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Squashfs: symlink operations

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Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
This commit is contained in:
Phillip Lougher 2009-01-05 08:46:24 +00:00
parent 1701aecb68
commit 1dc4bba39d
1 changed files with 118 additions and 0 deletions
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fs/squashfs/symlink.c Normal file
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/*
* Squashfs - a compressed read only filesystem for Linux
*
* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
* Phillip Lougher <phillip@lougher.demon.co.uk>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2,
* or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* symlink.c
*/
/*
* This file implements code to handle symbolic links.
*
* The data contents of symbolic links are stored inside the symbolic
* link inode within the inode table. This allows the normally small symbolic
* link to be compressed as part of the inode table, achieving much greater
* compression than if the symbolic link was compressed individually.
*/
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/pagemap.h>
#include <linux/zlib.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"
static int squashfs_symlink_readpage(struct file *file, struct page *page)
{
struct inode *inode = page->mapping->host;
struct super_block *sb = inode->i_sb;
struct squashfs_sb_info *msblk = sb->s_fs_info;
int index = page->index << PAGE_CACHE_SHIFT;
u64 block = squashfs_i(inode)->start;
int offset = squashfs_i(inode)->offset;
int length = min_t(int, i_size_read(inode) - index, PAGE_CACHE_SIZE);
int bytes, copied;
void *pageaddr;
struct squashfs_cache_entry *entry;
TRACE("Entered squashfs_symlink_readpage, page index %ld, start block "
"%llx, offset %x\n", page->index, block, offset);
/*
* Skip index bytes into symlink metadata.
*/
if (index) {
bytes = squashfs_read_metadata(sb, NULL, &block, &offset,
index);
if (bytes < 0) {
ERROR("Unable to read symlink [%llx:%x]\n",
squashfs_i(inode)->start,
squashfs_i(inode)->offset);
goto error_out;
}
}
/*
* Read length bytes from symlink metadata. Squashfs_read_metadata
* is not used here because it can sleep and we want to use
* kmap_atomic to map the page. Instead call the underlying
* squashfs_cache_get routine. As length bytes may overlap metadata
* blocks, we may need to call squashfs_cache_get multiple times.
*/
for (bytes = 0; bytes < length; offset = 0, bytes += copied) {
entry = squashfs_cache_get(sb, msblk->block_cache, block, 0);
if (entry->error) {
ERROR("Unable to read symlink [%llx:%x]\n",
squashfs_i(inode)->start,
squashfs_i(inode)->offset);
squashfs_cache_put(entry);
goto error_out;
}
pageaddr = kmap_atomic(page, KM_USER0);
copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
length - bytes);
if (copied == length - bytes)
memset(pageaddr + length, 0, PAGE_CACHE_SIZE - length);
else
block = entry->next_index;
kunmap_atomic(pageaddr, KM_USER0);
squashfs_cache_put(entry);
}
flush_dcache_page(page);
SetPageUptodate(page);
unlock_page(page);
return 0;
error_out:
SetPageError(page);
unlock_page(page);
return 0;
}
const struct address_space_operations squashfs_symlink_aops = {
.readpage = squashfs_symlink_readpage
};