util-linux/losetup.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini losetup implementation for busybox
   4  *
   5  * Copyright (C) 2002  Matt Kraai.
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8  */
   9 //config:config LOSETUP
  10 //config:       bool "losetup (5.5 kb)"
  11 //config:       default y
  12 //config:       select PLATFORM_LINUX
  13 //config:       help
  14 //config:       losetup is used to associate or detach a loop device with a regular
  15 //config:       file or block device, and to query the status of a loop device. This
  16 //config:       version does not currently support enabling data encryption.
  17
  18 //applet:IF_LOSETUP(APPLET_NOEXEC(losetup, losetup, BB_DIR_SBIN, BB_SUID_DROP, losetup))
  19
  20 //kbuild:lib-$(CONFIG_LOSETUP) += losetup.o
  21
  22 //usage:#define losetup_trivial_usage
  23 //usage:       "[-rP] [-o OFS] {-f|LOOPDEV} FILE: associate loop devices\n"
  24 //usage:       "        losetup -c LOOPDEV: reread file size\n"
  25 //usage:       "        losetup -d LOOPDEV: disassociate\n"
  26 //usage:       "        losetup -a: show status\n"
  27 //usage:       "        losetup -f: show next free loop device"
  28 //usage:#define losetup_full_usage "\n\n"
  29 //usage:       "        -o OFS  Start OFS bytes into FILE"
  30 //usage:     "\n        -P      Scan for partitions"
  31 //usage:     "\n        -r      Read-only"
  32 //usage:     "\n        -f      Show/use next free loop device"
  33 //usage:
  34 //usage:#define losetup_notes_usage
  35 //usage:       "One argument (losetup /dev/loop1) will display the current association\n"
  36 //usage:       "(if any), or disassociate it (with -d). The display shows the offset\n"
  37 //usage:       "and filename of the file the loop device is currently bound to.\n\n"
  38 //usage:       "Two arguments (losetup /dev/loop1 file.img) create a new association,\n"
  39 //usage:       "with optional partition scanning (creates /dev/loop1p1, /dev/loop1p2\n"
  40 //usage:       "etc. with -P) and with an optional offset (-o 12345). Encryption is\n"
  41 //usage:       "not yet supported. losetup -f will show the first free loop device\n\n"
  42
  43 #include "libbb.h"
  44
  45 /* 1048575 is a max possible minor number in Linux circa 2010 */
  46 /* for now use something less extreme */
  47 #define MAX_LOOP_NUM 1023
  48
  49 int losetup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  50 int losetup_main(int argc UNUSED_PARAM, char **argv)
  51 {
  52         unsigned opt;
  53         char *opt_o;
  54         char dev[LOOP_NAMESIZE];
  55         enum {
  56                 OPT_c = (1 << 0),
  57                 OPT_d = (1 << 1),
  58                 OPT_P = (1 << 2),
  59                 OPT_o = (1 << 3),
  60                 OPT_f = (1 << 4),
  61                 OPT_a = (1 << 5),
  62                 OPT_r = (1 << 6),
  63         };
  64
  65         opt = getopt32(argv, "^" "cdPo:far" "\0" "?2:d--Pofar:a--Pofr", &opt_o);
  66         argv += optind;
  67
  68         /* LOOPDEV */
  69         if (!opt && argv[0] && !argv[1]) {
  70                 char *s;
  71
  72                 s = query_loop(argv[0]);
  73                 if (!s)
  74                         bb_simple_perror_msg_and_die(argv[0]);
  75                 printf("%s: %s\n", argv[0], s);
  76                 if (ENABLE_FEATURE_CLEAN_UP)
  77                         free(s);
  78                 return EXIT_SUCCESS;
  79         }
  80
  81         /* -c LOOPDEV */
  82         if (opt == OPT_c && argv[0]) {
  83                 int fd = xopen(argv[0], O_RDONLY);
  84 #ifndef LOOP_SET_CAPACITY
  85 # define LOOP_SET_CAPACITY 0x4C07
  86 #endif
  87                 xioctl(fd, LOOP_SET_CAPACITY, /*ignored:*/0);
  88                 return EXIT_SUCCESS;
  89         }
  90
  91         /* -d LOOPDEV */
  92         if (opt == OPT_d && argv[0]) {
  93                 if (del_loop(argv[0]))
