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Re: [Qemu-devel] [PATCH v6 4/4] contrib/vhost-user-blk: introduce a vhos


From: Liu, Changpeng
Subject: Re: [Qemu-devel] [PATCH v6 4/4] contrib/vhost-user-blk: introduce a vhost-user-blk sample application
Date: Tue, 12 Dec 2017 01:36:31 +0000


> -----Original Message-----
> From: Stefan Hajnoczi [mailto:address@hidden
> Sent: Monday, December 11, 2017 10:33 PM
> To: Liu, Changpeng <address@hidden>
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; Harris, James R
> <address@hidden>
> Subject: Re: [PATCH v6 4/4] contrib/vhost-user-blk: introduce a vhost-user-blk
> sample application
> 
> > +static int vub_virtio_process_req(VubDev *vdev_blk,
> > +                                     VuVirtq *vq)
> > +{
> > +    VugDev *gdev = &vdev_blk->parent;
> > +    VuDev *vu_dev = &gdev->parent;
> > +    VuVirtqElement *elem;
> > +    uint32_t type;
> > +    unsigned in_num;
> > +    unsigned out_num;
> > +    VubReq *req;
> > +
> > +    elem = vu_queue_pop(vu_dev, vq, sizeof(VuVirtqElement));
> > +    if (!elem) {
> > +        return -1;
> > +    }
> > +
> > +    /* refer to hw/block/virtio_blk.c */
> > +    if (elem->out_num < 1 || elem->in_num < 1) {
> > +        fprintf(stderr, "virtio-blk request missing headers\n");
> > +        free(elem);
> > +        return -1;
> > +    }
> > +
> > +    req = g_new0(VubReq, 1);
> > +    req->vdev_blk = vdev_blk;
> > +    req->vq = vq;
> > +    req->elem = elem;
> > +
> > +    in_num = elem->in_num;
> > +    out_num = elem->out_num;
> > +
> > +    /* don't support VIRTIO_F_ANY_LAYOUT and virtio 1.0 only */
> > +    if (elem->out_sg[0].iov_len < sizeof(struct virtio_blk_outhdr)) {
> > +        fprintf(stderr, "Invalid outhdr size\n");
> > +        goto err;
> > +    }
> 
> QEMU has iov_discard_front() and iov_discard_back().  They make it
> pretty easy to support VIRTIO_F_ANY_LAYOUT.  If you have time, please
> consider adding it to libvhost-user, but it's not a requirement for this
> patch series.
> 
> > +    req->out = (struct virtio_blk_outhdr *)elem->out_sg[0].iov_base;
> > +    out_num--;
> > +
> > +    if (elem->in_sg[in_num - 1].iov_len < sizeof(struct virtio_blk_inhdr)) 
> > {
> > +        fprintf(stderr, "Invalid inhdr size\n");
> > +        goto err;
> > +    }
> > +    req->in = (struct virtio_blk_inhdr *)elem->in_sg[in_num - 1].iov_base;
> > +    in_num--;
> > +
> > +    type = le32toh(req->out->type);
> 
> Endianness is more complicated if you want to support both VIRTIO 1.0
> and Legacy (0.9.7).  I guess it's okay to make libvhost-user code only
> support VIRTIO 1.0.
> > +static void vub_queue_set_started(VuDev *vu_dev, int idx, bool started)
> > +{
> > +    VuVirtq *vq;
> > +
> > +    assert(vu_dev);
> > +
> > +    if ((idx < 0) || (idx >= VHOST_MAX_NR_VIRTQUEUE)) {
> > +        fprintf(stderr, "VQ Index out of range: %d\n", idx);
> > +        vub_panic_cb(vu_dev, NULL);
> > +        return;
> > +    }
> 
> Is it necessary to check num_queues?  The vhost-user master should not
> be able to enable idx >= num_queues.
Yes, this part of code can be removed.



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