_success 'update-index --no-skip-worktree' '
+	git update-index --no-skip-worktree 1 sub/1 &&
+	git ls-files -t | test_cmp expect.full -
+'
+
+test_expect_success 'index version is back to 2 when there is no skip-worktree entry' '
+	test "$(test-index-version < .git/index)" = 2
+'
+
+test_done
diff --git a/t/t3001-ls-files-others-exclude.sh b/t/t3001-ls-files-others-exclude.sh
index c65bca8388..132c4765cb 100755
--- a/t/t3001-ls-files-others-exclude.sh
+++ b/t/t3001-ls-files-others-exclude.sh
@@ -64,6 +64,8 @@ two/*.4
 echo '!*.2
 !*.8' >one/two/.gitignore
 
+allignores='.gitignore one/.gitignore one/two/.gitignore'
+
 test_expect_success \
     'git ls-files --others with various exclude options.' \
     'git ls-files --others \
@@ -85,6 +87,26 @@ test_expect_success \
        >output &&
      test_cmp expect output'
 
+test_expect_success 'setup skip-worktree gitignore' '
+	git add $allignores &&
+	git update-index --skip-worktree $allignores &&
+	rm $allignores
+'
+
+test_expect_success \
+    'git ls-files --others with various exclude options.' \
+    'git ls-files --others \
+       --exclude=\*.6 \
+       --exclude-per-directory=.gitignore \
+       --exclude-from=.git/ignore \
+       >output &&
+     test_cmp expect output'
+
+test_expect_success 'restore gitignore' '
+	git checkout $allignores &&
+	rm .git/index
+'
+
 cat > excludes-file <<\EOF
 *.[1-8]
 e*
diff --git a/t/t3415-rebase-onto-threedots.sh b/t/t3415-rebase-onto-threedots.sh
new file mode 100755
index 0000000000..ddf2f64853
--- /dev/null
+++ b/t/t3415-rebase-onto-threedots.sh
@@ -0,0 +1,105 @@
+#!/bin/sh
+
+test_description='git rebase --onto A...B'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-rebase.sh"
+
+# Rebase only the tip commit of "topic" on merge base between "master"
+# and "topic".  Cannot do this for "side" with "master" because there
+# is no single merge base.
+#
+#
+#	    F---G topic                             G'
+#	   /                                       /
+# A---B---C---D---E master      -->       A---B---C---D---E
+#      \   \ /
+#	\   x
+#	 \ / \
+#	  H---I---J---K side
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	git branch side &&
+	test_commit C &&
+	git branch topic &&
+	git checkout side &&
+	test_commit H &&
+	git checkout master &&
+	test_tick &&
+	git merge H &&
+	git tag D &&
+	test_commit E &&
+	git checkout topic &&
+	test_commit F &&
+	test_commit G &&
+	git checkout side &&
+	test_tick &&
+	git merge C &&
+	git tag I &&
+	test_commit J &&
+	test_commit K
+'
+
+test_expect_success 'rebase --onto master...topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --onto master...topic F &&
+	git rev-parse HEAD^1 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --onto master...' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --onto master... F &&
+	git rev-parse HEAD^1 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --onto master...side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --onto master...side J
+'
+
+test_expect_success 'rebase -i --onto master...topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+	set_fake_editor &&
+	EXPECT_COUNT=1 git rebase -i --onto master...topic F &&
+	git rev-parse HEAD^1 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --onto master...' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+	set_fake_editor &&
+	EXPECT_COUNT=1 git rebase -i --onto master... F &&
+	git rev-parse HEAD^1 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --onto master...side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase -i --onto master...side J
+'
+
+test_done
diff --git a/t/t5551-http-fetch.sh b/t/t5551-http-fetch.sh
index c0505ecd7b..7faa31a299 100755
--- a/t/t5551-http-fetch.sh
+++ b/t/t5551-http-fetch.sh
@@ -38,7 +38,7 @@ cat >exp <<EOF
 > POST /smart/repo.git/git-upload-pack HTTP/1.1
 > Accept-Encoding: deflate, gzip
 > Content-Type: application/x-git-upload-pack-request
-> Accept: application/x-git-upload-pack-response
+> Accept: application/x-git-upload-pack-result
 > Content-Length: xxx
 < HTTP/1.1 200 OK
 < Pragma: no-cache
diff --git a/t/t7002-grep.sh b/t/t7002-grep.sh
index abd14bf819..76c5e091b7 100755
--- a/t/t7002-grep.sh
+++ b/t/t7002-grep.sh
@@ -8,6 +8,18 @@ test_description='git grep various.
 
 . ./test-lib.sh
 
+test_expect_success 'Check for external grep support' '
+	case "$(git grep -h 2>&1|grep ext-grep)" in
+	*"(default)"*)
+		test_set_prereq EXTGREP
+		true;;
+	*"(ignored by this build)"*)
+		true;;
+	*)
+		false;;
+	esac
+'
+
 cat >hello.c <<EOF
 #include <stdio.h>
 int main(int argc, const char **argv)
@@ -426,4 +438,16 @@ test_expect_success 'grep -Fi' '
 	test_cmp expected actual
 '
 
