fsys_ext2fs.c

open source bios with linux platform, very good and can be reused.

  logical_block -= (1 << (EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK) * 2));
  if (mapblock1 != 3
      && !ext2_rdfsb (__le32_to_cpu(INODE->i_block[EXT2_TIND_BLOCK]), DATABLOCK1))
    {
      errnum = ERR_FSYS_CORRUPT;
      return -1;
    }
  mapblock1 = 3;
  if (!ext2_rdfsb (__le32_to_cpu(((__u32 *) DATABLOCK1)
		   [logical_block >> (EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK)
				      * 2)]),
		   DATABLOCK2))
    {
      errnum = ERR_FSYS_CORRUPT;
      return -1;
    }
  if (!ext2_rdfsb (__le32_to_cpu(((__u32 *) DATABLOCK2)
		   [(logical_block >> EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK))
		    & (EXT2_ADDR_PER_BLOCK (SUPERBLOCK) - 1)]),
		   DATABLOCK2))
    {
      errnum = ERR_FSYS_CORRUPT;
      return -1;
    }
  return __le32_to_cpu(((__u32 *) DATABLOCK2)
    [logical_block & (EXT2_ADDR_PER_BLOCK (SUPERBLOCK) - 1)]);
}

/* preconditions: all preconds of ext2fs_block_map */
int
ext2fs_read (char *buf, int len)
{
  int logical_block;
  int offset;
  int map;
  int ret = 0;
  int size = 0;

#ifdef E2DEBUG
  printf("ext2fs_read(0x%x, %d)\n", buf, len);
  dump_inode(INODE);
  dump_inode_data((unsigned char *)INODE, sizeof (struct ext2_inode));
#endif /* E2DEBUG */
  while (len > 0)
    {
      /* find the (logical) block component of our location */
      logical_block = filepos >> EXT2_BLOCK_SIZE_BITS (SUPERBLOCK);
      offset = filepos & (EXT2_BLOCK_SIZE (SUPERBLOCK) - 1);
      map = ext2fs_block_map (logical_block);
#ifdef E2DEBUG
      printf ("map=%d\n", map);
#endif /* E2DEBUG */
      if (map < 0)
	break;

      size = EXT2_BLOCK_SIZE (SUPERBLOCK);
      size -= offset;
      if (size > len)
	size = len;

      disk_read_func = disk_read_hook;

      devread (map * (EXT2_BLOCK_SIZE (SUPERBLOCK) / DEV_BSIZE),
	       offset, size, buf);

      disk_read_func = 0;

      buf += size;
      len -= size;
      filepos += size;
      ret += size;
    }

  if (errnum)
    ret = 0;

  return ret;
}


/* Based on:
   def_blk_fops points to
   blkdev_open, which calls (I think):
   sys_open()
   do_open()
   open_namei()
   dir_namei() which accesses current->fs->root
     fs->root was set during original mount:
     (something)... which calls (I think):
     ext2_read_super()
     iget()
     __iget()
     read_inode()
     ext2_read_inode()
       uses desc_per_block_bits, which is set in ext2_read_super()
       also uses group descriptors loaded during ext2_read_super()
   lookup()
   ext2_lookup()
   ext2_find_entry()
   ext2_getblk()

*/

/* preconditions: ext2fs_mount already executed, therefore supblk in buffer
 *   known as SUPERBLOCK
 * returns: 0 if error, nonzero iff we were able to find the file successfully
 * postconditions: on a nonzero return, buffer known as INODE contains the
 *   inode of the file we were trying to look up
 * side effects: messes up GROUP_DESC buffer area
 */
int
ext2fs_dir (char *dirname)
{
  int current_ino = EXT2_ROOT_INO;	/* start at the root */
  int updir_ino = current_ino;	/* the parent of the current directory */
  int group_id;			/* which group the inode is in */
  int group_desc;		/* fs pointer to that group */
  int desc;			/* index within that group */
  int ino_blk;			/* fs pointer of the inode's information */
  int str_chk = 0;		/* used to hold the results of a string compare */
  struct ext2_group_desc *gdp;
  struct ext2_inode *raw_inode;	/* inode info corresponding to current_ino */

  char linkbuf[PATH_MAX];	/* buffer for following symbolic links */
  int link_count = 0;

  char *rest;
  char ch;			/* temp char holder */

  int off;			/* offset within block of directory entry (off mod blocksize) */
  int loc;			/* location within a directory */
  int blk;			/* which data blk within dir entry (off div blocksize) */
  long map;			/* fs pointer of a particular block from dir entry */
  struct ext2_dir_entry *dp;	/* pointer to directory entry */

  /* loop invariants:
     current_ino = inode to lookup
     dirname = pointer to filename component we are cur looking up within
     the directory known pointed to by current_ino (if any)
   */

