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: help
13 //config: losetup is used to associate or detach a loop device with a regular
14 //config: file or block device, and to query the status of a loop device. This
15 //config: version does not currently support enabling data encryption.
16
17 //applet:IF_LOSETUP(APPLET_NOEXEC(losetup, losetup, BB_DIR_SBIN, BB_SUID_DROP, losetup))
18
19 //kbuild:lib-$(CONFIG_LOSETUP) += losetup.o
20
21 //usage:#define losetup_trivial_usage
22 //usage: "[-rP] [-o OFS] {-f|LOOPDEV} FILE: associate loop devices\n"
23 //usage: " losetup -c LOOPDEV: reread file size\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 -P Scan for partitions"
30 //usage: "\n -r Read-only"
31 //usage: "\n -f Show/use next free loop device"
32 //usage:
33 //usage:#define losetup_notes_usage
34 //usage: "One argument (losetup /dev/loop1) will display the current association\n"
35 //usage: "(if any), or disassociate it (with -d). The display shows the offset\n"
36 //usage: "and filename of the file the loop device is currently bound to.\n\n"
37 //usage: "Two arguments (losetup /dev/loop1 file.img) create a new association,\n"
38 //usage: "with optional partition scanning (creates /dev/loop1p1, /dev/loop1p2\n"
39 //usage: "etc. with -P) and with an optional offset (-o 12345). Encryption is\n"
40 //usage: "not yet supported. losetup -f will show the first free loop device\n\n"
41
42 #include "libbb.h"
43
44 /* 1048575 is a max possible minor number in Linux circa 2010 */
45 /* for now use something less extreme */
46 #define MAX_LOOP_NUM 1023
47
48 int losetup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
losetup_main(int argc UNUSED_PARAM,char ** argv)49 int losetup_main(int argc UNUSED_PARAM, char **argv)
50 {
51 unsigned opt;
52 char *opt_o;
53 char dev[LOOP_NAMESIZE];
54 enum {
55 OPT_c = (1 << 0),
56 OPT_d = (1 << 1),
57 OPT_P = (1 << 2),
58 OPT_o = (1 << 3),
59 OPT_f = (1 << 4),
60 OPT_a = (1 << 5),
61 OPT_r = (1 << 6),
62 };
63
64 opt = getopt32(argv, "^" "cdPo:far" "\0" "?2:d--Pofar:a--Pofr", &opt_o);
65 argv += optind;
66
67 /* LOOPDEV */
68 if (!opt && argv[0] && !argv[1]) {
69 char *s;
70
71 s = query_loop(argv[0]);
72 if (!s)
73 bb_simple_perror_msg_and_die(argv[0]);
74 printf("%s: %s\n", argv[0], s);
75 if (ENABLE_FEATURE_CLEAN_UP)
76 free(s);
77 return EXIT_SUCCESS;
78 }
79
80 /* -c LOOPDEV */
81 if (opt == OPT_c && argv[0]) {
82 int fd = xopen(argv[0], O_RDONLY);
83 #ifndef LOOP_SET_CAPACITY
84 # define LOOP_SET_CAPACITY 0x4C07
85 #endif
86 xioctl(fd, LOOP_SET_CAPACITY, /*ignored:*/0);
87 return EXIT_SUCCESS;
88 }
89
90 /* -d LOOPDEV */
91 if (opt == OPT_d && argv[0]) {
92 if (del_loop(argv[0]))
93 bb_simple_perror_msg_and_die(argv[0]);
94 return EXIT_SUCCESS;
95 }
96
97 /* -a */
98 if (opt == OPT_a) {
99 int n;
100 for (n = 0; n < MAX_LOOP_NUM; n++) {
101 char *s;
102
103 sprintf(dev, LOOP_FORMAT, n);
104 s = query_loop(dev);
105 if (s) {
106 printf("%s: %s\n", dev, s);
107 free(s);
108 }
109 }
110 return EXIT_SUCCESS;
111 }
112
113 /* contains -f */
114 if (opt & OPT_f) {
115 char *s;
116 int n;
117
118 n = get_free_loop();
119 if (n == -1)
120 bb_simple_error_msg_and_die("no free loop devices");
121 if (n < 0) /* n == -2: no /dev/loop-control, use legacy method */
122 n = 0;
123 /* or: n >= 0: the number of next free loopdev, just verify it */
124 do {
125 if (n > MAX_LOOP_NUM)
126 bb_simple_error_msg_and_die("no free loop devices");
127 sprintf(dev, LOOP_FORMAT, n++);
128 s = query_loop(dev);
129 free(s);
130 } while (s);
131 /* now: dev is next free "/dev/loopN" */
132 if ((opt == OPT_f) && !argv[0]) {
133 puts(dev);
134 return EXIT_SUCCESS;
135 }
136 }
137
138 /* [-rP] [-o OFS] {-f|LOOPDEV} FILE */
139 if (argv[0] && ((opt & OPT_f) || argv[1])) {
140 unsigned long long offset = 0;
141 char *d = dev;
142
143 if (opt & OPT_o)
144 offset = xatoull(opt_o);
145 if (!(opt & OPT_f))
146 d = *argv++;
147
148 if (argv[0]) {
149 unsigned flags = (opt & OPT_r) ? BB_LO_FLAGS_READ_ONLY : 0;
150 if (opt & OPT_P) {
151 flags |= BB_LO_FLAGS_PARTSCAN;
152 }
153 if (set_loop(&d, argv[0], offset, 0, flags) < 0)
154 bb_simple_perror_msg_and_die(argv[0]);
155 return EXIT_SUCCESS;
156 }
157 }
158
159 /* TODO: util-linux 2.28 shows this when run w/o params:
160 * NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO
161 * /dev/loop0 0 0 1 0 /PATH/TO/FILE 0
162 *
163 * implemented by reading /sys:
164 *
165 * open("/sys/block", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
166 * newfstatat(3, "loop0/loop/backing_file", {st_mode=S_IFREG|0444, st_size=4096, ...}, 0) = 0
167 * stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
168 * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
169 * read(5, "0\n", 4096) = 2
170 * open("/sys/dev/block/7:0/loop/sizelimit", O_RDONLY|O_CLOEXEC) = 5
171 * read(5, "0\n", 4096) = 2
172 * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
173 * read(5, "0\n", 4096) = 2
174 * open("/sys/dev/block/7:0/loop/autoclear", O_RDONLY|O_CLOEXEC) = 5
175 * read(5, "1\n", 4096) = 2
176 * open("/sys/dev/block/7:0/ro", O_RDONLY|O_CLOEXEC) = 5
177 * read(5, "0\n", 4096) = 2
178 * open("/sys/dev/block/7:0/loop/backing_file", O_RDONLY|O_CLOEXEC) = 5
179 * read(5, "/PATH/TO/FILE", 4096) = 37
180 * open("/sys/dev/block/7:0/loop/dio", O_RDONLY|O_CLOEXEC) = 5
181 * read(5, "0\n", 4096) = 2
182 */
183
184 bb_show_usage(); /* does not return */
185 /*return EXIT_FAILURE;*/
186 }
187