Re: [PATCH] file-posix: allow -EBUSY errors during write zeros on block

[ChangLimin <changlm@chinatelecom.cn>]

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>> After Linux 5.10, write zeros to a multipath device using
>> ioctl(fd, BLKZEROOUT, range) with cache none or directsync will return EBUSY.
>>
>> Similar to handle_aiocb_write_zeroes_unmap, handle_aiocb_write_zeroes_block
>> allow -EBUSY errors during ioctl(fd, BLKZEROOUT, range).
>>
>> Reference commit in Linux 5.10:
>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=384d87ef2c954fc58e6c5fd8253e4a1984f5fe02
> 
>But this can happen only when the block device is used by a file system or
>maybe someone else. In qemu we assume that we are the only user of the
>block device, so EBUSY is a fatal error that should never happen, no?
> 
>Can you explain a real world use case when we get EBUSY?
> 
>Nir
> 

Please refer to https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_device_mapper_multipath/index
Where multipath is configured to a SAN LUN, ioctl(fd, BLKZEROOUT, range)
to the /dev/dm-x return EBUSY permanently since Linux 5.10.

ChangLimin

>> Signed-off-by: ChangLimin <changlm@chinatelecom.cn>
>> ---
>>  block/file-posix.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/file-posix.c b/block/file-posix.c
>> index 05079b40ca..3e60c96214 100644
>> --- a/block/file-posix.c
>> +++ b/block/file-posix.c
>> @@ -1629,8 +1629,13 @@ static ssize_t handle_aiocb_write_zeroes_block(RawPosixAIOData *aiocb)
>>          } while (errno == EINTR);
>>
>>          ret = translate_err(-errno);
>> -        if (ret == -ENOTSUP) {
>> +        switch (ret) {
>> +        case -ENOTSUP:
>> +        case -EINVAL:
>> +        case -EBUSY:
>>              s->has_write_zeroes = false;
>> +            return -ENOTSUP;
>> +            break;
>>          }
>>      }
>>  #endif
>> --
>> 2.27.0
>>
 
 

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