+test_expect_success EXTGREP 'external grep is called' '
+	GIT_TRACE=2 git grep foo >/dev/null 2>actual &&
+	grep "trace: grep:.*foo" actual >/dev/null
+'
+
+test_expect_success EXTGREP 'no external grep when skip-worktree entries exist' '
+	git update-index --skip-worktree file &&
+	GIT_TRACE=2 git grep foo >/dev/null 2>actual &&
+	! grep "trace: grep:" actual >/dev/null &&
+	git update-index --no-skip-worktree file
+'
+
 test_done
diff --git a/t/t7011-skip-worktree-reading.sh b/t/t7011-skip-worktree-reading.sh
new file mode 100755
index 0000000000..bb4066f767
--- /dev/null
+++ b/t/t7011-skip-worktree-reading.sh
@@ -0,0 +1,163 @@
+#!/bin/sh
+#
+# Copyright (c) 2008 Nguyễn Thái Ngọc Duy
+#
+
+test_description='skip-worktree bit test'
+
+. ./test-lib.sh
+
+cat >expect.full <<EOF
+H 1
+H 2
+H init.t
+H sub/1
+H sub/2
+EOF
+
+cat >expect.skip <<EOF
+S 1
+H 2
+H init.t
+S sub/1
+H sub/2
+EOF
+
+NULL_SHA1=e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
+ZERO_SHA0=0000000000000000000000000000000000000000
+setup_absent() {
+	test -f 1 && rm 1
+	git update-index --remove 1 &&
+	git update-index --add --cacheinfo 100644 $NULL_SHA1 1 &&
+	git update-index --skip-worktree 1
+}
+
+test_absent() {
+	echo "100644 $NULL_SHA1 0	1" > expected &&
+	git ls-files --stage 1 > result &&
+	test_cmp expected result &&
+	test ! -f 1
+}
+
+setup_dirty() {
+	git update-index --force-remove 1 &&
+	echo dirty > 1 &&
+	git update-index --add --cacheinfo 100644 $NULL_SHA1 1 &&
+	git update-index --skip-worktree 1
+}
+
+test_dirty() {
+	echo "100644 $NULL_SHA1 0	1" > expected &&
+	git ls-files --stage 1 > result &&
+	test_cmp expected result &&
+	echo dirty > expected
+	test_cmp expected 1
+}
+
+test_expect_success 'setup' '
+	test_commit init &&
+	mkdir sub &&
+	touch ./1 ./2 sub/1 sub/2 &&
+	git add 1 2 sub/1 sub/2 &&
+	git update-index --skip-worktree 1 sub/1 &&
+	git ls-files -t > result &&
+	test_cmp expect.skip result
+'
+
+test_expect_success 'update-index' '
+	setup_absent &&
+	git update-index 1 &&
+	test_absent
+'
+
+test_expect_success 'update-index' '
+	setup_dirty &&
+	git update-index 1 &&
+	test_dirty
+'
+
+test_expect_success 'update-index --remove' '
+	setup_absent &&
+	git update-index --remove 1 &&
+	test -z "$(git ls-files 1)" &&
+	test ! -f 1
+'
+
+test_expect_success 'update-index --remove' '
+	setup_dirty &&
+	git update-index --remove 1 &&
+	test -z "$(git ls-files 1)" &&
+	echo dirty > expected &&
+	test_cmp expected 1
+'
+
+test_expect_success 'ls-files --delete' '
+	setup_absent &&
+	test -z "$(git ls-files -d)"
+'
+
+test_expect_success 'ls-files --delete' '
+	setup_dirty &&
+	test -z "$(git ls-files -d)"
+'
+
+test_expect_success 'ls-files --modified' '
+	setup_absent &&
+	test -z "$(git ls-files -m)"
+'
+
+test_expect_success 'ls-files --modified' '
+	setup_dirty &&
+	test -z "$(git ls-files -m)"
+'
+
+test_expect_success 'grep with skip-worktree file' '
+	git update-index --no-skip-worktree 1 &&
+	echo test > 1 &&
+	git update-index 1 &&
+	git update-index --skip-worktree 1 &&
+	rm 1 &&
+	test "$(git grep --no-ext-grep test)" = "1:test"
+'
+
+echo ":000000 100644 $ZERO_SHA0 $NULL_SHA1 A	1" > expected
+test_expect_success 'diff-index does not examine skip-worktree absent entries' '
+	setup_absent &&
+	git diff-index HEAD -- 1 > result &&
+	test_cmp expected result
+'
+
+test_expect_success 'diff-index does not examine skip-worktree dirty entries' '
+	setup_dirty &&
+	git diff-index HEAD -- 1 > result &&
+	test_cmp expected result
+'
+
+test_expect_success 'diff-files does not examine skip-worktree absent entries' '
+	setup_absent &&
+	test -z "$(git diff-files -- one)"
+'
+
+test_expect_success 'diff-files does not examine skip-worktree dirty entries' '
+	setup_dirty &&
+	test -z "$(git diff-files -- one)"
+'
+
+test_expect_success 'git-rm succeeds on skip-worktree absent entries' '
+	setup_absent &&
+	git rm 1
+'
+
+test_expect_success 'commit on skip-worktree absent entries' '
+	git reset &&
+	setup_absent &&
+	test_must_fail git commit -m null 1
+'
+
+test_expect_success 'commit on skip-worktree dirty entries' '
+	git reset &&
+	setup_dirty &&
+	test_must_fail git commit -m null 1
+'
+
+test_done
diff --git a/t/t7012-skip-worktree-writing.sh b/t/t7012-skip-worktree-writing.sh
new file mode 100755
index 0000000000..8d8b1c0e25
--- /dev/null
+++ b/t/t7012-skip-worktree-writing.sh
@@ -0,0 +1,146 @@
+#!/bin/sh
+#
+# Copyright (c) 2008 Nguyễn Thái Ngọc Duy
+#
+
+test_description='test worktree writing operations when skip-worktree is used'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit init &&
+	echo modified >> init.t &&
+	touch added &&
+	git add init.t added &&
+	git commit -m "modified and added" &&
+	git tag top
+'
+
+test_expect_success 'read-tree updates worktree, absent case' '
+	git checkout -f top &&
+	git update-index --skip-worktree init.t &&
+	rm init.t &&
+	git read-tree -m -u HEAD^ &&
+	echo init > expected &&
+	test_cmp expected init.t
+'
+
+test_expect_success 'read-tree updates worktree, dirty case' '
+	git checkout -f top &&
+	git update-index --skip-worktree init.t &&
+	echo dirty >> init.t &&
+	test_must_fail git read-tree -m -u HEAD^ &&
+	grep -q dirty init.t &&
+	test "$(git ls-files -t init.t)" = "S init.t" &&
+	git update-index --no-skip-worktree init.t
+'
+
+test_expect_success 'read-tree removes worktree, absent case' '
+	git checkout -f top &&
+	git update-index --skip-worktree added &&
+	rm added &&
+	git read-tree -m -u HEAD^ &&
+	test ! -f added
+'
+
+test_expect_success 'read-tree removes worktree, dirty case' '
+	git checkout -f top &&
+	git update-index --skip-worktree added &&
+	echo dirty >> added &&
+	test_must_fail git read-tree -m -u HEAD^ &&
+	grep -q dirty added &&
+	test "$(git ls-files -t added)" = "S added" &&
+	git update-index --no-skip-worktree added
+'
+
+NULL_SHA1=e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
+ZERO_SHA0=0000000000000000000000000000000000000000
+setup_absent() {
+	test -f 1 && rm 1
+	git update-index --remove 1 &&
+	git update-index --add --cacheinfo 100644 $NULL_SHA1 1 &&
+	git update-index --skip-worktree 1
+}
+
+test_absent() {
+	echo "100644 $NULL_SHA1 0	1" > expected &&
+	git ls-files --stage 1 > result &&
+	test_cmp expected result &&
+	test ! -f 1
+}
+
+setup_dirty() {
+	git update-index --force-remove 1 &&
+	echo dirty > 1 &&
+	git update-index --add --cacheinfo 100644 $NULL_SHA1 1 &&
+	git update-index --skip-worktree 1
+}
+
+test_dirty() {
+	echo "100644 $NULL_SHA1 0	1" > expected &&
+	git ls-files --stage 1 > result &&
+	test_cmp expected result &&
+	echo dirty > expected
+	test_cmp expected 1
+}
+
+cat >expected <<EOF
+S 1
+H 2
+H init.t
+S sub/1
+H sub/2
+EOF
+
+test_expect_success 'index setup' '
+	git checkout -f init &&
+	mkdir sub &&
+	touch ./1 ./2 sub/1 sub/2 &&
+	git add 1 2 sub/1 sub/2 &&
+	git update-index --skip-worktree 1 sub/1 &&
+	git ls-files -t > result &&
+	test_cmp expected result
+'
+
+test_expect_success 'git-add ignores worktree content' '
+	setup_absent &&
+	git add 1 &&
+	test_absent
+'
+
+test_expect_success 'git-add ignores worktree content' '
+	setup_dirty &&
+	git add 1 &&
+	test_dirty
+'
+
+test_expect_success 'git-rm fails if worktree is dirty' '
+	setup_dirty &&
+	test_must_fail git rm 1 &&
+	test_dirty
+'
+
+cat >expected <<EOF
+Would remove expected
+Would remove result
+EOF
+test_expect_success 'git-clean, absent case' '
+	setup_absent &&
+	git clean -n > result &&
+	test_cmp expected result
+'
+
+test_expect_success 'git-clean, dirty case' '
+	setup_dirty &&
+	git clean -n > result &&
+	test_cmp expected result
+'
+
+test_expect_failure 'git-apply adds file' false
+test_expect_failure 'git-apply updates file' false
+test_expect_failure 'git-apply removes file' false
+test_expect_failure 'git-mv to skip-worktree' false
+test_expect_failure 'git-mv from skip-worktree' false
+test_expect_failure 'git-checkout' false
+
+test_done
diff --git a/t/t7110-reset-merge.sh b/t/t7110-reset-merge.sh
new file mode 100755
index 0000000000..8704d00196
--- /dev/null
+++ b/t/t7110-reset-merge.sh
@@ -0,0 +1,183 @@
+#!/bin/sh
+#
+# Copyright (c) 2009 Christian Couder
+#
+
+test_description='Tests for "git reset --merge"'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+    for i in 1 2 3; do echo line $i; done >file1 &&
+    cat file1 >file2 &&
+    git add file1 file2 &&
+    test_tick &&
+    git commit -m "Initial commit" &&
+    git tag initial &&
+    echo line 4 >>file1 &&
+    cat file1 >file2 &&
+    test_tick &&
+    git commit -m "add line 4 to file1" file1 &&
+    git tag second
+'
+
+# The next test will test the following:
+#
+#           working index HEAD target         working index HEAD
+#           ----------------------------------------------------
+# file1:     C       C     C    D     --merge  D       D     D
+# file2:     C       D     D    D     --merge  C       D     D
+test_expect_success 'reset --merge is ok with changes in file it does not touch' '
+    git reset --merge HEAD^ &&
+    ! grep 4 file1 &&
+    grep 4 file2 &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse initial)" &&
+    test -z "$(git diff --cached)"
+'
+
+test_expect_success 'reset --merge is ok when switching back' '
+    git reset --merge second &&
+    grep 4 file1 &&
+    grep 4 file2 &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse second)" &&
+    test -z "$(git diff --cached)"
+'
+
+# The next test will test the following:
+#
+#           working index HEAD target         working index HEAD
+#           ----------------------------------------------------
+# file1:     B       B     C    D     --merge  D       D     D
+# file2:     C       D     D    D     --merge  C       D     D
+test_expect_success 'reset --merge discards changes added to index (1)' '
+    git reset --hard second &&
+    cat file1 >file2 &&
+    echo "line 5" >> file1 &&
+    git add file1 &&
+    git reset --merge HEAD^ &&
+    ! grep 4 file1 &&
+    ! grep 5 file1 &&
+    grep 4 file2 &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse initial)" &&
+    test -z "$(git diff --cached)"
+'
+
+test_expect_success 'reset --merge is ok again when switching back (1)' '
+    git reset --hard initial &&
+    echo "line 5" >> file2 &&
+    git add file2 &&
+    git reset --merge second &&
+    ! grep 4 file2 &&
+    ! grep 5 file1 &&
+    grep 4 file1 &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse second)" &&
+    test -z "$(git diff --cached)"
+'
+
+# The next test will test the following:
+#
+#           working index HEAD target         working index HEAD
+#           ----------------------------------------------------
+# file1:     C       C     C    D     --merge  D       D     D
+# file2:     C       C     D    D     --merge  D       D     D
+test_expect_success 'reset --merge discards changes added to index (2)' '
+    git reset --hard second &&
+    echo "line 4" >> file2 &&
+    git add file2 &&
+    git reset --merge HEAD^ &&
+    ! grep 4 file2 &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse initial)" &&
+    test -z "$(git diff)" &&
+    test -z "$(git diff --cached)"
+'
+
+test_expect_success 'reset --merge is ok again when switching back (2)' '
+    git reset --hard initial &&
+    git reset --merge second &&
+    ! grep 4 file2 &&
+    grep 4 file1 &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse second)" &&
+    test -z "$(git diff --cached)"
+'
+
+# The next test will test the following:
+#
+#           working index HEAD target         working index HEAD
+#           ----------------------------------------------------
+# file1:     A       B     B    C     --merge  (disallowed)
+test_expect_success 'reset --merge fails with changes in file it touches' '
+    git reset --hard second &&
+    echo "line 5" >> file1 &&
+    test_tick &&
+    git commit -m "add line 5" file1 &&
+    sed -e "s/line 1/changed line 1/" <file1 >file3 &&
+    mv file3 file1 &&
+    test_must_fail git reset --merge HEAD^ 2>err.log &&
+    grep file1 err.log | grep "not uptodate"
+'
+
+test_expect_success 'setup 3 different branches' '
+    git reset --hard second &&
+    git branch branch1 &&
+    git branch branch2 &&
+    git branch branch3 &&
+    git checkout branch1 &&
+    echo "line 5 in branch1" >> file1 &&
+    test_tick &&
+    git commit -a -m "change in branch1" &&
+    git checkout branch2 &&
+    echo "line 5 in branch2" >> file1 &&
+    test_tick &&
+    git commit -a -m "change in branch2" &&
+    git tag third &&
+    git checkout branch3 &&
+    echo a new file >file3 &&
+    rm -f file1 &&
+    git add file3 &&
+    test_tick &&
+    git commit -a -m "change in branch3"
+'
+
+# The next test will test the following:
+#
+#           working index HEAD target         working index HEAD
+#           ----------------------------------------------------
+# file1:     X       U     B    C     --merge  C       C     C
+test_expect_success '"reset --merge HEAD^" is ok with pending merge' '
+    git checkout third &&
+    test_must_fail git merge branch1 &&
+    git reset --merge HEAD^ &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse second)" &&
+    test -z "$(git diff --cached)" &&
+    test -z "$(git diff)"
+'
+
+# The next test will test the following:
+#
+#           working index HEAD target         working index HEAD
+#           ----------------------------------------------------
+# file1:     X       U     B    B     --merge  B       B     B
+test_expect_success '"reset --merge HEAD" is ok with pending merge' '
+    git reset --hard third &&
+    test_must_fail git merge branch1 &&
+    git reset --merge HEAD &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse third)" &&
+    test -z "$(git diff --cached)" &&
+    test -z "$(git diff)"
+'
+
+test_expect_success '--merge with added/deleted' '
+    git reset --hard third &&
+    rm -f file2 &&
+    test_must_fail git merge branch3 &&
+    ! test -f file2 &&
+    test -f file3 &&
+    git diff --exit-code file3 &&
+    git diff --exit-code branch3 file3 &&
+    git reset --merge HEAD &&
+    ! test -f file3 &&
+    ! test -f file2 &&
+    git diff --exit-code --cached
+'
+
+test_done
diff --git a/t/t7111-reset-table.sh b/t/t7111-reset-table.sh
new file mode 100755
index 0000000000..0a362a12bf
--- /dev/null
+++ b/t/t7111-reset-table.sh
@@ -0,0 +1,113 @@
+#!/bin/sh
+#
+# Copyright (c) 2010 Christian Couder
+#
+
+test_description='Tests to check that "reset" options follow a known table'
+
+. ./test-lib.sh
+
+
+test_expect_success 'creating initial commits' '
+    test_commit E file1 &&
+    test_commit D file1 &&
+    test_commit C file1
+'
+
+while read W1 I1 H1 T opt W2 I2 H2
+do
+    test_expect_success "check: $W1 $I1 $H1 $T --$opt $W2 $I2 $H2" '
+	git reset --hard C &&
+	if test "$I1" != "$H1"
+	then
+	    echo "$I1" >file1 &&
+	    git add file1
+	fi &&
+	if test "$W1" != "$I1"
+	then
+	    echo "$W1" >file1
+	fi &&
+	if test "$W2" != "XXXXX"
+	then
+	    git reset --$opt $T &&
+	    test "$(cat file1)" = "$W2" &&
+	    git checkout-index -f -- file1 &&
+	    test "$(cat file1)" = "$I2" &&
+	    git checkout -f HEAD -- file1 &&
+	    test "$(cat file1)" = "$H2"
+	else
+	    test_must_fail git reset --$opt $T
+	fi
+    '
+done <<\EOF
+A B C D soft   A B D
+A B C D mixed  A D D
+A B C D hard   D D D
+A B C D merge  XXXXX
+A B C C soft   A B C
+A B C C mixed  A C C
+A B C C hard   C C C
+A B C C merge  XXXXX
+B B C D soft   B B D
+B B C D mixed  B D D
+B B C D hard   D D D
+B B C D merge  D D D
+B B C C soft   B B C
+B B C C mixed  B C C
+B B C C hard   C C C
+B B C C merge  C C C
+B C C D soft   B C D
+B C C D mixed  B D D
+B C C D hard   D D D
+B C C D merge  XXXXX
+B C C C soft   B C C
+B C C C mixed  B C C
+B C C C hard   C C C
+B C C C merge  B C C
+EOF
+
+test_expect_success 'setting up branches to test with unmerged entries' '
+    git reset --hard C &&
+    git branch branch1 &&
+    git branch branch2 &&
+    git checkout branch1 &&
+    test_commit B1 file1 &&
+    git checkout branch2 &&
+    test_commit B2 file1
+'
+
+while read W1 I1 H1 T opt W2 I2 H2
+do
+    test_expect_success "check: $W1 $I1 $H1 $T --$opt $W2 $I2 $H2" '
+	git reset --hard B2 &&
+	test_must_fail git merge branch1 &&
+	cat file1 >X_file1 &&
+	if test "$W2" != "XXXXX"
+	then
+	    git reset --$opt $T &&
+	    if test "$W2" = "X"
+	    then
+		test_cmp file1 X_file1
+	    else
+		test "$(cat file1)" = "$W2"
+	    fi &&
+	    git checkout-index -f -- file1 &&
+	    test "$(cat file1)" = "$I2" &&
+	    git checkout -f HEAD -- file1 &&
+	    test "$(cat file1)" = "$H2"
+	else
+	    test_must_fail git reset --$opt $T
+	fi
+    '
+done <<\EOF
+X U C D soft   XXXXX
+X U C D mixed  X D D
+X U C D hard   D D D
+X U C D merge  D D D
+X U C C soft   XXXXX
+X U C C mixed  X C C
+X U C C hard   C C C
+X U C C merge  C C C
+EOF
+
+test_done
diff --git a/t/t7300-clean.sh b/t/t7300-clean.sh
index 118c6ebb18..7d8ed68bef 100755
--- a/t/t7300-clean.sh
+++ b/t/t7300-clean.sh
@@ -22,6 +22,25 @@ test_expect_success 'setup' '
 
