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 GPLv2 or later, see file LICENSE in this source tree.
   9 */
  10#include "libbb.h"
  11#include <linux/version.h>
  12
  13#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,0)
  14
  15/* For 2.6, use the cleaned up header to get the 64 bit API. */
  16// Commented out per Rob's request
  17//# include "fix_u32.h" /* some old toolchains need __u64 for linux/loop.h */
  18# include <linux/loop.h>
  19typedef struct loop_info64 bb_loop_info;
  20# define BB_LOOP_SET_STATUS LOOP_SET_STATUS64
  21# define BB_LOOP_GET_STATUS LOOP_GET_STATUS64
  22
  23#else
  24
  25/* For 2.4 and earlier, use the 32 bit API (and don't trust the headers) */
  26/* Stuff stolen from linux/loop.h for 2.4 and earlier kernels */
  27# include <linux/posix_types.h>
  28# define LO_NAME_SIZE        64
  29# define LO_KEY_SIZE         32
  30# define LOOP_SET_FD         0x4C00
  31# define LOOP_CLR_FD         0x4C01
  32# define BB_LOOP_SET_STATUS  0x4C02
  33# define BB_LOOP_GET_STATUS  0x4C03
  34typedef struct {
  35        int                lo_number;
  36        __kernel_dev_t     lo_device;
  37        unsigned long      lo_inode;
  38        __kernel_dev_t     lo_rdevice;
  39        int                lo_offset;
  40        int                lo_encrypt_type;
  41        int                lo_encrypt_key_size;
  42        int                lo_flags;
  43        char               lo_file_name[LO_NAME_SIZE];
  44        unsigned char      lo_encrypt_key[LO_KEY_SIZE];
  45        unsigned long      lo_init[2];
  46        char               reserved[4];
  47} bb_loop_info;
  48#endif
  49
  50char* FAST_FUNC query_loop(const char *device)
  51{
  52        int fd;
  53        bb_loop_info loopinfo;
  54        char *dev = NULL;
  55
  56        fd = open(device, O_RDONLY);
  57        if (fd >= 0) {
  58                if (ioctl(fd, BB_LOOP_GET_STATUS, &loopinfo) == 0) {
  59                        dev = xasprintf("%"OFF_FMT"u %s", (off_t) loopinfo.lo_offset,
  60                                        (char *)loopinfo.lo_file_name);
  61                }
  62                close(fd);
  63        }
  64
  65        return dev;
  66}
  67
  68int FAST_FUNC del_loop(const char *device)
  69{
  70        int fd, rc;
  71
  72        fd = open(device, O_RDONLY);
  73        if (fd < 0)
  74                return fd; /* -1 */
  75        rc = ioctl(fd, LOOP_CLR_FD, 0);
  76        close(fd);
  77
  78        return rc;
  79}
  80
  81/* Obtain an unused loop device number */
  82int FAST_FUNC get_free_loop(void)
  83{
  84        int fd;
  85        int loopdevno;
  86
  87        fd = open("/dev/loop-control", O_RDWR | O_CLOEXEC);
  88        if (fd == -1)
  89                return fd - 1; /* -2: "no /dev/loop-control" */
  90
  91#ifndef LOOP_CTL_GET_FREE
  92# define LOOP_CTL_GET_FREE 0x4C82
  93#endif
  94        loopdevno = ioctl(fd, LOOP_CTL_GET_FREE);
  95        close(fd);
  96        return loopdevno; /* can be -1 if error */
  97}
  98
  99static int get_next_free_loop(char *dev, int id)
 100{
 101        int loopdevno;
 102
 103        loopdevno = get_free_loop();
 104        if (loopdevno != -1) {
 105                /* loopdevno is -2 (use id) or >= 0 (use id = loopdevno): */
 106                if (loopdevno >= 0)
 107                        id = loopdevno;
 108                sprintf(dev, LOOP_FORMAT, id);
 109        }
 110        return loopdevno;
 111}
 112
 113#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
 114# define LOOP_CONFIGURE 0x4C0A
 115struct bb_loop_config {
 116        uint32_t fd;
 117        uint32_t block_size;
 118        struct loop_info64 info;
 119        uint64_t __reserved[8];
 120};
 121#endif
 122
 123static int set_loopdev_params(int lfd,
 124                int ffd, const char *file,
 125                unsigned long long offset,
 126                unsigned long long sizelimit,
 127                unsigned flags)
 128{
 129        int rc;
 130#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
 131        struct bb_loop_config lconfig;
 132# define loopinfo lconfig.info
 133#else
 134        bb_loop_info loopinfo;
 135#endif
 136
 137        rc = ioctl(lfd, BB_LOOP_GET_STATUS, &loopinfo);
 138
 139        /* If device is free, try to claim it */
 140        if (rc && errno == ENXIO) {
 141#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
 142                memset(&lconfig, 0, sizeof(lconfig));
 143#else
 144                memset(&loopinfo, 0, sizeof(loopinfo));
 145#endif
 146                safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
 147                loopinfo.lo_offset = offset;
 148                loopinfo.lo_sizelimit = sizelimit;
 149                /*
 150                 * LO_FLAGS_READ_ONLY is not set because RO is controlled
 151                 * by open type of the lfd.
