linux-kernel - Re: [PATCH v1] virtio-scsi: get and set the queue limits for sg device

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Date:	Tue, 21 Aug 2012 09:53:59 +0100
From:	Stefan Hajnoczi <stefanha@...il.com>
To:	Cong Meng <mc@...ux.vnet.ibm.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, stefanha@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, zwanp@...ibm.com,
	linuxram@...ibm.com, qemu-devel@...gnu.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v1] virtio-scsi: get and set the queue limits for sg device

On Tue, Aug 21, 2012 at 9:26 AM, Cong Meng <mc@...ux.vnet.ibm.com> wrote:
> Each virtio scsi HBA has global request queue limits. But the passthrough
> LUNs (scsi-generic) come from different host HBAs may have different request
> queue limits. If the guest sends commands that exceed the host limits, the
> commands will be rejected by host HAB.
>
> This patch addresses this issue by getting the per-LUN queue limits via the the
> newly added virtio control request, then setting them properly.
>
> Signed-off-by: Cong Meng <mc@...ux.vnet.ibm.com>
> ---
>  drivers/scsi/virtio_scsi.c  |  113 +++++++++++++++++++++++++++++++++++++------
>  include/linux/virtio_scsi.h |   18 +++++++
>  2 files changed, 116 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index 173cb39..ec5066f 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -35,12 +35,14 @@ struct virtio_scsi_cmd {
>                 struct virtio_scsi_cmd_req       cmd;
>                 struct virtio_scsi_ctrl_tmf_req  tmf;
>                 struct virtio_scsi_ctrl_an_req   an;
> +               struct virtio_scsi_ctrl_lq_req   lq;
>         } req;
>         union {
>                 struct virtio_scsi_cmd_resp      cmd;
>                 struct virtio_scsi_ctrl_tmf_resp tmf;
>                 struct virtio_scsi_ctrl_an_resp  an;
>                 struct virtio_scsi_event         evt;
> +               struct virtio_scsi_ctrl_lq_resp  lq;
>         } resp;
>  } ____cacheline_aligned_in_smp;
>
> @@ -469,6 +471,46 @@ out:
>         return ret;
>  }
>
> +static u32 virtscsi_lun_query(struct scsi_device *sdev, u32 *value, u32 subtype)
> +{
> +       struct Scsi_Host *shost = sdev->host;
> +       struct virtio_scsi *vscsi = shost_priv(shost);
> +       DECLARE_COMPLETION_ONSTACK(comp);
> +       struct virtio_scsi_cmd *cmd;
> +       struct virtio_scsi_target_state *tgt = vscsi->tgt[sdev->id];
> +       unsigned int ret = VIRTIO_SCSI_S_FAILURE;
> +
> +       cmd = mempool_alloc(virtscsi_cmd_pool, GFP_ATOMIC);
> +       if (!cmd)
> +               goto out;
> +
> +       memset(cmd, 0, sizeof(*cmd));
> +       cmd->comp = &comp;
> +       cmd->req.lq = (struct virtio_scsi_ctrl_lq_req){
> +               .type = VIRTIO_SCSI_T_LUN_QUERY,
> +               .subtype = subtype,
> +               .lun[0] = 1,
> +               .lun[1] = sdev->id,
> +               .lun[2] = (sdev->lun >> 8) | 0x40,
> +               .lun[3] = sdev->lun & 0xff,

The LUN addressing code has been duplicated several times now.  How
about replacing it with something like

static void virtio_scsi_set_lun(u8 *lun, struct scsi_device *sdev)
{
    lun[0] = 1;
    lun[1] = sdev->id;
    lun[2] = (sdev->lun >> 8) | 0x40;
    lun[3] = sdev->lun & 0xff;
    lun[4] = lun[5] = lun[6] = lun[7] = 0;
}
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