qemu-sockets: introduce socket_address_parse_named_fd()

Add function that transforms named fd inside SocketAddress structure
into number representation. This way it may be then used in a context
where current monitor is not available.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210610100802.5888-6-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: comment tweak]
Signed-off-by: Eric Blake <eblake@redhat.com>

include/qemu/sockets.h

@@ -111,4 +111,15 @@ SocketAddress *socket_remote_address(int fd, Error **errp);
  */
 SocketAddress *socket_address_flatten(SocketAddressLegacy *addr);
 
+/**
+ * socket_address_parse_named_fd:
+ *
+ * Modify @addr, replacing a named fd by its corresponding number.
+ * Needed for callers that plan to pass @addr to a context where the
+ * current monitor is not available.
+ *
+ * Return 0 on success.
+ */
+int socket_address_parse_named_fd(SocketAddress *addr, Error **errp);
+
 #endif /* QEMU_SOCKETS_H */

util/qemu-sockets.c

@@ -1164,6 +1164,25 @@ static int socket_get_fd(const char *fdstr, Error **errp)
     return fd;
 }
 
+int socket_address_parse_named_fd(SocketAddress *addr, Error **errp)
+{
+    int fd;
+
+    if (addr->type != SOCKET_ADDRESS_TYPE_FD) {
+        return 0;
+    }
+
+    fd = socket_get_fd(addr->u.fd.str, errp);
+    if (fd < 0) {
+        return fd;
+    }
+
+    g_free(addr->u.fd.str);
+    addr->u.fd.str = g_strdup_printf("%d", fd);
+
+    return 0;
+}
+
 int socket_connect(SocketAddress *addr, Error **errp)
 {
     int fd;