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Re: [PATCH] qcow2: set bdi->is_dirty


From: Eric Blake
Subject: Re: [PATCH] qcow2: set bdi->is_dirty
Date: Tue, 4 May 2021 11:20:42 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1

On 5/4/21 11:06 AM, Vladimir Sementsov-Ogievskiy wrote:
> Set bdi->is_dirty, so that qemu-img info could show dirty flag.
> 
> After this commit the following check will show '"dirty-flag": true':
> 
> ./build/qemu-img create -f qcow2 -o lazy_refcounts=on x 1M
> ./build/qemu-io x
> qemu-io> write 0 1M
> 
>  After "write" command success, kill the qemu-io process:
> 
> kill -9 <qemu-io pid>
> 
> ./build/qemu-img info --output=json x
> 
> This will show '"dirty-flag": true' among other things. (before this
> commit it shows '"dirty-flag": false')
> 
> Note, that qcow2's dirty-bit is not a "dirty bit for the image". It
> only protects qcow2 lazy refcounts feature. So, there are a lot of
> conditions when qcow2 session may be not closed correctly, but bit is
> 0. Still, when bit is set, the last session is definitely not finished
> correctly and it's better to report it.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/qcow2.c | 1 +
>  1 file changed, 1 insertion(+)

Reviewed-by: Eric Blake <eblake@redhat.com>


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org




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