btrfs-progs: mkfs: print only first warning when --rootdir finds a hardlink

There's a report that newly added --rootdir print too many warnings for
hardlinks, which is maybe not that uncommon. We still want to let the
user know about that so print it just once and count how many were
found:

  $ mkfs.btrfs --rootdir ...
  WARNING: '/tmp/btrfs-progs-mkfs-rootdir-hardlinks.7RcdfR/rootdir/inside_link' has extra hardlinks, they will be converted into new inodes
  WARNING: 12 hardlinks were detected in /tmp/btrfs-progs-mkfs-rootdir-hardlinks.7RcdfR/rootdir, all converted to new inodes

Link: #872 (comment)
Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

mkfs/rootdir.c

@@ -90,6 +90,9 @@ static struct rootdir_path current_path = {
 	.level = 0,
 };
 
+/* Track if a hardlink was found and a warning was printed. */
+static bool g_hardlink_warning;
+static u64 g_hardlink_count;
 static struct btrfs_trans_handle *g_trans = NULL;
 
 static inline struct inode_entry *rootdir_path_last(struct rootdir_path *path)
@@ -428,9 +431,14 @@ static int ftw_add_inode(const char *full_path, const struct stat *st,
 	 * On most filesystems st_nlink of a directory is the number of
 	 * subdirs, including "." and "..", so skip directory inodes.
 	 */
-	if (unlikely(!S_ISDIR(st->st_mode) && st->st_nlink > 1))
-		warning("'%s' has extra hard links, they will be converted into new inodes",
-			full_path);
+	if (unlikely(!S_ISDIR(st->st_mode) && st->st_nlink > 1)) {
+		if (!g_hardlink_warning) {
+			warning("'%s' has extra hardlinks, they will be converted into new inodes",
+				full_path);
+			g_hardlink_warning = true;
+		}
+		g_hardlink_count++;
+	}
 
 	/* The rootdir itself. */
 	if (unlikely(ftwbuf->level == 0)) {
@@ -612,6 +620,8 @@ int btrfs_mkfs_fill_dir(const char *source_dir, struct btrfs_root *root)
 	}
 
 	g_trans = trans;
+	g_hardlink_warning = false;
+	g_hardlink_count = 0;
 	INIT_LIST_HEAD(&current_path.inode_list);
 
 	ret = nftw(source_dir, ftw_add_inode, 32, FTW_PHYS);
@@ -625,6 +635,11 @@ int btrfs_mkfs_fill_dir(const char *source_dir, struct btrfs_root *root)
 		error_msg(ERROR_MSG_COMMIT_TRANS, "%m");
 		goto out;
 	}
+
+	if (g_hardlink_warning)
+		warning("%llu hardlinks were detected in %s, all converted to new inodes",
+			g_hardlink_count, source_dir);
+
 	while (current_path.level > 0)
 		rootdir_path_pop(&current_path);
 

tests/mkfs-tests/034-rootdir-extra-hard-links/test.sh

@@ -13,6 +13,12 @@ run_check mkdir "$tmpdir/rootdir"
 run_check touch "$tmpdir/rootdir/inside_link"
 run_check ln "$tmpdir/rootdir/inside_link" "$tmpdir/outside_link"
 
+# Add more links to trigger the warnings
+run_check touch "$tmpdir/rootdir/link0"
+for i in {1..10}; do
+	run_check ln "$tmpdir/rootdir/link0" "$tmpdir/rootdir/link$i"
+done
+
 run_check_mkfs_test_dev --rootdir "$tmpdir/rootdir"
 
 # For older mkfs.btrfs --rootdir we will create inside_link with 2 links,