/*
   * Squashfs - a compressed read only filesystem for Linux
   *
   * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   * Phillip Lougher <phillip@squashfs.org.uk>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version 2,
   * or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
   *
   * namei.c
   */
  
  /*
   * This file implements code to do filename lookup in directories.
   *
   * Like inodes, directories are packed into compressed metadata blocks, stored
   * in a directory table.  Directories are accessed using the start address of
   * the metablock containing the directory and the offset into the
   * decompressed block (<block, offset>).
   *
   * Directories are organised in a slightly complex way, and are not simply
   * a list of file names.  The organisation takes advantage of the
   * fact that (in most cases) the inodes of the files will be in the same
   * compressed metadata block, and therefore, can share the start block.
   * Directories are therefore organised in a two level list, a directory
   * header containing the shared start block value, and a sequence of directory
   * entries, each of which share the shared start block.  A new directory header
   * is written once/if the inode start block changes.  The directory
   * header/directory entry list is repeated as many times as necessary.
   *
   * Directories are sorted, and can contain a directory index to speed up
   * file lookup.  Directory indexes store one entry per metablock, each entry
   * storing the index/filename mapping to the first directory header
   * in each metadata block.  Directories are sorted in alphabetical order,
   * and at lookup the index is scanned linearly looking for the first filename
   * alphabetically larger than the filename being looked up.  At this point the
   * location of the metadata block the filename is in has been found.
   * The general idea of the index is ensure only one metadata block needs to be
   * decompressed to do a lookup irrespective of the length of the directory.
   * This scheme has the advantage that it doesn't require extra memory overhead
   * and doesn't require much extra storage on disk.
   */
  
  #include <linux/fs.h>
  #include <linux/vfs.h>
  #include <linux/slab.h>
  #include <linux/string.h>
  #include <linux/dcache.h>
  #include <linux/xattr.h>
  
  #include "squashfs_fs.h"
  #include "squashfs_fs_sb.h"
  #include "squashfs_fs_i.h"
  #include "squashfs.h"
  #include "xattr.h"
  
  /*
   * Lookup name in the directory index, returning the location of the metadata
   * block containing it, and the directory index this represents.
   *
   * If we get an error reading the index then return the part of the index
   * (if any) we have managed to read - the index isn't essential, just
   * quicker.
   */
  static int get_dir_index_using_name(struct super_block *sb,
  			u64 *next_block, int *next_offset, u64 index_start,
  			int index_offset, int i_count, const char *name,
  			int len)
  {
  	struct squashfs_sb_info *msblk = sb->s_fs_info;
  	int i, length = 0, err;
  	unsigned int size;
  	struct squashfs_dir_index *index;
  	char *str;
  
  	TRACE("Entered get_dir_index_using_name, i_count %d
  ", i_count);
  
  	index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
  	if (index == NULL) {
  		ERROR("Failed to allocate squashfs_dir_index
  ");
  		goto out;
  	}
  
  	str = &index->name[SQUASHFS_NAME_LEN + 1];
  	strncpy(str, name, len);
  	str[len] = '\0';
  
  	for (i = 0; i < i_count; i++) {
  		err = squashfs_read_metadata(sb, index, &index_start,
  					&index_offset, sizeof(*index));
  		if (err < 0)
  			break;
  
  
  		size = le32_to_cpu(index->size) + 1;
  		if (size > SQUASHFS_NAME_LEN)
  			break;
  
  		err = squashfs_read_metadata(sb, index->name, &index_start,
  					&index_offset, size);
  		if (err < 0)
  			break;
  
  		index->name[size] = '\0';
  
  		if (strcmp(index->name, str) > 0)
  			break;
  
  		length = le32_to_cpu(index->index);
  		*next_block = le32_to_cpu(index->start_block) +
  					msblk->directory_table;
  	}
  
