[Qemu-devel] [PATCH] virtio-scsi: fix "written length" field in the used ring

[Paolo Bonzini]

qsgl->size is the size of the data field after the request or
response header (virtio-scsi currently supports only one such
field; bidirectional requests are not supported).  However,
the used ring's len field is not concerned about the field
after the request header, so do not count it unless req->mode
signals the request was a read.

Also, do not report that anything was written if the request
failed, and subtract any residual bytes in case of buffer underrun.

Signed-off-by: Paolo Bonzini <address@hidden>
---
 hw/scsi/virtio-scsi.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index c9bea06..4995f6e 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -65,6 +65,19 @@ void virtio_scsi_free_req(VirtIOSCSIReq *req)
     g_slice_free1(sizeof(*req) + vs->cdb_size, req);
 }
 
+static size_t virtio_scsi_written_length(VirtIODevice *vdev, VirtIOSCSIReq 
*req)
+{
+    size_t sz = req->resp_iov.size;
+
+    if (req->sreq &&
+        req->mode == SCSI_XFER_FROM_DEV &&
+        req->resp.cmd.response == VIRTIO_SCSI_S_OK) {
+        sz += req->qsgl.size - virtio_tswap32(vdev, req->resp.cmd.resid);
+    }
+
+    return sz;
+}
+
 static void virtio_scsi_complete_req(VirtIOSCSIReq *req)
 {
     VirtIOSCSI *s = req->dev;
@@ -76,7 +89,7 @@ static void virtio_scsi_complete_req(VirtIOSCSIReq *req)
         assert(req->vq == NULL);
         virtio_scsi_vring_push_notify(req);
     } else {
-        virtqueue_push(vq, &req->elem, req->qsgl.size + req->resp_iov.size);
+        virtqueue_push(vq, &req->elem, virtio_scsi_written_length(vdev, req));
         virtio_notify(vdev, vq);
     }
 
-- 
2.3.5