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