Re: [PATCH 3/6] btrfs: split-brain case for scanned changing device with INCOMPAT_METADATA_UUID

[Su Yue <Damenly_Su@gmx.com>]

On 2019/12/12 7:01 PM, damenly.su@gmail.com wrote:
> From: Su Yue <Damenly_Su@gmx.com>
>
> This patch adds the case for scanned changing device with
> 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.
> So add the check of Heather fsid of scanned device equals

s/Heather/whether/g, blame my spellchecker.

> metadata_uuid of fs_devices which is with INCOMPAT_METADATA_UUID
> feature.
>
> Signed-off-by: Su Yue <Damenly_Su@gmx.com>
> ---
>   fs/btrfs/volumes.c | 29 ++++++++++++++++++++++++++---
>   1 file changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index b08b06a89a77..61b4a107bb58 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -654,7 +654,6 @@ static struct btrfs_fs_devices *find_fsid_inprogress(
>   	return NULL;
>   }
>
> -
>   static struct btrfs_fs_devices *find_fsid_changed(
>   					struct btrfs_super_block *disk_super)
>   {
> @@ -663,9 +662,14 @@ static struct btrfs_fs_devices *find_fsid_changed(
>   	/*
>   	 * Handles the case where scanned device is part of an fs that had
>   	 * multiple successful changes of FSID but curently device didn't
> -	 * observe it. Meaning our fsid will be different than theirs.
> +	 * observe it.
> +	 *
> +	 * Case 1: the devices already changed still owns the feature, their
> +	 * fsid must differ from the disk_super->fsid.
>   	 */
>   	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
> +		if (fs_devices->fsid_change)
> +			continue;
>   		if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
>   			   BTRFS_FSID_SIZE) != 0 &&
>   		    memcmp(fs_devices->metadata_uuid, disk_super->metadata_uuid,
> @@ -676,7 +680,26 @@ static struct btrfs_fs_devices *find_fsid_changed(
>   		}
>   	}
>
> -	return NULL;
> +	/*
> +	 * Case 2: the synced devices doesn't have the metadata_uuid feature.
> +	 * NOTE: the fs_devices has same metadata_uuid and fsid in memory, but
> +	 * they differs in disk, because fs_id is copied to
> +	 * fs_devices->metadata_id while alloc_fs_devices if no metadata
> +	 * feature.
> +	 */
> +	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
> +		if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
> +			   BTRFS_FSID_SIZE) == 0 &&
> +		    memcmp(fs_devices->fsid, disk_super->metadata_uuid,
> +			   BTRFS_FSID_SIZE) == 0 && !fs_devices->fsid_change)
> +			return fs_devices;
> +	}
> +
> +	/*
> +	 * Okay, can't found any fs_devices already synced, back to
> +	 * search devices unchanged or changing like the device.
> +	 */
> +	return find_fsid(disk_super->fsid, disk_super->metadata_uuid);
>   }
>
>   static struct btrfs_fs_devices *find_fsid_changing_metada_uuid(
>