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

[Su Yue <Damenly_Su@gmx.com>]

On 2019/12/12 9:05 PM, Nikolay Borisov wrote:
>
>
> 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.
>

Thanks for the changelog! will replace.
>
>>
>> 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 -		 * has an outdated pair of fsid/metadata_uuid and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.

Fine. Naming is so hard to me.

Thanks.
>
>> +					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,
>>