Add chardev-send-break monitor command

Sending a break on a serial console can be useful for debugging the
guest. But not all chardev backends support sending breaks (only telnet
and mux do). The chardev-send-break command allows to send a break even
if using other backends.

Signed-off-by: Stefan Fritsch <sf@sfritsch.de>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170611074817.13621-1-sf@sfritsch.de>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  Use 'send a break' in all 3 pieces of text as suggested by eblake

chardev/char.c

@@ -951,6 +951,18 @@ void qmp_chardev_remove(const char *id, Error **errp)
     object_unparent(OBJECT(chr));
 }
 
+void qmp_chardev_send_break(const char *id, Error **errp)
+{
+    Chardev *chr;
+
+    chr = qemu_chr_find(id);
+    if (chr == NULL) {
+        error_setg(errp, "Chardev '%s' not found", id);
+        return;
+    }
+    qemu_chr_be_event(chr, CHR_EVENT_BREAK);
+}
+
 void qemu_chr_cleanup(void)
 {
     object_unparent(get_chardevs_root());

hmp-commands.hx

@@ -1742,6 +1742,22 @@ STEXI
 @findex chardev-remove
 Removes the chardev @var{id}.
 
+ETEXI
+
+    {
+        .name       = "chardev-send-break",
+        .args_type  = "id:s",
+        .params     = "id",
+        .help       = "send a break on chardev",
+        .cmd        = hmp_chardev_send_break,
+        .command_completion = chardev_remove_completion,
+    },
+
+STEXI
+@item chardev-send-break id
+@findex chardev-send-break
+Send a break on the chardev @var{id}.
+
 ETEXI
 
     {

hmp.c

@@ -2236,6 +2236,14 @@ void hmp_chardev_remove(Monitor *mon, const QDict *qdict)
     hmp_handle_error(mon, &local_err);
 }
 
+void hmp_chardev_send_break(Monitor *mon, const QDict *qdict)
+{
+    Error *local_err = NULL;
+
+    qmp_chardev_send_break(qdict_get_str(qdict, "id"), &local_err);
+    hmp_handle_error(mon, &local_err);
+}
+
 void hmp_qemu_io(Monitor *mon, const QDict *qdict)
 {
     BlockBackend *blk;

hmp.h

@@ -103,6 +103,7 @@ void hmp_nbd_server_add(Monitor *mon, const QDict *qdict);
 void hmp_nbd_server_stop(Monitor *mon, const QDict *qdict);
 void hmp_chardev_add(Monitor *mon, const QDict *qdict);
 void hmp_chardev_remove(Monitor *mon, const QDict *qdict);
+void hmp_chardev_send_break(Monitor *mon, const QDict *qdict);
 void hmp_qemu_io(Monitor *mon, const QDict *qdict);
 void hmp_cpu_add(Monitor *mon, const QDict *qdict);
 void hmp_object_add(Monitor *mon, const QDict *qdict);

qapi-schema.json

@@ -5116,6 +5116,26 @@
 ##
 { 'command': 'chardev-remove', 'data': {'id': 'str'} }
 
+##
+# @chardev-send-break:
+#
+# Send a break to a character device
+#
+# @id: the chardev's ID, must exist
+#
+# Returns: Nothing on success
+#
+# Since: 2.10
+#
+# Example:
+#
+# -> { "execute": "chardev-send-break", "arguments": { "id" : "foo" } }
+# <- { "return": {} }
+#
+##
+{ 'command': 'chardev-send-break', 'data': {'id': 'str'} }
+
+
 ##
 # @TpmModel:
 #

tests/test-char.c

@@ -53,7 +53,9 @@ static void fe_event(void *opaque, int event)
     FeHandler *h = opaque;
 
     h->last_event = event;
-    quit = true;
+    if (event != CHR_EVENT_BREAK) {
+        quit = true;
+    }
 }
 
 #ifdef CONFIG_HAS_GLIB_SUBPROCESS_TESTS
@@ -517,7 +519,7 @@ static void char_file_test(void)
 
         file.in = fifo;
         file.has_in = true;
-        chr = qemu_chardev_new(NULL, TYPE_CHARDEV_FILE, &backend,
+        chr = qemu_chardev_new("label-file", TYPE_CHARDEV_FILE, &backend,
                                &error_abort);
 
         qemu_chr_fe_init(&be, chr, &error_abort);
@@ -527,6 +529,12 @@ static void char_file_test(void)
                                  fe_event,
                                  &fe, NULL, true);
 
+        g_assert_cmpint(fe.last_event, !=, CHR_EVENT_BREAK);
+        qmp_chardev_send_break("label-foo", NULL);
+        g_assert_cmpint(fe.last_event, !=, CHR_EVENT_BREAK);
+        qmp_chardev_send_break("label-file", NULL);
+        g_assert_cmpint(fe.last_event, ==, CHR_EVENT_BREAK);
+
         main_loop();
 
         close(fd);

tests/test-hmp.c

@@ -22,6 +22,7 @@ static int verbose;
 static const char *hmp_cmds[] = {
     "boot_set ndc",
     "chardev-add null,id=testchardev1",
+    "chardev-send-break testchardev2",
     "chardev-remove testchardev1",
     "commit all",
     "cpu-add 1",