#ifdef E2DEBUG
  printf("****** ext2fs_dir(%s)\n", dirname);
  dump_super(SUPERBLOCK);
#endif /* E2DEBUG */

  while (1)
    {
#ifdef E2DEBUG
      printf ("ext2fs_dir: inode %d\n", current_ino);
      printf ("ext2fs_dir: dirname=%s\n", dirname);
#endif /* E2DEBUG */

      /* look up an inode */
      group_id = (current_ino - 1) / __le32_to_cpu(SUPERBLOCK->s_inodes_per_group);
      group_desc = group_id >> log2 (EXT2_DESC_PER_BLOCK (SUPERBLOCK));
      desc = group_id & (EXT2_DESC_PER_BLOCK (SUPERBLOCK) - 1);
#ifdef E2DEBUG
      printf ("ext2fs_dir: ipg=%d, dpb=%d\n", __le32_to_cpu(SUPERBLOCK->s_inodes_per_group),
	      EXT2_DESC_PER_BLOCK (SUPERBLOCK));
      printf ("ext2fs_dir: group_id=%d group_desc=%d desc=%d\n", group_id, group_desc, desc);
#endif /* E2DEBUG */
      if (!ext2_rdfsb (
			(WHICH_SUPER + group_desc + __le32_to_cpu(SUPERBLOCK->s_first_data_block)),
			(char*) GROUP_DESC))
	{
	  return 0;
	}

#ifdef E2DEBUG
      dump_group_desc(GROUP_DESC);
#endif /* E2DEBUG */	

      gdp = GROUP_DESC;
      ino_blk = __le32_to_cpu(gdp[desc].bg_inode_table) +
	(((current_ino - 1) % __le32_to_cpu(SUPERBLOCK->s_inodes_per_group))
	 >> log2 (EXT2_BLOCK_SIZE (SUPERBLOCK) / sizeof (struct ext2_inode)));
#ifdef E2DEBUG
      printf ("ext2fs_dir: itab_blk=%d, i_in_grp=%d, log2=%d\n", 
	 __le32_to_cpu(gdp[desc].bg_inode_table),
	 ((current_ino - 1) % __le32_to_cpu(SUPERBLOCK->s_inodes_per_group)),
	 log2 (EXT2_BLOCK_SIZE (SUPERBLOCK) / sizeof (struct ext2_inode)));
      printf ("ext2fs_dir: inode table fsblock=%d\n", ino_blk);
#endif /* E2DEBUG */
      if (!ext2_rdfsb (ino_blk, (int) INODE))
	{
	  return 0;
	}

      /* reset indirect blocks! */
      mapblock2 = mapblock1 = -1;

      raw_inode = INODE +
	((current_ino - 1)
	 & (EXT2_BLOCK_SIZE (SUPERBLOCK) / sizeof (struct ext2_inode) - 1));
#ifdef E2DEBUG
      printf ("ext2fs_dir: ipb=%d, sizeof(inode)=%d\n",
	      (EXT2_BLOCK_SIZE (SUPERBLOCK) / sizeof (struct ext2_inode)),
	      sizeof (struct ext2_inode));
      printf ("ext2fs_dir: inode=%x, raw_inode=%x\n", INODE, raw_inode);
      printf ("ext2fs_dir: offset into inode table block=%d\n", (int) raw_inode - (int) INODE);
      dump_inode(raw_inode);
      dump_inode_data((unsigned char *)INODE, EXT2_BLOCK_SIZE(SUPERBLOCK));
      printf ("ext2fs_dir: first word=%x\n", *((int *) raw_inode));
#endif /* E2DEBUG */

      /* copy inode to fixed location */
      memmove ((void *) INODE, (void *) raw_inode, sizeof (struct ext2_inode));

#ifdef E2DEBUG
      dump_inode(INODE);
      printf ("ext2fs_dir: first word=%x\n", *((int *) INODE));
#endif /* E2DEBUG */

      /* If we've got a symbolic link, then chase it. */
      if (S_ISLNK (__le16_to_cpu(INODE->i_mode)))
	{
	  int len;
	  if (++link_count > MAX_LINK_COUNT)
	    {
	      errnum = ERR_SYMLINK_LOOP;
	      return 0;
	    }

	  /* Find out how long our remaining name is. */
	  len = 0;
	  while (dirname[len] && !isspace (dirname[len]))
	    len++;

	  /* Get the symlink size. */
	  filemax = __le32_to_cpu(INODE->i_size);
	  if (filemax + len > sizeof (linkbuf) - 2)
	    {
	      errnum = ERR_FILELENGTH;
	      return 0;
	    }

	  if (len)
	    {
	      /* Copy the remaining name to the end of the symlink data.
	         Note that DIRNAME and LINKBUF may overlap! */
	      memmove (linkbuf + filemax, dirname, len);
	    }
	  linkbuf[filemax + len] = '\0';

