To: akpm@linux-foundation.org, linux-embedded@vger.kernel.org,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
       tim.bird@am.sony.com
Subject: Subject: [PATCH 02/16] Squashfs: directory lookup operations
Message-Id: <E1KqrTW-0001xG-Cl@dylan>
From: Phillip Lougher <phillip@lougher.demon.co.uk>
Date: Fri, 17 Oct 2008 16:42:50 +0100
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 8142
Lines: 246


Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
---
 fs/squashfs/namei.c |  226 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 226 insertions(+), 0 deletions(-)

diff --git a/fs/squashfs/namei.c b/fs/squashfs/namei.c
new file mode 100644
index 0000000..fdc1b03
--- /dev/null
+++ b/fs/squashfs/namei.c
@@ -0,0 +1,226 @@
+/*
+ * 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.
+ *
+ * namei.c
+ */
+
+/*
+ * This file implements code to do filename lookup in directories.
+ *
+ * Like inodes, directories are packed into compressed metadata blocks, stored
+ * in a directory table.  Directories are accessed using the start address of
+ * the metablock containing the directory and the offset into the
+ * decompressed block (<block, offset>).
+ *
+ * Directories are organised in a slightly complex way, and are not simply
+ * a list of file names.  The organisation takes advantage of the
+ * fact that (in most cases) the inodes of the files will be in the same
+ * compressed metadata block, and therefore, can share the start block.
+ * Directories are therefore organised in a two level list, a directory
+ * header containing the shared start block value, and a sequence of directory
+ * entries, each of which share the shared start block.  A new directory header
+ * is written once/if the inode start block changes.  The directory
+ * header/directory entry list is repeated as many times as necessary.
+ *
+ * Directories are sorted, and can contain a directory index to speed up
+ * file lookup.  Directory indexes store one entry per metablock, each entry
+ * storing the index/filename mapping to the first directory header
+ * in each metadata block.  Directories are sorted in alphabetical order,
+ * and at lookup the index is scanned linearly looking for the first filename
+ * alphabetically larger than the filename being looked up.  At this point the
+ * location of the metadata block the filename is in has been found.
+ * The general idea of the index is ensure only one metadata block needs to be
+ * decompressed to do a lookup irrespective of the length of the directory.
+ * This scheme has the advantage that it doesn't require extra memory overhead
+ * and doesn't require much extra storage on disk.
+ */
+
+#include <linux/fs.h>
+#include <linux/vfs.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/dcache.h>
+#include <linux/zlib.h>
+#include <linux/squashfs_fs.h>
+#include <linux/squashfs_fs_sb.h>
+#include <linux/squashfs_fs_i.h>
+
+#include "squashfs.h"
+
+/*
+ * Lookup name in the directory index, returning the location of the metadata
+ * block containing it, and the directory index this represents.
+ */
+static int get_dir_index_using_name(struct super_block *s,
+			long long *next_block, unsigned int *next_offset,
+			long long index_start, unsigned int index_offset,
+			int i_count, const char *name, int len)
+{
+	struct squashfs_sb_info *msblk = s->s_fs_info;
+	int i, size, length = 0;
+	struct squashfs_dir_index *index;
+	char *str;
+
+	TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
+
+	str = kmalloc(sizeof(*index) + (SQUASHFS_NAME_LEN + 1) * 2, GFP_KERNEL);
+	if (str == NULL) {
+		ERROR("Failed to allocate squashfs_dir_index\n");
+		goto out;
+	}
+
+	index = (struct squashfs_dir_index *) (str + SQUASHFS_NAME_LEN + 1);
