Re: [Qemu-devel] [PATCH] virtio-scsi Fix some endian bugs with virtio-scsi

[Paolo Bonzini <pbonzini@redhat.com>]

Il 23/11/2012 06:08, David Gibson ha scritto:
> The virtio-scsi specification does not specify the correct endianness for
> fields in the request structure.  It's therefore best to assume that it is
> "guest native" endian since that's the (stupid and poorly defined) norm in
> virtio.

Indeed.

> However, the qemu device for virtio-scsi has no byteswaps at all, and so
> will break if the guest has different endianness from the host.  This patch
> fixes it by adding tswap() calls for the sense_len and resid fields in
> the request structure.  In theory status_qualifier needs swaps as well,
> but that field is never actually touched.  The tag field is a uint64_t, but
> since its value is completely arbitrary, it might as well be uint8_t[8]
> and so it does not need swapping.

Thanks, I adjusted the patch to use a separate variable for the argument
of tswap32 and pushed to the scsi branch.

Paolo

> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Paul 'Rusty' Russell <rusty@rustcorp.com.au>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  hw/virtio-scsi.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio-scsi.c b/hw/virtio-scsi.c
> index 7d546f6..9d27d1d 100644
> --- a/hw/virtio-scsi.c
> +++ b/hw/virtio-scsi.c
> @@ -428,11 +428,12 @@ static void virtio_scsi_command_complete(SCSIRequest *r, uint32_t status,
>      req->resp.cmd->response = VIRTIO_SCSI_S_OK;
>      req->resp.cmd->status = status;
>      if (req->resp.cmd->status == GOOD) {
> -        req->resp.cmd->resid = resid;
> +        req->resp.cmd->resid = tswap32(resid);
>      } else {
>          req->resp.cmd->resid = 0;
>          req->resp.cmd->sense_len =
> -            scsi_req_get_sense(r, req->resp.cmd->sense, VIRTIO_SCSI_SENSE_SIZE);
> +            tswap32(scsi_req_get_sense(r, req->resp.cmd->sense,
> +                                       VIRTIO_SCSI_SENSE_SIZE));
>      }
>      virtio_scsi_complete_req(req);
>  }
>