High: ipcs: Api function allowing server to retrieve client connection's ipc buffer size

include/qb/qbipcs.h

@@ -260,6 +260,10 @@ ssize_t qb_ipcs_response_send(qb_ipcs_connection_t *c, const void *data,
  *
  * @note the iov[0] must be a qb_ipc_response_header. The client will
  * read the size field to determine how much to recv.
+ *
+ * @note When send returns -EMSGSIZE, this means the msg is too
+ * large and will never succeed. To determine the max msg size
+ * a client can be sent, use qb_ipcs_connection_get_buffer_size()
  */
 ssize_t qb_ipcs_response_sendv(qb_ipcs_connection_t *c,
 			       const struct iovec * iov, size_t iov_len);
@@ -275,6 +279,10 @@ ssize_t qb_ipcs_response_sendv(qb_ipcs_connection_t *c,
  * @note the data must include a qb_ipc_response_header at
  * the top of the message. The client will read the size field
  * to determine how much to recv.
+ *
+ * @note When send returns -EMSGSIZE, this means the msg is too
+ * large and will never succeed. To determine the max msg size
+ * a client can be sent, use qb_ipcs_connection_get_buffer_size()
  */
 ssize_t qb_ipcs_event_send(qb_ipcs_connection_t *c, const void *data,
 			   size_t size);
@@ -289,6 +297,10 @@ ssize_t qb_ipcs_event_send(qb_ipcs_connection_t *c, const void *data,
  *
  * @note the iov[0] must be a qb_ipc_response_header. The client will
  * read the size field to determine how much to recv.
+ *
+ * @note When send returns -EMSGSIZE, this means the msg is too
+ * large and will never succeed. To determine the max msg size
+ * a client can be sent, use qb_ipcs_connection_get_buffer_size()
  */
 ssize_t qb_ipcs_event_sendv(qb_ipcs_connection_t *c, const struct iovec * iov,
 			    size_t iov_len);
@@ -423,6 +435,14 @@ qb_ipcs_connection_t * qb_ipcs_connection_next_get(qb_ipcs_service_t* pt,
 void qb_ipcs_connection_auth_set(qb_ipcs_connection_t *conn, uid_t uid,
 				 gid_t gid, mode_t mode);
 
+/**
+ * Retrieve the connection ipc buffer size. This reflects the
+ * largest size msg that can be sent or received.
+ *
+ * @param conn connection instance
+ * @return msg size in bytes, negative value on error.
+ */
+int32_t qb_ipcs_connection_get_buffer_size(qb_ipcs_connection_t *conn);
 
 /* *INDENT-OFF* */
 #ifdef __cplusplus

lib/ipcs.c

@@ -941,3 +941,16 @@ qb_ipcs_connection_auth_set(qb_ipcs_connection_t *c, uid_t uid,
 		c->auth.mode = mode;
 	}
 }
+
+int32_t
+qb_ipcs_connection_get_buffer_size(qb_ipcs_connection_t *c)
+{
+	if (c == NULL) {
+		return -EINVAL;
+	}
+
+	/* request, response, and event shoud all have the same
+	 * buffer size allocated. It doesn't matter which we return
+	 * here. */
+	return c->response.max_msg_size;
+}

tests/check_ipc.c

@@ -312,6 +312,8 @@ s1_connection_destroyed(qb_ipcs_connection_t *c)
 static void
 s1_connection_created(qb_ipcs_connection_t *c)
 {
+	int32_t max = MAX_MSG_SIZE;
+
 	if (send_event_on_created) {
 		struct qb_ipc_response_header response;
 		int32_t res;
@@ -333,6 +335,10 @@ s1_connection_created(qb_ipcs_connection_t *c)
 		memcpy(context, "test", 4);
 		qb_ipcs_context_set(c, context);
 	}
+
+
+	ck_assert_int_eq(max, qb_ipcs_connection_get_buffer_size(c));
+
 }
 
 static void