 '
 
+test_expect_success 'git clean with skip-worktree .gitignore' '
+	git update-index --skip-worktree .gitignore &&
+	rm .gitignore &&
+	mkdir -p build docs &&
+	touch a.out src/part3.c docs/manual.txt obj.o build/lib.so &&
+	git clean &&
+	test -f Makefile &&
+	test -f README &&
+	test -f src/part1.c &&
+	test -f src/part2.c &&
+	test ! -f a.out &&
+	test ! -f src/part3.c &&
+	test -f docs/manual.txt &&
+	test -f obj.o &&
+	test -f build/lib.so &&
+	git update-index --no-skip-worktree .gitignore &&
+	git checkout .gitignore
+'
+
 test_expect_success 'git clean' '
 
 	mkdir -p build docs &&
diff --git a/test-index-version.c b/test-index-version.c
new file mode 100644
index 0000000000..bfaad9e09e
--- /dev/null
+++ b/test-index-version.c
@@ -0,0 +1,14 @@
+#include "cache.h"
+
+int main(int argc, const char **argv)
+{
+	struct cache_header hdr;
+	int version;
+
+	memset(&hdr,0,sizeof(hdr));
+	if (read(0, &hdr, sizeof(hdr)) != sizeof(hdr))
+		return 0;
+	version = ntohl(hdr.hdr_version);
+	printf("%d\n", version);
+	return 0;
+}
diff --git a/transport-helper.c b/transport-helper.c
index 11f3d7ec52..6ece0d9875 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -8,6 +8,8 @@
 #include "quote.h"
 #include "remote.h"
 
+static int debug;
+
 struct helper_data
 {
 	const char *name;
@@ -16,12 +18,81 @@ struct helper_data
 	unsigned fetch : 1,
 		import : 1,
 		option : 1,
-		push : 1;
+		push : 1,
+		connect : 1,
+		no_disconnect_req : 1;
 	/* These go from remote name (as in "list") to private name */
 	struct refspec *refspecs;
 	int refspec_nr;
+	/* Transport options for fetch-pack/send-pack (should one of
+	 * those be invoked).
+	 */
+	struct git_transport_options transport_options;
 };
 
