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cow.c

#include <stddef.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <byteswap.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/param.h>
#include <sys/user.h>
#include <netinet/in.h>

#include "cow.h"
#include "cow_sys.h"

#define PATH_LEN_V1 256

00017 struct cow_header_v1 {
      int magic;
      int version;
      char backing_file[PATH_LEN_V1];
      time_t mtime;
      __u64 size;
      int sectorsize;
};

#define PATH_LEN_V2 MAXPATHLEN

00028 struct cow_header_v2 {
      unsigned long magic;
      unsigned long version;
      char backing_file[PATH_LEN_V2];
      time_t mtime;
      __u64 size;
      int sectorsize;
};

/* Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in 
 * case other systems have different values for MAXPATHLEN
 */
#define PATH_LEN_V3 4096

/* Changes from V2 - 
 *    PATH_LEN_V3 as described above
 *    Explicitly specify field bit lengths for systems with different
 *          lengths for the usual C types.  Not sure whether char or
 *          time_t should be changed, this can be changed later without
 *          breaking compatibility
 *    Add alignment field so that different alignments can be used for the
 *          bitmap and data
 *    Add cow_format field to allow for the possibility of different ways
 *          of specifying the COW blocks.  For now, the only value is 0,
 *          for the traditional COW bitmap.
 *    Move the backing_file field to the end of the header.  This allows
 *          for the possibility of expanding it into the padding required
 *          by the bitmap alignment.
 *    The bitmap and data portions of the file will be aligned as specified
 *          by the alignment field.  This is to allow COW files to be
 *          put on devices with restrictions on access alignments, such as
 *          /dev/raw, with a 512 byte alignment restriction.  This also
 *          allows the data to be more aligned more strictly than on
 *          sector boundaries.  This is needed for ubd-mmap, which needs
 *          the data to be page aligned.
 *    Fixed (finally!) the rounding bug
 */

00066 struct cow_header_v3 {
      __u32 magic;
      __u32 version;
      time_t mtime;
      __u64 size;
      __u32 sectorsize;
      __u32 alignment;
      __u32 cow_format;
      char backing_file[PATH_LEN_V3];
};

/* COW format definitions - for now, we have only the usual COW bitmap */
#define COW_BITMAP 0

00080 union cow_header {
      struct cow_header_v1 v1;
      struct cow_header_v2 v2;
      struct cow_header_v3 v3;
};

#define COW_MAGIC 0x4f4f4f4d  /* MOOO */
#define COW_VERSION 3

#define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
#define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)

void cow_sizes(int version, __u64 size, int sectorsize, int align, 
             int bitmap_offset, unsigned long *bitmap_len_out, 
             int *data_offset_out)
{
      if(version < 3){
            *bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);

            *data_offset_out = bitmap_offset + *bitmap_len_out;
            *data_offset_out = (*data_offset_out + sectorsize - 1) / 
                  sectorsize;
            *data_offset_out *= sectorsize;
      }
      else {
            *bitmap_len_out = DIV_ROUND(size, sectorsize);
            *bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);

            *data_offset_out = bitmap_offset + *bitmap_len_out;
            *data_offset_out = ROUND_UP(*data_offset_out, align);
      }
}

static int absolutize(char *to, int size, char *from)
{
      char save_cwd[256], *slash;
      int remaining;

      if(getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
            cow_printf("absolutize : unable to get cwd - errno = %d\n", 
                     errno);
            return(-1);
      }
      slash = strrchr(from, '/');
      if(slash != NULL){
            *slash = '\0';
            if(chdir(from)){
                  *slash = '/';
                  cow_printf("absolutize : Can't cd to '%s' - " 
                           "errno = %d\n", from, errno);
                  return(-1);
            }
            *slash = '/';
            if(getcwd(to, size) == NULL){
                  cow_printf("absolutize : unable to get cwd of '%s' - "
                         "errno = %d\n", from, errno);
                  return(-1);
            }
            remaining = size - strlen(to);
            if(strlen(slash) + 1 > remaining){
                  cow_printf("absolutize : unable to fit '%s' into %d "
                         "chars\n", from, size);
                  return(-1);
            }
            strcat(to, slash);
      }
      else {
            if(strlen(save_cwd) + 1 + strlen(from) + 1 > size){
                  cow_printf("absolutize : unable to fit '%s' into %d "
                         "chars\n", from, size);
                  return(-1);
            }
            strcpy(to, save_cwd);
            strcat(to, "/");
            strcat(to, from);
      }
      chdir(save_cwd);
      return(0);
}

int write_cow_header(char *cow_file, int fd, char *backing_file, 
                 int sectorsize, int alignment, long long *size)
{
        struct cow_header_v3 *header;
      struct stat64 buf;
      int err;

      err = cow_seek_file(fd, 0);
      if(err != 0){
            cow_printf("write_cow_header - lseek failed, errno = %d\n", 
                     errno);
            return(-errno);
      }

      err = -ENOMEM;
      header = cow_malloc(sizeof(*header));
      if(header == NULL){
            cow_printf("Failed to allocate COW V3 header\n");
            goto out;
      }
      header->magic = htonl(COW_MAGIC);
      header->version = htonl(COW_VERSION);

      err = -EINVAL;
      if(strlen(backing_file) > sizeof(header->backing_file) - 1){
            cow_printf("Backing file name \"%s\" is too long - names are "
                     "limited to %d characters\n", backing_file, 
                     sizeof(header->backing_file) - 1);
            goto out_free;
      }

