arch/um/drivers/cow_user.c

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