+static void sendline(struct helper_data *helper, struct strbuf *buffer)
+{
+	if (debug)
+		fprintf(stderr, "Debug: Remote helper: -> %s", buffer->buf);
+	if (write_in_full(helper->helper->in, buffer->buf, buffer->len)
+		!= buffer->len)
+		die_errno("Full write to remote helper failed");
+}
+
+static int recvline_fh(FILE *helper, struct strbuf *buffer)
+{
+	strbuf_reset(buffer);
+	if (debug)
+		fprintf(stderr, "Debug: Remote helper: Waiting...\n");
+	if (strbuf_getline(buffer, helper, '\n') == EOF) {
+		if (debug)
+			fprintf(stderr, "Debug: Remote helper quit.\n");
+		exit(128);
+	}
+
+	if (debug)
+		fprintf(stderr, "Debug: Remote helper: <- %s\n", buffer->buf);
+	return 0;
+}
+
+static int recvline(struct helper_data *helper, struct strbuf *buffer)
+{
+	return recvline_fh(helper->out, buffer);
+}
+
+static void xchgline(struct helper_data *helper, struct strbuf *buffer)
+{
+	sendline(helper, buffer);
+	recvline(helper, buffer);
+}
+
+static void write_constant(int fd, const char *str)
+{
+	if (debug)
+		fprintf(stderr, "Debug: Remote helper: -> %s", str);
+	if (write_in_full(fd, str, strlen(str)) != strlen(str))
+		die_errno("Full write to remote helper failed");
+}
+
+const char *remove_ext_force(const char *url)
+{
+	if (url) {
+		const char *colon = strchr(url, ':');
+		if (colon && colon[1] == ':')
+			return colon + 2;
+	}
+	return url;
+}
+
+static void do_take_over(struct transport *transport)
+{
+	struct helper_data *data;
+	data = (struct helper_data *)transport->data;
+	transport_take_over(transport, data->helper);
+	fclose(data->out);
+	free(data);
+}
+
 static struct child_process *get_helper(struct transport *transport)
 {
 	struct helper_data *data = transport->data;
@@ -30,6 +101,7 @@ static struct child_process *get_helper(struct transport *transport)
 	const char **refspecs = NULL;
 	int refspec_nr = 0;
 	int refspec_alloc = 0;
+	int duped;
 
 	if (data->helper)
 		return data->helper;
@@ -42,34 +114,60 @@ static struct child_process *get_helper(struct transport *transport)
 	strbuf_addf(&buf, "remote-%s", data->name);
 	helper->argv[0] = strbuf_detach(&buf, NULL);
 	helper->argv[1] = transport->remote->name;
-	helper->argv[2] = transport->url;
+	helper->argv[2] = remove_ext_force(transport->url);
 	helper->git_cmd = 1;
 	if (start_command(helper))
 		die("Unable to run helper: git %s", helper->argv[0]);
 	data->helper = helper;
+	data->no_disconnect_req = 0;
 
-	write_str_in_full(helper->in, "capabilities\n");
+	/*
+	 * Open the output as FILE* so strbuf_getline() can be used.
+	 * Do this with duped fd because fclose() will close the fd,
+	 * and stuff like taking over will require the fd to remain.
+	 */
+	duped = dup(helper->out);
+	if (duped < 0)
+		die_errno("Can't dup helper output fd");
+	data->out = xfdopen(duped, "r");
+
+	write_constant(helper->in, "capabilities\n");
 
-	data->out = xfdopen(helper->out, "r");
 	while (1) {
-		if (strbuf_getline(&buf, data->out, '\n') == EOF)
-			exit(128); /* child died, message supplied already */
+		const char *capname;
+		int mandatory = 0;
+		recvline(data, &buf);
 
 		if (!*buf.buf)
 			break;
-		if (!strcmp(buf.buf, "fetch"))
+
+		if (*buf.buf == '*') {
+			capname = buf.buf + 1;
+			mandatory = 1;
+		} else
+			capname = buf.buf;
+
+		if (debug)
+			fprintf(stderr, "Debug: Got cap %s\n", capname);
+		if (!strcmp(capname, "fetch"))
 			data->fetch = 1;
-		if (!strcmp(buf.buf, "option"))
+		else if (!strcmp(capname, "option"))
 			data->option = 1;
-		if (!strcmp(buf.buf, "push"))
+		else if (!strcmp(capname, "push"))
 			data->push = 1;
-		if (!strcmp(buf.buf, "import"))
+		else if (!strcmp(capname, "import"))
 			data->import = 1;
-		if (!data->refspecs && !prefixcmp(buf.buf, "refspec ")) {
+		else if (!data->refspecs && !prefixcmp(capname, "refspec ")) {
 			ALLOC_GROW(refspecs,
 				   refspec_nr + 1,
 				   refspec_alloc);
 			refspecs[refspec_nr++] = strdup(buf.buf + strlen("refspec "));
+		} else if (!strcmp(capname, "connect")) {
+			data->connect = 1;
+		} else if (mandatory) {
+			die("Unknown madatory capability %s. This remote "
+			    "helper probably needs newer version of Git.\n",
+			    capname);
 		}
 	}
 	if (refspecs) {
@@ -82,15 +180,25 @@ static struct child_process *get_helper(struct transport *transport)
 		free(refspecs);
 	}
 	strbuf_release(&buf);
+	if (debug)
+		fprintf(stderr, "Debug: Capabilities complete.\n");
 	return data->helper;
 }
 
 static int disconnect_helper(struct transport *transport)
 {
 	struct helper_data *data = transport->data;
+	struct strbuf buf = STRBUF_INIT;
+
 	if (data->helper) {
-		write_str_in_full(data->helper->in, "\n");
+		if (debug)
+			fprintf(stderr, "Debug: Disconnecting.\n");
+		if (!data->no_disconnect_req) {
+			strbuf_addf(&buf, "\n");
+			sendline(data, &buf);
+		}
 		close(data->helper->in);
+		close(data->helper->out);
 		fclose(data->out);
 		finish_command(data->helper);
 		free((char *)data->helper->argv[0]);
@@ -117,10 +225,11 @@ static int set_helper_option(struct transport *transport,
 			  const char *name, const char *value)
 {
 	struct helper_data *data = transport->data;
-	struct child_process *helper = get_helper(transport);
 	struct strbuf buf = STRBUF_INIT;
 	int i, ret, is_bool = 0;
 
+	get_helper(transport);
+
 	if (!data->option)
 		return 1;
 
@@ -143,12 +252,7 @@ static int set_helper_option(struct transport *transport,
 		quote_c_style(value, &buf, NULL, 0);
 	strbuf_addch(&buf, '\n');
 
-	if (write_in_full(helper->in, buf.buf, buf.len) != buf.len)
-		die_errno("cannot send option to %s", data->name);
-
-	strbuf_reset(&buf);
-	if (strbuf_getline(&buf, data->out, '\n') == EOF)
-		exit(128); /* child died, message supplied already */
+	xchgline(data, &buf);
 
 	if (!strcmp(buf.buf, "ok"))
 		ret = 0;
@@ -208,13 +312,10 @@ static int fetch_with_fetch(struct transport *transport,
 	}
 
 	strbuf_addch(&buf, '\n');
-	if (write_in_full(data->helper->in, buf.buf, buf.len) != buf.len)
-		die_errno("cannot send fetch to %s", data->name);
+	sendline(data, &buf);
 
 	while (1) {
-		strbuf_reset(&buf);
-		if (strbuf_getline(&buf, data->out, '\n') == EOF)
-			exit(128); /* child died, message supplied already */
+		recvline(data, &buf);
 
 		if (!prefixcmp(buf.buf, "lock ")) {
 			const char *name = buf.buf + 5;
@@ -249,12 +350,13 @@ static int fetch_with_import(struct transport *transport,
 			     int nr_heads, struct ref **to_fetch)
 {
 	struct child_process fastimport;
-	struct child_process *helper = get_helper(transport);
 	struct helper_data *data = transport->data;
 	int i;
 	struct ref *posn;
 	struct strbuf buf = STRBUF_INIT;
 
+	get_helper(transport);
+
 	if (get_importer(transport, &fastimport))
 		die("Couldn't run fast-import");
 
@@ -264,7 +366,7 @@ static int fetch_with_import(struct transport *transport,
 			continue;
 
 		strbuf_addf(&buf, "import %s\n", posn->name);
-		write_in_full(helper->in, buf.buf, buf.len);
+		sendline(data, &buf);
 		strbuf_reset(&buf);
 	}
 	disconnect_helper(transport);
@@ -288,12 +390,112 @@ static int fetch_with_import(struct transport *transport,
 	return 0;
 }
 
