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