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Re: [Qemu-devel] [Qemu-block] [PATCH 6/9] block: Support BDRV_REQ_WRITE_


From: Alberto Garcia
Subject: Re: [Qemu-devel] [Qemu-block] [PATCH 6/9] block: Support BDRV_REQ_WRITE_UNCHANGED in filters
Date: Fri, 20 Apr 2018 14:19:17 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Mon 16 Apr 2018 06:58:46 PM CEST, 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 <address@hidden>

Reviewed-by: Alberto Garcia <address@hidden>

Berto



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