	  /* Read the symlink data. */
	  if (__le32_to_cpu(INODE->i_blocks))
	    {
	      /* Read the necessary blocks, and reset the file pointer. */
	      len = file_read (linkbuf, filemax);
	      filepos = 0;
	      if (!len)
		return 0;
	    }
	  else
	    {
	      /* Copy the data directly from the inode. */
	      len = filemax;
	      memmove (linkbuf, (char *) INODE->i_block, len);
	    }

#ifdef E2DEBUG
	  printf ("ext2fs_dir: symlink=%s\n", linkbuf);
#endif

	  dirname = linkbuf;
	  if (*dirname == '/')
	    {
	      /* It's an absolute link, so look it up in root. */
	      current_ino = EXT2_ROOT_INO;
	      updir_ino = current_ino;
	    }
	  else
	    {
	      /* Relative, so look it up in our parent directory. */
	      current_ino = updir_ino;
	    }

	  /* Try again using the new name. */
	  continue;
	}

      /* if end of filename, INODE points to the file's inode */
      if (!*dirname || isspace (*dirname))
	{
	  if (!S_ISREG (__le16_to_cpu(INODE->i_mode)))
	    {
	      errnum = ERR_BAD_FILETYPE;
	      return 0;
	    }

	  filemax = __le32_to_cpu(INODE->i_size);
	  return 1;
	}

      /* else we have to traverse a directory */
      updir_ino = current_ino;

      /* skip over slashes */
      while (*dirname == '/')
	dirname++;

      /* if this isn't a directory of sufficient size to hold our file, abort */
      if (!(__le32_to_cpu(INODE->i_size)) || !S_ISDIR (__le16_to_cpu(INODE->i_mode)))
	{
	  errnum = ERR_BAD_FILETYPE;
	  return 0;
	}

      /* skip to next slash or end of filename (space) */
      for (rest = dirname; (ch = *rest) && !isspace (ch) && ch != '/';
	   rest++);

      /* look through this directory and find the next filename component */
      /* invariant: rest points to slash after the next filename component */
      *rest = 0;
      loc = 0;

      do
	{

#ifdef E2DEBUG
	  printf ("ext2fs_dir: dirname=%s, rest=%s, loc=%d\n", dirname, rest, loc);
#endif /* E2DEBUG */

	  /* if our location/byte offset into the directory exceeds the size,
	     give up */
	  if (loc >= __le32_to_cpu(INODE->i_size))
	    {
	      if (print_possibilities < 0)
		{
# if 0
		  putchar ('\n');
# endif
		}
	      else
		{
		  errnum = ERR_FILE_NOT_FOUND;
		  *rest = ch;
		}
	      return (print_possibilities < 0);
	    }

	  /* else, find the (logical) block component of our location */
	  blk = loc >> EXT2_BLOCK_SIZE_BITS (SUPERBLOCK);

	  /* we know which logical block of the directory entry we are looking
	     for, now we have to translate that to the physical (fs) block on
	     the disk */
	  map = ext2fs_block_map (blk);
#ifdef E2DEBUG
	  printf ("ext2fs_dir: fs block=%d\n", map);
#endif /* E2DEBUG */
	  mapblock2 = -1;
	  if ((map < 0) || !ext2_rdfsb (map, DATABLOCK2))
	    {
	      errnum = ERR_FSYS_CORRUPT;
	      *rest = ch;
	      return 0;
	    }
	  off = loc & (EXT2_BLOCK_SIZE (SUPERBLOCK) - 1);
	  dp = (struct ext2_dir_entry *) (DATABLOCK2 + off);
	  /* advance loc prematurely to next on-disk directory entry  */
	  loc += __le16_to_cpu(dp->rec_len);

	  /* NOTE: ext2fs filenames are NOT null-terminated */

#ifdef E2DEBUG
	  printf ("ext2fs_dir: directory entry ino=%d\n", __le32_to_cpu(dp->inode));
	  if (__le32_to_cpu(dp->inode))
	    printf ("entry=%s\n", dp->name);
#endif /* E2DEBUG */

	  if (__le32_to_cpu(dp->inode))
	    {
	      int saved_c = dp->name[dp->name_len];

	      dp->name[dp->name_len] = 0;
	      str_chk = substring (dirname, dp->name);

# ifndef STAGE1_5
	      if (print_possibilities && ch != '/'
		  && (!*dirname || str_chk <= 0))
		{
		  if (print_possibilities > 0)
		    print_possibilities = -print_possibilities;
		  print_a_completion (dp->name);
		}
# endif

	      dp->name[dp->name_len] = saved_c;
	    }

	}
      while (!__le32_to_cpu(dp->inode) || (str_chk || (print_possibilities && ch != '/')));

      current_ino = __le32_to_cpu(dp->inode);
      *(dirname = rest) = ch;
    }
  /* never get here */
}

#endif /* FSYS_EXT2_FS */