Re: [RFC] Provide a mechanism to turn off symlink resolution in ceiling paths

	GIT_CEILING_DIRECTORIES=:/foo/bar:/xyzzy or
	GIT_CEILING_DIRECTORIES=/foo/bar::/xyzzy

we will not readlink("/xyzzy"), and with the former, we will not
readlink("/foo/bar"), either.
---
 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 6710cb0..5c03616 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 are read to resolve any symlinks 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 f108c4b..1b12017 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 cce87a5..3d51615 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/"