blob: 972302a187d0d5ede77aac29a9900a59333b35c7 [file] [log] [blame]
/* vi: set sw=4 ts=4: */
* readahead implementation for busybox
* Preloads the given files in RAM, to reduce access time.
* Does this by calling the readahead(2) system call.
* Copyright (C) 2006 Michael Opdenacker <>
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
//config:config READAHEAD
//config: bool "readahead (2 kb)"
//config: default y
//config: depends on LFS
//config: select PLATFORM_LINUX
//config: help
//config: Preload the files listed on the command line into RAM cache so that
//config: subsequent reads on these files will not block on disk I/O.
//config: This applet just calls the readahead(2) system call on each file.
//config: It is mainly useful in system startup scripts to preload files
//config: or executables before they are used. When used at the right time
//config: (in particular when a CPU bound process is running) it can
//config: significantly speed up system startup.
//config: As readahead(2) blocks until each file has been read, it is best to
//config: run this applet as a background job.
//kbuild:lib-$(CONFIG_READAHEAD) += readahead.o
//usage:#define readahead_trivial_usage
//usage: "[FILE]..."
//usage:#define readahead_full_usage "\n\n"
//usage: "Preload FILEs to RAM"
#include "libbb.h"
int readahead_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int readahead_main(int argc UNUSED_PARAM, char **argv)
int retval = EXIT_SUCCESS;
if (!argv[1]) {
while (*++argv) {
int fd = open_or_warn(*argv, O_RDONLY);
if (fd >= 0) {
off_t len;
int r;
/* fdlength was reported to be unreliable - use seek */
len = xlseek(fd, 0, SEEK_END);
xlseek(fd, 0, SEEK_SET);
r = readahead(fd, 0, len);
if (r >= 0)
retval = EXIT_FAILURE;
return retval;