wrapper: add git_mkdtemp()

Extend git_mkstemps_mode() to optionally call mkdir(2) instead of
open(2), then use that ability to create a mkdtemp(3) replacement,
git_mkdtemp().  We'll start using it in the next commit.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wrapper.c

@@ -446,7 +446,11 @@ int xmkstemp(char *filename_template)
 #undef TMP_MAX
 #define TMP_MAX 16384
 
-int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
+/*
+ * Returns -1 on error, 0 if it created a directory, or an open file
+ * descriptor to the created regular file.
+ */
+static int git_mkdstemps_mode(char *pattern, int suffix_len, int mode, bool dir)
 {
 	static const char letters[] =
 		"abcdefghijklmnopqrstuvwxyz"
@@ -488,7 +492,10 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 			v /= num_letters;
 		}
 
-		fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
+		if (dir)
+			fd = mkdir(pattern, mode);
+		else
+			fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
 		if (fd >= 0)
 			return fd;
 		/*
@@ -503,6 +510,16 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 	return -1;
 }
 
+char *git_mkdtemp(char *pattern)
+{
+	return git_mkdstemps_mode(pattern, 0, 0700, true) ? NULL : pattern;
+}
+
+int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
+{
+	return git_mkdstemps_mode(pattern, suffix_len, mode, false);
+}
+
 int git_mkstemp_mode(char *pattern, int mode)
 {
 	/* mkstemp is just mkstemps with no suffix */

wrapper.h

@@ -37,6 +37,8 @@ int xsnprintf(char *dst, size_t max, const char *fmt, ...);
 
 int xgethostname(char *buf, size_t len);
 
+char *git_mkdtemp(char *pattern);
+
 /* set default permissions by passing mode arguments to open(2) */
 int git_mkstemps_mode(char *pattern, int suffix_len, int mode);
 int git_mkstemp_mode(char *pattern, int mode);