linux/arch/um/drivers/cow_user.c
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   1/*
   2 * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
   3 * Licensed under the GPL
   4 */
   5
   6/*
   7 * _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
   8 * that.
   9 */
  10#include <unistd.h>
  11#include <errno.h>
  12#include <string.h>
  13#include <arpa/inet.h>
  14#include <endian.h>
  15#include "cow.h"
  16#include "cow_sys.h"
  17
  18#define PATH_LEN_V1 256
  19
  20typedef __u32 time32_t;
  21
  22struct cow_header_v1 {
  23        __s32 magic;
  24        __s32 version;
  25        char backing_file[PATH_LEN_V1];
  26        time32_t mtime;
  27        __u64 size;
  28        __s32 sectorsize;
  29} __attribute__((packed));
  30
  31/*
  32 * Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
  33 * case other systems have different values for MAXPATHLEN.
  34 *
  35 * The same must hold for V2 - we want file format compatibility, not anything
  36 * else.
  37 */
  38#define PATH_LEN_V3 4096
  39#define PATH_LEN_V2 PATH_LEN_V3
  40
  41struct cow_header_v2 {
  42        __u32 magic;
  43        __u32 version;
  44        char backing_file[PATH_LEN_V2];
  45        time32_t mtime;
  46        __u64 size;
  47        __s32 sectorsize;
  48} __attribute__((packed));
  49
  50/*
  51 * Changes from V2 -
  52 *      PATH_LEN_V3 as described above
  53 *      Explicitly specify field bit lengths for systems with different
  54 *              lengths for the usual C types.  Not sure whether char or
  55 *              time_t should be changed, this can be changed later without
  56 *              breaking compatibility
  57 *      Add alignment field so that different alignments can be used for the
  58 *              bitmap and data
  59 *      Add cow_format field to allow for the possibility of different ways
  60 *              of specifying the COW blocks.  For now, the only value is 0,
  61 *              for the traditional COW bitmap.
  62 *      Move the backing_file field to the end of the header.  This allows
  63 *              for the possibility of expanding it into the padding required
  64 *              by the bitmap alignment.
  65 *      The bitmap and data portions of the file will be aligned as specified
  66 *              by the alignment field.  This is to allow COW files to be
  67 *              put on devices with restrictions on access alignments, such as
  68 *              /dev/raw, with a 512 byte alignment restriction.  This also
  69 *              allows the data to be more aligned more strictly than on
  70 *              sector boundaries.  This is needed for ubd-mmap, which needs
  71 *              the data to be page aligned.
  72 *      Fixed (finally!) the rounding bug
  73 */
  74
  75/*
  76 * Until Dec2005, __attribute__((packed)) was left out from the below
  77 * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
  78 * align size to 8-byte alignment.  This shifted all fields above (no padding
  79 * was present on 32-bit, no other padding was added).
