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Provide a mechanism to turn off symlink resolution in ceiling paths

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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>
This commit is contained in:
Michael Haggerty
2013-02-20 10:09:24 +01:00
committed by Junio C Hamano
parent 1b77d83cab
commit 7ec30aaa5b
3 changed files with 52 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
setup.c
View File

@ -624,22 +624,32 @@ static dev_t get_device_or_die(const char *path, const char *prefix, int prefix_
/*
* A "string_list_each_func_t" function that canonicalizes an entry
* from GIT_CEILING_DIRECTORIES using real_path_if_valid(), or
* discards it if unusable.
* discards it if unusable. The presence of an empty entry in
* GIT_CEILING_DIRECTORIES turns off canonicalization for all
* subsequent entries.
*/
static int canonicalize_ceiling_entry(struct string_list_item *item,
void *unused)
void *cb_data)
{
int *empty_entry_found = cb_data;
char *ceil = item->string;
const char *real_path;
if (!*ceil || !is_absolute_path(ceil))
if (!*ceil) {
*empty_entry_found = 1;
return 0;
real_path = real_path_if_valid(ceil);
if (!real_path)
} else if (!is_absolute_path(ceil)) {
return 0;
free(item->string);
item->string = xstrdup(real_path);
return 1;
} else if (*empty_entry_found) {
/* Keep entry but do not canonicalize it */
return 1;
} else {
const char *real_path = real_path_if_valid(ceil);
if (!real_path)
return 0;
free(item->string);
item->string = xstrdup(real_path);
return 1;
}
}
/*
@ -679,9 +689,11 @@ static const char *setup_git_directory_gently_1(int *nongit_ok)
return setup_explicit_git_dir(gitdirenv, cwd, len, nongit_ok);
if (env_ceiling_dirs) {
int empty_entry_found = 0;
string_list_split(&ceiling_dirs, env_ceiling_dirs, PATH_SEP, -1);
filter_string_list(&ceiling_dirs, 0,
canonicalize_ceiling_entry, NULL);
canonicalize_ceiling_entry, &empty_entry_found);
ceil_offset = longest_ancestor_length(cwd, &ceiling_dirs);
string_list_clear(&ceiling_dirs, 0);
}