arch/um/drivers/cow_user.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
   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
  20 /* unsigned time_t works until year 2106 */
  21 typedef __u32 time32_t;
  22
  23 struct cow_header_v1 {
  24         __s32 magic;
  25         __s32 version;
  26         char backing_file[PATH_LEN_V1];
  27         time32_t mtime;
  28         __u64 size;
  29         __s32 sectorsize;
  30 } __attribute__((packed));
  31
  32 /*
  33  * Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
  34  * case other systems have different values for MAXPATHLEN.
  35  *
  36  * The same must hold for V2 - we want file format compatibility, not anything
  37  * else.
  38  */
  39 #define PATH_LEN_V3 4096
  40 #define PATH_LEN_V2 PATH_LEN_V3
  41
  42 struct cow_header_v2 {
  43         __u32 magic;
  44         __u32 version;
  45         char backing_file[PATH_LEN_V2];
  46         time32_t mtime;
  47         __u64 size;
  48         __s32 sectorsize;
  49 } __attribute__((packed));
  50
  51 /*
  52  * Changes from V2 -
  53  *      PATH_LEN_V3 as described above
  54  *      Explicitly specify field bit lengths for systems with different
  55  *              lengths for the usual C types.  Not sure whether char or
  56  *              time_t should be changed, this can be changed later without
  57  *              breaking compatibility
  58  *      Add alignment field so that different alignments can be used for the
  59  *              bitmap and data
  60  *      Add cow_format field to allow for the possibility of different ways
  61  *              of specifying the COW blocks.  For now, the only value is 0,
  62  *              for the traditional COW bitmap.
  63  *      Move the backing_file field to the end of the header.  This allows
  64  *              for the possibility of expanding it into the padding required
  65  *              by the bitmap alignment.
  66  *      The bitmap and data portions of the file will be aligned as specified
  67  *              by the alignment field.  This is to allow COW files to be
  68  *              put on devices with restrictions on access alignments, such as
  69  *              /dev/raw, with a 512 byte alignment restriction.  This also
  70  *              allows the data to be more aligned more strictly than on
  71  *              sector boundaries.  This is needed for ubd-mmap, which needs
  72  *              the data to be page aligned.
  73  *      Fixed (finally!) the rounding bug
  74  */
  75
  76 /*
  77  * Until Dec2005, __attribute__((packed)) was left out from the below
  78  * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
  79  * align size to 8-byte alignment.  This shifted all fields above (no padding
  80  * was present on 32-bit, no other padding was added).
  81  *
  82  * However, this _can be detected_: it means that cow_format (always 0 until
  83  * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
  84  * impossible to find 4 zeros. -bb */
  85
  86 struct cow_header_v3 {
  87         __u32 magic;
  88         __u32 version;
  89         __u32 mtime;
  90         __u64 size;
  91         __u32 sectorsize;
  92         __u32 alignment;
  93         __u32 cow_format;
  94         char backing_file[PATH_LEN_V3];
  95 } __attribute__((packed));
  96
  97 /* This is the broken layout used by some 64-bit binaries. */
  98 struct cow_header_v3_broken {
  99         __u32 magic;
 100         __u32 version;
 101         __s64 mtime;
 102         __u64 size;
 103         __u32 sectorsize;
 104         __u32 alignment;
 105         __u32 cow_format;
 106         char backing_file[PATH_LEN_V3];
 107 };
 108
 109 /* COW format definitions - for now, we have only the usual COW bitmap */
 110 #define COW_BITMAP 0
 111
 112 union cow_header {
 113         struct cow_header_v1 v1;
 114         struct cow_header_v2 v2;
 115         struct cow_header_v3 v3;
 116         struct cow_header_v3_broken v3_b;
 117 };
 118
 119 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
 120 #define COW_VERSION 3
 121
 122 #define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
 123 #define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
 124
 125 void cow_sizes(int version, __u64 size, int sectorsize, int align,
 126                int bitmap_offset, unsigned long *bitmap_len_out,
 127                int *data_offset_out)
 128 {
 129         if (version < 3) {
