From 7ec30aaa5ba2a71287879d7bd9a5c55363ea1bbe Mon Sep 17 00:00:00 2001 From: Michael Haggerty Date: Wed, 20 Feb 2013 10:09:24 +0100 Subject: [PATCH] Provide a mechanism to turn off symlink resolution in ceiling paths MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 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 Signed-off-by: Junio C Hamano --- Documentation/git.txt | 19 +++++++++++++------ setup.c | 32 ++++++++++++++++++++++---------- t/t1504-ceiling-dirs.sh | 17 +++++++++++++++++ 3 files changed, 52 insertions(+), 16 deletions(-) diff --git a/Documentation/git.txt b/Documentation/git.txt index 6710cb0a41..6bc18014cd 100644 --- a/Documentation/git.txt +++ b/Documentation/git.txt @@ -653,12 +653,19 @@ git so take care if using Cogito etc. The '--namespace' command-line option also sets this value. 'GIT_CEILING_DIRECTORIES':: - This should be a colon-separated list of absolute paths. - If set, it is a list of directories that git should not chdir - up into while looking for a repository directory. - It will not exclude the current working directory or - a GIT_DIR set on the command line or in the environment. - (Useful for excluding slow-loading network directories.) + This should be a colon-separated list of absolute paths. If + set, it is a list of directories that git should not chdir up + into while looking for a repository directory (useful for + excluding slow-loading network directories). It will not + exclude the current working directory or a GIT_DIR set on the + command line or in the environment. Normally, Git has to read + the entries in this list and resolve any symlink that + might be present in order to compare them with the current + directory. However, if even this access is slow, you + can add an empty entry to the list to tell Git that the + subsequent entries are not symlinks and needn't be resolved; + e.g., + 'GIT_CEILING_DIRECTORIES=/maybe/symlink::/very/slow/non/symlink'. 'GIT_DISCOVERY_ACROSS_FILESYSTEM':: When run in a directory that does not have ".git" repository diff --git a/setup.c b/setup.c index f108c4b990..1b120175f2 100644 --- a/setup.c +++ b/setup.c @@ -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); } diff --git a/t/t1504-ceiling-dirs.sh b/t/t1504-ceiling-dirs.sh index cce87a5ab5..3d51615e42 100755 --- a/t/t1504-ceiling-dirs.sh +++ b/t/t1504-ceiling-dirs.sh @@ -44,6 +44,10 @@ test_prefix ceil_at_sub "" GIT_CEILING_DIRECTORIES="$TRASH_ROOT/sub/" test_prefix ceil_at_sub_slash "" +if test_have_prereq SYMLINKS +then + ln -s sub top +fi mkdir -p sub/dir || exit 1 cd sub/dir || exit 1 @@ -68,6 +72,19 @@ test_fail subdir_ceil_at_sub GIT_CEILING_DIRECTORIES="$TRASH_ROOT/sub/" test_fail subdir_ceil_at_sub_slash +if test_have_prereq SYMLINKS +then + GIT_CEILING_DIRECTORIES="$TRASH_ROOT/top" + test_fail subdir_ceil_at_top + GIT_CEILING_DIRECTORIES="$TRASH_ROOT/top/" + test_fail subdir_ceil_at_top_slash + + GIT_CEILING_DIRECTORIES=":$TRASH_ROOT/top" + test_prefix subdir_ceil_at_top_no_resolve "sub/dir/" + GIT_CEILING_DIRECTORIES=":$TRASH_ROOT/top/" + test_prefix subdir_ceil_at_top_slash_no_resolve "sub/dir/" +fi + GIT_CEILING_DIRECTORIES="$TRASH_ROOT/sub/dir" test_prefix subdir_ceil_at_subdir "sub/dir/" -- 2.11.4.GIT