LXR busybox/miscutils/readahead.c

   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:       select PLATFORM_LINUX
  17//config:       help
  18//config:       Preload the files listed on the command line into RAM cache so that
  19//config:       subsequent reads on these files will not block on disk I/O.
  20//config:
  21//config:       This applet just calls the readahead(2) system call on each file.
  22//config:       It is mainly useful in system startup scripts to preload files
  23//config:       or executables before they are used. When used at the right time
  24//config:       (in particular when a CPU bound process is running) it can
  25//config:       significantly speed up system startup.
  26//config:
  27//config:       As readahead(2) blocks until each file has been read, it is best to
  28//config:       run this applet as a background job.
  29
  30//applet:IF_READAHEAD(APPLET(readahead, BB_DIR_USR_SBIN, BB_SUID_DROP))
  31
  32//kbuild:lib-$(CONFIG_READAHEAD) += readahead.o
  33
  34//usage:#define readahead_trivial_usage
  35//usage:       "[FILE]..."
  36//usage:#define readahead_full_usage "\n\n"
  37//usage:       "Preload FILEs to RAM"
  38
  39#include "libbb.h"
  40
  41int readahead_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  42int readahead_main(int argc UNUSED_PARAM, char **argv)
  43{
  44        int retval = EXIT_SUCCESS;
  45
  46        if (!argv[1]) {
  47                bb_show_usage();
  48        }
  49
  50        while (*++argv) {
  51                int fd = open_or_warn(*argv, O_RDONLY);
  52                if (fd >= 0) {
  53                        off_t len;
  54                        int r;
  55
  56                        /* fdlength was reported to be unreliable - use seek */
  57                        len = xlseek(fd, 0, SEEK_END);
  58                        xlseek(fd, 0, SEEK_SET);
  59                        r = readahead(fd, 0, len);
  60                        close(fd);
  61                        if (r >= 0)
  62                                continue;
  63                }
  64                retval = EXIT_FAILURE;
  65        }
  66
  67        return retval;
  68}
  69