  80 *
  81 * However, this _can be detected_: it means that cow_format (always 0 until
  82 * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
  83 * impossible to find 4 zeros. -bb */
  84
  85struct cow_header_v3 {
  86        __u32 magic;
  87        __u32 version;
  88        __u32 mtime;
  89        __u64 size;
  90        __u32 sectorsize;
  91        __u32 alignment;
  92        __u32 cow_format;
  93        char backing_file[PATH_LEN_V3];
  94} __attribute__((packed));
  95
  96/* This is the broken layout used by some 64-bit binaries. */
  97struct cow_header_v3_broken {
  98        __u32 magic;
  99        __u32 version;
 100        __s64 mtime;
 101        __u64 size;
 102        __u32 sectorsize;
 103        __u32 alignment;
 104        __u32 cow_format;
 105        char backing_file[PATH_LEN_V3];
 106};
 107
 108/* COW format definitions - for now, we have only the usual COW bitmap */
 109#define COW_BITMAP 0
 110
 111union cow_header {
 112        struct cow_header_v1 v1;
 113        struct cow_header_v2 v2;
 114        struct cow_header_v3 v3;
 115        struct cow_header_v3_broken v3_b;
 116};
 117
 118#define COW_MAGIC 0x4f4f4f4d  /* MOOO */
 119#define COW_VERSION 3
 120
 121#define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
 122#define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
 123
 124void cow_sizes(int version, __u64 size, int sectorsize, int align,
 125               int bitmap_offset, unsigned long *bitmap_len_out,
 126               int *data_offset_out)
 127{
 128        if (version < 3) {
 129                *bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);
 130
 131                *data_offset_out = bitmap_offset + *bitmap_len_out;
 132                *data_offset_out = (*data_offset_out + sectorsize - 1) /
 133                        sectorsize;
 134                *data_offset_out *= sectorsize;
 135        }
 136        else {
 137                *bitmap_len_out = DIV_ROUND(size, sectorsize);
 138                *bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);
 139
 140                *data_offset_out = bitmap_offset + *bitmap_len_out;
 141                *data_offset_out = ROUND_UP(*data_offset_out, align);
 142        }
 143}
 144
 145static int absolutize(char *to, int size, char *from)
 146{
 147        char save_cwd[256], *slash;
 148        int remaining;
 149
 150        if (getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
 151                cow_printf("absolutize : unable to get cwd - errno = %d\n",
 152                           errno);
 153                return -1;
 154        }
 155        slash = strrchr(from, '/');
 156        if (slash != NULL) {
 157                *slash = '\0';
 158                if (chdir(from)) {
 159                        *slash = '/';
 160                        cow_printf("absolutize : Can't cd to '%s' - "
 161                                   "errno = %d\n", from, errno);
 162                        return -1;
 163                }
 164                *slash = '/';
 165                if (getcwd(to, size) == NULL) {
 166                        cow_printf("absolutize : unable to get cwd of '%s' - "
 167                               "errno = %d\n", from, errno);
 168                        return -1;
 169                }
 170                remaining = size - strlen(to);
 171                if (strlen(slash) + 1 > remaining) {
 172                        cow_printf("absolutize : unable to fit '%s' into %d "
 173                               "chars\n", from, size);
 174                        return -1;
 175                }
 176                strcat(to, slash);
 177        }
 178        else {
 179                if (strlen(save_cwd) + 1 + strlen(from) + 1 > size) {
 180                        cow_printf("absolutize : unable to fit '%s' into %d "
 181                               "chars\n", from, size);
 182                        return -1;
 183                }
 184                strcpy(to, save_cwd);
 185                strcat(to, "/");
 186                strcat(to, from);
 187        }
 188        if (chdir(save_cwd)) {
 189                cow_printf("absolutize : Can't cd to '%s' - "
 190                           "errno = %d\n", save_cwd, errno);
 191                return -1;
 192        }
 193        return 0;
 194}
 195
 196int write_cow_header(char *cow_file, int fd, char *backing_file,
 197                     int sectorsize, int alignment, unsigned long long *size)
 198{
 199        struct cow_header_v3 *header;
 200        unsigned long modtime;
 201        int err;
 202
 203        err = cow_seek_file(fd, 0);
 204        if (err < 0) {
 205                cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
 206                goto out;
 207        }
 208
 209        err = -ENOMEM;
 210        header = cow_malloc(sizeof(*header));
 211        if (header == NULL) {
