Re: [PATCH] Btrfs: set right total device count for seeding support

[Anand Jain <Anand.Jain@oracle.com>]

Wang,

  when we unmount && mount (instead of remount) and followed
  with device del <seed> it ends up with null pointer deref at
  btrfs_shrink_dev. Thats because the btrfs_root is not set for
  seed disk as we mounted the writable sprout disk. I am writing
  a separate fix for that as its a new bug.

Thanks, Anand


On 16/05/14 22:14, Anand Jain wrote:
>
> Wang,
>
>   There seems to be a problem - after we delete the seed
>   disk, the total_devices didn't decrement back to 1.
>   reproducer as in the below test case. (I used btrfs-devlist
>   (posted) to check fs_devices).
>
>   > # mkfs.btrfs -f /dev/sdb
>   > # btrfstune -S 1 /dev/sdb
>   > # mount /dev/sdb /mnt
>   > # btrfs device add -f /dev/sdc /mnt --->fs_devices->total_devices = 1
>   mount -o rw,remount /mnt
>   btrfs dev del /dev/sdb /mnt --> fs_devices->total_devices is still 2
>
> Thanks, Anand
>
>
> On 13/05/14 17:05, Wang Shilong wrote:
>> Seeding device support allows us to create a new filesystem
>> based on existed filesystem.
>>
>> However newly created filesystem's @total_devices should include seed
>> devices. This patch fix the following problem:
>>
>>   # mkfs.btrfs -f /dev/sdb
>>   # btrfstune -S 1 /dev/sdb
>>   # mount /dev/sdb /mnt
>>   # btrfs device add -f /dev/sdc /mnt --->fs_devices->total_devices = 1
>>   # umount /mnt
>>   # mount /dev/sdc /mnt               --->fs_devices->total_devices = 2
>>
>> This is because we record right @total_devices in superblock, but
>> @fs_devices->total_devices is reset to be 0 in btrfs_prepare_sprout().
>>
>> Fix this problem by not resetting @fs_devices->total_devices.
>>
>> Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
>> ---
>>   fs/btrfs/volumes.c | 1 -
>>   1 file changed, 1 deletion(-)
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 6fd7fe6..19b2d32 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -1883,7 +1883,6 @@ static int btrfs_prepare_sprout(struct
>> btrfs_root *root)
>>       fs_devices->seeding = 0;
>>       fs_devices->num_devices = 0;
>>       fs_devices->open_devices = 0;
>> -    fs_devices->total_devices = 0;
>>       fs_devices->seed = seed_devices;
>>
>>       generate_random_uuid(fs_devices->fsid);
>>
> --
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