root/arch/um/drivers/cow_user.c

DEFINITIONS

1. cow_sizes
2. absolutize
3. write_cow_header
4. file_reader
5. read_cow_header
6. init_cow_file

   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 typedef __u32 time32_t;
  21 
  22 struct 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 
  41 struct 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 
  85 struct 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. */
  97 struct 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 
 111 union 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 
 124 void 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 
 145 static 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 
 196 int 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 
 268 int 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 
 277 int 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 
 402 int 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 }