+static int process_connect_service(struct transport *transport,
+				   const char *name, const char *exec)
+{
+	struct helper_data *data = transport->data;
+	struct strbuf cmdbuf = STRBUF_INIT;
+	struct child_process *helper;
+	int r, duped, ret = 0;
+	FILE *input;
+
+	helper = get_helper(transport);
+
+	/*
+	 * Yes, dup the pipe another time, as we need unbuffered version
+	 * of input pipe as FILE*. fclose() closes the underlying fd and
+	 * stream buffering only can be changed before first I/O operation
+	 * on it.
+	 */
+	duped = dup(helper->out);
+	if (duped < 0)
+		die_errno("Can't dup helper output fd");
+	input = xfdopen(duped, "r");
+	setvbuf(input, NULL, _IONBF, 0);
+
+	/*
+	 * Handle --upload-pack and friends. This is fire and forget...
+	 * just warn if it fails.
+	 */
+	if (strcmp(name, exec)) {
+		r = set_helper_option(transport, "servpath", exec);
+		if (r > 0)
+			warning("Setting remote service path not supported by protocol.");
+		else if (r < 0)
+			warning("Invalid remote service path.");
+	}
+
+	if (data->connect)
+		strbuf_addf(&cmdbuf, "connect %s\n", name);
+	else
+		goto exit;
+
+	sendline(data, &cmdbuf);
+	recvline_fh(input, &cmdbuf);
+	if (!strcmp(cmdbuf.buf, "")) {
+		data->no_disconnect_req = 1;
+		if (debug)
+			fprintf(stderr, "Debug: Smart transport connection "
+				"ready.\n");
+		ret = 1;
+	} else if (!strcmp(cmdbuf.buf, "fallback")) {
+		if (debug)
+			fprintf(stderr, "Debug: Falling back to dumb "
+				"transport.\n");
+	} else
+		die("Unknown response to connect: %s",
+			cmdbuf.buf);
+
+exit:
+	fclose(input);
+	return ret;
+}
+
+static int process_connect(struct transport *transport,
+				     int for_push)
+{
+	struct helper_data *data = transport->data;
+	const char *name;
+	const char *exec;
+
+	name = for_push ? "git-receive-pack" : "git-upload-pack";
+	if (for_push)
+		exec = data->transport_options.receivepack;
+	else
+		exec = data->transport_options.uploadpack;
+
+	return process_connect_service(transport, name, exec);
+}
+
+static int connect_helper(struct transport *transport, const char *name,
+		   const char *exec, int fd[2])
+{
+	struct helper_data *data = transport->data;
+
+	/* Get_helper so connect is inited. */
+	get_helper(transport);
+	if (!data->connect)
+		die("Operation not supported by protocol.");
+
+	if (!process_connect_service(transport, name, exec))
+		die("Can't connect to subservice %s.", name);
+
+	fd[0] = data->helper->out;
+	fd[1] = data->helper->in;
+	return 0;
+}
+
 static int fetch(struct transport *transport,
 		 int nr_heads, struct ref **to_fetch)
 {
 	struct helper_data *data = transport->data;
 	int i, count;
 
+	if (process_connect(transport, 0)) {
+		do_take_over(transport);
+		return transport->fetch(transport, nr_heads, to_fetch);
+	}
+
 	count = 0;
 	for (i = 0; i < nr_heads; i++)
 		if (!(to_fetch[i]->status & REF_STATUS_UPTODATE))
@@ -321,6 +523,11 @@ static int push_refs(struct transport *transport,
 	struct child_process *helper;
 	struct ref *ref;
 
+	if (process_connect(transport, 1)) {
+		do_take_over(transport);
+		return transport->push_refs(transport, remote_refs, flags);
+	}
+
 	if (!remote_refs)
 		return 0;
 
@@ -369,17 +576,14 @@ static int push_refs(struct transport *transport,
 	}
 
 	strbuf_addch(&buf, '\n');
-	if (write_in_full(helper->in, buf.buf, buf.len) != buf.len)
-		exit(128);
+	sendline(data, &buf);
 
 	ref = remote_refs;
 	while (1) {
 		char *refname, *msg;
 		int status;
 
-		strbuf_reset(&buf);
-		if (strbuf_getline(&buf, data->out, '\n') == EOF)
-			exit(128); /* child died, message supplied already */
+		recvline(data, &buf);
 		if (!buf.len)
 			break;
 
@@ -464,6 +668,11 @@ static struct ref *get_refs_list(struct transport *transport, int for_push)
 
 	helper = get_helper(transport);
 
+	if (process_connect(transport, for_push)) {
+		do_take_over(transport);
+		return transport->get_refs_list(transport, for_push);
+	}
+
 	if (data->push && for_push)
 		write_str_in_full(helper->in, "list for-push\n");
 	else
@@ -471,8 +680,7 @@ static struct ref *get_refs_list(struct transport *transport, int for_push)
 
 	while (1) {
 		char *eov, *eon;
-		if (strbuf_getline(&buf, data->out, '\n') == EOF)
-			exit(128); /* child died, message supplied already */
+		recvline(data, &buf);
 
 		if (!*buf.buf)
 			break;
@@ -497,6 +705,8 @@ static struct ref *get_refs_list(struct transport *transport, int for_push)
 		}
 		tail = &((*tail)->next);
 	}
+	if (debug)
+		fprintf(stderr, "Debug: Read ref listing.\n");
 	strbuf_release(&buf);
 
 	for (posn = ret; posn; posn = posn->next)
@@ -510,11 +720,16 @@ int transport_helper_init(struct transport *transport, const char *name)
 	struct helper_data *data = xcalloc(sizeof(*data), 1);
 	data->name = name;
 
+	if (getenv("GIT_TRANSPORT_HELPER_DEBUG"))
+		debug = 1;
+
 	transport->data = data;
 	transport->set_option = set_helper_option;
 	transport->get_refs_list = get_refs_list;
 	transport->fetch = fetch;
 	transport->push_refs = push_refs;
 	transport->disconnect = release_helper;
+	transport->connect = connect_helper;
+	transport->smart_options = &(data->transport_options);
 	return 0;
 }
diff --git a/transport.c b/transport.c
index 3eea836a33..b5332c018b 100644
--- a/transport.c
+++ b/transport.c
@@ -395,41 +395,36 @@ static int close_bundle(struct transport *transport)
 }
 
 struct git_transport_data {
-	unsigned thin : 1;
-	unsigned keep : 1;
-	unsigned followtags : 1;
-	int depth;
+	struct git_transport_options options;
 	struct child_process *conn;
 	int fd[2];
-	const char *uploadpack;
-	const char *receivepack;
+	unsigned got_remote_heads : 1;
 	struct extra_have_objects extra_have;
 };
 
-static int set_git_option(struct transport *connection,
+static int set_git_option(struct git_transport_options *opts,
 			  const char *name, const char *value)
 {
-	struct git_transport_data *data = connection->data;
 	if (!strcmp(name, TRANS_OPT_UPLOADPACK)) {
-		data->uploadpack = value;
+		opts->uploadpack = value;
 		return 0;
 	} else if (!strcmp(name, TRANS_OPT_RECEIVEPACK)) {
-		data->receivepack = value;
+		opts->receivepack = value;
 		return 0;
 	} else if (!strcmp(name, TRANS_OPT_THIN)) {
-		data->thin = !!value;
+		opts->thin = !!value;
 		return 0;
 	} else if (!strcmp(name, TRANS_OPT_FOLLOWTAGS)) {
-		data->followtags = !!value;
+		opts->followtags = !!value;
 		return 0;
 	} else if (!strcmp(name, TRANS_OPT_KEEP)) {
-		data->keep = !!value;
+		opts->keep = !!value;
 		return 0;
 	} else if (!strcmp(name, TRANS_OPT_DEPTH)) {
 		if (!value)
-			data->depth = 0;
+			opts->depth = 0;
 		else
-			data->depth = atoi(value);
+			opts->depth = atoi(value);
 		return 0;
 	}
 	return 1;
@@ -438,9 +433,15 @@ static int set_git_option(struct transport *connection,
 static int connect_setup(struct transport *transport, int for_push, int verbose)
 {
 	struct git_transport_data *data = transport->data;
+
+	if (data->conn)
+		return 0;
+
 	data->conn = git_connect(data->fd, transport->url,
-				 for_push ? data->receivepack : data->uploadpack,
+				 for_push ? data->options.receivepack :
+				 data->options.uploadpack,
 				 verbose ? CONNECT_VERBOSE : 0);
+
 	return 0;
 }
 
@@ -452,6 +453,7 @@ static struct ref *get_refs_via_connect(struct transport *transport, int for_pus
 	connect_setup(transport, for_push, 0);
 	get_remote_heads(data->fd[0], &refs, 0, NULL,
 			 for_push ? REF_NORMAL : 0, &data->extra_have);
+	data->got_remote_heads = 1;
 
 	return refs;
 }
@@ -469,22 +471,23 @@ static int fetch_refs_via_pack(struct transport *transport,
 	struct ref *refs_tmp = NULL;
 
 	memset(&args, 0, sizeof(args));
-	args.uploadpack = data->uploadpack;
-	args.keep_pack = data->keep;
+	args.uploadpack = data->options.uploadpack;
+	args.keep_pack = data->options.keep;
 	args.lock_pack = 1;
-	args.use_thin_pack = data->thin;
-	args.include_tag = data->followtags;
+	args.use_thin_pack = data->options.thin;
+	args.include_tag = data->options.followtags;
 	args.verbose = (transport->verbose > 0);
 	args.quiet = (transport->verbose < 0);
 	args.no_progress = args.quiet || (!transport->progress && !isatty(1));
-	args.depth = data->depth;
+	args.depth = data->options.depth;
 
 	for (i = 0; i < nr_heads; i++)
 		origh[i] = heads[i] = xstrdup(to_fetch[i]->name);
 
