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Re: [Qemu-devel] [PATCH v4 4/8] block: Fix dirty bitmap in bdrv_co_disca

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v4 4/8] block: Fix dirty bitmap in bdrv_co_discard
Date: Fri, 22 May 2015 14:22:04 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 05/21/2015 09:40 PM, Fam Zheng wrote:
> Unsetting dirty globally with discard is not very correct. The discard may 
> zero
> out sectors (depending on can_write_zeroes_with_unmap), we should replicate
> this change to destinition side to make sure that the guest sees the same 
> data.


> Calling bdrv_reset_dirty also troubles mirror job because the hbitmap iterator
> doesn't expect unsetting of bits after current position.
> So let's do it the opposite way which fixes both problems: set the dirty bits
> if we are to discard it.
> Reported-by: address@hidden
> Signed-off-by: Fam Zheng <address@hidden>
> Reviewed-by: Paolo Bonzini <address@hidden>
> ---
>  block/io.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Eric Blake <address@hidden>

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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