Re: [Qemu-devel] [PATCH 07/24] qcow2: add bitmaps extension

[Max Reitz <mreitz@redhat.com>]

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On 23.01.2017 13:10, Vladimir Sementsov-Ogievskiy wrote:
> Add bitmap extension as specified in docs/specs/qcow2.txt.
> For now, just mirror extension header into Qcow2 state and check
> constraints.
> 
> For now, disable image resize if it has bitmaps. It will be fixed later.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/qcow2.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  block/qcow2.h |  24 ++++++++++++
>  2 files changed, 141 insertions(+), 2 deletions(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 96fb8a8f16..a8835988c7 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c

[...]

> @@ -185,6 +265,15 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
>          offset += ((ext.len + 7) & ~7);
>      }
>  
> +    if (need_update && !bdrv_is_root_node(bs) &&
> +        !(bdrv_get_flags(bs) & BDRV_O_INACTIVE))
> +    {
> +        ret = qcow2_update_header(bs);

Good idea, but qcow2_read_extensions() can be called pretty early in
qcow2_open(). Therefore, some fields in the BDRVQcow2State are not
necessarily set already.

For instance, it is always called before s->snapshots_offset and
s->nb_snapshots are set. Thus, this will effectively always discard all
snapshots.

Max


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