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
  40 #include "squashfs_fs.h"
  41 #include "squashfs_fs_sb.h"
  42 #include "squashfs_fs_i.h"
  43 #include "squashfs.h"
  44
  45 static int squashfs_symlink_readpage(struct file *file, struct page *page)
  46 {
  47         struct inode *inode = page->mapping->host;
  48         struct super_block *sb = inode->i_sb;
  49         struct squashfs_sb_info *msblk = sb->s_fs_info;
  50         int index = page->index << PAGE_CACHE_SHIFT;
  51         u64 block = squashfs_i(inode)->start;
  52         int offset = squashfs_i(inode)->offset;
  53         int length = min_t(int, i_size_read(inode) - index, PAGE_CACHE_SIZE);
  54         int bytes, copied;
  55         void *pageaddr;
  56         struct squashfs_cache_entry *entry;
  57
  58         TRACE("Entered squashfs_symlink_readpage, page index %ld, start block "
  59                         "%llx, offset %x\n", page->index, block, offset);
  60
  61         /*
  62          * Skip index bytes into symlink metadata.
  63          */
  64         if (index) {
  65                 bytes = squashfs_read_metadata(sb, NULL, &block, &offset,
  66                                                                 index);
  67                 if (bytes < 0) {
  68                         ERROR("Unable to read symlink [%llx:%x]\n",
  69                                 squashfs_i(inode)->start,
  70                                 squashfs_i(inode)->offset);
  71                         goto error_out;
  72                 }
  73         }
  74
  75         /*
  76          * Read length bytes from symlink metadata.  Squashfs_read_metadata
  77          * is not used here because it can sleep and we want to use
  78          * kmap_atomic to map the page.  Instead call the underlying
  79          * squashfs_cache_get routine.  As length bytes may overlap metadata
  80          * blocks, we may need to call squashfs_cache_get multiple times.
  81          */
  82         for (bytes = 0; bytes < length; offset = 0, bytes += copied) {
  83                 entry = squashfs_cache_get(sb, msblk->block_cache, block, 0);
  84                 if (entry->error) {
  85                         ERROR("Unable to read symlink [%llx:%x]\n",
  86                                 squashfs_i(inode)->start,
  87                                 squashfs_i(inode)->offset);
  88                         squashfs_cache_put(entry);
  89                         goto error_out;
  90                 }
  91
  92                 pageaddr = kmap_atomic(page, KM_USER0);
  93                 copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
  94                                                                 length - bytes);
  95                 if (copied == length - bytes)
  96                         memset(pageaddr + length, 0, PAGE_CACHE_SIZE - length);
  97                 else
  98                         block = entry->next_index;
  99                 kunmap_atomic(pageaddr, KM_USER0);
 100                 squashfs_cache_put(entry);
 101         }
 102
 103         flush_dcache_page(page);
 104         SetPageUptodate(page);
 105         unlock_page(page);
 106         return 0;
 107
 108 error_out:
 109         SetPageError(page);
 110         unlock_page(page);
 111         return 0;
 112 }
 113
 114
 115 const struct address_space_operations squashfs_symlink_aops = {
 116         .readpage = squashfs_symlink_readpage
 117 };