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Re: [Qemu-devel] [PATCH v2 4/6] block/dirty-bitmap: explicitly lock bitm

From: John Snow
Subject: Re: [Qemu-devel] [PATCH v2 4/6] block/dirty-bitmap: explicitly lock bitmaps with successors
Date: Mon, 18 Feb 2019 17:13:16 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0

On 2/18/19 11:52 AM, Vladimir Sementsov-Ogievskiy wrote:
> 14.02.2019 2:23, John Snow wrote:
>> Instead of implying a locked status, make it explicit.
> locked interferes with bitmap mutex, so may be better "qmp_locked state", but 
> not sure.

I agree that "locked" has too many meanings, so in patch 5 I start using
the term "busy" instead.

>> Now, bitmaps in use by migration, NBD or backup operations
>> are all treated the same way with the same code paths.
>> Signed-off-by: John Snow <address@hidden>
>> Reviewed-by: Eric Blake <address@hidden>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Hmm. Isn't it better to make successor-related staff unrelated to locking at 
> all?

Maybe -- but it doesn't make sense to allow users to modify bitmaps that
have a successor because we know it's definitely busy. I'll take a
further cleanup patch if you think it's better -- just be careful to
make sure that any interface calls will work gracefully with a bitmap
with a successor.

> So, backup will call set_qmp_locked like others? And then do create_successor,
> abdicate, reclaim, whatever it wants, and finally set_qmp_locked(false) ?
> To make it work even more in the same path. But it may be done separately, if 
> we
> want.

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