virtio-serial-bus: Add a port 'name' property for port discovery in guests

The port 'id' or number is internal state between the guest kernel and
our bus implementation. This is invocation-dependent and isn't part of
the guest-host ABI.

To correcly enumerate and map ports between the host and the guest, the
'name' property is used.

Example:

    -device virtserialport,name=org.qemu.port.0

This invocation will get us a char device in the guest at:

    /dev/virtio-ports/org.qemu.port.0

which can be a symlink to

    /dev/vport0p3

This 'name' property is exposed by the guest kernel in a sysfs
attribute:

    /sys/kernel/virtio-ports/vport0p3/name

A simple udev script can pick up this name and create the symlink
mentioned above.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/virtio-serial-bus.c

@@ -204,6 +204,8 @@ static void handle_control_message(VirtIOSerial *vser, void *buf)
 {
     struct VirtIOSerialPort *port;
     struct virtio_console_control cpkt, *gcpkt;
+    uint8_t *buffer;
+    size_t buffer_len;
 
     gcpkt = buf;
     port = find_port_by_id(vser, ldl_p(&gcpkt->id));
@@ -226,6 +228,21 @@ static void handle_control_message(VirtIOSerial *vser, void *buf)
             send_control_event(port, VIRTIO_CONSOLE_CONSOLE_PORT, 1);
         }
 
+        if (port->name) {
+            stw_p(&cpkt.event, VIRTIO_CONSOLE_PORT_NAME);
+            stw_p(&cpkt.value, 1);
+
+            buffer_len = sizeof(cpkt) + strlen(port->name) + 1;
+            buffer = qemu_malloc(buffer_len);
+
+            memcpy(buffer, &cpkt, sizeof(cpkt));
+            memcpy(buffer + sizeof(cpkt), port->name, strlen(port->name));
+            buffer[buffer_len - 1] = 0;
+
+            send_control_msg(port, buffer, buffer_len);
+            qemu_free(buffer);
+        }
+
         if (port->host_connected) {
             send_control_event(port, VIRTIO_CONSOLE_PORT_OPEN, 1);
         }

hw/virtio-serial.c

@@ -100,6 +100,7 @@ static VirtIOSerialPortInfo virtconsole_info = {
     .qdev.props = (Property[]) {
         DEFINE_PROP_UINT8("is_console", VirtConsole, port.is_console, 1),
         DEFINE_PROP_CHR("chardev", VirtConsole, chr),
+        DEFINE_PROP_STRING("name", VirtConsole, port.name),
         DEFINE_PROP_END_OF_LIST(),
     },
 };

hw/virtio-serial.h

@@ -50,6 +50,7 @@ struct virtio_console_control {
 #define VIRTIO_CONSOLE_CONSOLE_PORT	1
 #define VIRTIO_CONSOLE_RESIZE		2
 #define VIRTIO_CONSOLE_PORT_OPEN	3
+#define VIRTIO_CONSOLE_PORT_NAME	4
 
 /* == In-qemu interface == */
 
@@ -83,6 +84,13 @@ struct VirtIOSerialPort {
 
     VirtQueue *ivq, *ovq;
 
+    /*
+     * This name is sent to the guest and exported via sysfs.
+     * The guest could create symlinks based on this information.
+     * The name is in the reverse fqdn format, like org.qemu.console.0
+     */
+    char *name;
+
     /*
      * This id helps identify ports between the guest and the host.
      * The guest sends a "header" with this id with each data packet