ptp: Add ttl configuration to gst_ptp_init_full()

This allows configuring the TTL that is used for multicast packets sent
out on the sockets, and is defaulting to 1 as before. The default might
change at some point.

In some networks multiple hops are needed to reach the PTP clock and
this allows to configure GStreamer in a way that works in such networks.

At a later time, per-domain or per-interface TTL configurations might be
added when needed.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5649>

subprojects/gstreamer/libs/gst/helpers/ptp/args.rs

@@ -21,6 +21,7 @@ pub struct Args {
     pub interfaces: Vec<String>,
     pub verbose: bool,
     pub clock_id: u64,
+    pub ttl: u32,
 }
 
 /// Parse the command-line arguments.
@@ -28,6 +29,7 @@ pub fn parse_args() -> Result<Args, Error> {
     let mut interfaces = Vec::new();
     let mut verbose = false;
     let mut clock_id = 0;
+    let mut ttl = 1;
 
     let mut args = env::args();
     // Skip executable name
@@ -50,6 +52,11 @@ pub fn parse_args() -> Result<Args, Error> {
                 clock_id =
                     u64::from_str_radix(&clock_id_arg[2..], 16).context("Invalid clock ID")?;
             }
+            "--ttl" => {
+                let ttl_arg = args.next().context("No TTL following --ttl")?;
+                ttl = ttl_arg.parse::<u32>().context("Invalid TTL value")?;
+            }
+
             arg => {
                 bail!("Unknown command-line argument {}", arg);
             }
@@ -60,6 +67,7 @@ pub fn parse_args() -> Result<Args, Error> {
         interfaces,
         verbose,
         clock_id,
+        ttl,
     };
 
     info!("Running with arguments {:#?}", args);

subprojects/gstreamer/libs/gst/helpers/ptp/main.rs

@@ -58,16 +58,18 @@ const MSG_TYPE_CLOCK_ID: u8 = 2;
 const MSG_TYPE_SEND_TIME_ACK: u8 = 3;
 
 /// Create a new `UdpSocket` for the given port and configure it for PTP.
-fn create_socket(port: u16, iface: &net::InterfaceInfo) -> Result<UdpSocket, Error> {
+fn create_socket(port: u16, iface: &net::InterfaceInfo, ttl: u32) -> Result<UdpSocket, Error> {
     let socket = net::create_udp_socket(&Ipv4Addr::UNSPECIFIED, port, Some(iface))
         .with_context(|| format!("Failed to bind socket to port {}", port))?;
 
     socket
         .set_nonblocking(true)
         .context("Failed setting socket non-blocking")?;
-    socket.set_ttl(1).context("Failed setting TTL on socket")?;
     socket
-        .set_multicast_ttl_v4(1)
+        .set_ttl(ttl)
+        .context("Failed setting TTL on socket")?;
+    socket
+        .set_multicast_ttl_v4(ttl)
         .context("Failed to set multicast TTL on socket")?;
 
     Ok(socket)
@@ -123,10 +125,10 @@ fn run() -> Result<(), Error> {
     for iface in &ifaces {
         info!("Binding to interface {}", iface.name);
 
-        let event_socket =
-            create_socket(PTP_EVENT_PORT, iface).context("Failed creating event socket")?;
-        let general_socket =
-            create_socket(PTP_GENERAL_PORT, iface).context("Failed creating general socket")?;
+        let event_socket = create_socket(PTP_EVENT_PORT, iface, args.ttl)
+            .context("Failed creating event socket")?;
+        let general_socket = create_socket(PTP_GENERAL_PORT, iface, args.ttl)
+            .context("Failed creating general socket")?;
 
         for socket in [&event_socket, &general_socket].iter() {
             net::join_multicast_v4(socket, &PTP_MULTICAST_ADDR, iface)

subprojects/gstreamer/libs/gst/net/gstptpclock.c

@@ -2680,6 +2680,8 @@ count_directories (const char *filepath)
  *     interface.
  * * #GStrv `interfaces`: The interface names to listen on for PTP packets. If
  *     none are provided then all compatible interfaces will be used.
+ * * #guint `ttl`: The TTL to use for multicast packets sent out by GStreamer.
+ *     This defaults to 1, i.e. packets will not leave the local network.
  *
  * This function is automatically called by gst_ptp_clock_new() with default
  * parameters if it wasn't called before.
@@ -2698,6 +2700,7 @@ gst_ptp_init_full (const GstStructure * config)
   guint64 clock_id = GST_CLOCK_TIME_NONE;
   const GValue *v;
   gchar **interfaces = NULL;
+  guint ttl = 1;
   GError *err = NULL;
 
   GST_DEBUG_CATEGORY_INIT (ptp_debug, "ptp", 0, "PTP clock");
@@ -2734,7 +2737,10 @@ gst_ptp_init_full (const GstStructure * config)
     interfaces = g_value_get_boxed (v);
   if (interfaces != NULL)
     argc += 2 * g_strv_length (interfaces);
+  gst_structure_get_uint (config, "ttl", &ttl);
+  argc += 2;
 
+  // 3 for: executable, -v and NULL
   argv = g_new0 (gchar *, argc + 3);
   argc_c = 0;
 
@@ -2814,6 +2820,9 @@ gst_ptp_init_full (const GstStructure * config)
     }
   }
 
+  argv[argc_c++] = g_strdup ("--ttl");
+  argv[argc_c++] = g_strdup_printf ("%u", ttl);
+
   /* Check if the helper process should be verbose */
   env = g_getenv ("GST_PTP_HELPER_VERBOSE");
   if (env && g_ascii_strcasecmp (env, "no") != 0) {