1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0-or-later
2*4882a593Smuzhiyun /*
3*4882a593Smuzhiyun * Squashfs - a compressed read only filesystem for Linux
4*4882a593Smuzhiyun *
5*4882a593Smuzhiyun * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
6*4882a593Smuzhiyun * Phillip Lougher <phillip@squashfs.org.uk>
7*4882a593Smuzhiyun *
8*4882a593Smuzhiyun * symlink.c
9*4882a593Smuzhiyun */
10*4882a593Smuzhiyun
11*4882a593Smuzhiyun /*
12*4882a593Smuzhiyun * This file implements code to handle symbolic links.
13*4882a593Smuzhiyun *
14*4882a593Smuzhiyun * The data contents of symbolic links are stored inside the symbolic
15*4882a593Smuzhiyun * link inode within the inode table. This allows the normally small symbolic
16*4882a593Smuzhiyun * link to be compressed as part of the inode table, achieving much greater
17*4882a593Smuzhiyun * compression than if the symbolic link was compressed individually.
18*4882a593Smuzhiyun */
19*4882a593Smuzhiyun
20*4882a593Smuzhiyun #include <linux/fs.h>
21*4882a593Smuzhiyun #include <linux/vfs.h>
22*4882a593Smuzhiyun #include <linux/kernel.h>
23*4882a593Smuzhiyun #include <linux/string.h>
24*4882a593Smuzhiyun #include <linux/pagemap.h>
25*4882a593Smuzhiyun #include <linux/xattr.h>
26*4882a593Smuzhiyun
27*4882a593Smuzhiyun #include "squashfs_fs.h"
28*4882a593Smuzhiyun #include "squashfs_fs_sb.h"
29*4882a593Smuzhiyun #include "squashfs_fs_i.h"
30*4882a593Smuzhiyun #include "squashfs.h"
31*4882a593Smuzhiyun #include "xattr.h"
32*4882a593Smuzhiyun
squashfs_symlink_readpage(struct file * file,struct page * page)33*4882a593Smuzhiyun static int squashfs_symlink_readpage(struct file *file, struct page *page)
34*4882a593Smuzhiyun {
35*4882a593Smuzhiyun struct inode *inode = page->mapping->host;
36*4882a593Smuzhiyun struct super_block *sb = inode->i_sb;
37*4882a593Smuzhiyun struct squashfs_sb_info *msblk = sb->s_fs_info;
38*4882a593Smuzhiyun int index = page->index << PAGE_SHIFT;
39*4882a593Smuzhiyun u64 block = squashfs_i(inode)->start;
40*4882a593Smuzhiyun int offset = squashfs_i(inode)->offset;
41*4882a593Smuzhiyun int length = min_t(int, i_size_read(inode) - index, PAGE_SIZE);
42*4882a593Smuzhiyun int bytes, copied;
43*4882a593Smuzhiyun void *pageaddr;
44*4882a593Smuzhiyun struct squashfs_cache_entry *entry;
45*4882a593Smuzhiyun
46*4882a593Smuzhiyun TRACE("Entered squashfs_symlink_readpage, page index %ld, start block "
47*4882a593Smuzhiyun "%llx, offset %x\n", page->index, block, offset);
48*4882a593Smuzhiyun
49*4882a593Smuzhiyun /*
50*4882a593Smuzhiyun * Skip index bytes into symlink metadata.
51*4882a593Smuzhiyun */
52*4882a593Smuzhiyun if (index) {
53*4882a593Smuzhiyun bytes = squashfs_read_metadata(sb, NULL, &block, &offset,
54*4882a593Smuzhiyun index);
55*4882a593Smuzhiyun if (bytes < 0) {
56*4882a593Smuzhiyun ERROR("Unable to read symlink [%llx:%x]\n",
57*4882a593Smuzhiyun squashfs_i(inode)->start,
58*4882a593Smuzhiyun squashfs_i(inode)->offset);
59*4882a593Smuzhiyun goto error_out;
60*4882a593Smuzhiyun }
61*4882a593Smuzhiyun }
62*4882a593Smuzhiyun
63*4882a593Smuzhiyun /*
64*4882a593Smuzhiyun * Read length bytes from symlink metadata. Squashfs_read_metadata
65*4882a593Smuzhiyun * is not used here because it can sleep and we want to use
66*4882a593Smuzhiyun * kmap_atomic to map the page. Instead call the underlying
67*4882a593Smuzhiyun * squashfs_cache_get routine. As length bytes may overlap metadata
68*4882a593Smuzhiyun * blocks, we may need to call squashfs_cache_get multiple times.
69*4882a593Smuzhiyun */
70*4882a593Smuzhiyun for (bytes = 0; bytes < length; offset = 0, bytes += copied) {
71*4882a593Smuzhiyun entry = squashfs_cache_get(sb, msblk->block_cache, block, 0);
72*4882a593Smuzhiyun if (entry->error) {
73*4882a593Smuzhiyun ERROR("Unable to read symlink [%llx:%x]\n",
74*4882a593Smuzhiyun squashfs_i(inode)->start,
75*4882a593Smuzhiyun squashfs_i(inode)->offset);
76*4882a593Smuzhiyun squashfs_cache_put(entry);
77*4882a593Smuzhiyun goto error_out;
78*4882a593Smuzhiyun }
79*4882a593Smuzhiyun
80*4882a593Smuzhiyun pageaddr = kmap_atomic(page);
81*4882a593Smuzhiyun copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
82*4882a593Smuzhiyun length - bytes);
83*4882a593Smuzhiyun if (copied == length - bytes)
84*4882a593Smuzhiyun memset(pageaddr + length, 0, PAGE_SIZE - length);
85*4882a593Smuzhiyun else
86*4882a593Smuzhiyun block = entry->next_index;
87*4882a593Smuzhiyun kunmap_atomic(pageaddr);
88*4882a593Smuzhiyun squashfs_cache_put(entry);
89*4882a593Smuzhiyun }
90*4882a593Smuzhiyun
91*4882a593Smuzhiyun flush_dcache_page(page);
92*4882a593Smuzhiyun SetPageUptodate(page);
93*4882a593Smuzhiyun unlock_page(page);
94*4882a593Smuzhiyun return 0;
95*4882a593Smuzhiyun
96*4882a593Smuzhiyun error_out:
97*4882a593Smuzhiyun SetPageError(page);
98*4882a593Smuzhiyun unlock_page(page);
99*4882a593Smuzhiyun return 0;
100*4882a593Smuzhiyun }
101*4882a593Smuzhiyun
102*4882a593Smuzhiyun
103*4882a593Smuzhiyun const struct address_space_operations squashfs_symlink_aops = {
104*4882a593Smuzhiyun .readpage = squashfs_symlink_readpage
105*4882a593Smuzhiyun };
106*4882a593Smuzhiyun
107*4882a593Smuzhiyun const struct inode_operations squashfs_symlink_inode_ops = {
108*4882a593Smuzhiyun .get_link = page_get_link,
109*4882a593Smuzhiyun .listxattr = squashfs_listxattr
110*4882a593Smuzhiyun };
111*4882a593Smuzhiyun
112