Re: [Qemu-devel] [PATCH] virtio-blk: Allow config-wce in dataplane

[Paolo Bonzini <pbonzini@redhat.com>]

Il 13/05/2014 04:24, Fam Zheng ha scritto:
> Dataplane now uses block layer. Protect bdrv_set_enable_write_cache with
> aio_context_acquire and aio_context_release, so we can enable config-wce
> to allow guest to modify the write cache online.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
>
> ---
> This applies on top of Stefan's "dataplane: use QEMU block layer"
> series.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  hw/block/dataplane/virtio-blk.c | 6 ------
>  hw/block/virtio-blk.c           | 9 ++++++++-
>  2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 79fb612..46a6824 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -332,12 +332,6 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
>          return;
>      }
>
> -    if (blk->config_wce) {
> -        error_setg(errp, "device is incompatible with x-data-plane, "
> -                         "use config-wce=off");
> -        return;
> -    }
> -
>      /* If dataplane is (re-)enabled while the guest is running there could be
>       * block jobs that can conflict.
>       */
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 8a568e5..a031e56 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -26,6 +26,7 @@
>  # include <scsi/sg.h>
>  #endif
>  #include "hw/virtio/virtio-bus.h"
> +#include "block/block_int.h"

You shouldn't need to include this header file.  Apart from this, the 
patch looks good.

Paolo

>
>  typedef struct VirtIOBlockReq
>  {
> @@ -523,7 +524,10 @@ static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
>      struct virtio_blk_config blkcfg;
>
>      memcpy(&blkcfg, config, sizeof(blkcfg));
> +
> +    aio_context_acquire(bdrv_get_aio_context(s->bs));
>      bdrv_set_enable_write_cache(s->bs, blkcfg.wce != 0);
> +    aio_context_release(bdrv_get_aio_context(s->bs));
>  }
>
>  static uint32_t virtio_blk_get_features(VirtIODevice *vdev, uint32_t features)
> @@ -582,7 +586,10 @@ static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t status)
>       * s->bs would erroneously be placed in writethrough mode.
>       */
>      if (!(features & (1 << VIRTIO_BLK_F_CONFIG_WCE))) {
> -        bdrv_set_enable_write_cache(s->bs, !!(features & (1 << VIRTIO_BLK_F_WCE)));
> +        aio_context_acquire(bdrv_get_aio_context(s->bs));
> +        bdrv_set_enable_write_cache(s->bs,
> +                                    !!(features & (1 << VIRTIO_BLK_F_WCE)));
> +        aio_context_release(bdrv_get_aio_context(s->bs));
>      }
>  }
>
>