net/netlink: Add doc for netlink route

Signed-off-by: meijian <meijian@xiaomi.com>

Documentation/components/net/index.rst

@@ -12,6 +12,7 @@ Network Support
   netdev.rst
   netdriver.rst
   netguardsize.rst
+  netlink.rst
   slip.rst
   wqueuedeadlocks.rst
 

Documentation/components/net/netlink.rst

@@ -0,0 +1,137 @@
+=====================
+Netlink Route support
+=====================
+
+Netlink Route (:c:macro:`NETLINK_ROUTE`) allow notifying msg when the network 
+changes. And then apps can obtain these changes by monitoring to netlink socket
+messages.
+
+NuttX supports Netlink Route groups
+
+- RTMGRP_IPV4_ROUTE | RTMGRP_IPV6_ROUTE
+  - Notify when IPV4|IPV6 routing table changes.
+
+- RTMGRP_NEIGH
+  - Notify when ARP (IPV4) or neighbors (IPV6) table changes.
+
+- RTNLGRP_IPV6_PREFIX
+  - Notify when IPV6 prefix changes.
+
+Messages content
+================
+
+1. RTMGRP_IPV4_ROUTE | RTMGRP_IPV6_ROUTE
+
+  ``RTM_NEWROUTE``, ``RTM_DELROUTE``, ``RTM_GETROUTE``:
+  Create, remove or receive information about a network route. These
+  messages contain an rtmsg structure with 3 optional sequence of
+  rtattr structures following.
+
+  .. code-block:: c
+
+    struct getroute_recvfrom_ipv4addr_s
+    {
+      struct rtattr attr;
+      in_addr_t     addr;
+    };
+
+    struct getroute_recvfrom_ipv4response_s
+    {
+      struct nlmsghdr hdr;
+      struct rtmsg    rte;
+      struct getroute_recvfrom_ipv4addr_s dst;
+      struct getroute_recvfrom_ipv4addr_s genmask;
+      struct getroute_recvfrom_ipv4addr_s gateway;
+    };
+
+    struct getroute_recvfrom_ipv6addr_s
+    {
+      struct rtattr  attr;
+      net_ipv6addr_t addr;
+    };
+
+    struct getroute_recvfrom_ipv6response_s
+    {
+      struct nlmsghdr hdr;
+      struct rtmsg    rte;
+      struct getroute_recvfrom_ipv6addr_s dst;
+      struct getroute_recvfrom_ipv6addr_s genmask;
+      struct getroute_recvfrom_ipv6addr_s gateway;
+    };
+
+2. RTMGRP_NEIGH
+
+  ``RTM_NEWNEIGH``, ``RTM_DELNEIGH``, ``RTM_GETNEIGH``:
+  Add, remove or receive information about a neighbor table entry (e.g.,
+  an ARP entry). The message contains an ndmsg structure and optional 
+  sequence of rtattr structures following. And the date will be ``struct arpreq``
+  in ``include/netinet/arp.h``or ``struct neighbor_entry_s`` in ``include/net/neighbor.h``
+
+  .. code-block:: c
+
+    struct getneigh_recvfrom_response_s
+    {
+      struct nlmsghdr hdr;
+      struct ndmsg    msg;
+      struct rtattr   attr;
+      uint8_t         data[1];
+    };
+
+3. RTNLGRP_IPV6_PREFIX
+
+  ``RTM_NEWPREFIX``: 
+  Receive information about IPV6 prefix. The message contains an prefixmsg structure
+  and two optional sequence of rtattr structures following. And the ``addr`` and  
+  ``prefix_cacheinfo`` are parsed from the RA message.
+
+  .. code-block:: c
+
+    struct getprefix_recvfrom_addr_s
+    {
+      struct rtattr  attr;
+      net_ipv6addr_t addr;
+    };
+
+    struct getprefix_recvfrom_cache_s
+    {
+      struct rtattr           attr;
+      struct prefix_cacheinfo pci;
+    };
+
+    struct getprefix_recvfrom_response_s
+    {
+      struct nlmsghdr  hdr;
+      struct prefixmsg pmsg;
+      struct getprefix_recvfrom_addr_s  prefix;
+      struct getprefix_recvfrom_cache_s pci;
+    };
+
+Usage
+=====
+
+.. code-block:: c
+
+  struct sockaddr_nl addr;
+  struct nlmsghdr *hdr;
+  uint8_t buffer[BUFSIZE];
+  int sd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); 
+
+  addr.nl_family  = AF_NETLINK;
+  addr.nl_groups  = RTMGRP_IPV4_ROUTE | RTMGRP_IPV6_ROUTE |
+                    RTMGRP_NEIGH | RTMGRP_IPV6_PREFIX;
+
+  bind(sd, (FAR struct sockaddr *)&addr, sizeof(addr)); /* Bind to device */
+  while (1)
+    {
+      recv(sd, buf, BUFSIZE, 0);
+      for (hdr = buf; NLMSG_OK(hdr, ret); hdr = NLMSG_NEXT(hdr, ret))
+        {
+          if (hdr->nlmsg_type == RTM_...)
+            {
+              /* Func parsed netlink msg*/
+              ...
+            }
+        }
+    }
+
+  close(sd); /* Close the socket */