Re: [PATCH 2/2] btrfs: Remove unneeded missing device number check

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

On 09/17/2015 06:01 PM, Qu Wenruo wrote:
> Thanks for pointing this out.


> Although previous patch is small enough, but for remount case, we need
> to iterate all the existing chunk cache.

  yes indeed.

  thinking hard on this - is there any test-case that these two patches 
are solving, which the original patch [1] didn't solve ?

  I tried to break both the approaches (this patch set and [1]) but I 
wasn't successful. sorry if I am missing something.

Thanks, Anand

[1] [PATCH 23/23] Btrfs: allow -o rw,degraded for single group profile


> So fix for remount will take a little more time.

> Thanks for reviewing.
> Qu
>
> 在 2015年09月17日 17:43, Anand Jain 写道:
>>
>>
>> On 09/16/2015 11:43 AM, Qu Wenruo wrote:
>>> As we do per-chunk missing device number check at read_one_chunk() time,
>>> it's not needed to do global missing device number check.
>>>
>>> Just remove it.
>>
>> However the missing device count, what we have during the remount is not
>> fine grained per chunk.
>> -----------
>> btrfs_remount
>> ::
>>                   if (fs_info->fs_devices->missing_devices >
>>                       fs_info->num_tolerated_disk_barrier_failures &&
>>                      !(*flags & MS_RDONLY ||
>>                          btrfs_test_opt(root, DEGRADED))) {
>>                          btrfs_warn(fs_info,
>>                                  "too many missing devices, writeable
>> remount is not allowed");
>>                          ret = -EACCES;
>>                          goto restore;
>>                  }
>> ---------
>>
>> Thanks, Anand
>>
>>
>>> Now btrfs can handle the following case:
>>>   # mkfs.btrfs -f -m raid1 -d single /dev/sdb /dev/sdc
>>>
>>>   Data chunk will be located in sdb, so we should be safe to wipe sdc
>>>   # wipefs -a /dev/sdc
>>>
>>>   # mount /dev/sdb /mnt/btrfs -o degraded
>>>
>>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>>> ---
>>>   fs/btrfs/disk-io.c | 8 --------
>>>   1 file changed, 8 deletions(-)
>>>
>>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>>> index 0b658d0..ac640ea 100644
>>> --- a/fs/btrfs/disk-io.c
>>> +++ b/fs/btrfs/disk-io.c
>>> @@ -2947,14 +2947,6 @@ retry_root_backup:
>>>       }
>>>       fs_info->num_tolerated_disk_barrier_failures =
>>>           btrfs_calc_num_tolerated_disk_barrier_failures(fs_info);
>>> -    if (fs_info->fs_devices->missing_devices >
>>> -         fs_info->num_tolerated_disk_barrier_failures &&
>>> -        !(sb->s_flags & MS_RDONLY)) {
>>> -        pr_warn("BTRFS: missing devices(%llu) exceeds the limit(%d),
>>> writeable mount is not allowed\n",
>>> -            fs_info->fs_devices->missing_devices,
>>> -            fs_info->num_tolerated_disk_barrier_failures);
>>> -        goto fail_sysfs;
>>> -    }
>>>
>>>       fs_info->cleaner_kthread = kthread_run(cleaner_kthread, tree_root,
>>>                              "btrfs-cleaner");
>>>
>> --
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