Re: [Qemu-devel] [PATCH] block: Fix race in gluster_finish_aiocb

[Bharata B Rao]

On Thu, Aug 22, 2013 at 12:00:48PM +0200, Paolo Bonzini wrote:
> Il 22/08/2013 11:55, Bharata B Rao ha scritto:
> > This was the first apporach I had. I used to abort when writes to pipe
> > fail. But there were concerns raised about handling the failures gracefully
> > and hence we ended up doing all that error handling of completing the aio
> > with -EIO, closing the pipe and making the disk inaccessible.
> > 
> >> > Under what circumstances could it happen?
> > Not very sure, I haven't seen that happening. I had to manually inject
> > faults to test this error path and verify the graceful recovery.
> 
> Looking at write(2), it looks like it is impossible
> 
>        EAGAIN or EWOULDBLOCK
>                can't happen, blocking file descriptor
> 
>        EBADF, EPIPE
>                shouldn't happen since the device is drained before
>                calling qemu_gluster_close.
> 
>        EDESTADDRREQ, EDQUOT, EFBIG, EIO, ENOSPC
>                cannot happen for pipes
> 
>        EFAULT
>                abort would be fine

In the case where we have separate system and data disks and if error (EFAULT)
happens for the data disk, don't we want to keep the VM up by gracefully
disabling IO to the data disk ? I remember this was one of the motivations to
handle this failure.

Regards,
Bharata.