 152                 */
 153                loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY);
 154
 155#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
 156                lconfig.fd = ffd;
 157                rc = ioctl(lfd, LOOP_CONFIGURE, &lconfig);
 158                if (rc == 0)
 159                        return rc; /* SUCCESS! */
 160# if ENABLE_TRY_LOOP_CONFIGURE
 161                if (errno != EINVAL)
 162                        return rc; /* error other than old kernel */
 163                /* Old kernel, fall through into old way to do it: */
 164# endif
 165#endif
 166#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_NO_LOOP_CONFIGURE
 167                /* Associate free loop device with file */
 168                rc = ioctl(lfd, LOOP_SET_FD, ffd);
 169                if (rc != 0) {
 170                        /* Ouch... race: the device already has a fd */
 171                        return rc;
 172                }
 173                rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
 174                if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {
 175                        /* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */
 176                        /* (this code path is not tested) */
 177                        loopinfo.lo_flags -= BB_LO_FLAGS_AUTOCLEAR;
 178                        rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
 179                }
 180                if (rc == 0)
 181                        return rc; /* SUCCESS! */
 182                /* failure, undo LOOP_SET_FD */
 183                ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
 184#endif
 185        }
 186        return -1;
 187#undef loopinfo
 188}
 189
 190/* Returns opened fd to the loop device, <0 on error.
 191 * *device is loop device to use, or if *device==NULL finds a loop device to
 192 * mount it on and sets *device to a strdup of that loop device name.
 193 */
 194int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset,
 195                unsigned long long sizelimit, unsigned flags)
 196{
 197        char dev[LOOP_NAMESIZE];
 198        char *try;
 199        struct stat statbuf;
 200        int i, lfd, ffd, mode, rc;
 201
 202        /* Open the file.  Barf if this doesn't work.  */
 203        mode = (flags & BB_LO_FLAGS_READ_ONLY) ? O_RDONLY : O_RDWR;
 204 open_ffd:
 205        ffd = open(file, mode);
 206        if (ffd < 0) {
 207                if (mode != O_RDONLY) {
 208                        mode = O_RDONLY;
 209                        goto open_ffd;
 210                }
 211                return -errno;
 212        }
 213
 214        try = *device;
 215        if (!try) {
 216                try = dev;
 217        }
 218
 219        /* Find a loop device */
 220        /* 0xfffff is a max possible minor number in Linux circa 2010 */
 221        for (i = 0; i <= 0xfffff; i++) {
 222                if (!*device) {
 223                        rc = get_next_free_loop(dev, i);
 224                        if (rc == -1)
 225                                break; /* no free loop devices (or other error in LOOP_CTL_GET_FREE) */
 226                        if (rc >= 0)
 227                                /* /dev/loop-control gave us the next free /dev/loopN */
 228                                goto open_lfd;
 229                        /* else: sequential /dev/loopN, needs to be tested/maybe_created */
 230                }
 231
 232                IF_FEATURE_MOUNT_LOOP_CREATE(errno = 0;)
 233                if (stat(try, &statbuf) != 0 || !S_ISBLK(statbuf.st_mode)) {
 234                        if (ENABLE_FEATURE_MOUNT_LOOP_CREATE
 235                         && errno == ENOENT
 236                         && (!*device)
 237                        ) {
 238                                /* Node doesn't exist, try to create it */
 239                                if (mknod(dev, S_IFBLK|0644, makedev(7, i)) == 0)
 240                                        goto open_lfd;
 241                        }
 242                        /* Ran out of block devices, return failure */
 243                        rc = -1;
 244                        break;
 245                }
 246 open_lfd:
 247                /* Open the sucker and check its loopiness */
 248                lfd = rc = open(try, mode);
 249                if (lfd < 0 && errno == EROFS) {
 250                        mode = O_RDONLY;
 251                        lfd = rc = open(try, mode);
 252                }
 253                if (lfd < 0) {
 254                        if (errno == ENXIO) {
 255                                /* Happens if loop module is not loaded */
 256                                /* rc is -1; */
 257                                break;
 258                        }
 259                        goto try_next_loopN;
 260                }
 261
 262                rc = set_loopdev_params(lfd, ffd, file, offset, sizelimit, flags);
 263                if (rc == 0) {
 264                        /* SUCCESS! */
 265                        if (!*device)
 266                                *device = xstrdup(dev);
 267                        /* Note: mount asks for LO_FLAGS_AUTOCLEAR loopdev.
 268                         * Closing LO_FLAGS_AUTOCLEARed lfd before mount
 269                         * is wrong (would free the loop device!),
 270                         * this is why we return without closing it.
 271                         */
 272                        rc = lfd; /* return this */
 273                        break;
 274                }
 275                close(lfd);
 276 try_next_loopN:
 277                rc = -1;
 278                if (*device) /* was looking for a particular "/dev/loopN"? */
 279                        break; /* yes, do not try other names */
 280        } /* for() */
 281
 282        close(ffd);
 283        return rc;
 284}
 285