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

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

On 16/05/14 22:50, Shilong Wang wrote:
> 2014-05-16 22:44 GMT+08:00 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.
>
> You means this one which was addressed by Liu few days ago?
> https://patchwork.kernel.org/patch/4150471/

  Ah there is already a patch. yes thats the one. Thanks.

>>>> 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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