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

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

[Trieu Huynh]

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

Signed-off-by: Trieu Huynh <vikingtc4@gmail.com>
---
 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 },
-- 
2.43.0

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

[Fabiano Rosas]

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 },

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

[Trieu Huynh]

On Mon, Apr 06, 2026 at 10:48:44AM -0300, Fabiano Rosas wrote:
> 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>
> 
Thanks for the review.
> 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?
> 
Agreed that it's a niche use-case. The immediate pain point was the
hard abort on restore, which this patch addresses. Migrating the
actual gdbstub connection state across snapshots would be a separate
and considerably more involved effort. Since the restored VM would
still need the user to re-attach gdb manually anyway, so the practical
value is limited.
> > ---
> >  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 },