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 (5.4 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:       "[-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 = getopt32(argv, "^" "do:far" "\0" "?2:d--ofar:a--ofr", &opt_o);
  61         argv += optind;
  62
  63         /* LOOPDEV */
  64         if (!opt && argv[0] && !argv[1]) {
  65                 char *s;
  66
  67                 s = query_loop(argv[0]);
  68                 if (!s)
  69                         bb_simple_perror_msg_and_die(argv[0]);
  70                 printf("%s: %s\n", argv[0], s);
  71                 if (ENABLE_FEATURE_CLEAN_UP)
  72                         free(s);
  73                 return EXIT_SUCCESS;
  74         }
  75
  76         /* -d LOOPDEV */
  77         if (opt == OPT_d && argv[0]) {
  78                 if (del_loop(argv[0]))
  79                         bb_simple_perror_msg_and_die(argv[0]);
  80                 return EXIT_SUCCESS;
  81         }
  82
  83         /* -a */
  84         if (opt == OPT_a) {
  85                 int n;
  86                 for (n = 0; n < MAX_LOOP_NUM; n++) {
  87                         char *s;
  88
  89                         sprintf(dev, LOOP_FORMAT, n);
  90                         s = query_loop(dev);
  91                         if (s) {
  92                                 printf("%s: %s\n", dev, s);
  93                                 free(s);
  94                         }
  95                 }
  96                 return EXIT_SUCCESS;
  97         }
  98
  99         /* contains -f */
 100         if (opt & OPT_f) {
 101                 char *s;
 102                 int n = 0;
 103
 104                 do {
 105                         if (n > MAX_LOOP_NUM)
 106                                 bb_error_msg_and_die("no free loop devices");
 107                         sprintf(dev, LOOP_FORMAT, n++);
 108                         s = query_loop(dev);
 109                         free(s);
 110                 } while (s);
 111                 /* now: dev is next free "/dev/loopN" */
 112                 if ((opt == OPT_f) && !argv[0]) {
 113                         puts(dev);
 114                         return EXIT_SUCCESS;
 115                 }
 116         }
 117
 118         /* [-r] [-o OFS] {-f|LOOPDEV} FILE */
 119         if (argv[0] && ((opt & OPT_f) || argv[1])) {
 120                 unsigned long long offset = 0;
 121                 char *d = dev;
 122
 123                 if (opt & OPT_o)
 124                         offset = xatoull(opt_o);
 125                 if (!(opt & OPT_f))
 126                         d = *argv++;
 127
 128                 if (argv[0]) {
 129                         if (set_loop(&d, argv[0], offset, (opt & OPT_r) ? BB_LO_FLAGS_READ_ONLY : 0) < 0)
 130                                 bb_simple_perror_msg_and_die(argv[0]);
 131                         return EXIT_SUCCESS;
 132                 }
 133         }
 134
 135         /* TODO: util-linux 2.28 shows this when run w/o params:
 136          * NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE     DIO
 137          * /dev/loop0         0      0         1  0 /PATH/TO/FILE   0
 138          *
 139          * implemented by reading /sys:
 140          *
 141          * open("/sys/block", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
 142          * newfstatat(3, "loop0/loop/backing_file", {st_mode=S_IFREG|0444, st_size=4096, ...}, 0) = 0
 143          * stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
 144          * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
 145          * read(5, "0\n", 4096)                    = 2
 146          * open("/sys/dev/block/7:0/loop/sizelimit", O_RDONLY|O_CLOEXEC) = 5
 147          * read(5, "0\n", 4096)                    = 2
 148          * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
 149          * read(5, "0\n", 4096)                    = 2
 150          * open("/sys/dev/block/7:0/loop/autoclear", O_RDONLY|O_CLOEXEC) = 5
 151          * read(5, "1\n", 4096)                    = 2
 152          * open("/sys/dev/block/7:0/ro", O_RDONLY|O_CLOEXEC)     = 5
 153          * read(5, "0\n", 4096)                    = 2
 154          * open("/sys/dev/block/7:0/loop/backing_file", O_RDONLY|O_CLOEXEC) = 5
 155          * read(5, "/PATH/TO/FILE", 4096) = 37
 156          * open("/sys/dev/block/7:0/loop/dio", O_RDONLY|O_CLOEXEC) = 5
 157          * read(5, "0\n", 4096)                    = 2
 158          */
 159
 160         bb_show_usage(); /* does not return */
 161         /*return EXIT_FAILURE;*/
 162 }