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

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

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.

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.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 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) {
-- 
2.19.0.271.gfe8321ec05