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"
  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 //kbuild:lib-$(CONFIG_LOSETUP) += losetup.o
  19
  20 //applet:IF_LOSETUP(APPLET(losetup, BB_DIR_SBIN, BB_SUID_DROP))
  21
  22 //usage:#define losetup_trivial_usage
  23 //usage:       "[-r] [-o OFS] {-f|LOOPDEV} FILE - associate loop devices\n"
  24 //usage:       "        losetup -d LOOPDEV - disassociate\n"
  25 //usage:       "        losetup -a - show status\n"
  26 //usage:       "        losetup -f - show next free loop device"
  27 //usage:#define losetup_full_usage "\n\n"
  28 //usage:       "        -o OFS  Start OFS bytes into FILE"
  29 //usage:     "\n        -r      Read-only"
  30 //usage:     "\n        -f      Show/use next free loop device"
  31 //usage:
  32 //usage:#define losetup_notes_usage
  33 //usage:       "One argument (losetup /dev/loop1) will display the current association\n"
  34 //usage:       "(if any), or disassociate it (with -d). The display shows the offset\n"
  35 //usage:       "and filename of the file the loop device is currently bound to.\n\n"
  36 //usage:       "Two arguments (losetup /dev/loop1 file.img) create a new association,\n"
  37 //usage:       "with an optional offset (-o 12345). Encryption is not yet supported.\n"
  38 //usage:       "losetup -f will show the first loop free loop device\n\n"
  39
  40 #include "libbb.h"
  41
  42 /* 1048575 is a max possible minor number in Linux circa 2010 */
  43 /* for now use something less extreme */
  44 #define MAX_LOOP_NUM 1023
  45
  46 int losetup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  47 int losetup_main(int argc UNUSED_PARAM, char **argv)
  48 {
  49         unsigned opt;
  50         char *opt_o;
  51         char dev[LOOP_NAMESIZE];
  52         enum {
  53                 OPT_d = (1 << 0),
  54                 OPT_o = (1 << 1),
  55                 OPT_f = (1 << 2),
  56                 OPT_a = (1 << 3),
  57                 OPT_r = (1 << 4), /* must be last */
  58         };
  59
  60         opt_complementary = "?2:d--ofar:a--ofr";
  61         opt = getopt32(argv, "do:far", &opt_o);
  62         argv += optind;
  63
  64         /* LOOPDEV */
  65         if (!opt && argv[0] && !argv[1]) {
  66                 char *s;
  67
  68                 s = query_loop(argv[0]);
  69                 if (!s)
  70                         bb_simple_perror_msg_and_die(argv[0]);
  71                 printf("%s: %s\n", argv[0], s);
  72                 if (ENABLE_FEATURE_CLEAN_UP)
  73                         free(s);
  74                 return EXIT_SUCCESS;
  75         }
  76
  77         /* -d LOOPDEV */
  78         if (opt == OPT_d && argv[0]) {
  79                 if (del_loop(argv[0]))
  80                         bb_simple_perror_msg_and_die(argv[0]);
  81                 return EXIT_SUCCESS;
  82         }
  83
  84         /* -a */
  85         if (opt == OPT_a) {
  86                 int n;
  87                 for (n = 0; n < MAX_LOOP_NUM; n++) {
  88                         char *s;
  89
  90                         sprintf(dev, LOOP_FORMAT, n);
  91                         s = query_loop(dev);
  92                         if (s) {
  93                                 printf("%s: %s\n", dev, s);
  94                                 free(s);
  95                         }
  96                 }
  97                 return EXIT_SUCCESS;
  98         }
  99
 100         /* contains -f */
 101         if (opt & OPT_f) {
 102                 char *s;
 103                 int n = 0;
 104
 105                 do {
 106                         if (n > MAX_LOOP_NUM)
 107                                 bb_error_msg_and_die("no free loop devices");
 108                         sprintf(dev, LOOP_FORMAT, n++);
 109                         s = query_loop(dev);
 110                         free(s);
 111                 } while (s);
 112                 /* now: dev is next free "/dev/loopN" */
 113                 if ((opt == OPT_f) && !argv[0]) {
 114                         puts(dev);
 115                         return EXIT_SUCCESS;
 116                 }
 117         }
 118
 119         /* [-r] [-o OFS] {-f|LOOPDEV} FILE */
 120         if (argv[0] && ((opt & OPT_f) || argv[1])) {
 121                 unsigned long long offset = 0;
 122                 char *d = dev;
 123
 124                 if (opt & OPT_o)
 125                         offset = xatoull(opt_o);
 126                 if (!(opt & OPT_f))
 127                         d = *argv++;
 128
 129                 if (argv[0]) {
 130                         if (set_loop(&d, argv[0], offset, (opt & OPT_r) ? BB_LO_FLAGS_READ_ONLY : 0) < 0)
 131                                 bb_simple_perror_msg_and_die(argv[0]);
 132                         return EXIT_SUCCESS;
 133                 }
 134         }
 135
 136         /* TODO: util-linux 2.28 shows this when run w/o params:
 137          * NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE     DIO
 138          * /dev/loop0         0      0         1  0 /PATH/TO/FILE   0
 139          *
 140          * implemented by reading /sys:
 141          *
 142          * open("/sys/block", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
 143          * newfstatat(3, "loop0/loop/backing_file", {st_mode=S_IFREG|0444, st_size=4096, ...}, 0) = 0
 144          * stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
 145          * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
 146          * read(5, "0\n", 4096)                    = 2
 147          * open("/sys/dev/block/7:0/loop/sizelimit", O_RDONLY|O_CLOEXEC) = 5
 148          * read(5, "0\n", 4096)                    = 2
 149          * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
 150          * read(5, "0\n", 4096)                    = 2
 151          * open("/sys/dev/block/7:0/loop/autoclear", O_RDONLY|O_CLOEXEC) = 5
 152          * read(5, "1\n", 4096)                    = 2
 153          * open("/sys/dev/block/7:0/ro", O_RDONLY|O_CLOEXEC)     = 5
 154          * read(5, "0\n", 4096)                    = 2
 155          * open("/sys/dev/block/7:0/loop/backing_file", O_RDONLY|O_CLOEXEC) = 5
 156          * read(5, "/PATH/TO/FILE", 4096) = 37
 157          * open("/sys/dev/block/7:0/loop/dio", O_RDONLY|O_CLOEXEC) = 5
 158          * read(5, "0\n", 4096)                    = 2
 159          */
 160
 161         bb_show_usage(); /* does not return */
 162         /*return EXIT_FAILURE;*/
 163 }