blob: b8e9b257f0c48ad47bbfa4debc774c3f41811d8a
| 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" |
| 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 | |
| 41 | int readahead_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
| 42 | int 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 |