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From: Markus Armbruster <armbru@redhat.com>
References: <20181205203737.9011-1-marcandre.lureau@redhat.com>
	<20181205203737.9011-5-marcandre.lureau@redhat.com>
Date: Thu, 06 Dec 2018 07:08:23 +0100
In-Reply-To: <20181205203737.9011-5-marcandre.lureau@redhat.com>
	(=?utf-8?Q?=22Marc-Andr=C3=A9?=
	Lureau"'s message of "Thu, 6 Dec 2018 00:37:34 +0400")
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Subject: Re: [Qemu-devel] [PATCH for-4.0 v4 4/7] monitor: check if chardev
 can switch gcontext for OOB
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To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org, Li Zhijian <lizhijian@cn.fujitsu.com>, Jason Wang <jasowang@redhat.com>, Zhang Chen <zhangckid@gmail.com>, peterx@redhat.com, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

One more question...

Marc-Andr=C3=A9 Lureau <marcandre.lureau@redhat.com> 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.

These chardevs don't provide QEMU_CHAR_FEATURE_GCONTEXT.

> We currently forbid MUX because not all frontends are ready to run
> outside main loop. Extend to add a context-switching feature check.

Why check CHARDEV_IS_MUX() when chardev-mux already fails the
qemu_char_feature_gcontext(chr, QEMU_CHAR_FEATURE_GCONTEXT) check?

> Signed-off-by: Marc-Andr=C3=A9 Lureau <marcandre.lureau@redhat.com>
> ---
>  monitor.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index 79afe99079..25cf4223e8 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -4562,9 +4562,11 @@ void monitor_init(Chardev *chr, int flags)
>      bool use_oob =3D flags & MONITOR_USE_OOB;
>=20=20
>      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) {