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 (at) 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 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, 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; 108 109 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
