btrfs-progs: tune: recover from failed btrfstune -m|M

Currently, to fix device following the write failure of one or more devices
during btrfstune -m|M, we rely on the kernel's ability to reassemble devices,
even when they possess distinct fsids.

Kernel hinges combinations of metadata_uuid and generation number, with
additional cues taken from the fsid and the BTRFS_SUPER_FLAG_CHANGING_FSID_V2
flag. This patch adds this logic to btrfs-progs.

In complex scenarios (such as multiple fsids with the same metadata_uuid and
matching generation), user intervention becomes necessary to resolve the
situations which btrfs-progs can do better.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

tune/change-metadata-uuid.c

@@ -21,9 +21,31 @@
 #include "kernel-shared/uapi/btrfs.h"
 #include "kernel-shared/ctree.h"
 #include "kernel-shared/transaction.h"
+#include "kernel-shared/volumes.h"
 #include "common/messages.h"
 #include "tune/tune.h"
 
+/*
+ * Return 0 for no unfinished metadata_uuid change.
+ * Return >0 for unfinished metadata_uuid change, and restore unfinished
+ * fsid/metadata_uuid into fsid_ret/metadata_uuid_ret.
+ */
+static int check_unfinished_metadata_uuid(struct btrfs_fs_info *fs_info,
+					  uuid_t fsid_ret,
+					  uuid_t metadata_uuid_ret)
+{
+	struct btrfs_root *tree_root = fs_info->tree_root;
+
+	if (fs_info->fs_devices->inconsistent_super) {
+		memcpy(fsid_ret, fs_info->super_copy->fsid, BTRFS_FSID_SIZE);
+		read_extent_buffer(tree_root->node, metadata_uuid_ret,
+				   btrfs_header_chunk_tree_uuid(tree_root->node),
+				   BTRFS_UUID_SIZE);
+		return 1;
+	}
+	return 0;
+}
+
 int set_metadata_uuid(struct btrfs_root *root, const char *new_fsid_string)
 {
 	struct btrfs_super_block *disk_super;
@@ -45,15 +67,24 @@ int set_metadata_uuid(struct btrfs_root *root, const char *new_fsid_string)
 		return 1;
 	}
 
-	if (check_unfinished_fsid_change(root->fs_info, fsid, metadata_uuid)) {
+	if (check_unfinished_metadata_uuid(root->fs_info, fsid, metadata_uuid)) {
-		error("UUID rewrite in progress, cannot change metadata_uuid");
+		if (new_fsid_string) {
-		return 1;
+			uuid_t tmp;
-	}
 
+			uuid_parse(new_fsid_string, tmp);
+			if (memcmp(tmp, fsid, BTRFS_FSID_SIZE) != 0) {
+				error(
+		"new fsid %s is not the same with unfinished fsid change",
+				      new_fsid_string);
+				return -EINVAL;
+			}
+		}
+	} else {
 		if (new_fsid_string)
 			uuid_parse(new_fsid_string, fsid);
 		else
 			uuid_generate(fsid);
+	}
 
 	new_fsid = (memcmp(fsid, disk_super->fsid, BTRFS_FSID_SIZE) != 0);
 

tune/change-uuid.c

@@ -210,7 +210,7 @@ static int change_fsid_done(struct btrfs_fs_info *fs_info)
  * Return >0 for unfinished fsid change, and restore unfinished fsid/
  * chunk_tree_id into fsid_ret/chunk_id_ret.
  */
-int check_unfinished_fsid_change(struct btrfs_fs_info *fs_info,
+static int check_unfinished_fsid_change(struct btrfs_fs_info *fs_info,
 					uuid_t fsid_ret, uuid_t chunk_id_ret)
 {
 	struct btrfs_root *tree_root = fs_info->tree_root;

tune/tune.h

@@ -24,8 +24,6 @@ struct btrfs_fs_info;
 
 int update_seeding_flag(struct btrfs_root *root, const char *device, int set_flag, int force);
 
-int check_unfinished_fsid_change(struct btrfs_fs_info *fs_info,
-				 uuid_t fsid_ret, uuid_t chunk_id_ret);
 int change_uuid(struct btrfs_fs_info *fs_info, const char *new_fsid_str);
 int set_metadata_uuid(struct btrfs_root *root, const char *uuid_string);