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 struct cow_header_v1 {
  21         int magic;
  22         int version;
  23         char backing_file[PATH_LEN_V1];
  24         time_t mtime;
  25         __u64 size;
  26         int sectorsize;
  27 };
  28
  29 #define PATH_LEN_V2 MAXPATHLEN
  30
  31 struct cow_header_v2 {
  32         __u32 magic;
  33         __u32 version;
  34         char backing_file[PATH_LEN_V2];
  35         time_t mtime;
  36         __u64 size;
  37         int sectorsize;
  38 };
  39
  40 /* Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
  41  * case other systems have different values for MAXPATHLEN
  42  */
  43 #define PATH_LEN_V3 4096
  44
  45 /* Changes from V2 -
  46  *      PATH_LEN_V3 as described above
  47  *      Explicitly specify field bit lengths for systems with different
  48  *              lengths for the usual C types.  Not sure whether char or
  49  *              time_t should be changed, this can be changed later without
  50  *              breaking compatibility
  51  *      Add alignment field so that different alignments can be used for the
  52  *              bitmap and data
  53  *      Add cow_format field to allow for the possibility of different ways
  54  *              of specifying the COW blocks.  For now, the only value is 0,
  55  *              for the traditional COW bitmap.
  56  *      Move the backing_file field to the end of the header.  This allows
  57  *              for the possibility of expanding it into the padding required
  58  *              by the bitmap alignment.
  59  *      The bitmap and data portions of the file will be aligned as specified
  60  *              by the alignment field.  This is to allow COW files to be
  61  *              put on devices with restrictions on access alignments, such as
  62  *              /dev/raw, with a 512 byte alignment restriction.  This also
  63  *              allows the data to be more aligned more strictly than on
  64  *              sector boundaries.  This is needed for ubd-mmap, which needs
  65  *              the data to be page aligned.
  66  *      Fixed (finally!) the rounding bug
  67  */
  68
  69 struct cow_header_v3 {
  70         __u32 magic;
  71         __u32 version;
  72         __u32 mtime;
  73         __u64 size;
  74         __u32 sectorsize;
  75         __u32 alignment;
  76         __u32 cow_format;
  77         char backing_file[PATH_LEN_V3];
  78 };
  79
  80 /* COW format definitions - for now, we have only the usual COW bitmap */
  81 #define COW_BITMAP 0
  82
  83 union cow_header {
  84         struct cow_header_v1 v1;
  85         struct cow_header_v2 v2;
  86         struct cow_header_v3 v3;
  87 };
  88
  89 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
  90 #define COW_VERSION 3
  91
  92 #define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
  93 #define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
  94
  95 void cow_sizes(int version, __u64 size, int sectorsize, int align,
  96                int bitmap_offset, unsigned long *bitmap_len_out,
  97                int *data_offset_out)
  98 {
  99         if(version < 3){
 100                 *bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);
 101
 102                 *data_offset_out = bitmap_offset + *bitmap_len_out;
 103                 *data_offset_out = (*data_offset_out + sectorsize - 1) /
 104                         sectorsize;
 105                 *data_offset_out *= sectorsize;
 106         }
 107         else {
 108                 *bitmap_len_out = DIV_ROUND(size, sectorsize);
 109                 *bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);
 110
 111                 *data_offset_out = bitmap_offset + *bitmap_len_out;
 112                 *data_offset_out = ROUND_UP(*data_offset_out, align);
 113         }
 114 }
 115
 116 static int absolutize(char *to, int size, char *from)
 117 {
 118         char save_cwd[256], *slash;
 119         int remaining;
 120
 121         if(getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
 122                 cow_printf("absolutize : unable to get cwd - errno = %d\n",
 123                            errno);
 124                 return(-1);
 125         }
 126         slash = strrchr(from, '/');
 127         if(slash != NULL){
 128                 *slash = '\0';
 129                 if(chdir(from)){
 130                         *slash = '/';
 131                         cow_printf("absolutize : Can't cd to '%s' - "
 132                                    "errno = %d\n", from, errno);
 133                         return(-1);
 134                 }
 135                 *slash = '/';
 136                 if(getcwd(to, size) == NULL){
 137                         cow_printf("absolutize : unable to get cwd of '%s' - "
