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 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
  99/* Returns opened fd to the loop device, <0 on error.
 100 * *device is loop device to use, or if *device==NULL finds a loop device to
 101 * mount it on and sets *device to a strdup of that loop device name.
 102 */
 103int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset,
 104                unsigned long long sizelimit, unsigned flags)
 105{
 106        char dev[LOOP_NAMESIZE];
 107        char *try;
 108        bb_loop_info loopinfo;
 109        struct stat statbuf;
 110        int i, lfd, ffd, mode, rc;
 111
 112        /* Open the file.  Barf if this doesn't work.  */
 113        mode = (flags & BB_LO_FLAGS_READ_ONLY) ? O_RDONLY : O_RDWR;
 114 open_ffd:
 115        ffd = open(file, mode);
 116        if (ffd < 0) {
 117                if (mode != O_RDONLY) {
 118                        mode = O_RDONLY;
 119                        goto open_ffd;
 120                }
 121                return -errno;
 122        }
 123
 124        try = *device;
 125        if (!try) {
 126 get_free_loopN:
 127                i = get_free_loop();
 128                if (i == -1) {
 129                        close(ffd);
 130                        return -1; /* no free loop devices */
 131                }
 132                if (i >= 0) {
 133                        try = xasprintf(LOOP_FORMAT, i);
 134                        goto open_lfd;
 135                }
 136                /* i == -2: no /dev/loop-control. Do an old-style search for a free device */
 137                try = dev;
 138        }
 139
 140        /* Find a loop device */
 141        /* 0xfffff is a max possible minor number in Linux circa 2010 */
 142        for (i = 0; i <= 0xfffff; i++) {
 143                sprintf(dev, LOOP_FORMAT, i);
 144
 145                IF_FEATURE_MOUNT_LOOP_CREATE(errno = 0;)
 146                if (stat(try, &statbuf) != 0 || !S_ISBLK(statbuf.st_mode)) {
 147                        if (ENABLE_FEATURE_MOUNT_LOOP_CREATE
 148                         && errno == ENOENT
 149                         && try == dev
 150                        ) {
 151                                /* Node doesn't exist, try to create it */
 152                                if (mknod(dev, S_IFBLK|0644, makedev(7, i)) == 0)
 153                                        goto open_lfd;
 154                        }
 155                        /* Ran out of block devices, return failure */
 156                        rc = -1;
 157                        break;
 158                }
 159 open_lfd:
 160                /* Open the sucker and check its loopiness */
 161                lfd = rc = open(try, mode);
 162                if (lfd < 0 && errno == EROFS) {
 163                        mode = O_RDONLY;
 164                        lfd = rc = open(try, mode);
 165                }
 166                if (lfd < 0) {
 167                        if (errno == ENXIO) {
 168                                /* Happens if loop module is not loaded */
 169                                /* rc is -1; */
 170                                break;
 171                        }
 172                        goto try_next_loopN;
 173                }
 174
 175                rc = ioctl(lfd, BB_LOOP_GET_STATUS, &loopinfo);
 176
 177                /* If device is free, try to claim it */
 178                if (rc && errno == ENXIO) {
 179                        /* Associate free loop device with file */
 180                        if (ioctl(lfd, LOOP_SET_FD, ffd)) {
 181                                /* Ouch. Are we racing with other mount? */
 182                                if (!*device   /* yes */
 183                                 && try != dev /* tried a _kernel-offered_ loopN? */
 184                                ) {
 185                                        free(try);
 186                                        close(lfd);
 187//TODO: add "if (--failcount != 0) ..."?
 188                                        goto get_free_loopN;
 189                                }
 190                                goto close_and_try_next_loopN;
 191                        }
 192                        memset(&loopinfo, 0, sizeof(loopinfo));
 193                        safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
 194                        loopinfo.lo_offset = offset;
 195                        loopinfo.lo_sizelimit = sizelimit;
 196                        /*
 197                         * Used by mount to set LO_FLAGS_AUTOCLEAR.
 198                         * LO_FLAGS_READ_ONLY is not set because RO is controlled by open type of the file.
 199                         * Note that closing LO_FLAGS_AUTOCLEARed lfd before mount
 200                         * is wrong (would free the loop device!)
 201                         */
 202                        loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY);
 203                        rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
 204                        if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {
 205                                /* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */
 206                                /* (this code path is not tested) */
 207                                loopinfo.lo_flags -= BB_LO_FLAGS_AUTOCLEAR;
 208                                rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
 209                        }
 210                        if (rc == 0) {
 211                                /* SUCCESS! */
 212                                if (try != dev) /* tried a kernel-offered free loopN? */
 213                                        *device = try; /* malloced */
 214                                if (!*device)   /* was looping in search of free "/dev/loopN"? */
 215                                        *device = xstrdup(dev);
 216                                rc = lfd; /* return this */
 217                                break;
 218                        }
 219                        /* failure, undo LOOP_SET_FD */
 220                        ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
 221                }
 222                /* else: device is not free (rc == 0) or error other than ENXIO */
 223 close_and_try_next_loopN:
 224                close(lfd);
 225 try_next_loopN:
 226                rc = -1;
 227                if (*device) /* was looking for a particular "/dev/loopN"? */
 228                        break; /* yes, do not try other names */
 229        } /* for() */
 230
 231        close(ffd);
 232        return rc;
 233}
 234