Re: [RFC-v2 4/6] virtio-scsi: Add start/stop functionality for vhost-scsi

[Paolo Bonzini <pbonzini@redhat.com>]

Il 13/08/2012 10:35, Nicholas A. Bellinger ha scritto:
> From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> 
> This patch starts and stops vhost as the virtio device transitions
> through its status phases.  Vhost can only be started once the guest
> reports its driver has successfully initialized, which means the
> virtqueues have been set up by the guest.
> 
> v2: - Squash virtio-scsi: use the vhost-scsi host device from stefan (nab)
>     - Fix up virtio_scsi_properties[] conflict w/ upstream qemu (nab)
>     - Drop usage of to_virtio_scsi() in virtio_scsi_set_status()
>       (reported by paolo)
>     - Use modern VirtIOSCSIConf define in virtio-scsi.h (reported by paolo)
>     - Use s->conf->vhost_scsi instead of proxyconf->vhost_scsi in
>       virtio_scsi_init() (reported by paolo)
>     - Only register QEMU SCSI bus is vhost-scsi is not active (reported
>       by paolo)

How much of the functionality of virtio-scsi.[ch] is still in use at
this point?  Would it make more sense to use a separate vhost-scsi-pci
device instead?

Especially since advertising VIRTIO_SCSI_F_HOTPLUG and
VIRTIO_SCSI_F_CHANGE is probably wrong for vhost-scsi...

Paolo

> Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> Cc: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
> ---
>  hw/virtio-pci.c  |    1 +
>  hw/virtio-scsi.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/virtio-scsi.h |    1 +
>  3 files changed, 50 insertions(+), 0 deletions(-)
> 
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index 125eded..b29fc3b 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -1036,6 +1036,7 @@ static void virtio_scsi_exit_pci(PCIDevice *pci_dev)
>  }
>  
>  static Property virtio_scsi_properties[] = {
> +    DEFINE_PROP_VHOST_SCSI("vhost-scsi", VirtIOPCIProxy, scsi.vhost_scsi),
>      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags, VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
>      DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, DEV_NVECTORS_UNSPECIFIED),
>      DEFINE_VIRTIO_SCSI_PROPERTIES(VirtIOPCIProxy, host_features, scsi),
> diff --git a/hw/virtio-scsi.c b/hw/virtio-scsi.c
> index 5f737ac..8130956 100644
> --- a/hw/virtio-scsi.c
> +++ b/hw/virtio-scsi.c
> @@ -13,9 +13,13 @@
>   *
>   */
>  
> +#include "qemu-common.h"
> +#include "qemu-error.h"
> +#include "vhost-scsi.h"
>  #include "virtio-scsi.h"
>  #include <hw/scsi.h>
>  #include <hw/scsi-defs.h>
> +#include "vhost.h"
>  
>  #define VIRTIO_SCSI_VQ_SIZE     128
>  #define VIRTIO_SCSI_CDB_SIZE    32
> @@ -147,6 +151,9 @@ typedef struct {
>      VirtQueue *ctrl_vq;
>      VirtQueue *event_vq;
>      VirtQueue *cmd_vqs[0];
> +
> +    bool vhost_started;
> +    VHostSCSI *vhost_scsi;
>  } VirtIOSCSI;
>  
>  typedef struct VirtIOSCSIReq {
> @@ -699,6 +706,38 @@ static struct SCSIBusInfo virtio_scsi_scsi_info = {
>      .load_request = virtio_scsi_load_request,
>  };
>  
> +static bool virtio_scsi_started(VirtIOSCSI *s, uint8_t val)
> +{
> +    return (val & VIRTIO_CONFIG_S_DRIVER_OK) && s->vdev.vm_running;
> +}
> +
> +static void virtio_scsi_set_status(VirtIODevice *vdev, uint8_t val)
> +{
> +    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
> +    bool start = virtio_scsi_started(s, val);
> +
> +    if (s->vhost_started == start) {
> +        return;
> +    }
> +
> +    if (start) {
> +        int ret;
> +
> +        ret = vhost_scsi_start(s->vhost_scsi, vdev);
> +        if (ret < 0) {
> +            error_report("virtio-scsi: unable to start vhost: %s\n",
> +                         strerror(-ret));
> +
> +            /* There is no userspace virtio-scsi fallback so exit */
> +            exit(1);
> +        }
> +    } else {
> +        vhost_scsi_stop(s->vhost_scsi, vdev);
> +    }
> +
> +    s->vhost_started = start;
> +}
> +
>  VirtIODevice *virtio_scsi_init(DeviceState *dev, VirtIOSCSIConf *proxyconf)
>  {
>      VirtIOSCSI *s;
> @@ -712,12 +751,17 @@ VirtIODevice *virtio_scsi_init(DeviceState *dev, VirtIOSCSIConf *proxyconf)
>  
>      s->qdev = dev;
>      s->conf = proxyconf;
> +    s->vhost_started = false;
> +    s->vhost_scsi = s->conf->vhost_scsi;
>  
>      /* TODO set up vdev function pointers */
>      s->vdev.get_config = virtio_scsi_get_config;
>      s->vdev.set_config = virtio_scsi_set_config;
>      s->vdev.get_features = virtio_scsi_get_features;
>      s->vdev.reset = virtio_scsi_reset;
> +    if (s->vhost_scsi) {
> +        s->vdev.set_status = virtio_scsi_set_status;
> +    }
>  
>      s->ctrl_vq = virtio_add_queue(&s->vdev, VIRTIO_SCSI_VQ_SIZE,
>                                     virtio_scsi_handle_ctrl);
> @@ -743,5 +787,9 @@ void virtio_scsi_exit(VirtIODevice *vdev)
>  {
>      VirtIOSCSI *s = (VirtIOSCSI *)vdev;
>      unregister_savevm(s->qdev, "virtio-scsi", s);
> +
> +    /* This will stop vhost backend if appropriate. */
> +    virtio_scsi_set_status(vdev, 0);
> +
>      virtio_cleanup(vdev);
>  }
> diff --git a/hw/virtio-scsi.h b/hw/virtio-scsi.h
> index 4bc889d..74e9422 100644
> --- a/hw/virtio-scsi.h
> +++ b/hw/virtio-scsi.h
> @@ -22,6 +22,7 @@
>  #define VIRTIO_ID_SCSI  8
>  
>  struct VirtIOSCSIConf {
> +    VHostSCSI *vhost_scsi;
>      uint32_t num_queues;
>      uint32_t max_sectors;
>      uint32_t cmd_per_lun;
>