Re: [PATCH 2/6] btrfs: metadata_uuid: move split-brain handling from fs_id() to new function

[Nikolay Borisov <nborisov@suse.com>]

On 12.12.19 г. 13:01 ч., damenly.su@gmail.com wrote:
> From: Su Yue <Damenly_Su@gmx.com>
> 
> The parameter @metadata_fsid of fs_id() is not NULL while scanned device
> has metadata_uuid but not changing. Obviously, the cases handling part
> in fs_id() is for this situation. Move the logic into new function
> find_fsid_changing_metadata_uuid().

I think the following changelog might sound better.

metadata_fsid parameter of find_fsid is non-null in once specific case
in device_list_add. Factor the code out of find_fsid to a dedicated
function to improve readability.


> 
> Signed-off-by: Su Yue <Damenly_Su@gmx.com>
> ---
>  fs/btrfs/volumes.c | 78 ++++++++++++++++++++++++----------------------
>  1 file changed, 41 insertions(+), 37 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 9efa4123c335..b08b06a89a77 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -438,40 +438,6 @@ static noinline struct btrfs_fs_devices *find_fsid(
>  
>  	ASSERT(fsid);
>  
> -	if (metadata_fsid) {
> -		/*
> -		 * Handle scanned device having completed its fsid change but
> -		 * belonging to a fs_devices that was created by first scanning
> -		 * a device which didn't have its fsid/metadata_uuid changed
> -		 * at all and the CHANGING_FSID_V2 flag set.
> -		 */
> -		list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
> -			if (fs_devices->fsid_change &&
> -			    memcmp(metadata_fsid, fs_devices->fsid,
> -				   BTRFS_FSID_SIZE) == 0 &&
> -			    memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
> -				   BTRFS_FSID_SIZE) == 0) {
> -				return fs_devices;
> -			}
> -		}
> -		/*
> -		 * Handle scanned device having completed its fsid change but
> -		 * belonging to a fs_devices that was created by a device that
> -		 * has an outdated pair of fsid/metadata_uuid and
> -		 * CHANGING_FSID_V2 flag set.
> -		 */
> -		list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
> -			if (fs_devices->fsid_change &&
> -			    memcmp(fs_devices->metadata_uuid,
> -				   fs_devices->fsid, BTRFS_FSID_SIZE) != 0 &&
> -			    memcmp(metadata_fsid, fs_devices->metadata_uuid,
> -				   BTRFS_FSID_SIZE) == 0) {
> -				return fs_devices;
> -			}
> -		}
> -	}
> -
> -	/* Handle non-split brain cases */
>  	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
>  		if (metadata_fsid) {
>  			if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0
> @@ -712,6 +678,46 @@ static struct btrfs_fs_devices *find_fsid_changed(
>  
>  	return NULL;
>  }
> +
> +static struct btrfs_fs_devices *find_fsid_changing_metada_uuid(

That function name is long (and contains a typo). More like something like:

find_fsid_with_metadata_uuid.

> +					struct btrfs_super_block *disk_super)
> +{
> +	struct btrfs_fs_devices *fs_devices;
> +
> +	/*
> +	 * Handle scanned device having completed its fsid change but
> +	 * belonging to a fs_devices that was created by first scanning
> +	 * a device which didn't have its fsid/metadata_uuid changed
> +	 * at all and the CHANGING_FSID_V2 flag set.
> +	 */
> +	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
> +		if (fs_devices->fsid_change &&
> +		    memcmp(disk_super->metadata_uuid, fs_devices->fsid,
> +			   BTRFS_FSID_SIZE) == 0 &&
> +		    memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
> +			   BTRFS_FSID_SIZE) == 0) {
> +			return fs_devices;
> +		}
> +	}
> +	/*
> +	 * Handle scanned device having completed its fsid change but
> +	 * belonging to a fs_devices that was created by a device that
> +	 * has an outdated pair of fsid/metadata_uuid and
> +	 * CHANGING_FSID_V2 flag set.
> +	 */
> +	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
> +		if (fs_devices->fsid_change &&
> +		    memcmp(fs_devices->metadata_uuid,
> +			   fs_devices->fsid, BTRFS_FSID_SIZE) != 0 &&
> +		    memcmp(disk_super->metadata_uuid, fs_devices->metadata_uuid,
> +			   BTRFS_FSID_SIZE) == 0) {
> +			return fs_devices;
> +		}
> +	}
> +
> +	return find_fsid(disk_super->fsid, disk_super->metadata_uuid);
> +}
> +
>  /*
>   * Add new device to list of registered devices
>   *
> @@ -751,13 +757,11 @@ static noinline struct btrfs_device *device_list_add(const char *path,
>  			fs_devices = find_fsid_changed(disk_super);
>  		}
>  	} else if (has_metadata_uuid) {
> -		fs_devices = find_fsid(disk_super->fsid,
> -				       disk_super->metadata_uuid);
> +		fs_devices = find_fsid_changing_metada_uuid(disk_super);
>  	} else {
>  		fs_devices = find_fsid(disk_super->fsid, NULL);
>  	}
>  
> -
>  	if (!fs_devices) {
>  		if (has_metadata_uuid)
>  			fs_devices = alloc_fs_devices(disk_super->fsid,
>