hmp: Fail gracefully if chardev is already in use

Trying to attach a HMP monitor to a chardev that is already in use
results in a crash because monitor_init_hmp() passes &error_abort to
qemu_chr_fe_init():

$ ./x86_64-softmmu/qemu-system-x86_64 --chardev stdio,id=foo --mon foo --mon foo
QEMU 4.2.50 monitor - type 'help' for more information
(qemu) Unexpected error in qemu_chr_fe_init() at chardev/char-fe.c:220:
qemu-system-x86_64: --mon foo: Device 'foo' is in use
Abgebrochen (Speicherabzug geschrieben)

Fix this by allowing monitor_init_hmp() to return an error and passing
any error in qemu_chr_fe_init() to its caller instead of aborting.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200224143008.13362-19-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 7 insertions, 3 deletions

diff --git a/monitor/hmp.c b/monitor/hmp.c
index 944fa9651e..d598dd02bb 100644
--- a/monitor/hmp.c
+++ b/monitor/hmp.c
@@ -1399,12 +1399,16 @@ static void monitor_readline_flush(void *opaque)
     monitor_flush(&mon->common);
 }
 
-void monitor_init_hmp(Chardev *chr, bool use_readline)
+void monitor_init_hmp(Chardev *chr, bool use_readline, Error **errp)
 {
     MonitorHMP *mon = g_new0(MonitorHMP, 1);
 
+    if (!qemu_chr_fe_init(&mon->common.chr, chr, errp)) {
+        g_free(mon);
+        return;
+    }
+
     monitor_data_init(&mon->common, false, false, false);
-    qemu_chr_fe_init(&mon->common.chr, chr, &error_abort);
 
     mon->use_readline = use_readline;
     if (mon->use_readline) {
diff --git a/monitor/monitor.c b/monitor/monitor.c
index 00d287655e..2282bf6780 100644
--- a/monitor/monitor.c
+++ b/monitor/monitor.c
@@ -631,7 +631,7 @@ int monitor_init(MonitorOptions *opts, Error **errp)
             warn_report("'pretty' is deprecated for HMP monitors, it has no "
                         "effect and will be removed in future versions");
         }
-        monitor_init_hmp(chr, true);
+        monitor_init_hmp(chr, true, &local_err);
         break;
     default:
         g_assert_not_reached();