Re: [Qemu-devel] [Qemu-block] [PATCH 6/9] block: Support BDRV_REQ_WRITE_UNCHANGED in filters

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Mon, Apr 16, 2018 at 06:58:46PM +0200, Max Reitz wrote:
> Update the rest of the filter drivers to support
> BDRV_REQ_WRITE_UNCHANGED.  They already forward write request flags to
> their children, so we just have to announce support for it.
> 
> This patch does not cover the replication driver because that currently
> does not support flags at all, and because it just grabs the WRITE
> permission for its children when it can, so we should be fine just
> submitting the incoming WRITE_UNCHANGED requests as normal writes.
> 
> It also does not cover format drivers for similar reasons.  They all use
> bdrv_format_default_perms() as their .bdrv_child_perm() implementation
> so they just always grab the WRITE permission for their file children
> whenever possible.  In addition, it often would be difficult to
> ascertain whether incoming unchanging writes end up as unchanging writes
> in their files.  So we just leave them as normal potentially changing
> writes.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/blkdebug.c   |  9 +++++----
>  block/blkreplay.c  |  3 +++
>  block/blkverify.c  |  3 +++
>  block/cor.c        | 10 ++++++----
>  block/mirror.c     |  2 ++
>  block/raw-format.c |  9 +++++----
>  block/throttle.c   |  6 ++++--
>  7 files changed, 28 insertions(+), 14 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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