-	if (!data->conn) {
+	if (!data->got_remote_heads) {
 		connect_setup(transport, 0, 0);
 		get_remote_heads(data->fd[0], &refs_tmp, 0, NULL, 0, NULL);
+		data->got_remote_heads = 1;
 	}
 
 	refs = fetch_pack(&args, data->fd, data->conn,
@@ -495,6 +498,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 	if (finish_connect(data->conn))
 		refs = NULL;
 	data->conn = NULL;
+	data->got_remote_heads = 0;
 
 	free_refs(refs_tmp);
 
@@ -723,18 +727,19 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 	struct send_pack_args args;
 	int ret;
 
-	if (!data->conn) {
+	if (!data->got_remote_heads) {
 		struct ref *tmp_refs;
 		connect_setup(transport, 1, 0);
 
 		get_remote_heads(data->fd[0], &tmp_refs, 0, NULL, REF_NORMAL,
 				 NULL);
+		data->got_remote_heads = 1;
 	}
 
 	memset(&args, 0, sizeof(args));
 	args.send_mirror = !!(flags & TRANSPORT_PUSH_MIRROR);
 	args.force_update = !!(flags & TRANSPORT_PUSH_FORCE);
-	args.use_thin_pack = data->thin;
+	args.use_thin_pack = data->options.thin;
 	args.verbose = !!(flags & TRANSPORT_PUSH_VERBOSE);
 	args.quiet = !!(flags & TRANSPORT_PUSH_QUIET);
 	args.dry_run = !!(flags & TRANSPORT_PUSH_DRY_RUN);
@@ -746,15 +751,28 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 	close(data->fd[0]);
 	ret |= finish_connect(data->conn);
 	data->conn = NULL;
+	data->got_remote_heads = 0;
 
 	return ret;
 }
 
+static int connect_git(struct transport *transport, const char *name,
+		       const char *executable, int fd[2])
+{
+	struct git_transport_data *data = transport->data;
+	data->conn = git_connect(data->fd, transport->url,
+				 executable, 0);
+	fd[0] = data->fd[0];
+	fd[1] = data->fd[1];
+	return 0;
+}
+
 static int disconnect_git(struct transport *transport)
 {
 	struct git_transport_data *data = transport->data;
 	if (data->conn) {
-		packet_flush(data->fd[1]);
+		if (data->got_remote_heads)
+			packet_flush(data->fd[1]);
 		close(data->fd[0]);
 		close(data->fd[1]);
 		finish_connect(data->conn);
@@ -764,6 +782,32 @@ static int disconnect_git(struct transport *transport)
 	return 0;
 }
 
+void transport_take_over(struct transport *transport,
+			 struct child_process *child)
+{
+	struct git_transport_data *data;
+
+	if (!transport->smart_options)
+		die("Bug detected: Taking over transport requires non-NULL "
+		    "smart_options field.");
+
+	data = xcalloc(1, sizeof(*data));
+	data->options = *transport->smart_options;
+	data->conn = child;
+	data->fd[0] = data->conn->out;
+	data->fd[1] = data->conn->in;
+	data->got_remote_heads = 0;
+	transport->data = data;
+
+	transport->set_option = NULL;
+	transport->get_refs_list = get_refs_via_connect;
+	transport->fetch = fetch_refs_via_pack;
+	transport->push = NULL;
+	transport->push_refs = git_transport_push;
+	transport->disconnect = disconnect_git;
+	transport->smart_options = &(data->options);
+}
+
 static int is_local(const char *url)
 {
 	const char *colon = strchr(url, ':');
@@ -780,6 +824,44 @@ static int is_file(const char *url)
 	return S_ISREG(buf.st_mode);
 }
 
+static int is_url(const char *url)
+{
+	const char *url2, *first_slash;
+
+	if (!url)
+		return 0;
+	url2 = url;
+	first_slash = strchr(url, '/');
+
+	/* Input with no slash at all or slash first can't be URL. */
+	if (!first_slash || first_slash == url)
+		return 0;
+	/* Character before must be : and next must be /. */
+	if (first_slash[-1] != ':' || first_slash[1] != '/')
+		return 0;
+	/* There must be something before the :// */
+	if (first_slash == url + 1)
+		return 0;
+	/*
+	 * Check all characters up to first slash - 1. Only alphanum
+	 * is allowed.
+	 */
+	url2 = url;
+	while (url2 < first_slash - 1) {
+		if (!isalnum((unsigned char)*url2))
+			return 0;
+		url2++;
+	}
+
+	/* Valid enough. */
+	return 1;
+}
+
+static int external_specification_len(const char *url)
+{
+	return strchr(url, ':') - url;
+}
+
 struct transport *transport_get(struct remote *remote, const char *url)
 {
 	struct transport *ret = xcalloc(1, sizeof(*ret));
@@ -793,6 +875,9 @@ struct transport *transport_get(struct remote *remote, const char *url)
 		url = remote->url[0];
 	ret->url = url;
 
+	/* In case previous URL had helper forced, reset it. */
+	remote->foreign_vcs = NULL;
+
 	/* maybe it is a foreign URL? */
 	if (url) {
 		const char *p = url;
@@ -805,46 +890,54 @@ struct transport *transport_get(struct remote *remote, const char *url)
 
 	if (remote && remote->foreign_vcs) {
 		transport_helper_init(ret, remote->foreign_vcs);
-		return ret;
-	}
-
-	if (!prefixcmp(url, "rsync:")) {
+	} else if (!prefixcmp(url, "rsync:")) {
 		ret->get_refs_list = get_refs_via_rsync;
 		ret->fetch = fetch_objs_via_rsync;
 		ret->push = rsync_transport_push;
-
-	} else if (!prefixcmp(url, "http://")
-	        || !prefixcmp(url, "https://")
-	        || !prefixcmp(url, "ftp://")) {
-		transport_helper_init(ret, "curl");
-#ifdef NO_CURL
-		error("git was compiled without libcurl support.");
-#endif
-
+		ret->smart_options = NULL;
 	} else if (is_local(url) && is_file(url)) {
 		struct bundle_transport_data *data = xcalloc(1, sizeof(*data));
 		ret->data = data;
 		ret->get_refs_list = get_refs_from_bundle;
 		ret->fetch = fetch_refs_from_bundle;
 		ret->disconnect = close_bundle;
-
-	} else {
+		ret->smart_options = NULL;
+	} else if (!is_url(url)
+		|| !prefixcmp(url, "file://")
+		|| !prefixcmp(url, "git://")
+		|| !prefixcmp(url, "ssh://")
+		|| !prefixcmp(url, "git+ssh://")
+		|| !prefixcmp(url, "ssh+git://")) {
+		/* These are builtin smart transports. */
 		struct git_transport_data *data = xcalloc(1, sizeof(*data));
 		ret->data = data;
-		ret->set_option = set_git_option;
+		ret->set_option = NULL;
 		ret->get_refs_list = get_refs_via_connect;
 		ret->fetch = fetch_refs_via_pack;
 		ret->push_refs = git_transport_push;
+		ret->connect = connect_git;
 		ret->disconnect = disconnect_git;
+		ret->smart_options = &(data->options);
 
-		data->thin = 1;
 		data->conn = NULL;
-		data->uploadpack = "git-upload-pack";
+		data->got_remote_heads = 0;
+	} else {
+		/* Unknown protocol in URL. Pass to external handler. */
+		int len = external_specification_len(url);
+		char *handler = xmalloc(len + 1);
+		handler[len] = 0;
+		strncpy(handler, url, len);
+		transport_helper_init(ret, handler);
+	}
+
+	if (ret->smart_options) {
+		ret->smart_options->thin = 1;
+		ret->smart_options->uploadpack = "git-upload-pack";
 		if (remote->uploadpack)
-			data->uploadpack = remote->uploadpack;
-		data->receivepack = "git-receive-pack";
+			ret->smart_options->uploadpack = remote->uploadpack;
+		ret->smart_options->receivepack = "git-receive-pack";
 		if (remote->receivepack)
-			data->receivepack = remote->receivepack;
+			ret->smart_options->receivepack = remote->receivepack;
 	}
 
 	return ret;
@@ -853,8 +946,23 @@ struct transport *transport_get(struct remote *remote, const char *url)
 int transport_set_option(struct transport *transport,
 			 const char *name, const char *value)
 {
+	int git_reports = 1, protocol_reports = 1;
+
+	if (transport->smart_options)
+		git_reports = set_git_option(transport->smart_options,
+					     name, value);
+
 	if (transport->set_option)
-		return transport->set_option(transport, name, value);
+		protocol_reports = transport->set_option(transport, name,
+							value);
+
+	/* If either report is 0, report 0 (success). */
+	if (!git_reports || !protocol_reports)
+		return 0;
+	/* If either reports -1 (invalid value), report -1. */
+	if ((git_reports == -1) || (protocol_reports == -1))
+		return -1;
+	/* Otherwise if both report unknown, report unknown. */
 	return 1;
 }
 
