Re: [Qemu-devel] [PATCH v2 4/6] monitor: check if chardev can switch gcontext for OOB

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> Not all backends are able to switch gcontext. Those backends cannot
> drive a OOB monitor (the monitor would then be blocking on main
> thread).
>
> For example, ringbuf, spice, or more esoteric input chardevs like
> braille or MUX.
>
> We currently forbid MUX because not all frontends are ready to run
> outside main loop. Extend to add a context-switching feature check.

Double-checking: the reason for forbidding MUX and the reason for
requiring QEMU_CHAR_FEATURE_GCONTEXT are orthogonal, right?

> Note: this patch will conflict with Peter "[PATCH v9 3/6] monitor:
> remove "x-oob", turn oob on by default", but can be trivially updated.

I intend to merge this series first, and drop this sentence.

> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  monitor.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index 511dd11d1c..fffeb27ef9 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -4560,9 +4560,11 @@ void monitor_init(Chardev *chr, int flags)
>      bool use_oob = flags & MONITOR_USE_OOB;
>  
>      if (use_oob) {
> -        if (CHARDEV_IS_MUX(chr)) {
> +        if (CHARDEV_IS_MUX(chr) ||
> +            !qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_GCONTEXT)) {
>              error_report("Monitor out-of-band is not supported with "
> -                         "MUX typed chardev backend");
> +                         "%s typed chardev backend",
> +                         object_get_typename(OBJECT(chr)));
>              exit(1);
>          }
>          if (use_readline) {