      if(absolutize(header->backing_file, sizeof(header->backing_file), 
                  backing_file))
            goto out_free;

      err = stat64(header->backing_file, &buf);
      if(err < 0){
            cow_printf("Stat of backing file '%s' failed, errno = %d\n",
                     header->backing_file, errno);
            err = -errno;
            goto out_free;
      }

      err = cow_file_size(header->backing_file, size);
      if(err){
            cow_printf("Couldn't get size of backing file '%s', "
                     "errno = %d\n", header->backing_file, -*size);
            goto out_free;
      }

      header->mtime = htonl(buf.st_mtime);
      header->size = htonll(*size);
      header->sectorsize = htonl(sectorsize);
      header->alignment = htonl(alignment);
      header->cow_format = COW_BITMAP;

      err = write(fd, header, sizeof(*header));
      if(err != sizeof(*header)){
            cow_printf("Write of header to new COW file '%s' failed, "
                     "errno = %d\n", cow_file, errno);
            goto out_free;
      }
      err = 0;
 out_free:
      cow_free(header);
 out:
      return(err);
}

int file_reader(__u64 offset, char *buf, int len, void *arg)
{
      int fd = *((int *) arg);

      return(pread(fd, buf, len, offset));
}

/* XXX Need to sanity-check the values read from the header */

int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg, 
                __u32 *version_out, char **backing_file_out, 
                time_t *mtime_out, __u64 *size_out, 
                int *sectorsize_out, __u32 *align_out, 
                int *bitmap_offset_out)
{
      union cow_header *header;
      char *file;
      int err, n;
      unsigned long version, magic;

      header = cow_malloc(sizeof(*header));
      if(header == NULL){
              cow_printf("read_cow_header - Failed to allocate header\n");
            return(-ENOMEM);
      }
      err = -EINVAL;
      n = (*reader)(0, (char *) header, sizeof(*header), arg);
      if(n < offsetof(typeof(header->v1), backing_file)){
            cow_printf("read_cow_header - short header\n");
            goto out;
      }

      magic = header->v1.magic;
      if(magic == COW_MAGIC) {
            version = header->v1.version;
      }
      else if(magic == ntohl(COW_MAGIC)){
            version = ntohl(header->v1.version);
      }
      /* No error printed because the non-COW case comes through here */
      else goto out;

      *version_out = version;

      if(version == 1){
            if(n < sizeof(header->v1)){
                  cow_printf("read_cow_header - failed to read V1 "
                           "header\n");
                  goto out;
            }
            *mtime_out = header->v1.mtime;
            *size_out = header->v1.size;
            *sectorsize_out = header->v1.sectorsize;
            *bitmap_offset_out = sizeof(header->v1);
            *align_out = *sectorsize_out;
            file = header->v1.backing_file;
      }
      else if(version == 2){
            if(n < sizeof(header->v2)){
                  cow_printf("read_cow_header - failed to read V2 "
                           "header\n");
                  goto out;
            }
            *mtime_out = ntohl(header->v2.mtime);
            *size_out = ntohll(header->v2.size);
            *sectorsize_out = ntohl(header->v2.sectorsize);
            *bitmap_offset_out = sizeof(header->v2);
            *align_out = *sectorsize_out;
            file = header->v2.backing_file;
      }
      else if(version == 3){
            if(n < sizeof(header->v3)){
                  cow_printf("read_cow_header - failed to read V2 "
                           "header\n");
                  goto out;
            }
            *mtime_out = ntohl(header->v3.mtime);
            *size_out = ntohll(header->v3.size);
            *sectorsize_out = ntohl(header->v3.sectorsize);
            *align_out = ntohl(header->v3.alignment);
            *bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
            file = header->v3.backing_file;
      }
      else {
            cow_printf("read_cow_header - invalid COW version\n");
            goto out;         
      }
      err = -ENOMEM;
      *backing_file_out = cow_strdup(file);
      if(*backing_file_out == NULL){
            cow_printf("read_cow_header - failed to allocate backing "
                     "file\n");
            goto out;
      }
      err = 0;
 out:
      cow_free(header);
      return(err);
}

int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
              int alignment, int *bitmap_offset_out, 
              unsigned long *bitmap_len_out, int *data_offset_out)
{
      __u64 size, offset;
      char zero = 0;
      int err;

      err = write_cow_header(cow_file, fd, backing_file, sectorsize, 
                         alignment, &size);
      if(err) 
            goto out;
      
      *bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
      cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
              bitmap_len_out, data_offset_out);

      offset = *data_offset_out + size - sizeof(zero);
      err = cow_seek_file(fd, offset);
      if(err){
            cow_printf("cow bitmap lseek failed : errno = %d\n", errno);
            goto out;
      }

      /* does not really matter how much we write it is just to set EOF 
       * this also sets the entire COW bitmap
       * to zero without having to allocate it 
       */
      err = cow_write_file(fd, &zero, sizeof(zero));
      if(err != sizeof(zero)){
            err = -EINVAL;
            cow_printf("Write of bitmap to new COW file '%s' failed, "
                     "errno = %d\n", cow_file, errno);
            goto out;
      }

      return(0);

 out:
      return(err);
}

/*
 * ---------------------------------------------------------------------------
 * Local variables:
 * c-file-style: "linux"
 * End:
 */

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