@@ -865,9 +973,9 @@ int transport_push(struct transport *transport,
 	*nonfastforward = 0;
 	verify_remote_names(refspec_nr, refspec);
 
-	if (transport->push)
+	if (transport->push) {
 		return transport->push(transport, refspec_nr, refspec, flags);
-	if (transport->push_refs) {
+	} else if (transport->push_refs) {
 		struct ref *remote_refs =
 			transport->get_refs_list(transport, 1);
 		struct ref *local_refs = get_local_heads();
@@ -911,6 +1019,7 @@ const struct ref *transport_get_remote_refs(struct transport *transport)
 {
 	if (!transport->remote_refs)
 		transport->remote_refs = transport->get_refs_list(transport, 0);
+
 	return transport->remote_refs;
 }
 
@@ -945,6 +1054,7 @@ int transport_fetch_refs(struct transport *transport, struct ref *refs)
 	}
 
 	rc = transport->fetch(transport, nr_heads, heads);
+
 	free(heads);
 	return rc;
 }
@@ -958,6 +1068,15 @@ void transport_unlock_pack(struct transport *transport)
 	}
 }
 
+int transport_connect(struct transport *transport, const char *name,
+		      const char *exec, int fd[2])
+{
+	if (transport->connect)
+		return transport->connect(transport, name, exec, fd);
+	else
+		die("Operation not supported by protocol");
+}
+
 int transport_disconnect(struct transport *transport)
 {
 	int ret = 0;
diff --git a/transport.h b/transport.h
index 9e74406fa2..97ba2519dd 100644
--- a/transport.h
+++ b/transport.h
@@ -4,6 +4,15 @@
 #include "cache.h"
 #include "remote.h"
 
+struct git_transport_options {
+	unsigned thin : 1;
+	unsigned keep : 1;
+	unsigned followtags : 1;
+	int depth;
+	const char *uploadpack;
+	const char *receivepack;
+};
+
 struct transport {
 	struct remote *remote;
 	const char *url;
@@ -55,6 +64,8 @@ struct transport {
 	 **/
 	int (*push_refs)(struct transport *transport, struct ref *refs, int flags);
 	int (*push)(struct transport *connection, int refspec_nr, const char **refspec, int flags);
+	int (*connect)(struct transport *connection, const char *name,
+		       const char *executable, int fd[2]);
 
 	/** get_refs_list(), fetch(), and push_refs() can keep
 	 * resources (such as a connection) reserved for futher
@@ -65,6 +76,12 @@ struct transport {
 	signed verbose : 3;
 	/* Force progress even if the output is not a tty */
 	unsigned progress : 1;
+	/*
+	 * If transport is at least potentially smart, this points to
+	 * git_transport_options structure to use in case transport
+	 * actually turns out to be smart.
+	 */
+	struct git_transport_options *smart_options;
 };
 
 #define TRANSPORT_PUSH_ALL 1
@@ -115,6 +132,11 @@ int transport_fetch_refs(struct transport *transport, struct ref *refs);
 void transport_unlock_pack(struct transport *transport);
 int transport_disconnect(struct transport *transport);
 char *transport_anonymize_url(const char *url);
+void transport_take_over(struct transport *transport,
+			 struct child_process *child);
+
+int transport_connect(struct transport *transport, const char *name,
+		      const char *exec, int fd[2]);
 
 /* Transport methods defined outside transport.c */
 int transport_helper_init(struct transport *transport, const char *name);
diff --git a/unpack-trees.c b/unpack-trees.c
index dd5999c356..acdd311737 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -32,6 +32,12 @@ static struct unpack_trees_error_msgs unpack_plumbing_errors = {
 
 	/* bind_overlap */
 	"Entry '%s' overlaps with '%s'.  Cannot bind.",
+
+	/* sparse_not_uptodate_file */
+	"Entry '%s' not uptodate. Cannot update sparse checkout.",
+
+	/* would_lose_orphaned */
+	"Working tree file '%s' would be %s by sparse checkout update.",
 };
 
 #define ERRORMSG(o,fld) \
@@ -78,7 +84,7 @@ static int check_updates(struct unpack_trees_options *o)
 	if (o->update && o->verbose_update) {
 		for (total = cnt = 0; cnt < index->cache_nr; cnt++) {
 			struct cache_entry *ce = index->cache[cnt];
-			if (ce->ce_flags & (CE_UPDATE | CE_REMOVE))
+			if (ce->ce_flags & (CE_UPDATE | CE_REMOVE | CE_WT_REMOVE))
 				total++;
 		}
 
@@ -92,6 +98,13 @@ static int check_updates(struct unpack_trees_options *o)
 	for (i = 0; i < index->cache_nr; i++) {
 		struct cache_entry *ce = index->cache[i];
 
+		if (ce->ce_flags & CE_WT_REMOVE) {
+			display_progress(progress, ++cnt);
+			if (o->update)
+				unlink_entry(ce);
+			continue;
+		}
+
 		if (ce->ce_flags & CE_REMOVE) {
 			display_progress(progress, ++cnt);
 			if (o->update)
@@ -118,6 +131,57 @@ static int check_updates(struct unpack_trees_options *o)
 	return errs != 0;
 }
 
+static int verify_uptodate_sparse(struct cache_entry *ce, struct unpack_trees_options *o);
+static int verify_absent_sparse(struct cache_entry *ce, const char *action, struct unpack_trees_options *o);
+
+static int will_have_skip_worktree(const struct cache_entry *ce, struct unpack_trees_options *o)
+{
+	const char *basename;
+
+	if (ce_stage(ce))
+		return 0;
+
+	basename = strrchr(ce->name, '/');
+	basename = basename ? basename+1 : ce->name;
+	return excluded_from_list(ce->name, ce_namelen(ce), basename, NULL, o->el) <= 0;
+}
+
+static int apply_sparse_checkout(struct cache_entry *ce, struct unpack_trees_options *o)
+{
+	int was_skip_worktree = ce_skip_worktree(ce);
+
+	if (will_have_skip_worktree(ce, o))
+		ce->ce_flags |= CE_SKIP_WORKTREE;
+	else
+		ce->ce_flags &= ~CE_SKIP_WORKTREE;
+
+	/*
+	 * We only care about files getting into the checkout area
+	 * If merge strategies want to remove some, go ahead, this
+	 * flag will be removed eventually in unpack_trees() if it's
+	 * outside checkout area.
+	 */
+	if (ce->ce_flags & CE_REMOVE)
+		return 0;
+
+	if (!was_skip_worktree && ce_skip_worktree(ce)) {
+		/*
+		 * If CE_UPDATE is set, verify_uptodate() must be called already
+		 * also stat info may have lost after merged_entry() so calling
+		 * verify_uptodate() again may fail
+		 */
+		if (!(ce->ce_flags & CE_UPDATE) && verify_uptodate_sparse(ce, o))
+			return -1;
+		ce->ce_flags |= CE_WT_REMOVE;
+	}
+	if (was_skip_worktree && !ce_skip_worktree(ce)) {
+		if (verify_absent_sparse(ce, "overwritten", o))
+			return -1;
+		ce->ce_flags |= CE_UPDATE;
+	}
+	return 0;
+}
+
 static inline int call_unpack_fn(struct cache_entry **src, struct unpack_trees_options *o)
 {
 	int ret = o->fn(src, o);
@@ -369,8 +433,9 @@ static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, str
  */
 int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
 {
-	int ret;
+	int i, ret;
 	static struct cache_entry *dfc;
+	struct exclude_list el;
 
 	if (len > MAX_UNPACK_TREES)
 		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
@@ -380,6 +445,16 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	state.quiet = 1;
 	state.refresh_cache = 1;
 
+	memset(&el, 0, sizeof(el));
+	if (!core_apply_sparse_checkout || !o->update)
+		o->skip_sparse_checkout = 1;
+	if (!o->skip_sparse_checkout) {
+		if (add_excludes_from_file_to_list(git_path("info/sparse-checkout"), "", 0, NULL, &el, 0) < 0)
+			o->skip_sparse_checkout = 1;
+		else
+			o->el = &el;
+	}
+
 	memset(&o->result, 0, sizeof(o->result));
 	o->result.initialized = 1;
 	if (o->src_index) {
@@ -400,26 +475,65 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		info.fn = unpack_callback;
 		info.data = o;
 
-		if (traverse_trees(len, t, &info) < 0)
-			return unpack_failed(o, NULL);
+		if (traverse_trees(len, t, &info) < 0) {
+			ret = unpack_failed(o, NULL);
+			goto done;
+		}
 	}
 
