[PATCH] Make .git directory validation code test HEAD

Inspired by a report by Kalle Valo, this changes git-sh-setup-script and
the "setup_git_directory()" function to test that $GIT_DIR/HEAD is a
symlink, since a number of core git features depend on that these days.

We used to allow a regular file there, but git-fsck-cache has been
complaining about that for a while, and anything that uses branches
depends on the HEAD file being a symlink, so let's just encode that as a
fundamental requirement.

Before, a non-symlink HEAD file would appear to work, but have subtle bugs
like not having the HEAD show up as a valid reference (because it wasn't
under "refs"). Now, we will complain loudly, and the user can fix it up
trivially instead of getting strange behaviour.

This also removes the tests for "$GIT_DIR" and "$GIT_OBJECT_DIRECTORY"
being directories, since the other tests will implicitly test for that
anyway (ie the tests for HEAD, refs and 00 would fail).

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

2 files changed, 21 insertions, 13 deletions

diff --git a/git-sh-setup-script b/git-sh-setup-script
index 5bf471f78..84e15df1b 100755
--- a/git-sh-setup-script
+++ b/git-sh-setup-script
@@ -11,7 +11,6 @@ die() {
 	exit 1
 }
 
-[ -d "$GIT_DIR" ] &&
+[ -h "$GIT_DIR/HEAD" ] &&
 [ -d "$GIT_DIR/refs" ] &&
-[ -d "$GIT_OBJECT_DIRECTORY" ] &&
 [ -d "$GIT_OBJECT_DIRECTORY/00" ]
diff --git a/setup.c b/setup.c
index b8789de5c..258da1761 100644
--- a/setup.c
+++ b/setup.c
@@ -72,6 +72,24 @@ const char **get_pathspec(const char *prefix, char **pathspec)
 	return (const char **) pathspec;
 }
 
+/*
+ * Test it it looks like we're at the top
+ * level git directory. We want to see a
+ *
+ *  - a HEAD symlink and a refs/ directory under ".git"
+ *  - either a .git/objects/ directory _or_ the proper
+ *    GIT_OBJECT_DIRECTORY environment variable
+ */
+static int is_toplevel_directory(void)
+{
+	struct stat st;
+
+	return	!lstat(".git/HEAD", &st) &&
+		S_ISLNK(st.st_mode) &&
+		!access(".git/refs/", X_OK) &&
+		(gitenv(DB_ENVIRONMENT) || !access(".git/objects/", X_OK));
+}
+
 const char *setup_git_directory(void)
 {
 	static char cwd[PATH_MAX+1];
@@ -89,17 +107,8 @@ const char *setup_git_directory(void)
 
 	offset = len = strlen(cwd);
 	for (;;) {
-		/*
-		 * We always want to see a .git/refs/ subdirectory
-		 */
-		if (!access(".git/refs/", X_OK)) {
-			/*
-			 * Then we need either a GIT_OBJECT_DIRECTORY define
-			 * or a .git/objects/ directory
-			 */
-			if (gitenv(DB_ENVIRONMENT) || !access(".git/objects/", X_OK))
-				break;
-		}
+		if (is_toplevel_directory())
+			break;
 		chdir("..");
 		do {
 			if (!offset)