Linux Device Drivers

IPC and lib Functions

Inter-Process Communication and library functions have two small directories dedicated to them.

The ipc directory includes a generic file called util.c and one source file for each communication facility: sem.c, shm.c, and msg.c. msg.c is in charge of message queues and the kerneld engine, kerneld_send. If IPC is not enabled at compile time, util.c exports empty functions that implement IPC-related system calls by returning -ENOSYS.

The library functions are like the utilities and variables that you usually use in C programs: sprintf, vsprintf, the errno integer variable, and the _ctype array used by the various <linux/ctype.h> macros. The file string.c contains portable implementations of the string functions, but they are compiled only if the architecture-specific code does not include optimized inline functions. If the inline functions are defined in the header, the implementations in string.c are left out of the game by #ifdef statements.

The most ``interesting'' file in lib is inflate.c, which is the ``gunzip'' part of gzip, extracted from gzip itself to allow using a compressed RAM disk at boot time. This technique is used whenever the needed data wouldn’t fit on a floppy unless compressed.