 212                cow_printf("write_cow_header - failed to allocate COW V3 "
 213                           "header\n");
 214                goto out;
 215        }
 216        header->magic = htobe32(COW_MAGIC);
 217        header->version = htobe32(COW_VERSION);
 218
 219        err = -EINVAL;
 220        if (strlen(backing_file) > sizeof(header->backing_file) - 1) {
 221                /* Below, %zd is for a size_t value */
 222                cow_printf("Backing file name \"%s\" is too long - names are "
 223                           "limited to %zd characters\n", backing_file,
 224                           sizeof(header->backing_file) - 1);
 225                goto out_free;
 226        }
 227
 228        if (absolutize(header->backing_file, sizeof(header->backing_file),
 229                      backing_file))
 230                goto out_free;
 231
 232        err = os_file_modtime(header->backing_file, &modtime);
 233        if (err < 0) {
 234                cow_printf("write_cow_header - backing file '%s' mtime "
 235                           "request failed, err = %d\n", header->backing_file,
 236                           -err);
 237                goto out_free;
 238        }
 239
 240        err = cow_file_size(header->backing_file, size);
 241        if (err < 0) {
 242                cow_printf("write_cow_header - couldn't get size of "
 243                           "backing file '%s', err = %d\n",
 244                           header->backing_file, -err);
 245                goto out_free;
 246        }
 247
 248        header->mtime = htobe32(modtime);
 249        header->size = htobe64(*size);
 250        header->sectorsize = htobe32(sectorsize);
 251        header->alignment = htobe32(alignment);
 252        header->cow_format = COW_BITMAP;
 253
 254        err = cow_write_file(fd, header, sizeof(*header));
 255        if (err != sizeof(*header)) {
 256                cow_printf("write_cow_header - write of header to "
 257                           "new COW file '%s' failed, err = %d\n", cow_file,
 258                           -err);
 259                goto out_free;
 260        }
 261        err = 0;
 262 out_free:
 263        cow_free(header);
 264 out:
 265        return err;
 266}
 267
 268int file_reader(__u64 offset, char *buf, int len, void *arg)
 269{
 270        int fd = *((int *) arg);
 271
 272        return pread(fd, buf, len, offset);
 273}
 274
 275/* XXX Need to sanity-check the values read from the header */
 276
 277int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
 278                    __u32 *version_out, char **backing_file_out,
 279                    time_t *mtime_out, unsigned long long *size_out,
 280                    int *sectorsize_out, __u32 *align_out,
 281                    int *bitmap_offset_out)
 282{
 283        union cow_header *header;
 284        char *file;
 285        int err, n;
 286        unsigned long version, magic;
 287
 288        header = cow_malloc(sizeof(*header));
 289        if (header == NULL) {
 290                cow_printf("read_cow_header - Failed to allocate header\n");
 291                return -ENOMEM;
 292        }
 293        err = -EINVAL;
 294        n = (*reader)(0, (char *) header, sizeof(*header), arg);
 295        if (n < offsetof(typeof(header->v1), backing_file)) {
 296                cow_printf("read_cow_header - short header\n");
 297                goto out;
 298        }
 299
 300        magic = header->v1.magic;
 301        if (magic == COW_MAGIC)
 302                version = header->v1.version;
 303        else if (magic == be32toh(COW_MAGIC))
 304                version = be32toh(header->v1.version);
 305        /* No error printed because the non-COW case comes through here */
 306        else goto out;
 307
 308        *version_out = version;
 309
 310        if (version == 1) {
 311                if (n < sizeof(header->v1)) {
 312                        cow_printf("read_cow_header - failed to read V1 "
 313                                   "header\n");
 314                        goto out;
 315                }
 316                *mtime_out = header->v1.mtime;
 317                *size_out = header->v1.size;
 318                *sectorsize_out = header->v1.sectorsize;
 319                *bitmap_offset_out = sizeof(header->v1);
 320                *align_out = *sectorsize_out;
 321                file = header->v1.backing_file;
 322        }
 323        else if (version == 2) {
 324                if (n < sizeof(header->v2)) {
 325                        cow_printf("read_cow_header - failed to read V2 "
 326                                   "header\n");
 327                        goto out;
 328                }
 329                *mtime_out = be32toh(header->v2.mtime);
 330                *size_out = be64toh(header->v2.size);
 331                *sectorsize_out = be32toh(header->v2.sectorsize);
