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

[Paolo Bonzini <pbonzini@redhat.com>]

Il 22/08/2013 12:28, Bharata B Rao ha scritto:
> 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 ?

EFAULT means the buffer address is invalid, I/O error would be EIO, but...

> I remember this was one of the motivations to
> handle this failure.

... this write is on the pipe, not on a disk.

Paolo