monitor: check if chardev can switch gcontext for OOB

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 already forbid MUX because not all frontends are ready to run outside
main loop.  Replace that by a context-switching feature check.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20181205203737.9011-5-marcandre.lureau@redhat.com>
[Error condition simplified, commit message adjusted accordingly]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

diff --git a/monitor.c b/monitor.c
index 79afe99079f55659b53ebec5ed5f13b4166d7b1d..a1329d8a8653444c304f4db05ef9e7ae4c40b6c1 100644 (file)
--- a/monitor.c
+++ b/monitor.c
@@ -4562,9 +4562,10 @@ void monitor_init(Chardev *chr, int flags)
     bool use_oob = flags & MONITOR_USE_OOB;
 
     if (use_oob) {
-        if (CHARDEV_IS_MUX(chr)) {
+        if (!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) {