Re: [PATCH 1/4] migration/savevm: Add a compatibility check for capabilities

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Mar 27, 2025 at 11:39:31AM -0300, Fabiano Rosas wrote:
> It has always been possible to enable arbitrary migration capabilities
> and attempt to take a snapshot of the VM with the savevm/loadvm
> commands as well as their QMP counterparts
> snapshot-save/snapshot-load.
> 
> Most migration capabilities are not meant to be used with snapshots
> and there's a risk of crashing QEMU or producing incorrect
> behavior. Ideally, every migration capability would either be
> implemented for savevm or explicitly rejected.

IMHO, this a prime example of why migration config shouldn't be held
as global state, and instead passed as parameters to the commands
that need them.  The snapshot-save/load commands would then only
be able to accept what few settings are actually relevant, instead
of inheriting any/all global migration state.

> Add a compatibility check routine and reject the snapshot command if
> an incompatible capability is enabled. For now only act on the the two
> that actually cause a crash: multifd and mapped-ram.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2818

Issue is 2881 not 2818                                   ^^^^^^^

> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/options.c | 26 ++++++++++++++++++++++++++
>  migration/options.h |  1 +
>  migration/savevm.c  |  8 ++++++++
>  3 files changed, 35 insertions(+)

With regards,
Daniel
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