Netlink Sockets: Linux Kernel-User communication (PART I)

• Ubuntu 14.04, Kernel version 3.11
• Netlink sockets provide full duplex, asynchronous, low-overhead communication channel between user-kernel space processes.
• Other solutions such as ioctl(), sysfs, UDP sockets are either blocking (hence expensive) or slow (UDP has more overhead compared to Netlink) and complex.
• Netlink can carry data buffers on a return trip from kernel to user and vice-verse.
• By nature, netlink sockets are non-blocking.
• It provides sender and receiver queues to handle burst of messages.
• User space APIs are exactly like ordinary sockets. You have to specify socket family as AF_NETLINK.
• Kernel space API is netlink_kernel_create().
• Default netlink queue size is 208K. To set a higher size of queue, run the following commands:

#default buffer size = 212992
echo 425984 > /proc/sys/net/core/wmem_max
echo 425984 > /proc/sys/net/core/wmem_default  
echo 425984 > /proc/sys/net/core/rmem_default
echo 425984 > /proc/sys/net/core/rmem_max

• Netlink do not care about the data buffer you wish to send/receive.
• It allows unicasting, multicasting and broadcasting of messages.