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("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("Backing file '%s' mtime request failed, "
 200                            "err = %d\n", header->backing_file, -err);
 201                 goto out_free;
 202         }
 203
 204         err = cow_file_size(header->backing_file, size);
 205         if(err < 0){
 206                 cow_printf("Couldn't get size of backing file '%s', "
 207                            "err = %d\n", header->backing_file, -err);
 208                 goto out_free;
 209         }
 210
 211         header->mtime = htonl(modtime);
 212         header->size = htonll(*size);
 213         header->sectorsize = htonl(sectorsize);
 214         header->alignment = htonl(alignment);
 215         header->cow_format = COW_BITMAP;
 216
 217         err = os_write_file(fd, header, sizeof(*header));
 218         if(err != sizeof(*header)){
 219                 cow_printf("Write of header to new COW file '%s' failed, "
 220                            "err = %d\n", cow_file, -err);
 221                 goto out_free;
 222         }
 223         err = 0;
 224  out_free:
 225         cow_free(header);
 226  out:
 227         return(err);
 228 }
 229
 230 int file_reader(__u64 offset, char *buf, int len, void *arg)
 231 {
 232         int fd = *((int *) arg);
 233
 234         return(pread(fd, buf, len, offset));
 235 }
 236
 237 /* XXX Need to sanity-check the values read from the header */
 238
 239 int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
 240                     __u32 *version_out, char **backing_file_out,
 241                     time_t *mtime_out, unsigned long long *size_out,
 242                     int *sectorsize_out, __u32 *align_out,
 243                     int *bitmap_offset_out)
 244 {
 245         union cow_header *header;
 246         char *file;
 247         int err, n;
 248         unsigned long version, magic;
 249
 250         header = cow_malloc(sizeof(*header));
 251         if(header == NULL){
 252                 cow_printf("read_cow_header - Failed to allocate header\n");
 253                 return(-ENOMEM);
 254         }
 255         err = -EINVAL;
 256         n = (*reader)(0, (char *) header, sizeof(*header), arg);
 257         if(n < offsetof(typeof(header->v1), backing_file)){
 258                 cow_printf("read_cow_header - short header\n");
 259                 goto out;
 260         }
 261
 262         magic = header->v1.magic;
 263         if(magic == COW_MAGIC) {
 264                 version = header->v1.version;
 265         }
 266         else if(magic == ntohl(COW_MAGIC)){
 267                 version = ntohl(header->v1.version);
 268         }
 269         /* No error printed because the non-COW case comes through here */
 270         else goto out;
 271
 272         *version_out = version;
 273
 274         if(version == 1){
 275                 if(n < sizeof(header->v1)){
 276                         cow_printf("read_cow_header - failed to read V1 "
 277                                    "header\n");
 278                         goto out;
 279                 }
 280                 *mtime_out = header->v1.mtime;
 281                 *size_out = header->v1.size;
 282                 *sectorsize_out = header->v1.sectorsize;
 283                 *bitmap_offset_out = sizeof(header->v1);
 284                 *align_out = *sectorsize_out;
 285                 file = header->v1.backing_file;
 286         }
 287         else if(version == 2){
 288                 if(n < sizeof(header->v2)){
 289                         cow_printf("read_cow_header - failed to read V2 "
 290                                    "header\n");
 291                         goto out;
 292                 }
 293                 *mtime_out = ntohl(header->v2.mtime);
 294                 *size_out = ntohll(header->v2.size);
 295                 *sectorsize_out = ntohl(header->v2.sectorsize);
 296                 *bitmap_offset_out = sizeof(header->v2);
 297                 *align_out = *sectorsize_out;
 298                 file = header->v2.backing_file;
 299         }
 300         else if(version == 3){
 301                 if(n < sizeof(header->v3)){
 302                         cow_printf("read_cow_header - failed to read V2 "
 303                                    "header\n");
 304                         goto out;
 305                 }
 306                 *mtime_out = ntohl(header->v3.mtime);
 307                 *size_out = ntohll(header->v3.size);
 308                 *sectorsize_out = ntohl(header->v3.sectorsize);
 309                 *align_out = ntohl(header->v3.alignment);
 310                 *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
 311                 file = header->v3.backing_file;
 312         }
 313         else {
 314                 cow_printf("read_cow_header - invalid COW version\n");
 315                 goto out;
 316         }
 317         err = -ENOMEM;
 318         *backing_file_out = cow_strdup(file);
 319         if(*backing_file_out == NULL){
 320                 cow_printf("read_cow_header - failed to allocate backing "
 321                            "file\n");
 322                 goto out;
 323         }
 324         err = 0;
 325  out:
 326         cow_free(header);
 327         return(err);
 328 }
 329
 330 int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
 331                   int alignment, int *bitmap_offset_out,
 332                   unsigned long *bitmap_len_out, int *data_offset_out)
 333 {
 334         unsigned long long size, offset;
 335         char zero = 0;
 336         int err;
 337
 338         err = write_cow_header(cow_file, fd, backing_file, sectorsize,
 339                                alignment, &size);
 340         if(err)
 341                 goto out;
 342
 343         *bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
 344         cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
 345                   bitmap_len_out, data_offset_out);
 346
 347         offset = *data_offset_out + size - sizeof(zero);
 348         err = cow_seek_file(fd, offset);
 349         if(err < 0){
 350                 cow_printf("cow bitmap lseek failed : err = %d\n", -err);
 351                 goto out;
 352         }
 353
 354         /* does not really matter how much we write it is just to set EOF
 355          * this also sets the entire COW bitmap
 356          * to zero without having to allocate it
 357          */
 358         err = cow_write_file(fd, &zero, sizeof(zero));
 359         if(err != sizeof(zero)){
 360                 cow_printf("Write of bitmap to new COW file '%s' failed, "
 361                            "err = %d\n", cow_file, -err);
 362                 err = -EINVAL;
 363                 goto out;
 364         }
 365
 366         return(0);
 367
 368  out:
 369         return(err);
 370 }
 371
 372 /*
 373  * ---------------------------------------------------------------------------
 374  * Local variables:
 375  * c-file-style: "linux"
 376  * End:
 377  */