LXR toybox/toys/other/losetup.c

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