 138                                "errno = %d\n", from, errno);
 139                         return(-1);
 140                 }
 141                 remaining = size - strlen(to);
 142                 if(strlen(slash) + 1 > remaining){
 143                         cow_printf("absolutize : unable to fit '%s' into %d "
 144                                "chars\n", from, size);
 145                         return(-1);
 146                 }
 147                 strcat(to, slash);
 148         }
 149         else {
 150                 if(strlen(save_cwd) + 1 + strlen(from) + 1 > size){
 151                         cow_printf("absolutize : unable to fit '%s' into %d "
 152                                "chars\n", from, size);
 153                         return(-1);
 154                 }
 155                 strcpy(to, save_cwd);
 156                 strcat(to, "/");
 157                 strcat(to, from);
 158         }
 159         chdir(save_cwd);
 160         return(0);
 161 }
 162
 163 int write_cow_header(char *cow_file, int fd, char *backing_file,
 164                      int sectorsize, int alignment, unsigned long long *size)
 165 {
 166         struct cow_header_v3 *header;
 167         unsigned long modtime;
 168         int err;
 169
 170         err = cow_seek_file(fd, 0);
 171         if(err < 0){
 172                 cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
 173                 goto out;
 174         }
 175
 176         err = -ENOMEM;
 177         header = cow_malloc(sizeof(*header));
 178         if(header == NULL){
 179                 cow_printf("write_cow_header - failed to allocate COW V3 header\n");
 180                 goto out;
 181         }
 182         header->magic = htonl(COW_MAGIC);
 183         header->version = htonl(COW_VERSION);
 184
 185         err = -EINVAL;
 186         if(strlen(backing_file) > sizeof(header->backing_file) - 1){
 187                 cow_printf("Backing file name \"%s\" is too long - names are "
 188                            "limited to %d characters\n", backing_file,
 189                            sizeof(header->backing_file) - 1);
 190                 goto out_free;
 191         }
 192
 193         if(absolutize(header->backing_file, sizeof(header->backing_file),
 194                       backing_file))
 195                 goto out_free;
 196
 197         err = os_file_modtime(header->backing_file, &modtime);
 198         if(err < 0){
 199                 cow_printf("write_cow_header - backing file '%s' mtime "
 200                            "request failed, err = %d\n", header->backing_file,
 201                            -err);
 202                 goto out_free;
 203         }
 204
 205         err = cow_file_size(header->backing_file, size);
 206         if(err < 0){
 207                 cow_printf("write_cow_header - couldn't get size of "
 208                            "backing file '%s', err = %d\n",
 209                            header->backing_file, -err);
 210                 goto out_free;
 211         }
 212
 213         header->mtime = htonl(modtime);
 214         header->size = htonll(*size);
 215         header->sectorsize = htonl(sectorsize);
 216         header->alignment = htonl(alignment);
 217         header->cow_format = COW_BITMAP;
 218
 219         err = cow_write_file(fd, header, sizeof(*header));
 220         if(err != sizeof(*header)){
 221                 cow_printf("write_cow_header - write of header to "
 222                            "new COW file '%s' failed, err = %d\n", cow_file,
 223                            -err);
 224                 goto out_free;
 225         }
 226         err = 0;
 227  out_free:
 228         cow_free(header);
 229  out:
 230         return(err);
 231 }
 232
 233 int file_reader(__u64 offset, char *buf, int len, void *arg)
 234 {
 235         int fd = *((int *) arg);
 236
 237         return(pread(fd, buf, len, offset));
 238 }
 239
 240 /* XXX Need to sanity-check the values read from the header */
 241
 242 int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
 243                     __u32 *version_out, char **backing_file_out,
 244                     time_t *mtime_out, unsigned long long *size_out,
 245                     int *sectorsize_out, __u32 *align_out,
 246                     int *bitmap_offset_out)
 247 {
 248         union cow_header *header;
 249         char *file;
 250         int err, n;
 251         unsigned long version, magic;
 252
 253         header = cow_malloc(sizeof(*header));
 254         if(header == NULL){
 255                 cow_printf("read_cow_header - Failed to allocate header\n");
 256                 return(-ENOMEM);
 257         }
 258         err = -EINVAL;
 259         n = (*reader)(0, (char *) header, sizeof(*header), arg);
