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Re: [Qemu-devel] [RFC PATCH for-2.9] block: Ignore guest dev permissions

From: Kevin Wolf
Subject: Re: [Qemu-devel] [RFC PATCH for-2.9] block: Ignore guest dev permissions during incoming migration
Date: Thu, 6 Apr 2017 13:15:43 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 04.04.2017 um 17:35 hat Kevin Wolf geschrieben:
> Usually guest devices don't like other writers to the same image, so
> they use blk_set_perm() to prevent this from happening. In the migration
> phase before the VM is actually running, though, they don't have a
> problem with writes to the image. On the other hand, storage migration
> needs to be able to write to the image in this phase, so the restrictive
> blk_set_perm() call of qdev devices breaks it.
> This patch flags all BlockBackends with a qdev device as
> blk->disable_perm during incoming migration, which means that the
> requested permissions are stored in the BlockBackend, but not actually
> applied to its root node yet.
> Once migration has finished and the VM should be resumed, the
> permissions are applied. If they cannot be applied (e.g. because the NBD
> server used for block migration hasn't been shut down), resuming the VM
> fails.
> Signed-off-by: Kevin Wolf <address@hidden>

Ciprian, can you give this patch a try and report back whether it fixes
the storage migration bug you encountered?


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