1 /* losetup.c - Loopback setup 2 * 3 * Copyright 2012 Rob Landley <rob (at) landley.net> 4 * 5 * No standard. (Sigh.) 6 7 USE_LOSETUP(NEWTOY(losetup, ">2S(sizelimit)#s(show)ro#j:fdca[!afj]", TOYFLAG_SBIN)) 8 9 config LOSETUP 10 bool "losetup" 11 default y 12 help 13 usage: losetup [-cdrs] [-o OFFSET] [-S SIZE] {-d DEVICE...|-j FILE|-af|{DEVICE FILE}} 14 15 Associate a loopback device with a file, or show current file (if any) 16 associated with a loop device. 17 18 Instead of a device: 19 -a Iterate through all loopback devices 20 -f Find first unused loop device (may create one) 21 -j Iterate through all loopback devices associated with FILE 22 23 existing: 24 -c Check capacity (file size changed) 25 -d Detach loopback device 26 27 new: 28 -s Show device name (alias --show) 29 -o Start assocation at OFFSET into FILE 30 -r Read only 31 -S Limit SIZE of loopback association (alias --sizelimit) 32 */ 33 34 #define FOR_losetup 35 #include "toys.h" 36 #include <linux/loop.h> 37 38 GLOBALS( 39 char *jfile; 40 long offset; 41 long size; 42 43 int openflags; 44 dev_t jdev; 45 ino_t jino; 46 ) 47 48 /* 49 todo: basic /dev file association 50 associate DEV FILE 51 #-a 52 cdfjosS 53 allocate new loop device: 54 /dev/loop-control 55 https://lkml.org/lkml/2011/7/26/148 56 */ 57 58 // -f: *device is NULL 59 60 // Perform requested operation on one device. Returns 1 if handled, 0 if error 61 static void loopback_setup(char *device, char *file) 62 { 63 struct loop_info64 *loop = (void *)(toybuf+32); 64 int lfd = -1, ffd = ffd; 65 unsigned flags = toys.optflags; 66 67 // Open file (ffd) and loop device (lfd) 68 69 if (file) ffd = xopen(file, TT.openflags); 70 if (!device) { 71 int i, cfd = open("/dev/loop-control", O_RDWR); 72 73 // We assume /dev is devtmpfs so device creation has no lag. Otherwise 74 // just preallocate loop devices and stay within them. 75 76 // mount -o loop depends on found device being at the start of toybuf. 77 if (cfd != -1) { 78 if (0 <= (i = ioctl(cfd, 0x4C82))) // LOOP_CTL_GET_FREE 79 sprintf(device = toybuf, "/dev/loop%d", i); 80 close(cfd); 81 } 82 } 83 84 if (device) lfd = open(device, TT.openflags); 85 86 // Stat the loop device to see if there's a current association. 87 memset(loop, 0, sizeof(struct loop_info64)); 88 if (-1 == lfd || ioctl(lfd, LOOP_GET_STATUS64, loop)) { 89 if (errno == ENXIO && (flags & (FLAG_a|FLAG_j))) goto done; 90 if (errno != ENXIO || !file) { 91 perror_msg_raw(device ? device : "-f"); 92 goto done; 93 } 94 } 95 96 // Skip -j filtered devices 97 if (TT.jfile && (loop->lo_device != TT.jdev || loop->lo_inode != TT.jino)) 98 goto done; 99 100 // Check size of file or delete existing association 101 if (flags & (FLAG_c|FLAG_d)) { 102 // The constant is LOOP_SET_CAPACITY 103 if (ioctl(lfd, (flags & FLAG_c) ? 0x4C07 : LOOP_CLR_FD, 0)) { 104 perror_msg_raw(device); 105 goto done; 106 } 107 // Associate file with this device? 108 } else if (file) { 109 char *s = xabspath(file, 1); 110 111 if (!s) perror_exit("file"); // already opened, but if deleted since... 112 if (ioctl(lfd, LOOP_SET_FD, ffd)) perror_exit("%s=%s", device, file); 113 loop->lo_offset = TT.offset; 114 loop->lo_sizelimit = TT.size; 115 xstrncpy((char *)loop->lo_file_name, s, LO_NAME_SIZE); 116 s[LO_NAME_SIZE-1] = 0; 117 if (ioctl(lfd, LOOP_SET_STATUS64, loop)) perror_exit("%s=%s", device, file); 118 if (flags & FLAG_s) printf("%s", device); 119 free(s); 120 } else if (flags & FLAG_f) printf("%s", device); 121 else { 122 xprintf("%s: [%04llx]:%llu (%s)", device, loop->lo_device, loop->lo_inode, 123 loop->lo_file_name); 124 if (loop->lo_offset) xprintf(", offset %llu", loop->lo_offset); 125 if (loop->lo_sizelimit) xprintf(", sizelimit %llu", loop->lo_sizelimit); 126 xputc('\n'); 127 } 128 129 done: 130 if (file) close(ffd); 131 if (lfd != -1) close(lfd); 132 } 133 134 // Perform an action on all currently existing loop devices 135 static int dash_a(struct dirtree *node) 136 { 137 char *s = node->name; 138 139 // Initial /dev node needs to recurse down one level, then only loop[0-9]* 140 if (*s == '/') return DIRTREE_RECURSE; 141 if (strncmp(s, "loop", 4) || !isdigit(s[4])) return 0; 142 143 s = dirtree_path(node, 0); 144 loopback_setup(s, 0); 145 free(s); 146 147 return 0; 148 } 149 150 void losetup_main(void) 151 { 152 char **s; 153 154 TT.openflags = (toys.optflags & FLAG_r) ? O_RDONLY : O_RDWR; 155 156 if (TT.jfile) { 157 struct stat st; 158 159 xstat(TT.jfile, &st); 160 TT.jdev = st.st_dev; 161 TT.jino = st.st_ino; 162 } 163 164 // With just device, display current association 165 // -a, -f substitute for device 166 // -j substitute for device 167 168 // new association: S size o offset rs - need a file 169 // existing association: cd 170 171 // -f(dc FILE) 172 173 if (toys.optflags & FLAG_f) { 174 if (toys.optc > 1) perror_exit("max 1 arg"); 175 loopback_setup(NULL, *toys.optargs); 176 } else if (toys.optflags & (FLAG_a|FLAG_j)) { 177 if (toys.optc) error_exit("bad args"); 178 dirtree_read("/dev", dash_a); 179 // Do we need one DEVICE argument? 180 } else { 181 char *file = (toys.optflags & (FLAG_d|FLAG_c)) ? NULL : toys.optargs[1]; 182 183 if (!toys.optc || (file && toys.optc != 2)) 184 help_exit("needs %d arg%s", 1+!!file, file ? "s" : ""); 185 for (s = toys.optargs; *s; s++) { 186 loopback_setup(*s, file); 187 if (file) break; 188 } 189 } 190 } 191
