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 (1.7 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;
  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 }