zhhyu7 commented on code in PR #20627:
URL: https://github.com/apache/nuttx/pull/20627#discussion_r4259643626
##########
net/tcp/tcp_recvfrom.c:
##########
@@ -680,6 +682,202 @@ static void tcp_notify_recvcpu(FAR struct tcp_conn_s
*conn)
*
****************************************************************************/
+#ifdef CONFIG_NET_TCPURGDATA
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+struct tcp_oob_s
+{
+ FAR struct tcp_conn_s *conn;
+ FAR struct devif_callback_s *cb;
+ sem_t sem;
+ int result;
+};
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: tcp_oob_eventhandler
+ *
+ * Description:
+ * Handle callback events for a thread waiting for urgent (OOB) data.
+ *
+ * Input Parameters:
+ * dev The network device driver
+ * pvpriv Private data (pointer to struct tcp_oob_s)
+ * flags Event flags
+ *
+ * Returned Value:
+ * Updated event flags
+ *
+ ****************************************************************************/
+
+static uint32_t tcp_oob_eventhandler(FAR struct net_driver_s *dev,
+ FAR void *pvpriv, uint32_t flags)
+{
+ FAR struct tcp_oob_s *pstate = (FAR struct tcp_oob_s *)pvpriv;
+
+ ninfo("flags: %08" PRIx32 "\n", flags);
+
+ if (pstate != NULL)
+ {
+ if ((flags & TCP_URGDATA) != 0)
+ {
+ pstate->result = OK;
+ nxsem_post(&pstate->sem);
+ }
+ else if ((flags & TCP_DISCONN_EVENTS) != 0)
+ {
+ pstate->result = -ENOTCONN;
+ nxsem_post(&pstate->sem);
+ }
+ else if ((flags & TCP_RXCLOSE) != 0)
+ {
+ pstate->result = -ENOTCONN;
+ nxsem_post(&pstate->sem);
+ }
+ }
+
+ return flags;
+}
+
+/****************************************************************************
+ * Name: tcp_recv_oob
+ *
+ * Description:
+ * Receive urgent (out-of-band) data from the connection
+ *
+ * Input Parameters:
+ * conn The TCP connection of interest
+ * buf The buffer to receive the data
+ * len The length of the buffer
+ * flags Receive flags
+ *
+ * Returned Value:
+ * Number of bytes received or negated errno value
+ *
+ * Assumptions:
+ * The network is locked.
+ *
+ ****************************************************************************/
+
+static ssize_t tcp_recv_oob(FAR struct tcp_conn_s *conn, FAR void *buf,
+ size_t len, int flags)
+{
+ FAR struct iob_s *iob;
+ ssize_t recvlen;
+ int ret;
+
+#ifdef CONFIG_NET_SOCKOPTS
+ /* POSIX Rule: If SO_OOBINLINE is enabled, MSG_OOB read is not allowed */
+
+ if (_SO_GETOPT(conn->sconn.s_options, _SO_OOBINLINE))
+ {
+ return -EINVAL;
+ }
+#endif
+
+ /* Wait while urgent buffer is empty */
+
+ while (conn->urgreadahead == NULL)
+ {
+ struct tcp_oob_s state;
+ struct tcp_callback_s info;
+
+ /* Non-blocking socket or MSG_DONTWAIT check */
+
+ if ((flags & MSG_DONTWAIT) != 0 || _SS_ISNONBLOCK(conn->sconn.s_flags))
+ {
+ return -EAGAIN;
+ }
+
+ /* Check if connection is disconnected */
+
+ if (!_SS_ISCONNECTED(conn->sconn.s_flags))
+ {
+ return -ENOTCONN;
+ }
+
+ /* Set up the devif callback to wait for TCP_URGDATA or disconnect */
+
+ state.conn = conn;
+ state.result = -EAGAIN;
+ nxsem_init(&state.sem, 0, 0);
+ nxsem_set_protocol(&state.sem, SEM_PRIO_NONE);
+
+ state.cb = tcp_callback_alloc(conn);
+ if (state.cb == NULL)
+ {
+ nxsem_destroy(&state.sem);
+ return -EBUSY;
+ }
+
+ state.cb->flags = TCP_URGDATA | TCP_DISCONN_EVENTS | TCP_RXCLOSE;
+ state.cb->priv = &state;
+ state.cb->event = tcp_oob_eventhandler;
+
+ /* Push cancellation cleanup */
+
+ info.tc_conn = conn;
+ info.tc_cb = &state.cb;
+ info.tc_sem = &state.sem;
+ tls_cleanup_push(tls_get_info(), tcp_callback_cleanup, &info);
+
+ /* Wait for urgent data arrival, disconnection, or timeout */
+
+#ifdef CONFIG_NET_SOCKOPTS
+ ret = conn_dev_sem_timedwait(&state.sem, true,
Review Comment:
```recv (MSG_OOB)``` should not block:
no urgent data, or the urgent byte was already read: return EINVAL;
urgent data announced but the byte has not arrived yet: return EAGAIN.
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