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Re: [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening
Date: Wed, 11 May 2016 13:56:05 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 11.05.2016 um 13:48 hat Richard W.M. Jones geschrieben:
> While I remember there is another concern that doesn't seem to be
> addressed in this patch series.  What happens when a guest is paused?
> I think exclusive locks should be converted to shared locks in that
> case, since (only while the guest is paused) it _is_ safe to fish
> around inside the guest's state.  Of course the lock must be restored
> before the guest resumes.

I think it's still one of the cases where it's appropriate to require an
"I know what I'm doing" flag. In paused guests, you still don't
necessarily see the same contents as the guest does (because of guest
caches). Apart from that, things like block jobs and NBD servers keep
running even with a stopped VM.

The lock can only be dropped in cases where we can justify switching to
BDRV_O_INACTIVE, and I don't think a simple stop/cont should do this.


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