 130                 *bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);
 131
 132                 *data_offset_out = bitmap_offset + *bitmap_len_out;
 133                 *data_offset_out = (*data_offset_out + sectorsize - 1) /
 134                         sectorsize;
 135                 *data_offset_out *= sectorsize;
 136         }
 137         else {
 138                 *bitmap_len_out = DIV_ROUND(size, sectorsize);
 139                 *bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);
 140
 141                 *data_offset_out = bitmap_offset + *bitmap_len_out;
 142                 *data_offset_out = ROUND_UP(*data_offset_out, align);
 143         }
 144 }
 145
 146 static int absolutize(char *to, int size, char *from)
 147 {
 148         char save_cwd[256], *slash;
 149         int remaining;
 150
 151         if (getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
 152                 cow_printf("absolutize : unable to get cwd - errno = %d\n",
 153                            errno);
 154                 return -1;
 155         }
 156         slash = strrchr(from, '/');
 157         if (slash != NULL) {
 158                 *slash = '\0';
 159                 if (chdir(from)) {
 160                         *slash = '/';
 161                         cow_printf("absolutize : Can't cd to '%s' - "
 162                                    "errno = %d\n", from, errno);
 163                         return -1;
 164                 }
 165                 *slash = '/';
 166                 if (getcwd(to, size) == NULL) {
 167                         cow_printf("absolutize : unable to get cwd of '%s' - "
 168                                "errno = %d\n", from, errno);
 169                         return -1;
 170                 }
 171                 remaining = size - strlen(to);
 172                 if (strlen(slash) + 1 > remaining) {
 173                         cow_printf("absolutize : unable to fit '%s' into %d "
 174                                "chars\n", from, size);
 175                         return -1;
 176                 }
 177                 strcat(to, slash);
 178         }
 179         else {
 180                 if (strlen(save_cwd) + 1 + strlen(from) + 1 > size) {
 181                         cow_printf("absolutize : unable to fit '%s' into %d "
 182                                "chars\n", from, size);
 183                         return -1;
 184                 }
 185                 strcpy(to, save_cwd);
 186                 strcat(to, "/");
 187                 strcat(to, from);
 188         }
 189         if (chdir(save_cwd)) {
 190                 cow_printf("absolutize : Can't cd to '%s' - "
 191                            "errno = %d\n", save_cwd, errno);
 192                 return -1;
 193         }
 194         return 0;
 195 }
 196
 197 int write_cow_header(char *cow_file, int fd, char *backing_file,
 198                      int sectorsize, int alignment, unsigned long long *size)
 199 {
 200         struct cow_header_v3 *header;
 201         long long modtime;
 202         int err;
 203
 204         err = cow_seek_file(fd, 0);
 205         if (err < 0) {
 206                 cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
 207                 goto out;
 208         }
 209
 210         err = -ENOMEM;
 211         header = cow_malloc(sizeof(*header));
 212         if (header == NULL) {
 213                 cow_printf("write_cow_header - failed to allocate COW V3 "
 214                            "header\n");
 215                 goto out;
 216         }
 217         header->magic = htobe32(COW_MAGIC);
 218         header->version = htobe32(COW_VERSION);
 219
 220         err = -EINVAL;
 221         if (strlen(backing_file) > sizeof(header->backing_file) - 1) {
 222                 /* Below, %zd is for a size_t value */
 223                 cow_printf("Backing file name \"%s\" is too long - names are "
 224                            "limited to %zd characters\n", backing_file,
 225                            sizeof(header->backing_file) - 1);
 226                 goto out_free;
 227         }
 228
 229         if (absolutize(header->backing_file, sizeof(header->backing_file),
 230                       backing_file))
 231                 goto out_free;
 232
 233         err = os_file_modtime(header->backing_file, &modtime);
 234         if (err < 0) {
 235                 cow_printf("write_cow_header - backing file '%s' mtime "
