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Re: [Qemu-block] Aborts in iotest 169

From: Eric Blake
Subject: Re: [Qemu-block] Aborts in iotest 169
Date: Thu, 24 Jan 2019 11:58:16 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0

On 1/24/19 4:15 AM, Kevin Wolf wrote:

>> But how to fix Qemu not to crash? May be, forbid some transitions 
>>   or at least error-out qmp_cont if runstate is  FINISH_MIGRATE?

> I wonder whether the QAPI schema should have a field 'run-states' for
> commands, and by default we would only include states where the VM has
> ownership of its resources (e.g. images are activated) and which are not
> temporary states that are automatically left, like finish-migrate.

We already have 'allow-oob' and 'allow-preconfig' flags on a per-command
basis; you're basically proposing that we extend this mechanism for
marking other attributes of commands,...

> Then the default for commands is to be rejected in "unusual" runstates
> where we're not expecting user intervention, and we must explicitly
> allow them if they are okay, in fact.
> Instead of listing every obscure runstate, maybe we should really use
> categories of runstates instead:
> 1. Running
> 2. Paused, owns all resources (like disk images)
> 3. Paused, doesn't own some resources (source VM after migration
>    completes, destination before migration completes)
> 4. Paused temporarily for internal reasons (e.g. finish-migrate,
>    restore-vm, save-vm)
> Most commands should be okay with 1 and 2, but possibly not 3, and
> almost never 4.

...then enforcing that commands are only executed according to the
attributes they have (where the default attributes match categories 1
and 2, and commands have to opt-in if they are safe to run in category 3
or 4 just like they have to opt-in for preconfig or oob usage).

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

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