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virtio-scsi: work around bug in old BIOSes

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Old BIOSes left some padding by mistake after the req_size/resp_size.
New QEMU does not like it, thinking it is a bidirectional command.

As a workaround, we can check if the ANY_LAYOUT bit is set; if not, we
always consider the first buffer as the virtio-scsi request/response,
because, back when QEMU did not support ANY_LAYOUT, it expected the
payload to start at the second element of the iovec.

This can show up during migration.

Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2014-11-07 14:00:02 +01:00
parent c3543fb5fe
commit 55783a5521
1 changed files with 17 additions and 0 deletions
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17
hw/scsi/virtio-scsi.c
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@ -118,6 +118,7 @@ static size_t qemu_sgl_concat(VirtIOSCSIReq *req, struct iovec *iov,
static int virtio_scsi_parse_req(VirtIOSCSIReq *req,
unsigned req_size, unsigned resp_size)
{
VirtIODevice *vdev = (VirtIODevice *) req->dev;
size_t in_size, out_size;
if (iov_to_buf(req->elem.out_sg, req->elem.out_num, 0,
@ -130,8 +131,24 @@ static int virtio_scsi_parse_req(VirtIOSCSIReq *req,
resp_size) < resp_size) {
return -EINVAL;
}
req->resp_size = resp_size;
/* Old BIOSes left some padding by mistake after the req_size/resp_size.
* As a workaround, always consider the first buffer as the virtio-scsi
* request/response, making the payload start at the second element
* of the iovec.
*
* The actual length of the response header, stored in req->resp_size,
* does not change.
*
* TODO: always disable this workaround for virtio 1.0 devices.
*/
if ((vdev->guest_features & VIRTIO_F_ANY_LAYOUT) == 0) {
req_size = req->elem.out_sg[0].iov_len;
resp_size = req->elem.in_sg[0].iov_len;
}
out_size = qemu_sgl_concat(req, req->elem.out_sg,
&req->elem.out_addr[0], req->elem.out_num,
req_size);