 236                            "request failed, err = %d\n", header->backing_file,
 237                            -err);
 238                 goto out_free;
 239         }
 240
 241         err = cow_file_size(header->backing_file, size);
 242         if (err < 0) {
 243                 cow_printf("write_cow_header - couldn't get size of "
 244                            "backing file '%s', err = %d\n",
 245                            header->backing_file, -err);
 246                 goto out_free;
 247         }
 248
 249         header->mtime = htobe32(modtime);
 250         header->size = htobe64(*size);
 251         header->sectorsize = htobe32(sectorsize);
 252         header->alignment = htobe32(alignment);
 253         header->cow_format = COW_BITMAP;
 254
 255         err = cow_write_file(fd, header, sizeof(*header));
 256         if (err != sizeof(*header)) {
 257                 cow_printf("write_cow_header - write of header to "
 258                            "new COW file '%s' failed, err = %d\n", cow_file,
 259                            -err);
 260                 goto out_free;
 261         }
 262         err = 0;
 263  out_free:
 264         cow_free(header);
 265  out:
 266         return err;
 267 }
 268
 269 int file_reader(__u64 offset, char *buf, int len, void *arg)
 270 {
 271         int fd = *((int *) arg);
 272
 273         return pread(fd, buf, len, offset);
 274 }
 275
 276 /* XXX Need to sanity-check the values read from the header */
 277
 278 int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
 279                     __u32 *version_out, char **backing_file_out,
 280                     long long *mtime_out, unsigned long long *size_out,
 281                     int *sectorsize_out, __u32 *align_out,
 282                     int *bitmap_offset_out)
 283 {
 284         union cow_header *header;
 285         char *file;
 286         int err, n;
 287         unsigned long version, magic;
 288
 289         header = cow_malloc(sizeof(*header));
 290         if (header == NULL) {
 291                 cow_printf("read_cow_header - Failed to allocate header\n");
 292                 return -ENOMEM;
 293         }
 294         err = -EINVAL;
 295         n = (*reader)(0, (char *) header, sizeof(*header), arg);
 296         if (n < offsetof(typeof(header->v1), backing_file)) {
 297                 cow_printf("read_cow_header - short header\n");
 298                 goto out;
 299         }
 300
 301         magic = header->v1.magic;
 302         if (magic == COW_MAGIC)
 303                 version = header->v1.version;
 304         else if (magic == be32toh(COW_MAGIC))
 305                 version = be32toh(header->v1.version);
 306         /* No error printed because the non-COW case comes through here */
 307         else goto out;
 308
 309         *version_out = version;
 310
 311         if (version == 1) {
 312                 if (n < sizeof(header->v1)) {
 313                         cow_printf("read_cow_header - failed to read V1 "
 314                                    "header\n");
 315                         goto out;
 316                 }
 317                 *mtime_out = header->v1.mtime;
 318                 *size_out = header->v1.size;
 319                 *sectorsize_out = header->v1.sectorsize;
 320                 *bitmap_offset_out = sizeof(header->v1);
 321                 *align_out = *sectorsize_out;
 322                 file = header->v1.backing_file;
 323         }
 324         else if (version == 2) {
 325                 if (n < sizeof(header->v2)) {
 326                         cow_printf("read_cow_header - failed to read V2 "
 327                                    "header\n");
 328                         goto out;
 329                 }
 330                 *mtime_out = be32toh(header->v2.mtime);
 331                 *size_out = be64toh(header->v2.size);
 332                 *sectorsize_out = be32toh(header->v2.sectorsize);
 333                 *bitmap_offset_out = sizeof(header->v2);
 334                 *align_out = *sectorsize_out;
 335                 file = header->v2.backing_file;
 336         }
 337         /* This is very subtle - see above at union cow_header definition */
 338         else if (version == 3 && (*((int*)header->v3.backing_file) != 0)) {
 339                 if (n < sizeof(header->v3)) {
 340                         cow_printf("read_cow_header - failed to read V3 "
