Re: [Qemu-devel] [PATCH 5/8] virtio-blk: fix "disabled data plane" mode

[Fam Zheng]

On Sun, 02/14 18:17, Paolo Bonzini wrote:
> In disabled mode, virtio-blk dataplane seems to be enabled, but flow
> actually goes through the normal virtio path.  This patch simplifies a bit
> the handling of disabled mode.  In disabled mode, virtio_blk_handle_output
> might be called even if s->dataplane is not NULL.
> 
> This is a bit tricky, because the current check for s->dataplane will
> always trigger, causing a continuous stream of calls to
> virtio_blk_data_plane_start.  Unfortunately, these calls will not
> do anything.  To fix this, set the "started" flag even in disabled
> mode, and skip virtio_blk_data_plane_start if the started flag is true.
> The resulting changes also prepare the code for the next patch, were
> virtio-blk dataplane will reuse the same virtio_blk_handle_output function
> as "regular" virtio-blk.
> 
> Because struct VirtIOBlockDataPlane is opaque in virtio-blk.c, we have
> to move s->dataplane->started inside struct VirtIOBlock.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  hw/block/dataplane/virtio-blk.c | 21 +++++++++------------
>  hw/block/virtio-blk.c           |  2 +-
>  include/hw/virtio/virtio-blk.h  |  1 +
>  3 files changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 03b81bc..cc521c1 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -28,7 +28,6 @@
>  #include "qom/object_interfaces.h"
>  
>  struct VirtIOBlockDataPlane {
> -    bool started;
>      bool starting;
>      bool stopping;
>      bool disabled;
> @@ -264,11 +263,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
>      VirtQueue *vq;
>      int r;
>  
> -    if (s->started || s->disabled) {
> -        return;
> -    }
> -
> -    if (s->starting) {
> +    if (vblk->dataplane_started || s->starting) {
>          return;
>      }
>  
> @@ -300,7 +295,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
>      vblk->complete_request = complete_request_vring;
>  
>      s->starting = false;
> -    s->started = true;
> +    vblk->dataplane_started = true;
>      trace_virtio_blk_data_plane_start(s);
>  
>      blk_set_aio_context(s->conf->conf.blk, s->ctx);
> @@ -319,9 +314,10 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
>      k->set_guest_notifiers(qbus->parent, 1, false);
>    fail_guest_notifiers:
>      vring_teardown(&s->vring, s->vdev, 0);
> -    s->disabled = true;
>    fail_vring:
> +    s->disabled = true;
>      s->starting = false;

Worth a comment here, or at definition of dataplane_started, explaining the
trick said in the commit message?

Reviewed-by: Fam Zheng <address@hidden>

> +    vblk->dataplane_started = true;
>  }
>  

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