 332                *bitmap_offset_out = sizeof(header->v2);
 333                *align_out = *sectorsize_out;
 334                file = header->v2.backing_file;
 335        }
 336        /* This is very subtle - see above at union cow_header definition */
 337        else if (version == 3 && (*((int*)header->v3.backing_file) != 0)) {
 338                if (n < sizeof(header->v3)) {
 339                        cow_printf("read_cow_header - failed to read V3 "
 340                                   "header\n");
 341                        goto out;
 342                }
 343                *mtime_out = be32toh(header->v3.mtime);
 344                *size_out = be64toh(header->v3.size);
 345                *sectorsize_out = be32toh(header->v3.sectorsize);
 346                *align_out = be32toh(header->v3.alignment);
 347                if (*align_out == 0) {
 348                        cow_printf("read_cow_header - invalid COW header, "
 349                                   "align == 0\n");
 350                }
 351                *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
 352                file = header->v3.backing_file;
 353        }
 354        else if (version == 3) {
 355                cow_printf("read_cow_header - broken V3 file with"
 356                           " 64-bit layout - recovering content.\n");
 357
 358                if (n < sizeof(header->v3_b)) {
 359                        cow_printf("read_cow_header - failed to read V3 "
 360                                   "header\n");
 361                        goto out;
 362                }
 363
 364                /*
 365                 * this was used until Dec2005 - 64bits are needed to represent
 366                 * 2038+. I.e. we can safely do this truncating cast.
 367                 *
 368                 * Additionally, we must use be32toh() instead of be64toh(), since
 369                 * the program used to use the former (tested - I got mtime
 370                 * mismatch "0 vs whatever").
 371                 *
 372                 * Ever heard about bug-to-bug-compatibility ? ;-) */
 373                *mtime_out = (time32_t) be32toh(header->v3_b.mtime);
 374
 375                *size_out = be64toh(header->v3_b.size);
 376                *sectorsize_out = be32toh(header->v3_b.sectorsize);
 377                *align_out = be32toh(header->v3_b.alignment);
 378                if (*align_out == 0) {
 379                        cow_printf("read_cow_header - invalid COW header, "
 380                                   "align == 0\n");
 381                }
 382                *bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
 383                file = header->v3_b.backing_file;
 384        }
 385        else {
 386                cow_printf("read_cow_header - invalid COW version\n");
 387                goto out;
 388        }
 389        err = -ENOMEM;
 390        *backing_file_out = cow_strdup(file);
 391        if (*backing_file_out == NULL) {
 392                cow_printf("read_cow_header - failed to allocate backing "
 393                           "file\n");
 394                goto out;
 395        }
 396        err = 0;
 397 out:
 398        cow_free(header);
 399        return err;
 400}
 401
 402int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
 403                  int alignment, int *bitmap_offset_out,
 404                  unsigned long *bitmap_len_out, int *data_offset_out)
 405{
 406        unsigned long long size, offset;
 407        char zero = 0;
 408        int err;
 409
 410        err = write_cow_header(cow_file, fd, backing_file, sectorsize,
 411                               alignment, &size);
 412        if (err)
 413                goto out;
 414
 415        *bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
 416        cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
 417                  bitmap_len_out, data_offset_out);
 418
 419        offset = *data_offset_out + size - sizeof(zero);
 420        err = cow_seek_file(fd, offset);
 421        if (err < 0) {
 422                cow_printf("cow bitmap lseek failed : err = %d\n", -err);
 423                goto out;
 424        }
 425
 426        /*
 427         * does not really matter how much we write it is just to set EOF
 428         * this also sets the entire COW bitmap
 429         * to zero without having to allocate it
 430         */
 431        err = cow_write_file(fd, &zero, sizeof(zero));
 432        if (err != sizeof(zero)) {
 433                cow_printf("Write of bitmap to new COW file '%s' failed, "
 434                           "err = %d\n", cow_file, -err);
 435                if (err >= 0)
 436                        err = -EINVAL;
 437                goto out;
 438        }
 439
 440        return 0;
 441 out:
 442        return err;
 443}
 444
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