diff options
| -rw-r--r-- | fs/squashfs/namei.c | 242 |
1 files changed, 242 insertions, 0 deletions
diff --git a/fs/squashfs/namei.c b/fs/squashfs/namei.c new file mode 100644 index 0000000..9e39865 --- /dev/null +++ b/fs/squashfs/namei.c @@ -0,0 +1,242 @@ +/* + * Squashfs - a compressed read only filesystem for Linux + * + * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 + * Phillip Lougher <phillip@lougher.demon.co.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/zlib.h> + +#include "squashfs_fs.h" +#include "squashfs_fs_sb.h" +#include "squashfs_fs_i.h" +#include "squashfs.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, size, length = 0, err; + struct squashfs_dir_index *index; + char *str; + + TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count); + + index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL); + if (index == NULL) { + ERROR("Failed to allocate squashfs_dir_index\n"); + 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; + + 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, + struct nameidata *nd) +{ + 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 = 0, dir_count, size; + + TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset); + + dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL); + if (dire == NULL) { + ERROR("Failed to allocate squashfs_dir_entry\n"); + 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; + 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; + + 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\n", name, + blk, off, ino_num); + + inode = squashfs_iget(dir->i_sb, ino, ino_num); + if (IS_ERR(inode)) { + err = PTR_ERR(inode); + goto failed; + } + + goto exit_lookup; + } + } + } + +exit_lookup: + kfree(dire); + if (inode) + return d_splice_alias(inode, dentry); + d_add(dentry, inode); + return ERR_PTR(0); + +read_failure: + ERROR("Unable to read directory block [%llx:%x]\n", + 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 +}; |
