linuxnetlinkh

Linuxnetlinkh refers to the Linux netlink header interface, primarily defined in include/linux/netlink.h and used by user-space programs through the <linux/netlink.h> interface. It represents the kernel’s netlink messaging system, an asynchronous, datagram-based IPC mechanism that enables communication between the kernel and user space and among user-space processes.

Netlink messages are transported over netlink sockets. Each message is structured with a header (the netlink message header) followed by a payload that is specific to the message type. The header is defined by structures such as struct nlmsghdr, which carries fields like nlmsg_len, nlmsg_type, nlmsg_flags, nlmsg_seq, and nlmsg_pid. Attributes within messages are encoded as TLV data using struct nlattr, with associated helpers and macros such as NLA_HEADER, nla_len, and nla_type. Alignment and length calculation macros help ensure proper packing of messages.

The linux/netlink.h interface defines a family-based protocol design. NETLINK_ROUTE handles networking stack routing information; NETLINK_NETFILTER relates to the kernel’s netfilter subsystem; NETLINK_GENERIC provides a flexible, extensible family for custom message types; NETLINK_USERSOCK and other families support various kernel-user space communication needs. Each family has its own message type namespace and conventions for payload structure.

Typical usage patterns include kernel subsystems emitting events or receiving configuration requests via netlink, and user-space tooling (such as iproute2, libnl-based utilities, and custom daemons) interacting with the kernel through these messages. The interface supports multipart messages, multicast groups, and sequence tracking for reliable communication, with careful handling required to respect kernel contexts and permissions.

See also the Linux kernel networking stack, netlink in general, and user-space libraries that implement netlink communication.