LXR busybox/libbb/loop.c

   1/* vi: set sw=4 ts=4: */
   2/*
   3 * Utility routines.
   4 *
   5 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
   6 * Copyright (C) 2005 by Rob Landley <rob@landley.net>
   7 *
   8 * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
   9 */
  10
  11#include "libbb.h"
  12
  13/* For 2.6, use the cleaned up header to get the 64 bit API. */
  14#include <linux/version.h>
  15#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,0)
  16#include <linux/loop.h>
  17typedef struct loop_info64 bb_loop_info;
  18#define BB_LOOP_SET_STATUS LOOP_SET_STATUS64
  19#define BB_LOOP_GET_STATUS LOOP_GET_STATUS64
  20
  21/* For 2.4 and earlier, use the 32 bit API (and don't trust the headers) */
  22#else
  23/* Stuff stolen from linux/loop.h for 2.4 and earlier kernels*/
  24#include <linux/posix_types.h>
  25#define LO_NAME_SIZE        64
  26#define LO_KEY_SIZE         32
  27#define LOOP_SET_FD         0x4C00
  28#define LOOP_CLR_FD         0x4C01
  29#define BB_LOOP_SET_STATUS  0x4C02
  30#define BB_LOOP_GET_STATUS  0x4C03
  31typedef struct {
  32        int                lo_number;
  33        __kernel_dev_t     lo_device;
  34        unsigned long      lo_inode;
  35        __kernel_dev_t     lo_rdevice;
  36        int                lo_offset;
  37        int                lo_encrypt_type;
  38        int                lo_encrypt_key_size;
  39        int                lo_flags;
  40        char               lo_file_name[LO_NAME_SIZE];
  41        unsigned char      lo_encrypt_key[LO_KEY_SIZE];
  42        unsigned long      lo_init[2];
  43        char               reserved[4];
  44} bb_loop_info;
  45#endif
  46
  47char* FAST_FUNC query_loop(const char *device)
  48{
  49        int fd;
  50        bb_loop_info loopinfo;
  51        char *dev = 0;
  52
  53        fd = open(device, O_RDONLY);
  54        if (fd < 0) return 0;
  55        if (!ioctl(fd, BB_LOOP_GET_STATUS, &loopinfo))
  56                dev = xasprintf("%ld %s", (long) loopinfo.lo_offset,
  57                                (char *)loopinfo.lo_file_name);
  58        close(fd);
  59
  60        return dev;
  61}
  62
  63
  64int FAST_FUNC del_loop(const char *device)
  65{
  66        int fd, rc;
  67
  68        fd = open(device, O_RDONLY);
  69        if (fd < 0) return 1;
  70        rc = ioctl(fd, LOOP_CLR_FD, 0);
  71        close(fd);
  72
  73        return rc;
  74}
  75
  76/* Returns 0 if mounted RW, 1 if mounted read-only, <0 for error.
  77   *device is loop device to use, or if *device==NULL finds a loop device to
  78   mount it on and sets *device to a strdup of that loop device name.  This
  79   search will re-use an existing loop device already bound to that
  80   file/offset if it finds one.
  81 */
  82int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset)
  83{
  84        char dev[LOOP_NAMESIZE];
  85        char *try;
  86        bb_loop_info loopinfo;
  87        struct stat statbuf;
  88        int i, dfd, ffd, mode, rc = -1;
  89
  90        /* Open the file.  Barf if this doesn't work.  */
  91        mode = O_RDWR;
  92        ffd = open(file, mode);
  93        if (ffd < 0) {
  94                mode = O_RDONLY;
  95                ffd = open(file, mode);
  96                if (ffd < 0)
  97                        return -errno;
  98        }
  99
 100        /* Find a loop device.  */
 101        try = *device ? : dev;
 102        for (i = 0; rc; i++) {
 103                sprintf(dev, LOOP_FORMAT, i);
 104
 105                /* Ran out of block devices, return failure.  */
 106                if (stat(try, &statbuf) || !S_ISBLK(statbuf.st_mode)) {
 107                        rc = -ENOENT;
 108                        break;
 109                }
 110                /* Open the sucker and check its loopiness.  */
 111                dfd = open(try, mode);
 112                if (dfd < 0 && errno == EROFS) {
 113                        mode = O_RDONLY;
 114                        dfd = open(try, mode);
 115                }
 116                if (dfd < 0)
 117                        goto try_again;
 118
 119                rc = ioctl(dfd, BB_LOOP_GET_STATUS, &loopinfo);
 120
 121                /* If device is free, claim it.  */
 122                if (rc && errno == ENXIO) {
 123                        memset(&loopinfo, 0, sizeof(loopinfo));
 124                        safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
 125                        loopinfo.lo_offset = offset;
 126                        /* Associate free loop device with file.  */
 127                        if (!ioctl(dfd, LOOP_SET_FD, ffd)) {
 128                                if (!ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo))
 129                                        rc = 0;
 130                                else
 131                                        ioctl(dfd, LOOP_CLR_FD, 0);
 132                        }
 133
 134                /* If this block device already set up right, re-use it.
 135                   (Yes this is racy, but associating two loop devices with the same
 136                   file isn't pretty either.  In general, mounting the same file twice
 137                   without using losetup manually is problematic.)
 138                 */
 139                } else if (strcmp(file, (char *)loopinfo.lo_file_name) != 0
 140                || offset != loopinfo.lo_offset) {
 141                        rc = -1;
 142                }
 143                close(dfd);
 144 try_again:
 145                if (*device) break;
 146        }
 147        close(ffd);
 148        if (!rc) {
 149                if (!*device)
 150                        *device = xstrdup(dev);
 151                return (mode == O_RDONLY); /* 1:ro, 0:rw */
 152        }
 153        return rc;
 154}
 155