On Tue, Nov 17, 2020 at 04:43:42PM +0000, Stefan Hajnoczi wrote:

On Tue, Nov 17, 2020 at 03:16:20PM +0100, Stefano Garzarella wrote:

quoted

On Tue, Nov 17, 2020 at 11:11:21AM +0000, Stefan Hajnoczi wrote:

quoted

On Fri, Nov 13, 2020 at 02:47:04PM +0100, Stefano Garzarella wrote:

quoted

+static void vdpasim_blk_work(struct work_struct *work)
+{
+	struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
+	u8 status = VIRTIO_BLK_S_OK;
+	int i;
+
+	spin_lock(&vdpasim->lock);
+
+	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
+		goto out;
+
+	for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
+		struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
+
+		if (!vq->ready)
+			continue;
+
+		while (vringh_getdesc_iotlb(&vq->vring, &vq->iov, &vq->iov,
+					    &vq->head, GFP_ATOMIC) > 0) {
+
+			int write;
+
+			vq->iov.i = vq->iov.used - 1;
+			write = vringh_iov_push_iotlb(&vq->vring, &vq->iov, &status, 1);
+			if (write <= 0)
+				break;

We're lucky the guest driver doesn't crash after VIRTIO_BLK_T_GET_ID? :)

The crash could happen if the simulator doesn't put the string terminator,
but in virtio_blk.c, the serial_show() initialize the buffer putting the
string terminator in the VIRTIO_BLK_ID_BYTES element:

    buf[VIRTIO_BLK_ID_BYTES] = '\0';
    err = virtblk_get_id(disk, buf);

This should prevent the issue, right?

However in the last patch of this series I implemented VIRTIO_BLK_T_GET_ID
support :-)

Windows, BSD, macOS, etc guest drivers aren't necessarily going to
terminate or initialize the serial string buffer.

Unfortunately I discovered that VIRTIO_BLK_T_GET_ID is not in the VIRTIO 
specs, so, just for curiosity, I checked the QEMU code and I found this:

     case VIRTIO_BLK_T_GET_ID:
     {
         /*
          * NB: per existing s/n string convention the string is
          * terminated by '\0' only when shorter than buffer.
          */
         const char *serial = s->conf.serial ? s->conf.serial : "";
         size_t size = MIN(strlen(serial) + 1,
                           MIN(iov_size(in_iov, in_num),
                               VIRTIO_BLK_ID_BYTES));
         iov_from_buf(in_iov, in_num, 0, serial, size);
         virtio_blk_req_complete(req, VIRTIO_BLK_S_OK);
         virtio_blk_free_request(req);
         break;
     }

It seems that the device emulation in QEMU expects that the driver 
terminates the serial string buffer.

Do you know why VIRTIO_BLK_T_GET_ID is not in the specs?
Should we add it?

Thanks,
Stefano

Anyway, the later patch that implements VIRTIO_BLK_T_GET_ID solves this
issue! Thanks.

Stefan

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