btrfs-progs: Introduce function to fix super block total bytes

Recent kernel (starting from v4.6) will refuse to mount if super block
total bytes is smaller than all devices' size.

This makes end user unable to do anything to their otherwise quite
healthy fs.

To fix such problem, introduce repair function to fix it on an unmounted
filesystem.

Reported-by: Asif Youssuff <yoasif@gmail.com>
Reported-by: Rich Rauenzahn <rrauenza@gmail.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/volumes.c b/volumes.c
index 652f0087..f6d5d351 100644
--- a/volumes.c
+++ b/volumes.c
@@ -2425,3 +2425,55 @@ err:
 	btrfs_release_path(&path);
 	return ret;
 }
+
+/*
+ * Return 0 if super block total_bytes matches all devices' total_bytes
+ * Return >0 if super block total_bytes mismatch but fixed without problem
+ * Return <0 if we failed to fix super block total_bytes
+ */
+int btrfs_fix_super_size(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_device *device;
+	struct list_head *dev_list = &fs_info->fs_devices->devices;
+	u64 total_bytes = 0;
+	u64 old_bytes = btrfs_super_total_bytes(fs_info->super_copy);
+	int ret;
+
+	list_for_each_entry(device, dev_list, dev_list) {
+		/*
+		 * Caller should ensure this function is called after aligning
+		 * all devices' total_bytes.
+		 */
+		if (!IS_ALIGNED(device->total_bytes, fs_info->sectorsize)) {
+			error("device %llu total_bytes %llu not aligned to %u",
+				device->devid, device->total_bytes,
+				fs_info->sectorsize);
+			return -EUCLEAN;
+		}
+		total_bytes += device->total_bytes;
+	}
+
+	if (total_bytes == old_bytes)
+		return 0;
+
+	btrfs_set_super_total_bytes(fs_info->super_copy, total_bytes);
+
+	/* Commit transaction to update all super blocks */
+	trans = btrfs_start_transaction(fs_info->tree_root, 1);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		error("error starting transaction:  %d (%s)",
+		      ret, strerror(-ret));
+		return ret;
+	}
+	ret = btrfs_commit_transaction(trans, fs_info->tree_root);
+	if (ret < 0) {
+		error("failed to commit current transaction: %d (%s)",
+			ret, strerror(-ret));
+		return ret;
+	}
+	printf("Fixed super total bytes, old size: %llu new size: %llu\n",
+		old_bytes, total_bytes);
+	return 1;
+}