Re: [Qemu-devel] Re: [PATCH] For AIO return -ENOSPC on short write

[Avi Kivity]

On 02/22/2011 01:45 PM, Jes Sorensen wrote:
> On 02/22/11 12:44, Kevin Wolf wrote:
> >>  @@ -62,6 +63,9 @@ static void qemu_laio_process_completion(struct 
> qemu_laio_state *s,
> >>       if (ret != -ECANCELED) {
> >>           if (ret == laiocb->nbytes)
> >>               ret = 0;
> >>  +        else if ((laiocb->type == QEMU_AIO_WRITE)&&  (ret>= 0)&&
> >>  +                 (ret<  laiocb->nbytes))
> >>  +            ret = -ENOSPC;
> >>           else if (ret>= 0)
> >>               ret = -EINVAL;
> >
> >  Isn't there a way to get the real error code instead of just making it
> >  up more cleverly? Like retrying for the rest of the request?
> >
> >  Kevin
>
> I guess we could retry the last part of the request, but if we already
> have an error, it seems silly to try to rewrite the same stuff again
> just to obtain the error code.

Why?  It's the standard Unix idiom.  Keep writing until you either 
complete your request or get an error.  We don't do this here, and 
instead invent an error.

Admittedly it's harder to do.

> I looked through the aio calls and I didn't find any obvious way to
> retrieve the error code, but maybe I missed something?

The existing code already has it: if ret is negative, that's what we return.

What you have to do on a short read or write is to schedule a new 
request that starts from the point where this completion ends, and let 
the completion of the new request return the error (or perhaps succeed).

--
error compiling committee.c: too many arguments to function