Re: [Qemu-devel] [PATCH v11 07/13] qmp: Add block-dirty-bitmap-enable and block-dirty-bitmap-disable

[Max Reitz <mreitz@redhat.com>]

On 2015-01-12 at 11:30, John Snow wrote:
> From: Fam Zheng <famz@redhat.com>
>
> This allows to put the dirty bitmap into a disabled state where no more
> writes will be tracked.
>
> It will be used before backup or writing to persistent file.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>   block.c               | 24 +++++++++++++++++++++++-
>   blockdev.c            | 40 ++++++++++++++++++++++++++++++++++++++++
>   include/block/block.h |  3 +++
>   qapi/block-core.json  | 28 ++++++++++++++++++++++++++++
>   qmp-commands.hx       | 10 ++++++++++
>   5 files changed, 104 insertions(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index 7bf7079..bd4b449 100644
> --- a/block.c
> +++ b/block.c
> @@ -56,6 +56,7 @@ struct BdrvDirtyBitmap {
>       int64_t size;
>       int64_t granularity;
>       char *name;
> +    bool enabled;
>       QLIST_ENTRY(BdrvDirtyBitmap) list;
>   };
>   
> @@ -5373,10 +5374,16 @@ BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
>       bitmap->granularity = granularity;
>       bitmap->bitmap = hbitmap_alloc(bitmap->size, ffs(sector_granularity) - 1);
>       bitmap->name = g_strdup(name);
> +    bitmap->enabled = true;
>       QLIST_INSERT_HEAD(&bs->dirty_bitmaps, bitmap, list);
>       return bitmap;
>   }
>   
> +bool bdrv_dirty_bitmap_enabled(BdrvDirtyBitmap *bitmap)
> +{
> +    return bitmap->enabled;
> +}
> +
>   void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap)
>   {
>       BdrvDirtyBitmap *bm, *next;
> @@ -5391,6 +5398,16 @@ void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap)
>       }
>   }
>   
> +void bdrv_disable_dirty_bitmap(BdrvDirtyBitmap *bitmap)
> +{
> +    bitmap->enabled = false;
> +}
> +
> +void bdrv_enable_dirty_bitmap(BdrvDirtyBitmap *bitmap)
> +{
> +    bitmap->enabled = true;
> +}
> +
>   BlockDirtyInfoList *bdrv_query_dirty_bitmaps(BlockDriverState *bs)
>   {
>       BdrvDirtyBitmap *bm;
> @@ -5458,7 +5475,9 @@ void bdrv_dirty_iter_init(BlockDriverState *bs,
>   void bdrv_set_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap,
>                              int64_t cur_sector, int nr_sectors)
>   {
> -    hbitmap_set(bitmap->bitmap, cur_sector, nr_sectors);
> +    if (bdrv_dirty_bitmap_enabled(bitmap)) {
> +        hbitmap_set(bitmap->bitmap, cur_sector, nr_sectors);
> +    }

Why are you checking whether the bitmap is enabled here in 
bdrv_set_dirty_bitmap(), but neither in bdrv_reset_dirty_bitmap() nor 
bdrv_clear_dirty_bitmap()?

It seems consistent with the commit message which only states that 
disabled state means that no more writes (i.e. bdrv_set_dirty_bitmap()) 
will be tracked, but it still seems strange to me.

>   }
>   
>   void bdrv_reset_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap,
> @@ -5481,6 +5500,9 @@ static void bdrv_set_dirty(BlockDriverState *bs, int64_t cur_sector,
>   {
>       BdrvDirtyBitmap *bitmap;
>       QLIST_FOREACH(bitmap, &bs->dirty_bitmaps, list) {
> +        if (!bdrv_dirty_bitmap_enabled(bitmap)) {
> +            continue;
> +        }

Same question as above, only this time it's about bdrv_reset_dirty().

In case the answer to the question is "that's intentional":

Reviewed-by: Max Reitz <mreitz@redhat.com>