linux-kernel - Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk

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Date:	Mon, 18 Jun 2012 10:37:06 +0100
From:	Stefan Hajnoczi <stefanha@...il.com>
To:	Asias He <asias@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Christoph Hellwig <hch@....de>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk

On Mon, Jun 18, 2012 at 7:53 AM, Asias He <asias@...hat.com> wrote:
> +static void virtblk_add_buf_wait(struct virtio_blk *vblk,
> +                                struct virtblk_req *vbr,
> +                                unsigned long out,
> +                                unsigned long in)
> +{
> +       DEFINE_WAIT(wait);
> +
> +       for (;;) {
> +               prepare_to_wait_exclusive(&vblk->queue_wait, &wait,
> +                                         TASK_UNINTERRUPTIBLE);
> +
> +               spin_lock_irq(vblk->disk->queue->queue_lock);
> +               if (virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr,
> +                                     GFP_ATOMIC) < 0) {
> +                       spin_unlock_irq(vblk->disk->queue->queue_lock);
> +                       io_schedule();
> +               } else {
> +                       virtqueue_kick(vblk->vq);
> +                       spin_unlock_irq(vblk->disk->queue->queue_lock);
> +                       break;
> +               }
> +
> +       }

Is there a meaningful condition where we would cancel this request
(e.g. signal)?  If the vring fills up for some reason and we get stuck
here the user might wish to kill hung processes.

Stefan
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