 341                                    "header\n");
 342                         goto out;
 343                 }
 344                 *mtime_out = be32toh(header->v3.mtime);
 345                 *size_out = be64toh(header->v3.size);
 346                 *sectorsize_out = be32toh(header->v3.sectorsize);
 347                 *align_out = be32toh(header->v3.alignment);
 348                 if (*align_out == 0) {
 349                         cow_printf("read_cow_header - invalid COW header, "
 350                                    "align == 0\n");
 351                 }
 352                 *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
 353                 file = header->v3.backing_file;
 354         }
 355         else if (version == 3) {
 356                 cow_printf("read_cow_header - broken V3 file with"
 357                            " 64-bit layout - recovering content.\n");
 358
 359                 if (n < sizeof(header->v3_b)) {
 360                         cow_printf("read_cow_header - failed to read V3 "
 361                                    "header\n");
 362                         goto out;
 363                 }
 364
 365                 /*
 366                  * this was used until Dec2005 - 64bits are needed to represent
 367                  * 2106+. I.e. we can safely do this truncating cast.
 368                  *
 369                  * Additionally, we must use be32toh() instead of be64toh(), since
 370                  * the program used to use the former (tested - I got mtime
 371                  * mismatch "0 vs whatever").
 372                  *
 373                  * Ever heard about bug-to-bug-compatibility ? ;-) */
 374                 *mtime_out = (time32_t) be32toh(header->v3_b.mtime);
 375
 376                 *size_out = be64toh(header->v3_b.size);
 377                 *sectorsize_out = be32toh(header->v3_b.sectorsize);
 378                 *align_out = be32toh(header->v3_b.alignment);
 379                 if (*align_out == 0) {
 380                         cow_printf("read_cow_header - invalid COW header, "
 381                                    "align == 0\n");
 382                 }
 383                 *bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
 384                 file = header->v3_b.backing_file;
 385         }
 386         else {
 387                 cow_printf("read_cow_header - invalid COW version\n");
 388                 goto out;
 389         }
 390         err = -ENOMEM;
 391         *backing_file_out = cow_strdup(file);
 392         if (*backing_file_out == NULL) {
 393                 cow_printf("read_cow_header - failed to allocate backing "
 394                            "file\n");
 395                 goto out;
 396         }
 397         err = 0;
 398  out:
 399         cow_free(header);
 400         return err;
 401 }
 402
 403 int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
 404                   int alignment, int *bitmap_offset_out,
 405                   unsigned long *bitmap_len_out, int *data_offset_out)
 406 {
 407         unsigned long long size, offset;
 408         char zero = 0;
 409         int err;
 410
 411         err = write_cow_header(cow_file, fd, backing_file, sectorsize,
 412                                alignment, &size);
 413         if (err)
 414                 goto out;
 415
 416         *bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
 417         cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
 418                   bitmap_len_out, data_offset_out);
 419
 420         offset = *data_offset_out + size - sizeof(zero);
 421         err = cow_seek_file(fd, offset);
 422         if (err < 0) {
 423                 cow_printf("cow bitmap lseek failed : err = %d\n", -err);
 424                 goto out;
 425         }
 426
 427         /*
 428          * does not really matter how much we write it is just to set EOF
 429          * this also sets the entire COW bitmap
 430          * to zero without having to allocate it
 431          */
 432         err = cow_write_file(fd, &zero, sizeof(zero));
 433         if (err != sizeof(zero)) {
 434                 cow_printf("Write of bitmap to new COW file '%s' failed, "
 435                            "err = %d\n", cow_file, -err);
 436                 if (err >= 0)
 437                         err = -EINVAL;
 438                 goto out;
 439         }
 440
 441         return 0;
 442  out:
 443         return err;
 444 }