net/netdev: Add signal notification for the case where the network goes down.

include/nuttx/signal.h

@@ -59,6 +59,7 @@ enum nxsig_evtype_e
   NXSIG_IOB_AVAIL  = 1, /* Signal availability of an IOB */
   NXSIG_NET_DOWN,       /* Signal that the network is down */
   NXSIG_TCP_READAHEAD,  /* Signal that TCP read-ahead data is available */
+  NXSIG_TCP_DISCONNECT, /* Signal loss of TCP connection */
   NXSIG_UDP_READAHEAD,  /* Signal that TCP read-ahead data is available */
 };
 

mm/iob/Kconfig

@@ -63,6 +63,7 @@ config IOB_NOTIFIER
 	bool "Support IOB notifications"
 	default n
 	select SIG_NOTIFIER
+	depends on !DISABLE_SIGNALS
 	---help---
 		Enable building of IOB notifier logic that will send a signal to
 		a kernel thread when an IOB is available.  This is is a general

net/netdev/Kconfig

@@ -36,4 +36,15 @@ config NETDEV_IFINDEX
 		When enabled, these option also enables the user interfaces:
 		if_nametoindex() and if_indextoname().
 
+config NETDOWN_NOTIFIER
+	bool "Support network down notifications"
+	default n
+	select SIG_NOTIFIER
+	depends on !DISABLE_SIGNALS
+	---help---
+		Enable building of logic that will send a signal to a kernel
+		thread when the network is taken down.  This is is a general purpose
+		notifier, but was developed specifically to support SIGHUP poll()
+		logic.
+
 endmenu # Network Device Operations

net/netdev/Make.defs

@@ -45,6 +45,10 @@ ifeq ($(CONFIG_NETDEV_IFINDEX),y)
 NETDEV_CSRCS += netdev_indextoname.c netdev_nametoindex.c
 endif
 
+ifeq ($(CONFIG_NETDOWN_NOTIFIER),y)
+SOCK_CSRCS += netdown_notifier.c
+endif
+
 # Include netdev build support
 
 DEPPATH += --dep-path netdev

net/netdev/netdev.h

@@ -466,6 +466,85 @@ int netdev_ipv6_ifconf(FAR struct lifconf *lifc);
 
 int netdev_dev_lladdrsize(FAR struct net_driver_s *dev);
 
+/****************************************************************************
+ * Name: netdown_notifier_setup
+ *
+ * Description:
+ *   Set up to notify the specified PID with the provided signal number.
+ *
+ *   NOTE: To avoid race conditions, the caller should set the sigprocmask
+ *   to block signal delivery.  The signal will be delivered once the
+ *   signal is removed from the sigprocmask.
+ *
+ * Input Parameters:
+ *   pid   - The PID to be notified.  If a zero value is provided, then the
+ *           PID of the calling thread will be used.
+ *   signo - The signal number to use with the notification.
+ *   dev   - The network driver to be monitored
+ *
+ * Returned Value:
+ *   > 0   - The signal notification is in place.  The returned value is a
+ *           key that may be used later in a call to
+ *           netdown_notifier_teardown().
+ *   == 0  - The the device is already down.  No signal notification will
+ *           be provided.
+ *   < 0   - An unexpected error occurred and no signal will be sent.  The
+ *           returned value is a negated errno value that indicates the
+ *           nature of the failure.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDOWN_NOTIFIER
+int netdown_notifier_setup(int pid, int signo, FAR struct net_driver_s *dev);
+#endif
+
+/****************************************************************************
+ * Name: netdown_notifier_teardown
+ *
+ * Description:
+ *   Eliminate a TCP read-ahead notification previously setup by
+ *   netdown_notifier_setup().  This function should only be called if the
+ *   notification should be aborted prior to the notification.  The
+ *   notification will automatically be torn down after the signal is sent.
+ *
+ * Input Parameters:
+ *   key - The key value returned from a previous call to
+ *         netdown_notifier_setup().
+ *
+ * Returned Value:
+ *   Zero (OK) is returned on success; a negated errno value is returned on
+ *   any failure.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDOWN_NOTIFIER
+int netdown_notifier_teardown(int key);
+#endif
+
+/****************************************************************************
+ * Name: netdown_notifier_signal
+ *
+ * Description:
+ *   Read-ahead data has been buffered.  Signal all threads waiting for
+ *   read-ahead data to become available.
+ *
+ *   When the read-ahead data becomes available, *all* of the waiters in
+ *   this thread will be signaled.  If there are multiple waiters then only
+ *   the highest priority thread will get the data.  Lower priority threads
+ *   will need to call netdown_notifier_setup() once again.
+ *
+ * Input Parameters:
+ *   dev  - The TCP connection where read-ahead data was just buffered.
+ *
+ * Returned Value:
+ *   None.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NETDOWN_NOTIFIER
+void netdown_notifier_signal(FAR struct net_driver_s *dev);
+#endif
+
 #undef EXTERN
 #ifdef __cplusplus
 }

net/netdev/netdev_ioctl.c

@@ -1789,6 +1789,15 @@ void netdev_ifdown(FAR struct net_driver_s *dev)
       /* Notify clients that the network has been taken down */
 
       (void)devif_dev_event(dev, NULL, NETDEV_DOWN);
+
+#ifdef CONFIG_NETDOWN_NOTIFIER
+      /* Provide signal notifications to threads that want to be
+       * notified of the network down state via signal.
+       */
+
+      netdown_notifier_signal(dev);
+#endif
+
     }
 }
 

net/tcp/Kconfig

@@ -70,7 +70,7 @@ config TCP_READAHEAD_NOTIFIER
 	bool "Support TCP read-ahead notifications"
 	default n
 	select SIG_NOTIFIER
-	depends on NET_TCP_READAHEAD && !DISABLE_POLL
+	depends on NET_TCP_READAHEAD && !DISABLE_SIGNALS
 	---help---
 		Enable building of TCP read-ahead notifier logic that will send a
 		signal to a kernel thread when an TCP read-ahead data has been

net/udp/Kconfig

@@ -61,7 +61,7 @@ config UDP_READAHEAD_NOTIFIER
 	bool "Support UDP read-ahead notifications"
 	default n
 	select SIG_NOTIFIER
-	depends on NET_UDP_READAHEAD && !DISABLE_POLL
+	depends on NET_UDP_READAHEAD && !DISABLE_SIGNALS
 	---help---
 		Enable building of UDP read-ahead notifier logic that will send a
 		signal to a kernel thread when an UDP read-ahead data has been

sched/Kconfig

@@ -1185,7 +1185,7 @@ config SIG_NOTIFIER
 
 config SIG_NOTIFIER_NWAITERS
 	int "Number of signal waiters"
-	default 4
+	default 8
 	range 1 32766
 	depends on SIG_NOTIFIER
 	---help---