1 /* vi: set sw=4 ts=4: */
2 /*
3 * readahead implementation for busybox
4 *
5 * Preloads the given files in RAM, to reduce access time.
6 * Does this by calling the readahead(2) system call.
7 *
8 * Copyright (C) 2006 Michael Opdenacker <michael@free-electrons.com>
9 *
10 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
11 */
12 //config:config READAHEAD
13 //config: bool "readahead (1.5 kb)"
14 //config: default y
15 //config: depends on LFS
16 //config: help
17 //config: Preload the files listed on the command line into RAM cache so that
18 //config: subsequent reads on these files will not block on disk I/O.
19 //config:
20 //config: This applet just calls the readahead(2) system call on each file.
21 //config: It is mainly useful in system startup scripts to preload files
22 //config: or executables before they are used. When used at the right time
23 //config: (in particular when a CPU bound process is running) it can
24 //config: significantly speed up system startup.
25 //config:
26 //config: As readahead(2) blocks until each file has been read, it is best to
27 //config: run this applet as a background job.
28
29 //applet:IF_READAHEAD(APPLET(readahead, BB_DIR_USR_SBIN, BB_SUID_DROP))
30
31 //kbuild:lib-$(CONFIG_READAHEAD) += readahead.o
32
33 //usage:#define readahead_trivial_usage
34 //usage: "[FILE]..."
35 //usage:#define readahead_full_usage "\n\n"
36 //usage: "Preload FILEs to RAM"
37
38 #include "libbb.h"
39
40 int readahead_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
readahead_main(int argc UNUSED_PARAM,char ** argv)41 int readahead_main(int argc UNUSED_PARAM, char **argv)
42 {
43 int retval = EXIT_SUCCESS;
44
45 if (!argv[1]) {
46 bb_show_usage();
47 }
48
49 while (*++argv) {
50 int fd = open_or_warn(*argv, O_RDONLY);
51 if (fd >= 0) {
52 off_t len;
53 int r;
54
55 /* fdlength was reported to be unreliable - use seek */
56 len = xlseek(fd, 0, SEEK_END);
57 xlseek(fd, 0, SEEK_SET);
58 r = readahead(fd, 0, len);
59 close(fd);
60 if (r >= 0)
61 continue;
62 }
63 retval = EXIT_FAILURE;
64 }
65
66 return retval;
67 }
68