Miscellany

#define NUM_READ_SECTORS 2
ssize_t fat_file_read(struct file_info *fp, void* buf, size_t count)
{
  char *bufp = buf;
  size_t ncopy;
  size_t n = 0;
  int readnumsectors, f_cluster, f_sector, countsectors; 
  struct libfat_fileinfo *fs_desc = (struct libfat_fileinfo*) fp->fs_desc;
  struct libfat_filesystem *fs = fs_desc->fs;
  struct libfat_direntry *dentry = &fs_desc->dentry;
  char buffer[LIBFAT_SECTOR_SIZE * NUM_READ_SECTORS];

  ncopy = NUM_READ_SECTORS*LIBFAT_SECTOR_SIZE;
  f_cluster = read16(&dentry->clustlo) + (read16(&dentry->clusthi) << 16);
  countsectors = count / ncopy;
  bytes_left = count - countsectors*LIBFAT_SECTOR_SIZE;

  f_sector = libfat_clustertosector(fs, f_cluster);

  while ( countsectors && f_sector > 0 ) {
    if ( fp->i.offset >= fp->i.length || !fp->i.filedes )
      return n;		/* As good as it gets... */

    status = fs->read(fs->readptr, bufp, f_sector, NUM_READ_SECTORS);
    if ( status < 0 ) {
      errno = EIO;
      return -1;
    }

    n += ncopy;
    bufp += ncopy;
    countsectors -= NUM_READ_SECTORS;
    fp->i.offset += ncopy;
    f_sector = libfat_nextsector(fs, f_sector);
  }

  if (bytes_left) {
    if ( fp->i.offset >= fp->i.length || !fp->i.filedes )
      return n;		/* As good as it gets... */

    status = fs->read(fs->readptr, buffer, f_sector, NUM_READ_SECTORS);
    if ( status < 0 ) {
      errno = EIO;
      return -1;
    }

    ncopy = bytes_left;
    memcpy(bufp, buffer, ncopy);
    n += ncopy;
    fp->i.offset += ncopy;
  }

  return n;
}