  	*next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
  	kfree(index);
  
  out:
  	/*
  	 * Return index (f_pos) of the looked up metadata block.  Translate
  	 * from internal f_pos to external f_pos which is offset by 3 because
  	 * we invent "." and ".." entries which are not actually stored in the
  	 * directory.
  	 */
  	return length + 3;
  }
  
  
  static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
  				 unsigned int flags)
  {
  	const unsigned char *name = dentry->d_name.name;
  	int len = dentry->d_name.len;
  	struct inode *inode = NULL;
  	struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
  	struct squashfs_dir_header dirh;
  	struct squashfs_dir_entry *dire;
  	u64 block = squashfs_i(dir)->start + msblk->directory_table;
  	int offset = squashfs_i(dir)->offset;
  	int err, length;
  	unsigned int dir_count, size;
  
  	TRACE("Entered squashfs_lookup [%llx:%x]
  ", block, offset);
  
  	dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
  	if (dire == NULL) {
  		ERROR("Failed to allocate squashfs_dir_entry
  ");
  		return ERR_PTR(-ENOMEM);
  	}
  
  	if (len > SQUASHFS_NAME_LEN) {
  		err = -ENAMETOOLONG;
  		goto failed;
  	}
  
  	length = get_dir_index_using_name(dir->i_sb, &block, &offset,
  				squashfs_i(dir)->dir_idx_start,
  				squashfs_i(dir)->dir_idx_offset,
  				squashfs_i(dir)->dir_idx_cnt, name, len);
  
  	while (length < i_size_read(dir)) {
  		/*
  		 * Read directory header.
  		 */
  		err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
  				&offset, sizeof(dirh));
  		if (err < 0)
  			goto read_failure;
  
  		length += sizeof(dirh);
  
  		dir_count = le32_to_cpu(dirh.count) + 1;
  
  		if (dir_count > SQUASHFS_DIR_COUNT)
  			goto data_error;
  
  		while (dir_count--) {
  			/*
  			 * Read directory entry.
  			 */
  			err = squashfs_read_metadata(dir->i_sb, dire, &block,
  					&offset, sizeof(*dire));
  			if (err < 0)
  				goto read_failure;
  
  			size = le16_to_cpu(dire->size) + 1;
  
  			/* size should never be larger than SQUASHFS_NAME_LEN */
  			if (size > SQUASHFS_NAME_LEN)
  				goto data_error;
  
  			err = squashfs_read_metadata(dir->i_sb, dire->name,
  					&block, &offset, size);
  			if (err < 0)
  				goto read_failure;
  
  			length += sizeof(*dire) + size;
  
  			if (name[0] < dire->name[0])
  				goto exit_lookup;
  
  			if (len == size && !strncmp(name, dire->name, len)) {
  				unsigned int blk, off, ino_num;
  				long long ino;
  				blk = le32_to_cpu(dirh.start_block);
  				off = le16_to_cpu(dire->offset);
  				ino_num = le32_to_cpu(dirh.inode_number) +
  					(short) le16_to_cpu(dire->inode_number);
  				ino = SQUASHFS_MKINODE(blk, off);
  
  				TRACE("calling squashfs_iget for directory "
  					"entry %s, inode  %x:%x, %d
  ", name,
  					blk, off, ino_num);
  
  				inode = squashfs_iget(dir->i_sb, ino, ino_num);
  				goto exit_lookup;
  			}
  		}
  	}
  
  exit_lookup:
  	kfree(dire);
  	return d_splice_alias(inode, dentry);
  
  data_error:
  	err = -EIO;
  
  read_failure:
  	ERROR("Unable to read directory block [%llx:%x]
  ",
  		squashfs_i(dir)->start + msblk->directory_table,
  		squashfs_i(dir)->offset);
  failed:
  	kfree(dire);
  	return ERR_PTR(err);
  }
  
  
  const struct inode_operations squashfs_dir_inode_ops = {
  	.lookup = squashfs_lookup,
  	.getxattr = generic_getxattr,
  	.listxattr = squashfs_listxattr
  };