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@squashfs.org.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/string.h>
37 #include <linux/pagemap.h>
38 #include <linux/xattr.h>
39
40 #include "squashfs_fs.h"
41 #include "squashfs_fs_sb.h"
42 #include "squashfs_fs_i.h"
43 #include "squashfs.h"
44 #include "xattr.h"
45
squashfs_symlink_readpage(struct file * file,struct page * page)46 static 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);
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);
101 squashfs_cache_put(entry);
102 }
103
104 flush_dcache_page(page);
105 SetPageUptodate(page);
106 unlock_page(page);
107 return 0;
108
109 error_out:
110 SetPageError(page);
111 unlock_page(page);
112 return 0;
113 }
114
115
116 const struct address_space_operations squashfs_symlink_aops = {
117 .readpage = squashfs_symlink_readpage
118 };
119
120 const struct inode_operations squashfs_symlink_inode_ops = {
121 .readlink = generic_readlink,
122 .follow_link = page_follow_link_light,
123 .put_link = page_put_link,
124 .getxattr = generic_getxattr,
125 .listxattr = squashfs_listxattr
126 };
127
128