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Re: [Qemu-devel] [PATCH] vl: don't use RUN_STATE_PRECONFIG unless --prec
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-devel] [PATCH] vl: don't use RUN_STATE_PRECONFIG unless --preconfig is given |
Date: |
Mon, 4 Jun 2018 11:35:15 +0100 |
User-agent: |
Mutt/1.9.5 (2018-04-13) |
On Mon, Jun 04, 2018 at 12:33:04PM +0200, Max Reitz wrote:
> On 2018-06-04 12:27, Daniel P. Berrangé wrote:
> > The RUN_STATE_PRECONFIG state is not supposed to be reachable unless the
> > --preconfig argument is given to QEMU, but when it was introduced in:
> >
> > commit 047f7038f586d2150f16c6d9ba9cfd0479f0f6ac
> > Author: Igor Mammedov <address@hidden>
> > Date: Fri May 11 19:24:43 2018 +0200
> >
> > cli: add --preconfig option
> >
> > The global 'current_run_state' variable was changed to have an initial
> > value of RUN_STATE_PRECONFIG regardless of whether --preconfig is given.
> >
> > It then relies on the main loop to toggle it back to RUN_STATE_PRELAUNCH
> > when --preconfig is not given. This is racy because it means that there
> > is a window where QEMU is in RUN_STATE_PRECONFIG despite --preconfig not
> > being given. This can be seen with the failure:
> >
> > $ echo | x86_64-softmmu/qemu-system-x86_64 -monitor stdio
> > QEMU 2.12.50 monitor - type 'help' for more information
> > (qemu)
> > HMP not available in preconfig state, use QMP instead
> >
> > Signed-off-by: Daniel P. Berrangé <address@hidden>
> > ---
> > vl.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
>
> This indeed fixes the issue that the preconfig state is reachable
> without --preconfig, but it still keeps the main loop being invoked
> twice (which means that e.g. HMP will process a single character before
> the main loop is actually really invoked:
>
> $ echo quit | x86_64-softmmu/qemu-system-x86_64 \
> -drive file=/dev/null,if=ide,readonly=on -monitor stdio
> QEMU 2.12.50 monitor - type 'help' for more information
> (qemu) qqemu-system-x86_64: Initialization of device ide-hd failed:
> Block node is read-only
>
> (Note the "q" before "qemu-system-x86_64"))
>
> (Naively,) I agree with Michal that the main loop should only be invoked
> twice if --preconfig has been given, which is implemented by his patch:
>
> http://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg00367.html
I think we probably need a combination of both patches for maximum safety.
Regards,
Daniel
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