 	/* Any left-over entries in the index? */
 	if (o->merge) {
 		while (o->pos < o->src_index->cache_nr) {
 			struct cache_entry *ce = o->src_index->cache[o->pos];
-			if (unpack_index_entry(ce, o) < 0)
-				return unpack_failed(o, NULL);
+			if (unpack_index_entry(ce, o) < 0) {
+				ret = unpack_failed(o, NULL);
+				goto done;
+			}
 		}
 	}
 
-	if (o->trivial_merges_only && o->nontrivial_merge)
-		return unpack_failed(o, "Merge requires file-level merging");
+	if (o->trivial_merges_only && o->nontrivial_merge) {
+		ret = unpack_failed(o, "Merge requires file-level merging");
+		goto done;
+	}
+
+	if (!o->skip_sparse_checkout) {
+		int empty_worktree = 1;
+		for (i = 0;i < o->result.cache_nr;i++) {
+			struct cache_entry *ce = o->result.cache[i];
+
+			if (apply_sparse_checkout(ce, o)) {
+				ret = -1;
+				goto done;
+			}
+			/*
+			 * Merge strategies may set CE_UPDATE|CE_REMOVE outside checkout
+			 * area as a result of ce_skip_worktree() shortcuts in
+			 * verify_absent() and verify_uptodate(). Clear them.
+			 */
+			if (ce_skip_worktree(ce))
+				ce->ce_flags &= ~(CE_UPDATE | CE_REMOVE);
+			else
+				empty_worktree = 0;
+
+		}
+		if (o->result.cache_nr && empty_worktree) {
+			ret = unpack_failed(o, "Sparse checkout leaves no entry on working directory");
+			goto done;
+		}
+	}
 
 	o->src_index = NULL;
 	ret = check_updates(o) ? (-2) : 0;
 	if (o->dst_index)
 		*o->dst_index = o->result;
+
+done:
+	for (i = 0;i < el.nr;i++)
+		free(el.excludes[i]);
+	if (el.excludes)
+		free(el.excludes);
+
 	return ret;
 }
 
@@ -436,6 +550,8 @@ static int same(struct cache_entry *a, struct cache_entry *b)
 		return 0;
 	if (!a && !b)
 		return 1;
+	if ((a->ce_flags | b->ce_flags) & CE_CONFLICTED)
+		return 0;
 	return a->ce_mode == b->ce_mode &&
 	       !hashcmp(a->sha1, b->sha1);
 }
@@ -445,16 +561,17 @@ static int same(struct cache_entry *a, struct cache_entry *b)
  * When a CE gets turned into an unmerged entry, we
  * want it to be up-to-date
  */
-static int verify_uptodate(struct cache_entry *ce,
-		struct unpack_trees_options *o)
+static int verify_uptodate_1(struct cache_entry *ce,
+				   struct unpack_trees_options *o,
+				   const char *error_msg)
 {
 	struct stat st;
 
-	if (o->index_only || o->reset || ce_uptodate(ce))
+	if (o->index_only || (!ce_skip_worktree(ce) && (o->reset || ce_uptodate(ce))))
 		return 0;
 
 	if (!lstat(ce->name, &st)) {
-		unsigned changed = ie_match_stat(o->src_index, ce, &st, CE_MATCH_IGNORE_VALID);
+		unsigned changed = ie_match_stat(o->src_index, ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
 		if (!changed)
 			return 0;
 		/*
@@ -471,7 +588,21 @@ static int verify_uptodate(struct cache_entry *ce,
 	if (errno == ENOENT)
 		return 0;
 	return o->gently ? -1 :
-		error(ERRORMSG(o, not_uptodate_file), ce->name);
+		error(error_msg, ce->name);
+}
+
+static int verify_uptodate(struct cache_entry *ce,
+			   struct unpack_trees_options *o)
+{
+	if (!o->skip_sparse_checkout && will_have_skip_worktree(ce, o))
+		return 0;
+	return verify_uptodate_1(ce, o, ERRORMSG(o, not_uptodate_file));
+}
+
+static int verify_uptodate_sparse(struct cache_entry *ce,
+				  struct unpack_trees_options *o)
+{
+	return verify_uptodate_1(ce, o, ERRORMSG(o, sparse_not_uptodate_file));
 }
 
 static void invalidate_ce_path(struct cache_entry *ce, struct unpack_trees_options *o)
@@ -572,15 +703,16 @@ static int icase_exists(struct unpack_trees_options *o, struct cache_entry *dst,
 	struct cache_entry *src;
 
 	src = index_name_exists(o->src_index, dst->name, ce_namelen(dst), 1);
-	return src && !ie_match_stat(o->src_index, src, st, CE_MATCH_IGNORE_VALID);
+	return src && !ie_match_stat(o->src_index, src, st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
 }
 
 /*
  * We do not want to remove or overwrite a working tree file that
  * is not tracked, unless it is ignored.
  */
-static int verify_absent(struct cache_entry *ce, const char *action,
-			 struct unpack_trees_options *o)
+static int verify_absent_1(struct cache_entry *ce, const char *action,
+				 struct unpack_trees_options *o,
+				 const char *error_msg)
 {
 	struct stat st;
 
@@ -660,13 +792,30 @@ static int verify_absent(struct cache_entry *ce, const char *action,
 	}
 	return 0;
 }
+static int verify_absent(struct cache_entry *ce, const char *action,
+			 struct unpack_trees_options *o)
+{
+	if (!o->skip_sparse_checkout && will_have_skip_worktree(ce, o))
+		return 0;
+	return verify_absent_1(ce, action, o, ERRORMSG(o, would_lose_untracked));
+}
+
+static int verify_absent_sparse(struct cache_entry *ce, const char *action,
+			 struct unpack_trees_options *o)
+{
+	return verify_absent_1(ce, action, o, ERRORMSG(o, would_lose_orphaned));
+}
 
 static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 		struct unpack_trees_options *o)
 {
 	int update = CE_UPDATE;
 
-	if (old) {
+	if (!old) {
+		if (verify_absent(merge, "overwritten", o))
+			return -1;
+		invalidate_ce_path(merge, o);
+	} else if (!(old->ce_flags & CE_CONFLICTED)) {
 		/*
 		 * See if we can re-use the old CE directly?
 		 * That way we get the uptodate stat info.
@@ -680,13 +829,16 @@ static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
 		} else {
 			if (verify_uptodate(old, o))
 				return -1;
+			if (ce_skip_worktree(old))
+				update |= CE_SKIP_WORKTREE;
 			invalidate_ce_path(old, o);
 		}
-	}
-	else {
-		if (verify_absent(merge, "overwritten", o))
-			return -1;
-		invalidate_ce_path(merge, o);
+	} else {
+		/*
+		 * Previously unmerged entry left as an existence
+		 * marker by read_index_unmerged();
+		 */
+		invalidate_ce_path(old, o);
 	}
 
 	add_entry(o, merge, update, CE_STAGEMASK);
@@ -702,7 +854,7 @@ static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
 			return -1;
 		return 0;
 	}
-	if (verify_uptodate(old, o))
+	if (!(old->ce_flags & CE_CONFLICTED) && verify_uptodate(old, o))
 		return -1;
 	add_entry(o, ce, CE_REMOVE, 0);
 	invalidate_ce_path(ce, o);
@@ -1004,10 +1156,10 @@ int oneway_merge(struct cache_entry **src, struct unpack_trees_options *o)
 
 	if (old && same(old, a)) {
 		int update = 0;
-		if (o->reset && !ce_uptodate(old)) {
+		if (o->reset && !ce_uptodate(old) && !ce_skip_worktree(old)) {
 			struct stat st;
 			if (lstat(old->name, &st) ||
-			    ie_match_stat(o->src_index, old, &st, CE_MATCH_IGNORE_VALID))
+			    ie_match_stat(o->src_index, old, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE))
 				update |= CE_UPDATE;
 		}
 		add_entry(o, old, update, 0);
diff --git a/unpack-trees.h b/unpack-trees.h
index d19df44f40..95ff36c824 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -4,6 +4,7 @@
 #define MAX_UNPACK_TREES 8
 
 struct unpack_trees_options;
+struct exclude_list;
 
 typedef int (*merge_fn_t)(struct cache_entry **src,
 		struct unpack_trees_options *options);
@@ -14,6 +15,8 @@ struct unpack_trees_error_msgs {
 	const char *not_uptodate_dir;
 	const char *would_lose_untracked;
 	const char *bind_overlap;
+	const char *sparse_not_uptodate_file;
+	const char *would_lose_orphaned;
 };
 
 struct unpack_trees_options {
@@ -28,6 +31,7 @@ struct unpack_trees_options {
 		     skip_unmerged,
 		     initial_checkout,
 		     diff_index_cached,
+		     skip_sparse_checkout,
 		     gently;
 	const char *prefix;
 	int pos;
@@ -44,6 +48,8 @@ struct unpack_trees_options {
 	struct index_state *dst_index;
 	struct index_state *src_index;
 	struct index_state result;
+
+	struct exclude_list *el; /* for internal use */
 };
 
 extern int unpack_trees(unsigned n, struct tree_desc *t,