Re: [PATCH] runstate: allow inmigrate -> debug transition on snapshot restore

[Fabiano Rosas <farosas@suse.de>]

Trieu Huynh <vikingtc4@gmail.com> writes:

> From: Trieu Huynh <vikingtc4@gmail.com>
>
> When a VM snapshot is taken while the guest is paused by a gdbstub
> (RUN_STATE_DEBUG), the saved runstate is 'debug', for instance:
>   (gdb) monitor info status
>   VM status: paused (debug)
>
> On restore, the destination starts in 'inmigrate' and transitions
> to the saved runstate, but the 'inmigrate -> debug' transition
> was missing from the table, causing an abort:
>
>   $ ./qemu-system-x86_64 -machine pc,accel=kvm:tcg  -m 128M
>   -display none -gdb tcp::1235 -incoming "exec:cat /tmp/snap.img"
>   > /tmp/qemu-restore.log 2>&1
>   Aborted (core dumped)
>   $ cat /tmp/qemu-restore.log
>   qemu-system-x86_64: invalid runstate transition: 'inmigrate'
>   -> 'debug'
>
> Fix it by adding the missing one (Point out by the author
> Dustin Spicuzza)
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1231

(note to self: stop giving time estimates)

>
> Signed-off-by: Trieu Huynh <vikingtc4@gmail.com>

I think this is reasonable as a standalone change:

Reviewed-by: Fabiano Rosas <farosas@suse.de>

As I mentioned in the Gitlab issue, it raises the question of whether
there's more to be done in terms of migrating the gdbstub
connection. Probably too niche of an use-case?

> ---
>  system/runstate.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/system/runstate.c b/system/runstate.c
> index 2d4e95a216..97a6a1c736 100644
> --- a/system/runstate.c
> +++ b/system/runstate.c
> @@ -94,6 +94,7 @@ static const RunStateTransition runstate_transitions_def[] = {
>      { RUN_STATE_INMIGRATE, RUN_STATE_PRELAUNCH },
>      { RUN_STATE_INMIGRATE, RUN_STATE_POSTMIGRATE },
>      { RUN_STATE_INMIGRATE, RUN_STATE_COLO },
> +    { RUN_STATE_INMIGRATE, RUN_STATE_DEBUG },
>  
>      { RUN_STATE_INTERNAL_ERROR, RUN_STATE_PAUSED },
>      { RUN_STATE_INTERNAL_ERROR, RUN_STATE_FINISH_MIGRATE },