linux-kernel - Re: [PATCH RFC v4 16/17] KVM: s390 allow virtio

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Date:	Thu, 23 Oct 2014 19:22:33 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux390@...ibm.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-s390@...r.kernel.org
Subject: Re: [PATCH RFC v4 16/17] KVM: s390 allow virtio_ccw status writes
 to fail

On Thu, 23 Oct 2014 19:25:01 +0300
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> Gracefully handle failure to write device status.
> We really should handle other errors as well, but this one is needed for
> virtio 1.0 compliance.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  drivers/s390/kvm/virtio_ccw.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/kvm/virtio_ccw.c b/drivers/s390/kvm/virtio_ccw.c
> index a994078..26e737c 100644
> --- a/drivers/s390/kvm/virtio_ccw.c
> +++ b/drivers/s390/kvm/virtio_ccw.c
> @@ -862,7 +862,9 @@ static u8 virtio_ccw_get_status(struct virtio_device *vdev)
>  static void virtio_ccw_set_status(struct virtio_device *vdev, u8 status)
>  {
>  	struct virtio_ccw_device *vcdev = to_vc_device(vdev);
> +	u8 old_status = vcdev->status;

*vcdev->status

>  	struct ccw1 *ccw;
> +	int ret;
> 
>  	ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);
>  	if (!ccw)
> @@ -874,7 +876,10 @@ static void virtio_ccw_set_status(struct virtio_device *vdev, u8 status)
>  	ccw->flags = 0;
>  	ccw->count = sizeof(status);
>  	ccw->cda = (__u32)(unsigned long)vcdev->status;
> -	ccw_io_helper(vcdev, ccw, VIRTIO_CCW_DOING_WRITE_STATUS);
> +	ret = ccw_io_helper(vcdev, ccw, VIRTIO_CCW_DOING_WRITE_STATUS);
> +	/* Write failed? We assume status is unchanged. */
> +	if (ret)
> +		*vcdev->status = old_status;

If we fail the write, ccw->cda should be unchanged; but this doesn't
hurt.

>  	kfree(ccw);
>  }
> 

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