[5/8] quorum: fix quorum_aio_cancel()

For a fifo read pattern, we only have one running aio (possible other cases that
has less number than num_children in the future), so we need to check if
.acb is NULL against bdrv_aio_cancel() to avoid segfault.

Cc: Eric Blake <eblake@redhat.com>
Cc: Benoit Canet <benoit@irqsave.net>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
---
 block/quorum.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

The Monday 01 Sep 2014 à 15:43:11 (+0800), Liu Yuan wrote :
> For a fifo read pattern, we only have one running aio

>(possible other cases that has less number than num_children in the future)
I have trouble understanding this part of the commit message could you try
to clarify it ?

> , so we need to check if
> .acb is NULL against bdrv_aio_cancel() to avoid segfault.
> 
> Cc: Eric Blake <eblake@redhat.com>
> Cc: Benoit Canet <benoit@irqsave.net>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Liu Yuan <namei.unix@gmail.com>
> ---
>  block/quorum.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/quorum.c b/block/quorum.c
> index 9e056d6..b9eeda3 100644
> --- a/block/quorum.c
> +++ b/block/quorum.c
> @@ -144,7 +144,9 @@ static void quorum_aio_cancel(BlockDriverAIOCB *blockacb)
>  
>      /* cancel all callbacks */
>      for (i = 0; i < s->num_children; i++) {
> -        bdrv_aio_cancel(acb->qcrs[i].aiocb);
> +        if (acb->qcrs[i].aiocb) {
> +            bdrv_aio_cancel(acb->qcrs[i].aiocb);
> +        }
>      }
>  
>      quorum_aio_release(acb);
> -- 
> 1.9.1
>

On Mon, Sep 01, 2014 at 10:35:27AM +0200, Benoît Canet wrote:
> The Monday 01 Sep 2014 à 15:43:11 (+0800), Liu Yuan wrote :
> > For a fifo read pattern, we only have one running aio
> 
> >(possible other cases that has less number than num_children in the future)
> I have trouble understanding this part of the commit message could you try
> to clarify it ?

Until this patch, we have two cases, read single or read all. But later patch
allow VMs to continue if some devices are down. So the discrete number 1 and N
becomes a range [1, N], that is possible running requests are from 1 to N.

Thanks
Yuan

The Monday 01 Sep 2014 à 17:26:09 (+0800), Liu Yuan wrote :
> On Mon, Sep 01, 2014 at 10:35:27AM +0200, Benoît Canet wrote:
> > The Monday 01 Sep 2014 à 15:43:11 (+0800), Liu Yuan wrote :
> > > For a fifo read pattern, we only have one running aio
> > 
> > >(possible other cases that has less number than num_children in the future)
> > I have trouble understanding this part of the commit message could you try
> > to clarify it ?
> 
> Until this patch, we have two cases, read single or read all. But later patch
> allow VMs to continue if some devices are down. So the discrete number 1 and N
> becomes a range [1, N], that is possible running requests are from 1 to N.

Why not 

(In some other cases some children of the num_children BDS could be disabled
reducing the number of requests needed) ?

> 
> Thanks
> Yuan

On Mon, Sep 01, 2014 at 11:32:04AM +0200, Benoît Canet wrote:
> The Monday 01 Sep 2014 à 17:26:09 (+0800), Liu Yuan wrote :
> > On Mon, Sep 01, 2014 at 10:35:27AM +0200, Benoît Canet wrote:
> > > The Monday 01 Sep 2014 à 15:43:11 (+0800), Liu Yuan wrote :
> > > > For a fifo read pattern, we only have one running aio
> > > 
> > > >(possible other cases that has less number than num_children in the future)
> > > I have trouble understanding this part of the commit message could you try
> > > to clarify it ?
> > 
> > Until this patch, we have two cases, read single or read all. But later patch
> > allow VMs to continue if some devices are down. So the discrete number 1 and N
> > becomes a range [1, N], that is possible running requests are from 1 to N.
> 
> Why not 
> 
> (In some other cases some children of the num_children BDS could be disabled
> reducing the number of requests needed) ?
> 

Sounds better, I'll take yours, thanks!

Yuan