gvstream: check socket buffer size is actually applied

In some cases, the `setsockopt()` call is ignored and the actual socket buffer
size is lower than the requested one. In this case, emit an aravis warning.
This patch alos improves the documentation of the socket buffer related
parameters.

Author: EmmanuelP

src/arvgvstream.c

@@ -1834,8 +1834,8 @@ arv_gv_stream_class_init (ArvGvStreamClass *gv_stream_class)
         /**
          * ArvGvStream:socket-buffer-size:
          *
-         * Size in bytes of the incoming socket buffer. A greater value helps to lower the number of missings packets,
-         * as the expense of an increased memory usage.
+         * Size in bytes of the incoming socket buffer. A greater value helps to lower the number of missing packets,
+         * as the expense of an increased memory usage. If the value is not strictly positive, this setting is ignored.
          */
 	g_object_class_install_property (
 		object_class, ARV_GV_STREAM_PROPERTY_SOCKET_BUFFER_SIZE,

src/arvgvstream.h

@@ -46,8 +46,9 @@ typedef enum {
 
 /**
  * ArvGvStreamSocketBuffer:
- * @ARV_GV_STREAM_SOCKET_BUFFER_FIXED: socket buffer is set to a given fixed value
- * @ARV_GV_STREAM_SOCKET_BUFFER_AUTO: socket buffer size is set to the payload size
+ * @ARV_GV_STREAM_SOCKET_BUFFER_FIXED: socket buffer is set using [[email protected]:socket-buffer-size] value
+ * @ARV_GV_STREAM_SOCKET_BUFFER_AUTO: socket buffer size is set to the payload size if
+ * [property@Aravis:socket-buffer-size] is not strictly positive, or the minimum of both values
  */
 
 typedef enum {

src/arvnetwork.c

@@ -456,23 +456,55 @@ arv_network_interface_free(ArvNetworkInterface *a)
 	g_free (a);
 }
 
-
 gboolean
 arv_socket_set_recv_buffer_size (int socket_fd, gint buffer_size)
 {
+#ifdef G_OS_WIN32
+	DWORD _buffer_size;
+	DWORD buffer_size_reported;
+#else
+	gint _buffer_size;
+	gint buffer_size_reported;
+#endif
 	int result;
+	socklen_t optlen;
 
-#ifndef G_OS_WIN32
-	result = setsockopt (socket_fd, SOL_SOCKET, SO_RCVBUF, &buffer_size, sizeof (buffer_size));
-#else
-	{
-		DWORD _buffer_size=buffer_size;
-		result = setsockopt (socket_fd, SOL_SOCKET, SO_RCVBUF,
-				     (const char*) &_buffer_size, sizeof (_buffer_size));
+        _buffer_size = buffer_size;
+        optlen = sizeof(buffer_size_reported);
+
+	result = setsockopt (socket_fd, SOL_SOCKET, SO_RCVBUF,
+			     (const char*) &_buffer_size, sizeof (_buffer_size));
+	if(result != 0) {
+	    arv_warning_interface ("[set_recv_buffer_size] Setting socket buffer to %d bytes failed (%s)",
+                                  _buffer_size, strerror(errno));
+	    return FALSE;
 	}
+
+        /* setsockopt() succeeded, but sometimes the requested size is not actually be set. Ask
+         * to see the new setting to confirm. */
+        result = getsockopt (socket_fd, SOL_SOCKET, SO_RCVBUF, &buffer_size_reported, &optlen);
+        if (result != 0) {
+                arv_warning_interface ("[set_recv_buffer_size] Read of socket buffer size (SO_RCVBUF) failed (%s)",
+                                       strerror(errno));
+                return FALSE;
+        }
+        g_assert (optlen == sizeof (buffer_size_reported));
+
+	if(buffer_size_reported < buffer_size)
+        {
+                arv_warning_interface ("[set_recv_buffer_size] Unexpected socket buffer size (SO_RCVBUF):"
+                                       " actual %d < expected %d bytes"
+                                       "\nYou might see missing packets and timeouts"
+#ifndef G_OS_WIN32
+                                       "\nMost likely /proc/sys/net/core/rmem_max is too low"
+                                       "\nSee the socket(7) manpage\n"
 #endif
+                                      , buffer_size_reported, buffer_size);
+
+                return FALSE;
+        }
 
-	return result == 0;
+	return TRUE;
 }