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 (5.4 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 //kbuild:lib-$(CONFIG_LOSETUP) += losetup.o
20 //applet:IF_LOSETUP(APPLET(losetup, BB_DIR_SBIN, BB_SUID_DROP))
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"
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"
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
46 int losetup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
47 int losetup_main(int argc UNUSED_PARAM, char **argv)
51 char dev[LOOP_NAMESIZE];
57 OPT_r = (1 << 4), /* must be last */
60 opt_complementary = "?2:d--ofar:a--ofr";
61 opt = getopt32(argv, "do:far", &opt_o);
65 if (!opt && argv[0] && !argv[1]) {
68 s = query_loop(argv[0]);
70 bb_simple_perror_msg_and_die(argv[0]);
71 printf("%s: %s\n", argv[0], s);
72 if (ENABLE_FEATURE_CLEAN_UP)
78 if (opt == OPT_d && argv[0]) {
79 if (del_loop(argv[0]))
80 bb_simple_perror_msg_and_die(argv[0]);
87 for (n = 0; n < MAX_LOOP_NUM; n++) {
90 sprintf(dev, LOOP_FORMAT, n);
93 printf("%s: %s\n", dev, s);
106 if (n > MAX_LOOP_NUM)
107 bb_error_msg_and_die("no free loop devices");
108 sprintf(dev, LOOP_FORMAT, n++);
112 /* now: dev is next free "/dev/loopN" */
113 if ((opt == OPT_f) && !argv[0]) {
119 /* [-r] [-o OFS] {-f|LOOPDEV} FILE */
120 if (argv[0] && ((opt & OPT_f) || argv[1])) {
121 unsigned long long offset = 0;
125 offset = xatoull(opt_o);
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]);
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
140 * implemented by reading /sys:
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
161 bb_show_usage(); /* does not return */
162 /*return EXIT_FAILURE;*/