[PATCH 4/6] btrfs: split-brain case for scanned changed device without INCOMPAT_METADATA_UUID

[damenly.su@gmail.com]

From: Su Yue <Damenly_Su@gmx.com>

This patch adds the case for scanned not changing device without
INCOMPAT_METADATA_UUID.
For this situation, the origin code only handles the case
the devices already pulled into disk with INCOMPAT_METADATA_UUID set.
There is an another case that the successful changed devices synced
without INCOMPAT_METADATA_UUID. And the scanned device is the exactly
changed one.

So we should check if there is any changing fs_devices with
INCOMPAT_METADATA_UUID.

Signed-off-by: Su Yue <Damenly_Su@gmx.com>
---
 fs/btrfs/volumes.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 61b4a107bb58..faf9cdd14f33 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -741,6 +741,35 @@ static struct btrfs_fs_devices *find_fsid_changing_metada_uuid(
 	return find_fsid(disk_super->fsid, disk_super->metadata_uuid);
 }
 
+static struct btrfs_fs_devices *find_fsid_changing(
+					struct btrfs_super_block *disk_super)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	/*
+	 * Handles the case where scanned device is part of an fs that had
+	 * multiple successful changes of FSID but currently device didn't
+	 * observe it.
+	 * Since the scanned devices does not own the metadata_uuid feature,
+	 * fsid and metadata_uuid of the changing devices must differ, and
+	 * their metadata_uuid must be same as disk_super->fsid.
+	 */
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
+		if (!fs_devices->fsid_change)
+			continue;
+		if (memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
+			   BTRFS_FSID_SIZE) != 0 &&
+		    memcmp(fs_devices->metadata_uuid, disk_super->fsid,
+			   BTRFS_FSID_SIZE) == 0)
+			return fs_devices;
+	}
+
+	/*
+	 * Back to find newer fs_devices is changeing or some in same stage.
+	 */
+	return find_fsid(disk_super->fsid, NULL);
+}
+
 /*
  * Add new device to list of registered devices
  *
@@ -782,7 +811,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
 	} else if (has_metadata_uuid) {
 		fs_devices = find_fsid_changing_metada_uuid(disk_super);
 	} else {
-		fs_devices = find_fsid(disk_super->fsid, NULL);
+		fs_devices = find_fsid_changing(disk_super);
 	}
 
 	if (!fs_devices) {
-- 
2.21.0 (Apple Git-122.2)