On 2019/11/18 下午7:38, Anand Jain wrote:
> On 18/11/19 3:05 PM, Qu Wenruo wrote:
>> One user reported an use case where one device can't be replaced due to
>> tiny device size difference.
>>
>> Since it's a RAID10 fs, if we go regular "remove missing" it can take a
>> long time and even not be possible due to lack of space.
>>
>> So here we work around this situation by allowing user to shrink missing
>> device.
>> Then user can go shrink the device first, then replace it.
> 
> 
>  Why not introduce --resize option in the replace command.
>  Which shall allow replace command to resize the source-device
>  to the size of the replace target-device.

Nope, it won't work for degraded mount.

That's the root problem the patch is going to solve.

Thanks,
Qu

> 
> Thanks, Anand
> 
>> Reported-by: Nathan Dehnel <ncdehnel@gmail.com>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   fs/btrfs/ioctl.c | 29 +++++++++++++++++++++++++----
>>   1 file changed, 25 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index de730e56d3f5..ebd2f40aca6f 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -1604,6 +1604,7 @@ static noinline int btrfs_ioctl_resize(struct
>> file *file,
>>       char *sizestr;
>>       char *retptr;
>>       char *devstr = NULL;
>> +    bool missing;
>>       int ret = 0;
>>       int mod = 0;
>>   @@ -1651,7 +1652,10 @@ static noinline int btrfs_ioctl_resize(struct
>> file *file,
>>           goto out_free;
>>       }
>>   -    if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
>> +
>> +    missing = test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
>> +    if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
>> +        !missing) {
>>           btrfs_info(fs_info,
>>                  "resizer unable to apply on readonly device %llu",
>>                  devid);
>> @@ -1659,13 +1663,24 @@ static noinline int btrfs_ioctl_resize(struct
>> file *file,
>>           goto out_free;
>>       }
>>   -    if (!strcmp(sizestr, "max"))
>> +    if (!strcmp(sizestr, "max")) {
>> +        if (missing) {
>> +            btrfs_info(fs_info,
>> +                "'max' can't be used for missing device %llu",
>> +                   devid);
>> +            ret = -EPERM;
>> +            goto out_free;
>> +        }
>>           new_size = device->bdev->bd_inode->i_size;
>> -    else {
>> +    } else {
>>           if (sizestr[0] == '-') {
>>               mod = -1;
>>               sizestr++;
>>           } else if (sizestr[0] == '+') {
>> +            if (missing)
>> +                btrfs_info(fs_info,
>> +                "'+size' can't be used for missing device %llu",
>> +                       devid);
>>               mod = 1;
>>               sizestr++;
>>           }
>> @@ -1694,6 +1709,12 @@ static noinline int btrfs_ioctl_resize(struct
>> file *file,
>>               ret = -ERANGE;
>>               goto out_free;
>>           }
>> +        if (missing) {
>> +            ret = -EINVAL;
>> +            btrfs_info(fs_info,
>> +            "can not increase device size for missing device %llu",
>> +                   devid);
>> +        }
>>           new_size = old_size + new_size;
>>       }
>>   @@ -1701,7 +1722,7 @@ static noinline int btrfs_ioctl_resize(struct
>> file *file,
>>           ret = -EINVAL;
>>           goto out_free;
>>       }
>> -    if (new_size > device->bdev->bd_inode->i_size) {
>> +    if (!missing && new_size > device->bdev->bd_inode->i_size) {
>>           ret = -EFBIG;
>>           goto out_free;
>>       }
>>
>