Re: [Qemu-devel] [PATCH v4] virtio dataplane: adapt dataplane for virtio Version 1

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Wed,  2 Sep 2015 18:53:44 +0200
Pierre Morel <pmorel@linux.vnet.ibm.com> wrote:

> Let dataplane allocate different region for the desc/avail/used
> ring regions.
> Take VIRTIO_RING_F_EVENT_IDX into account to increase the used/avail
> rings accordingly.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
> 
> ---

Yet another remark, see below.

Cheers.

--
Greg

> Changes from V2:
> - incorporate the code directly in vring_setup().
> - added room for the event indexes used with VIRTIO_RING_F_EVENT_IDX
> 
> Changes from v1:
> - use a macro to gain LOCs inside of vring_setup()
> 
>  hw/virtio/dataplane/vring.c         | 61 ++++++++++++++++++++++++++++---------
>  include/hw/virtio/dataplane/vring.h |  4 ++-
>  2 files changed, 50 insertions(+), 15 deletions(-)
> 
> diff --git a/hw/virtio/dataplane/vring.c b/hw/virtio/dataplane/vring.c
> index 07fd69c..08e1f4f 100644
> --- a/hw/virtio/dataplane/vring.c
> +++ b/hw/virtio/dataplane/vring.c
> @@ -67,22 +67,45 @@ static void vring_unmap(void *buffer, bool is_write)
>  /* Map the guest's vring to host memory */
>  bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
>  {
> -    hwaddr vring_addr = virtio_queue_get_ring_addr(vdev, n);
> -    hwaddr vring_size = virtio_queue_get_ring_size(vdev, n);
> -    void *vring_ptr;
> +    struct vring *vr = &vring->vr;
> +    hwaddr addr;
> +    hwaddr size;
> +    void *ptr;
> 
>      vring->broken = false;
> -
> -    vring_ptr = vring_map(&vring->mr, vring_addr, vring_size, true);
> -    if (!vring_ptr) {
> -        error_report("Failed to map vring "
> -                     "addr %#" HWADDR_PRIx " size %" HWADDR_PRIu,
> -                     vring_addr, vring_size);
> -        vring->broken = true;
> -        return false;
> +    vr->num = virtio_queue_get_num(vdev, n);
> +
> +    addr = virtio_queue_get_desc_addr(vdev, n);
> +    size = virtio_queue_get_desc_size(vdev, n);
> +    ptr = vring_map(&vring->mr_desc, addr, size, true);

Shouldn't we pass false since the device isn't supposed to write
into the descriptor table ?

> +    if (!ptr) {
> +        error_report("Failed to map 0x%16lx byte for vring desc at %16lx",
> +                      size, addr);
> +        goto out_err_desc;
>      }
> -
> -    vring_init(&vring->vr, virtio_queue_get_num(vdev, n), vring_ptr, 4096);
> +    vr->desc = ptr;
> +
> +    addr = virtio_queue_get_avail_addr(vdev, n);
> +    size = virtio_queue_get_avail_size(vdev, n);
> +    size += sizeof(__virtio16);
> +    ptr = vring_map(&vring->mr_avail, addr, size, true);

Same remark for the available ring.

> +    if (!ptr) {
> +        error_report("Failed to map 0x%16lx byte for vring avail at %16lx",
> +                      size, addr);
> +        goto out_err_avail;
> +    }
> +    vr->avail = ptr;
> +
> +    addr = virtio_queue_get_used_addr(vdev, n);
> +    size = virtio_queue_get_used_size(vdev, n);
> +    size += sizeof(__virtio16);
> +    ptr = vring_map(&vring->mr_used, addr, size, true);
> +    if (!ptr) {
> +        error_report("Failed to map 0x%16lx byte for vring used at %16lx",
> +                      size, addr);
> +        goto out_err_used;
> +    }
> +    vr->used = ptr;
> 
>      vring->last_avail_idx = virtio_queue_get_last_avail_idx(vdev, n);
>      vring->last_used_idx = vring_get_used_idx(vdev, vring);
> @@ -92,6 +115,14 @@ bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
>      trace_vring_setup(virtio_queue_get_ring_addr(vdev, n),
>                        vring->vr.desc, vring->vr.avail, vring->vr.used);
>      return true;
> +
> +out_err_used:
> +    memory_region_unref(vring->mr_avail);
> +out_err_avail:
> +    memory_region_unref(vring->mr_desc);
> +out_err_desc:
> +    vring->broken = true;
> +    return false;
>  }
> 
>  void vring_teardown(Vring *vring, VirtIODevice *vdev, int n)
> @@ -99,7 +130,9 @@ void vring_teardown(Vring *vring, VirtIODevice *vdev, int n)
>      virtio_queue_set_last_avail_idx(vdev, n, vring->last_avail_idx);
>      virtio_queue_invalidate_signalled_used(vdev, n);
> 
> -    memory_region_unref(vring->mr);
> +    memory_region_unref(vring->mr_desc);
> +    memory_region_unref(vring->mr_avail);
> +    memory_region_unref(vring->mr_used);
>  }
> 
>  /* Disable guest->host notifies */
> diff --git a/include/hw/virtio/dataplane/vring.h b/include/hw/virtio/dataplane/vring.h
> index 8d97db9..a596e4c 100644
> --- a/include/hw/virtio/dataplane/vring.h
> +++ b/include/hw/virtio/dataplane/vring.h
> @@ -22,7 +22,9 @@
>  #include "hw/virtio/virtio.h"
> 
>  typedef struct {
> -    MemoryRegion *mr;               /* memory region containing the vring */
> +    MemoryRegion *mr_desc;          /* memory region for the vring desc */
> +    MemoryRegion *mr_avail;         /* memory region for the vring avail */
> +    MemoryRegion *mr_used;          /* memory region for the vring used */
>      struct vring vr;                /* virtqueue vring mapped to host memory */
>      uint16_t last_avail_idx;        /* last processed avail ring index */
>      uint16_t last_used_idx;         /* last processed used ring index */