monitor: new parameter "x-oob"

Add new parameter to optionally enable Out-Of-Band for a QMP server.

An example command line:

  ./qemu-system-x86_64 -chardev stdio,id=char0 \
                       -mon chardev=char0,mode=control,x-oob=on

By default, Out-Of-Band is off.

It is not allowed if either MUX or non-QMP is detected, since
Out-Of-Band is currently only for QMP, and non-MUX chardev backends.

Note that the client STILL has to request 'oob' during qmp_capabilities;
in part because the x-oob command line option may disappear in the
future if we decide the capabilities negotiation is sufficient.

Signed-off-by: Peter Xu <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]>
[eblake: enhance commit message]
Tested-by: Christian Borntraeger <[email protected]>
Signed-off-by: Eric Blake <[email protected]>

include/monitor/monitor.h

@@ -13,6 +13,7 @@ extern Monitor *cur_mon;
 #define MONITOR_USE_READLINE  0x02
 #define MONITOR_USE_CONTROL   0x04
 #define MONITOR_USE_PRETTY    0x08
+#define MONITOR_USE_OOB       0x10
 
 bool monitor_cur_is_qmp(void);
 

monitor.c

@@ -36,6 +36,7 @@
 #include "net/slirp.h"
 #include "chardev/char-fe.h"
 #include "chardev/char-io.h"
+#include "chardev/char-mux.h"
 #include "ui/qemu-spice.h"
 #include "sysemu/numa.h"
 #include "monitor/monitor.h"
@@ -4562,12 +4563,26 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
 void monitor_init(Chardev *chr, int flags)
 {
     Monitor *mon = g_malloc(sizeof(*mon));
+    bool use_readline = flags & MONITOR_USE_READLINE;
+    bool use_oob = flags & MONITOR_USE_OOB;
+
+    if (use_oob) {
+        if (CHARDEV_IS_MUX(chr)) {
+            error_report("Monitor Out-Of-Band is not supported with "
+                         "MUX typed chardev backend");
+            exit(1);
+        }
+        if (use_readline) {
+            error_report("Monitor Out-Of-band is only supported by QMP");
+            exit(1);
+        }
+    }
 
-    monitor_data_init(mon, false, false);
+    monitor_data_init(mon, false, use_oob);
 
     qemu_chr_fe_init(&mon->chr, chr, &error_abort);
     mon->flags = flags;
-    if (flags & MONITOR_USE_READLINE) {
+    if (use_readline) {
         mon->rs = readline_init(monitor_readline_printf,
                                 monitor_readline_flush,
                                 mon,
@@ -4663,6 +4678,9 @@ QemuOptsList qemu_mon_opts = {
         },{
             .name = "pretty",
             .type = QEMU_OPT_BOOL,
+        },{
+            .name = "x-oob",
+            .type = QEMU_OPT_BOOL,
         },
         { /* end of list */ }
     },

vl.c

@@ -2404,6 +2404,11 @@ static int mon_init_func(void *opaque, QemuOpts *opts, Error **errp)
     if (qemu_opt_get_bool(opts, "pretty", 0))
         flags |= MONITOR_USE_PRETTY;
 
+    /* OOB is off by default */
+    if (qemu_opt_get_bool(opts, "x-oob", 0)) {
+        flags |= MONITOR_USE_OOB;
+    }
+
     chardev = qemu_opt_get(opts, "chardev");
     chr = qemu_chr_find(chardev);
     if (chr == NULL) {