Re: [PATCH] NFS: Fix "BUG at fs/aio.c:554!"

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On Jan 19, 2011, at 6:49 PM, Trond Myklebust wrote:

> On Thu, 2011-01-20 at 10:37 +1100, Nick Piggin wrote: 
>> On Thu, Jan 20, 2011 at 10:31 AM, Trond Myklebust
>> <Trond.Myklebust@xxxxxxxxxx> wrote:
>>> On Thu, 2011-01-20 at 10:26 +1100, Nick Piggin wrote:
>>>> On Thu, Jan 20, 2011 at 10:25 AM, Trond Myklebust
>> 
>>>>> Also, why is EIO the correct reply when no bytes were read/written? Why
>>>>> shouldn't the VFS aio code be able to cope with a zero byte reply?
>>>> 
>>>> What would it do?
>>> 
>>> Just return that zero byte reply to userland.
>>> 
>>> zero bytes is a valid reply for ordinary read() and write(), so why
>>> should we have to do anything different for aio_read()/aio_write()?
>> 
>> It doesn't give userspace much to do. zero reply from read means
>> EOF. Zero reply from write is pretty useless, I don't think we do it
>> in the buffered write path -- we either ensure we write at least
>> something or have a meaningful error to return.
> 
> zero reply from read means EOF _or_ user supplied a zero length buffer.
> 
> zero reply from write may also be useless, but it is a valid value. It
> can simply mean the user supplied a zero length buffer.

This code is in the forward path.  So, here we are just dealing with starting the I/O.  If the server replies with a short read or write, that's handled in the callbacks, not here.

So, -EIO is appropriate if we couldn't even start the I/O, right?

Anyway, this is copied from the existing code, not something new with this patch.  If we want to change this part of the logic, maybe it should be part of a different patch?

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com




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