 260         if(n < offsetof(typeof(header->v1), backing_file)){
 261                 cow_printf("read_cow_header - short header\n");
 262                 goto out;
 263         }
 264
 265         magic = header->v1.magic;
 266         if(magic == COW_MAGIC) {
 267                 version = header->v1.version;
 268         }
 269         else if(magic == ntohl(COW_MAGIC)){
 270                 version = ntohl(header->v1.version);
 271         }
 272         /* No error printed because the non-COW case comes through here */
 273         else goto out;
 274
 275         *version_out = version;
 276
 277         if(version == 1){
 278                 if(n < sizeof(header->v1)){
 279                         cow_printf("read_cow_header - failed to read V1 "
 280                                    "header\n");
 281                         goto out;
 282                 }
 283                 *mtime_out = header->v1.mtime;
 284                 *size_out = header->v1.size;
 285                 *sectorsize_out = header->v1.sectorsize;
 286                 *bitmap_offset_out = sizeof(header->v1);
 287                 *align_out = *sectorsize_out;
 288                 file = header->v1.backing_file;
 289         }
 290         else if(version == 2){
 291                 if(n < sizeof(header->v2)){
 292                         cow_printf("read_cow_header - failed to read V2 "
 293                                    "header\n");
 294                         goto out;
 295                 }
 296                 *mtime_out = ntohl(header->v2.mtime);
 297                 *size_out = ntohll(header->v2.size);
 298                 *sectorsize_out = ntohl(header->v2.sectorsize);
 299                 *bitmap_offset_out = sizeof(header->v2);
 300                 *align_out = *sectorsize_out;
 301                 file = header->v2.backing_file;
 302         }
 303         else if(version == 3){
 304                 if(n < sizeof(header->v3)){
 305                         cow_printf("read_cow_header - failed to read V3 "
 306                                    "header\n");
 307                         goto out;
 308                 }
 309                 *mtime_out = ntohl(header->v3.mtime);
 310                 *size_out = ntohll(header->v3.size);
 311                 *sectorsize_out = ntohl(header->v3.sectorsize);
 312                 *align_out = ntohl(header->v3.alignment);
 313                 *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
 314                 file = header->v3.backing_file;
 315         }
 316         else {
 317                 cow_printf("read_cow_header - invalid COW version\n");
 318                 goto out;
 319         }
 320         err = -ENOMEM;
 321         *backing_file_out = cow_strdup(file);
 322         if(*backing_file_out == NULL){
 323                 cow_printf("read_cow_header - failed to allocate backing "
 324                            "file\n");
 325                 goto out;
 326         }
 327         err = 0;
 328  out:
 329         cow_free(header);
 330         return(err);
 331 }
 332
 333 int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
 334                   int alignment, int *bitmap_offset_out,
 335                   unsigned long *bitmap_len_out, int *data_offset_out)
 336 {
 337         unsigned long long size, offset;
 338         char zero = 0;
 339         int err;
 340
 341         err = write_cow_header(cow_file, fd, backing_file, sectorsize,
 342                                alignment, &size);
 343         if(err)
 344                 goto out;
 345
 346         *bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
 347         cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
 348                   bitmap_len_out, data_offset_out);
 349
 350         offset = *data_offset_out + size - sizeof(zero);
 351         err = cow_seek_file(fd, offset);
 352         if(err < 0){
 353                 cow_printf("cow bitmap lseek failed : err = %d\n", -err);
 354                 goto out;
 355         }
 356
 357         /* does not really matter how much we write it is just to set EOF
 358          * this also sets the entire COW bitmap
 359          * to zero without having to allocate it
 360          */
 361         err = cow_write_file(fd, &zero, sizeof(zero));
 362         if(err != sizeof(zero)){
 363                 cow_printf("Write of bitmap to new COW file '%s' failed, "
 364                            "err = %d\n", cow_file, -err);
 365                 if (err >= 0)
 366                         err = -EINVAL;
 367                 goto out;
 368         }
 369
 370         return(0);
 371
 372  out:
 373         return(err);
 374 }
 375
 376 /*
 377  * ---------------------------------------------------------------------------
 378  * Local variables:
 379  * c-file-style: "linux"
 380  * End:
 381  */