Re: [Qemu-devel] [PATCH] vl: don't use RUN_STATE_PRECONFIG unless --preconfig is given

[Max Reitz]

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

Max

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