Squashfs: symlink operations
Phillip Lougher [Mon, 5 Jan 2009 08:46:24 +0000 (08:46 +0000)]
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>

fs/squashfs/symlink.c [new file with mode: 0644]

diff --git a/fs/squashfs/symlink.c b/fs/squashfs/symlink.c
new file mode 100644 (file)
index 0000000..83d8788
--- /dev/null
@@ -0,0 +1,118 @@
+/*
+ * 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
+};