LXR linux/fs/squashfs/symlink.c

   1/*
   2 * Squashfs - a compressed read only filesystem for Linux
   3 *
   4 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   5 * Phillip Lougher <phillip@lougher.demon.co.uk>
   6 *
   7 * This program is free software; you can redistribute it and/or
   8 * modify it under the terms of the GNU General Public License
   9 * as published by the Free Software Foundation; either version 2,
  10 * or (at your option) any later version.
  11 *
  12 * This program is distributed in the hope that it will be useful,
  13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 * GNU General Public License for more details.
  16 *
  17 * You should have received a copy of the GNU General Public License
  18 * along with this program; if not, write to the Free Software
  19 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  20 *
  21 * symlink.c
  22 */
  23
  24/*
  25 * This file implements code to handle symbolic links.
  26 *
  27 * The data contents of symbolic links are stored inside the symbolic
  28 * link inode within the inode table.  This allows the normally small symbolic
  29 * link to be compressed as part of the inode table, achieving much greater
  30 * compression than if the symbolic link was compressed individually.
  31 */
  32
  33#include <linux/fs.h>
  34#include <linux/vfs.h>
  35#include <linux/kernel.h>
  36#include <linux/slab.h>
  37#include <linux/string.h>
  38#include <linux/pagemap.h>
  39#include <linux/zlib.h>
  40
  41#include "squashfs_fs.h"
  42#include "squashfs_fs_sb.h"
  43#include "squashfs_fs_i.h"
  44#include "squashfs.h"
  45
  46static int squashfs_symlink_readpage(struct file *file, struct page *page)
  47{
  48        struct inode *inode = page->mapping->host;
  49        struct super_block *sb = inode->i_sb;
  50        struct squashfs_sb_info *msblk = sb->s_fs_info;
  51        int index = page->index << PAGE_CACHE_SHIFT;
  52        u64 block = squashfs_i(inode)->start;
  53        int offset = squashfs_i(inode)->offset;
  54        int length = min_t(int, i_size_read(inode) - index, PAGE_CACHE_SIZE);
  55        int bytes, copied;
  56        void *pageaddr;
  57        struct squashfs_cache_entry *entry;
  58
  59        TRACE("Entered squashfs_symlink_readpage, page index %ld, start block "
  60                        "%llx, offset %x\n", page->index, block, offset);
  61
  62        /*
  63         * Skip index bytes into symlink metadata.
  64         */
  65        if (index) {
  66                bytes = squashfs_read_metadata(sb, NULL, &block, &offset,
  67                                                                index);
  68                if (bytes < 0) {
  69                        ERROR("Unable to read symlink [%llx:%x]\n",
  70                                squashfs_i(inode)->start,
  71                                squashfs_i(inode)->offset);
  72                        goto error_out;
  73                }
  74        }
  75
  76        /*
  77         * Read length bytes from symlink metadata.  Squashfs_read_metadata
  78         * is not used here because it can sleep and we want to use
  79         * kmap_atomic to map the page.  Instead call the underlying
  80         * squashfs_cache_get routine.  As length bytes may overlap metadata
  81         * blocks, we may need to call squashfs_cache_get multiple times.
  82         */
  83        for (bytes = 0; bytes < length; offset = 0, bytes += copied) {
  84                entry = squashfs_cache_get(sb, msblk->block_cache, block, 0);
  85                if (entry->error) {
  86                        ERROR("Unable to read symlink [%llx:%x]\n",
  87                                squashfs_i(inode)->start,
  88                                squashfs_i(inode)->offset);
  89                        squashfs_cache_put(entry);
  90                        goto error_out;
  91                }
  92
  93                pageaddr = kmap_atomic(page, KM_USER0);
  94                copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
  95                                                                length - bytes);
  96                if (copied == length - bytes)
  97                        memset(pageaddr + length, 0, PAGE_CACHE_SIZE - length);
  98                else
  99                        block = entry->next_index;
 100                kunmap_atomic(pageaddr, KM_USER0);
 101                squashfs_cache_put(entry);
 102        }
 103
 104        flush_dcache_page(page);
 105        SetPageUptodate(page);
 106        unlock_page(page);
 107        return 0;
 108
 109error_out:
 110        SetPageError(page);
 111        unlock_page(page);
 112        return 0;
 113}
 114
 115
 116const struct address_space_operations squashfs_symlink_aops = {
 117        .readpage = squashfs_symlink_readpage
 118};
 119