+	strncpy(str, name, len);
+	str[len] = '\0';
+
+	for (i = 0; i < i_count; i++) {
+		squashfs_read_metadata(s, index, index_start, index_offset,
+					sizeof(*index), &index_start,
+					&index_offset);
+
+		size = le32_to_cpu(index->size) + 1;
+
+		squashfs_read_metadata(s, index->name, index_start,
+					index_offset, size, &index_start,
+					&index_offset);
+
+		index->name[size] = '\0';
+
+		if (strcmp(index->name, str) > 0)
+			break;
+
+		length = le32_to_cpu(index->index);
+		*next_block = le32_to_cpu(index->start_block) +
+					msblk->directory_table_start;
+	}
+
+	*next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
+	kfree(str);
+
+out:
+	/*
+	 * Return index (f_pos) of the looked up metadata block.  Translate
+	 * from internal f_pos to external f_pos which is offset by 3 because
+	 * we invent "." and ".." entries which are not actually stored in the
+	 * directory.
+	 */
+	return length + 3;
+}
+
+
+static struct dentry *squashfs_lookup(struct inode *i, struct dentry *dentry,
+				struct nameidata *nd)
+{
+	const unsigned char *name = dentry->d_name.name;
+	int len = dentry->d_name.len;
+	struct inode *inode = NULL;
+	struct squashfs_sb_info *msblk = i->i_sb->s_fs_info;
+	long long next_block = SQUASHFS_I(i)->start_block +
+				msblk->directory_table_start;
+	int next_offset = SQUASHFS_I(i)->offset, length = 0, dir_count, size;
+	struct squashfs_dir_header dirh;
+	struct squashfs_dir_entry *dire;
+	unsigned int start_block, offset, ino_number;
+	long long ino;
+
+	TRACE("Entered squashfs_lookup [%llx:%x]\n", next_block, next_offset);
+
+	dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
+	if (dire == NULL) {
+		ERROR("Failed to allocate squashfs_dir_entry\n");
+		goto exit_lookup;
+	}
+
+	if (len > SQUASHFS_NAME_LEN)
+		goto exit_lookup;
+
+	length = get_dir_index_using_name(i->i_sb, &next_block, &next_offset,
+				SQUASHFS_I(i)->dir_index_start,
+				SQUASHFS_I(i)->dir_index_offset,
+				SQUASHFS_I(i)->dir_index_count, name, len);
+
+	while (length < i_size_read(i)) {
+		/*
+		 * Read directory header.
+		 */
+		if (!squashfs_read_metadata(i->i_sb, &dirh, next_block,
+				next_offset, sizeof(dirh), &next_block,
+				&next_offset))
+			goto failed_read;
+
+		length += sizeof(dirh);
+
+		dir_count = le32_to_cpu(dirh.count) + 1;
+		while (dir_count--) {
+			/*
+			 * Read directory entry.
+			 */
+			if (!squashfs_read_metadata(i->i_sb, dire,
+					next_block, next_offset, sizeof(*dire),
+					&next_block, &next_offset))
+				goto failed_read;
+
+			size = le16_to_cpu(dire->size) + 1;
+
+			if (!squashfs_read_metadata(i->i_sb, dire->name,
+					next_block, next_offset, size,
+					&next_block, &next_offset))
+				goto failed_read;
+
+			length += sizeof(*dire) + size;
+
+			if (name[0] < dire->name[0])
+				goto exit_lookup;
+
+			if (len == size && !strncmp(name, dire->name, len)) {
+				start_block = le32_to_cpu(dirh.start_block);
+				offset = le16_to_cpu(dire->offset);
+				ino_number = le32_to_cpu(dirh.inode_number) +
+					(short) le16_to_cpu(dire->inode_number);
+				ino = SQUASHFS_MKINODE(start_block, offset);
+
+				TRACE("calling squashfs_iget for directory "
+					"entry %s, inode  %x:%x, %d\n", name,
+					start_block, offset, ino_number);
+
+				inode = squashfs_iget(i->i_sb, ino, ino_number);
+
+				goto exit_lookup;
+			}
+		}
+	}
+
+exit_lookup:
+	kfree(dire);
+	if (inode)
+		return d_splice_alias(inode, dentry);
+	d_add(dentry, inode);
+	return ERR_PTR(0);
+
+failed_read:
+	ERROR("Unable to read directory block [%llx:%x]\n", next_block,
+		next_offset);
+	goto exit_lookup;
+}
+
+
+const struct inode_operations squashfs_dir_inode_ops = {
+	.lookup = squashfs_lookup
+};
-- 
1.5.2.5

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