Re: [PATCH v5 1/2] Return bytes transferred for partial direct I/O

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 1/20/18 7:23 PM, Goldwyn Rodrigues wrote:
> 
> 
> On 01/20/2018 08:11 PM, Andi Kleen wrote:
>> Goldwyn Rodrigues <rgoldwyn@xxxxxxx> writes:
>>
>>> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>>>
>>> In case direct I/O encounters an error midway, it returns the error.
>>> Instead it should be returning the number of bytes transferred so far.
>>
>> It's likely there's a lot of code in user space that does
>>
>>      if (write(..., N) < 0) handle error
>>
>> With your change it would need to be
>>
>>      if (write(..., N) != N) handle error
>>
>> How much code is actually doing that?
>>
>> I can understand it fixes your artifical test suite, but it seems to me your
>> change has a high potential to break a lot of existing user code
>> in subtle ways. So it seems to be a bad idea.
>>
>> -Andi
>>
> 
> 
> Quoting 'man 2 write':
> 
> RETURN VALUE
>  On  success,  the  number  of bytes written is returned (zero indicates
>  nothing was written).  It is not an error if  this  number  is  smaller
>  than the number of bytes requested; this may happen for example because
>  the disk device was filled.  See also NOTES.

You can quote as much man page as you want - Andi is well aware of how
read/write system call works, as I'm sure all of us are, that is not the
issue. The issue is that there are potentially LOTS of applications out
there that do not check for short writes, they do exactly what Andi
speculated above. If you break it with this change, it doesn't matter
what's in the man page. What matters is previous behavior, and that
you are breaking user space. At that point nobody cares what's in the
man page.

-- 
Jens Axboe




[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux