netlink: move docs to README

README.adoc

@@ -3920,6 +3920,42 @@ Reads to that inode return the sequence: `1`, `10`, `100`, ... `10000000`, `1`,
 
 Bibliography: https://stackoverflow.com/questions/4508998/what-is-an-anonymous-inode-in-linux
 
+==== netlink sockets
+
+Netlink sockets offer a socket API for kernel / userland communication:
+
+....
+/netlink.sh
+echo $?
+....
+
+Outcome: the test passes:
+
+....
+0
+....
+
+Sources:
+
+* link:kernel_module/netlink.c[]
+* link:kernel_module/netlink.h[]
+* link:kernel_module/user/netlink.c[]
+* link:rootfs_overlay/netlink.sh[]
+
+Launch multiple user requests in parallel to stress our socket:
+
+....
+insmod /netlink.ko sleep=1
+for i in `seq 16`; do /netlink.out & done
+....
+
+TODO: what is the advantage over `read`, `write` and `poll`? https://stackoverflow.com/questions/16727212/how-netlink-socket-in-linux-kernel-is-different-from-normal-polling-done-by-appl
+
+Bibliography:
+
+* https://stackoverflow.com/questions/3299386/how-to-use-netlink-socket-to-communicate-with-a-kernel-module
+* https://en.wikipedia.org/wiki/Netlink
+
 === Linux kernel asynchronous APIs
 
 In this section we will document asynchronous APIs of Linux kernel, especially kthread-related scheduled events.