Re: [Qemu-devel] [RFC PATCH 06/16] block: Introduce bdrv_dirty_bitmap_set_persistent

[John Snow <jsnow@redhat.com>]

On 01/26/2016 05:38 AM, Fam Zheng wrote:
> By implementing bdrv_dirty_bitmap_set_persistent, a driver can support
> the persistent dirty bitmap feature.
> 
> Once a dirty bitmap is made persistent, the driver is responsible for saving
> the dirty bitmap when appropriate, for example before close; if a persistent
> bitmap is removed or made non-persistent, .bdrv_dirty_bitmap_set_persistent
> will be called, the driver should then remove the dirty bitmap from the disk.
> 
> This operation is not recursed in block layer, a filter such as blkdebug needs
> to implement the callback and explicitly pass down to bs->file, etc.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/dirty-bitmap.c         | 38 ++++++++++++++++++++++++++++++++++++++
>  include/block/block_int.h    |  8 ++++++++
>  include/block/dirty-bitmap.h |  4 ++++
>  3 files changed, 50 insertions(+)
> 
> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
> index 1aa7f76..882a0db 100644
> --- a/block/dirty-bitmap.c
> +++ b/block/dirty-bitmap.c
> @@ -43,6 +43,7 @@ struct BdrvDirtyBitmap {
>      int64_t size;               /* Size of the bitmap (Number of sectors) */
>      bool disabled;              /* Bitmap is read-only */
>      int active_iterators;       /* How many iterators are active */
> +    bool persistent;            /* Whether this bitmap is persistent. */
>      QLIST_ENTRY(BdrvDirtyBitmap) list;
>  };
>  
> @@ -71,6 +72,37 @@ void bdrv_dirty_bitmap_make_anon(BdrvDirtyBitmap *bitmap)
>      bitmap->name = NULL;
>  }
>  

What's the intended usage of flag_only? (/keeps reading/...)

> +int bdrv_dirty_bitmap_set_persistent(BlockDriverState *bs,
> +                                     BdrvDirtyBitmap *bitmap,
> +                                     bool persistent, bool flag_only,
> +                                     Error **errp)
> +{
> +    int ret = 0;
> +
> +    if (!bitmap->name) {
> +        error_setg(errp, "Cannot change the persistent status of an anonymous"
> +                         "bitmap");
> +        return -EINVAL;
> +    }
> +
> +    if (persistent == bitmap->persistent) {
> +        return 0;
> +    }
> +
> +    if (!flag_only) {
> +        if (!bs->drv || !bs->drv->bdrv_dirty_bitmap_set_persistent) {
> +            error_setg(errp, "Not supported in this format.");
> +            return -ENOTSUP;
> +        }
> +        ret = bs->drv->bdrv_dirty_bitmap_set_persistent(bs, bitmap, persistent,
> +                                                        errp);
> +    }
> +    if (!ret) {
> +        bitmap->persistent = persistent;
> +    }
> +    return ret;
> +}
> +
>  BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
>                                            uint32_t granularity,
>                                            const char *name,
> @@ -194,6 +226,12 @@ int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
>      uint64_t granularity;
>      BdrvDirtyBitmap *child;
>  
> +    if (bitmap->persistent) {
> +        error_setg(errp, "Cannot create a successor for a bitmap that is "
> +                   "persistent");
> +        return -1;
> +    }
> +
>      if (bdrv_dirty_bitmap_frozen(bitmap)) {
>          error_setg(errp, "Cannot create a successor for a bitmap that is "
>                     "currently frozen");
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 5fa58e8..fbc34af 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -305,6 +305,14 @@ struct BlockDriver {
>       */
>      void (*bdrv_drain)(BlockDriverState *bs);
>  
> +    /**
> +     * Make the dirty bitmap persistent if persistent=true or transient
> +     * otherwise.
> +     */
> +    int (*bdrv_dirty_bitmap_set_persistent)(BlockDriverState *bs,
> +                                            BdrvDirtyBitmap *bitmap,
> +                                            bool persistent, Error **errp);
> +
>      QLIST_ENTRY(BlockDriver) list;
>  };
>  
> diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
> index d14d923..5885720 100644
> --- a/include/block/dirty-bitmap.h
> +++ b/include/block/dirty-bitmap.h
> @@ -24,6 +24,10 @@ BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap(BlockDriverState *bs,
>  BdrvDirtyBitmap *bdrv_find_dirty_bitmap(BlockDriverState *bs,
>                                          const char *name);
>  void bdrv_dirty_bitmap_make_anon(BdrvDirtyBitmap *bitmap);
> +int bdrv_dirty_bitmap_set_persistent(BlockDriverState *bs,
> +                                     BdrvDirtyBitmap *bitmap,
> +                                     bool persistent, bool flag_only,
> +                                     Error **errp);
>  void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap);
>  void bdrv_disable_dirty_bitmap(BdrvDirtyBitmap *bitmap);
>  void bdrv_enable_dirty_bitmap(BdrvDirtyBitmap *bitmap);
>