1 /* vi: set sw=4 ts=4: */
3 * Mini losetup implementation for busybox
5 * Copyright (C) 2002 Matt Kraai.
7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
9 //config:config LOSETUP
10 //config: bool "losetup (5.5 kb)"
12 //config: select PLATFORM_LINUX
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.
18 //applet:IF_LOSETUP(APPLET_NOEXEC(losetup, losetup, BB_DIR_SBIN, BB_SUID_DROP, losetup))
20 //kbuild:lib-$(CONFIG_LOSETUP) += losetup.o
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"
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"
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
49 int losetup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
50 int losetup_main(int argc UNUSED_PARAM, char **argv)
54 char dev[LOOP_NAMESIZE];
65 opt = getopt32(argv, "^" "cdPo:far" "\0" "?2:d--Pofar:a--Pofr", &opt_o);
69 if (!opt && argv[0] && !argv[1]) {
72 s = query_loop(argv[0]);
74 bb_simple_perror_msg_and_die(argv[0]);
75 printf("%s: %s\n", argv[0], s);
76 if (ENABLE_FEATURE_CLEAN_UP)
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
87 xioctl(fd, LOOP_SET_CAPACITY, /*ignored:*/0);
92 if (opt == OPT_d && argv[0]) {
93 if (del_loop(argv[0]))
94 bb_simple_perror_msg_and_die(argv[0]);
101 for (n = 0; n < MAX_LOOP_NUM; n++) {
104 sprintf(dev, LOOP_FORMAT, n);
107 printf("%s: %s\n", dev, s);
121 bb_simple_error_msg_and_die("no free loop devices");
122 if (n < 0) /* n == -2: no /dev/loop-control, use legacy method */
124 /* or: n >= 0: the number of next free loopdev, just verify it */
126 if (n > MAX_LOOP_NUM)
127 bb_simple_error_msg_and_die("no free loop devices");
128 sprintf(dev, LOOP_FORMAT, n++);
132 /* now: dev is next free "/dev/loopN" */
133 if ((opt == OPT_f) && !argv[0]) {
139 /* [-rP] [-o OFS] {-f|LOOPDEV} FILE */
140 if (argv[0] && ((opt & OPT_f) || argv[1])) {
141 unsigned long long offset = 0;
145 offset = xatoull(opt_o);
150 unsigned flags = (opt & OPT_r) ? BB_LO_FLAGS_READ_ONLY : 0;
152 flags |= BB_LO_FLAGS_PARTSCAN;
154 if (set_loop(&d, argv[0], offset, flags) < 0)
155 bb_simple_perror_msg_and_die(argv[0]);
160 /* TODO: util-linux 2.28 shows this when run w/o params:
161 * NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO
162 * /dev/loop0 0 0 1 0 /PATH/TO/FILE 0
164 * implemented by reading /sys:
166 * open("/sys/block", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
167 * newfstatat(3, "loop0/loop/backing_file", {st_mode=S_IFREG|0444, st_size=4096, ...}, 0) = 0
168 * stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
169 * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
170 * read(5, "0\n", 4096) = 2
171 * open("/sys/dev/block/7:0/loop/sizelimit", O_RDONLY|O_CLOEXEC) = 5
172 * read(5, "0\n", 4096) = 2
173 * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
174 * read(5, "0\n", 4096) = 2
175 * open("/sys/dev/block/7:0/loop/autoclear", O_RDONLY|O_CLOEXEC) = 5
176 * read(5, "1\n", 4096) = 2
177 * open("/sys/dev/block/7:0/ro", O_RDONLY|O_CLOEXEC) = 5
178 * read(5, "0\n", 4096) = 2
179 * open("/sys/dev/block/7:0/loop/backing_file", O_RDONLY|O_CLOEXEC) = 5
180 * read(5, "/PATH/TO/FILE", 4096) = 37
181 * open("/sys/dev/block/7:0/loop/dio", O_RDONLY|O_CLOEXEC) = 5
182 * read(5, "0\n", 4096) = 2
185 bb_show_usage(); /* does not return */
186 /*return EXIT_FAILURE;*/