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Linux/fs/squashfs/symlink.c

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  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 
 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_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_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_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         .get_link = page_get_link,
122         .listxattr = squashfs_listxattr
123 };
124 
125 

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