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Commit 1b77d83cab 'setup_git_directory_gently_1(): resolve symlinks
in ceiling paths' changed the setup code to resolve symlinks in the
entries in GIT_CEILING_DIRECTORIES. Because those entries are
compared textually to the symlink-resolved current directory, an
entry in GIT_CEILING_DIRECTORIES that contained a symlink would have
no effect. It was known that this could cause performance problems
if the symlink resolution *itself* touched slow filesystems, but it
was thought that such use cases would be unlikely. The intention of
the earlier change was to deal with a case when the user has this:
GIT_CEILING_DIRECTORIES=/home/gitster
but in reality, /home/gitster is a symbolic link to somewhere else,
e.g. /net/machine/home4/gitster. A textual comparison between the
specified value /home/gitster and the location getcwd(3) returns
would not help us, but readlink("/home/gitster") would still be
fast.
After this change was released, Anders Kaseorg <andersk@mit.edu>
reported:
> [...] my computer has been acting so slow when I’m not connected to
> the network. I put various network filesystem paths in
> $GIT_CEILING_DIRECTORIES, such as
> /afs/athena.mit.edu/user/a/n/andersk (to avoid hitting its parents
> /afs/athena.mit.edu, /afs/athena.mit.edu/user/a, and
> /afs/athena.mit.edu/user/a/n which all live in different AFS
> volumes). Now when I’m not connected to the network, every
> invocation of Git, including the __git_ps1 in my shell prompt, waits
> for AFS to timeout.
To allow users to work around this problem, give them a mechanism to
turn off symlink resolution in GIT_CEILING_DIRECTORIES entries. All
the entries that follow an empty entry will not be checked for symbolic
links and used literally in comparison. E.g. with these:
GIT_CEILING_DIRECTORIES=:/foo/bar:/xyzzy or
GIT_CEILING_DIRECTORIES=/foo/bar::/xyzzy
we will not readlink("/xyzzy") because it comes after an empty entry.
With the former (but not with the latter), "/foo/bar" comes after an
empty entry, and we will not readlink it, either.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>