Teach "fsck" not to follow subproject links

Since the subprojects don't necessarily even exist in the current tree,
much less in the current git repository (they are totally independent
repositories), we do not want to try to follow the chain from one git
repository to another through a gitlink.

This involves teaching fsck to ignore references to gitlink objects from
a tree and from the current index.

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

builtin-fsck.c

@@ -253,6 +253,7 @@ static int fsck_tree(struct tree *item)
 		case S_IFREG | 0644:
 		case S_IFLNK:
 		case S_IFDIR:
+		case S_IFDIRLNK:
 			break;
 		/*
 		 * This is nonstandard, but we had a few of these
@@ -695,8 +696,14 @@ int cmd_fsck(int argc, char **argv, const char *prefix)
 		int i;
 		read_cache();
 		for (i = 0; i < active_nr; i++) {
-			struct blob *blob = lookup_blob(active_cache[i]->sha1);
+			unsigned int mode;
+			struct blob *blob;
 			struct object *obj;
+
+			mode = ntohl(active_cache[i]->ce_mode);
+			if (S_ISDIRLNK(mode))
+				continue;
+			blob = lookup_blob(active_cache[i]->sha1);
 			if (!blob)
 				continue;
 			obj = &blob->object;

tree.c

@@ -143,6 +143,14 @@ struct tree *lookup_tree(const unsigned char *sha1)
 	return (struct tree *) obj;
 }
 
+/*
+ * NOTE! Tree refs to external git repositories
+ * (ie gitlinks) do not count as real references.
+ *
+ * You don't have to have those repositories
+ * available at all, much less have the objects
+ * accessible from the current repository.
+ */
 static void track_tree_refs(struct tree *item)
 {
 	int n_refs = 0, i;
@@ -152,8 +160,11 @@ static void track_tree_refs(struct tree *item)
 
 	/* Count how many entries there are.. */
 	init_tree_desc(&desc, item->buffer, item->size);
-	while (tree_entry(&desc, &entry))
+	while (tree_entry(&desc, &entry)) {
+		if (S_ISDIRLNK(entry.mode))
+			continue;
 		n_refs++;
+	}
 
 	/* Allocate object refs and walk it again.. */
 	i = 0;
@@ -162,6 +173,8 @@ static void track_tree_refs(struct tree *item)
 	while (tree_entry(&desc, &entry)) {
 		struct object *obj;
 
+		if (S_ISDIRLNK(entry.mode))
+			continue;
 		if (S_ISDIR(entry.mode))
 			obj = &lookup_tree(entry.sha1)->object;
 		else