  94                         bb_simple_perror_msg_and_die(argv[0]);
  95                 return EXIT_SUCCESS;
  96         }
  97
  98         /* -a */
  99         if (opt == OPT_a) {
 100                 int n;
 101                 for (n = 0; n < MAX_LOOP_NUM; n++) {
 102                         char *s;
 103
 104                         sprintf(dev, LOOP_FORMAT, n);
 105                         s = query_loop(dev);
 106                         if (s) {
 107                                 printf("%s: %s\n", dev, s);
 108                                 free(s);
 109                         }
 110                 }
 111                 return EXIT_SUCCESS;
 112         }
 113
 114         /* contains -f */
 115         if (opt & OPT_f) {
 116                 char *s;
 117                 int n = 0;
 118
 119                 do {
 120                         if (n > MAX_LOOP_NUM)
 121                                 bb_error_msg_and_die("no free loop devices");
 122                         sprintf(dev, LOOP_FORMAT, n++);
 123                         s = query_loop(dev);
 124                         free(s);
 125                 } while (s);
 126                 /* now: dev is next free "/dev/loopN" */
 127                 if ((opt == OPT_f) && !argv[0]) {
 128                         puts(dev);
 129                         return EXIT_SUCCESS;
 130                 }
 131         }
 132
 133         /* [-rP] [-o OFS] {-f|LOOPDEV} FILE */
 134         if (argv[0] && ((opt & OPT_f) || argv[1])) {
 135                 unsigned long long offset = 0;
 136                 char *d = dev;
 137
 138                 if (opt & OPT_o)
 139                         offset = xatoull(opt_o);
 140                 if (!(opt & OPT_f))
 141                         d = *argv++;
 142
 143                 if (argv[0]) {
 144                         unsigned flags = (opt & OPT_r) ? BB_LO_FLAGS_READ_ONLY : 0;
 145                         if (opt & OPT_P) {
 146                                 flags |= BB_LO_FLAGS_PARTSCAN;
 147                         }
 148                         if (set_loop(&d, argv[0], offset, flags) < 0)
 149                                 bb_simple_perror_msg_and_die(argv[0]);
 150                         return EXIT_SUCCESS;
 151                 }
 152         }
 153
 154         /* TODO: util-linux 2.28 shows this when run w/o params:
 155          * NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE     DIO
 156          * /dev/loop0         0      0         1  0 /PATH/TO/FILE   0
 157          *
 158          * implemented by reading /sys:
 159          *
 160          * open("/sys/block", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
 161          * newfstatat(3, "loop0/loop/backing_file", {st_mode=S_IFREG|0444, st_size=4096, ...}, 0) = 0
 162          * stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
 163          * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
 164          * read(5, "0\n", 4096)                    = 2
 165          * open("/sys/dev/block/7:0/loop/sizelimit", O_RDONLY|O_CLOEXEC) = 5
 166          * read(5, "0\n", 4096)                    = 2
 167          * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
 168          * read(5, "0\n", 4096)                    = 2
 169          * open("/sys/dev/block/7:0/loop/autoclear", O_RDONLY|O_CLOEXEC) = 5
 170          * read(5, "1\n", 4096)                    = 2
 171          * open("/sys/dev/block/7:0/ro", O_RDONLY|O_CLOEXEC)     = 5
 172          * read(5, "0\n", 4096)                    = 2
 173          * open("/sys/dev/block/7:0/loop/backing_file", O_RDONLY|O_CLOEXEC) = 5
 174          * read(5, "/PATH/TO/FILE", 4096) = 37
 175          * open("/sys/dev/block/7:0/loop/dio", O_RDONLY|O_CLOEXEC) = 5
 176          * read(5, "0\n", 4096)                    = 2
 177          */
 178
 179         bb_show_usage(); /* does not return */
 180         /*return EXIT_FAILURE;*/
 181 }