chardev: add qmp hotplug commands, with null chardev support

Add chardev-add and chardev-remove qmp commands.  Hotplugging
a null chardev is supported for now, more will be added later.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

qapi-schema.json

@@ -3017,3 +3017,52 @@
 # Since: 1.3.0
 ##
 { 'command': 'nbd-server-stop' }
+
+##
+# @ChardevBackend:
+#
+# Configuration info for the new chardev backend.
+#
+# Since: 1.4
+##
+{ 'type': 'ChardevDummy', 'data': { } }
+
+{ 'union': 'ChardevBackend', 'data': { 'null' : 'ChardevDummy' } }
+
+##
+# @ChardevReturn:
+#
+# Return info about the chardev backend just created.
+#
+# Since: 1.4
+##
+{ 'type' : 'ChardevReturn', 'data': { } }
+
+##
+# @chardev-add:
+#
+# Add a file chardev
+#
+# @id: the chardev's ID, must be unique
+# @backend: backend type and parameters
+#
+# Returns: chardev info.
+#
+# Since: 1.4
+##
+{ 'command': 'chardev-add', 'data': {'id'      : 'str',
+                                     'backend' : 'ChardevBackend' },
+  'returns': 'ChardevReturn' }
+
+##
+# @chardev-remove:
+#
+# Remove a chardev
+#
+# @id: the chardev's ID, must exist and not be in use
+#
+# Returns: Nothing on success
+#
+# Since: 1.4
+##
+{ 'command': 'chardev-remove', 'data': {'id': 'str'} }

qemu-char.c

@@ -3010,3 +3010,56 @@ QemuOptsList qemu_chardev_opts = {
         { /* end of list */ }
     },
 };
+
+ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
+                               Error **errp)
+{
+    ChardevReturn *ret = g_new0(ChardevReturn, 1);
+    CharDriverState *chr = NULL;
+
+    chr = qemu_chr_find(id);
+    if (chr) {
+        error_setg(errp, "Chardev '%s' already exists", id);
+        g_free(ret);
+        return NULL;
+    }
+
+    switch (backend->kind) {
+    case CHARDEV_BACKEND_KIND_NULL:
+        chr = qemu_chr_open_null(NULL);
+        break;
+    default:
+        error_setg(errp, "unknown chardev backend (%d)", backend->kind);
+        break;
+    }
+
+    if (chr == NULL && !error_is_set(errp)) {
+        error_setg(errp, "Failed to create chardev");
+    }
+    if (chr) {
+        chr->label = g_strdup(id);
+        chr->avail_connections = 1;
+        QTAILQ_INSERT_TAIL(&chardevs, chr, next);
+        return ret;
+    } else {
+        g_free(ret);
+        return NULL;
+    }
+}
+
+void qmp_chardev_remove(const char *id, Error **errp)
+{
+    CharDriverState *chr;
+
+    chr = qemu_chr_find(id);
+    if (NULL == chr) {
+        error_setg(errp, "Chardev '%s' not found", id);
+        return;
+    }
+    if (chr->chr_can_read || chr->chr_read ||
+        chr->chr_event || chr->handler_opaque) {
+        error_setg(errp, "Chardev '%s' is busy", id);
+        return;
+    }
+    qemu_chr_delete(chr);
+}

qmp-commands.hx

@@ -2654,3 +2654,53 @@ EQMP
         .args_type  = "",
         .mhandler.cmd_new = qmp_marshal_input_query_target,
     },
+
+    {
+        .name       = "chardev-add",
+        .args_type  = "id:s,backend:q",
+        .mhandler.cmd_new = qmp_marshal_input_chardev_add,
+    },
+
+SQMP
+chardev-add
+----------------
+
+Add a chardev.
+
+Arguments:
+
+- "id": the chardev's ID, must be unique (json-string)
+- "backend": chardev backend type + parameters
+
+Example:
+
+-> { "execute" : "chardev-add",
+     "arguments" : { "id" : "foo",
+                     "backend" : { "type" : "null", "data" : {} } } }
+<- { "return": {} }
+
+EQMP
+
+    {
+        .name       = "chardev-remove",
+        .args_type  = "id:s",
+        .mhandler.cmd_new = qmp_marshal_input_chardev_remove,
+    },
+
+
+SQMP
+chardev-remove
+--------------
+
+Remove a chardev.
+
+Arguments:
+
+- "id": the chardev's ID, must exist and not be in use (json-string)
+
+Example:
+
+-> { "execute": "chardev-remove", "arguments": { "id" : "foo" } }
+<- { "return": {} }
+
+EQMP