1.) L4_IPC System Call

 int l4_ipc(l4id_t to, l4id_t from, unsigned int flags)

Purpose

Provides inter-process communication between threads.

Operational Model

IPC calls transfer messages between threads that are stored in each thread's unique UTCB area accessible in the thread's address space.
UTCB is a system-defined memory block that provides thread-local storage. See UTCB for more details.
There are 3 types of IPC defined as shown in the table below:

IPC Type	Description
Short IPC	Transfers only the Primary Message Registers
Full IPC	Transfers the complete UTCB of the thread.
Extended IPC	Transfers a message buffer of up to 2 Kilobytes in size, using any address located in the address space.

L4 Userspace Library Functions

/* Short IPC Calls */
static inline int l4_send(l4id_t to, unsigned int tag);
static inline int l4_receive(l4id_t from);
static inline int l4_sendrecv(l4id_t to, l4id_t from, unsigned int tag)

/* Full IPC Calls */
static inline int l4_send_full(l4id_t to, unsigned int tag);
static inline int l4_receive_full(l4id_t from);
static inline int l4_sendrecv_full(l4id_t to, l4id_t from, unsigned int tag)

/* Extended IPC Calls */
static inline int l4_send_extended(l4id_t to, unsigned int tag, unsigned int size, void *buf)
static inline int l4_receive_extended(l4id_t from, unsigned int size, void *buf)

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