Date:	Thu, 16 Dec 2010 17:40:07 +0100
From:	stefani@...bold.net
To:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>
Cc:	stefani@...bold.net
Subject: [PATCH] cramfs: generate unique inode number for better inode cache usage

From: Stefani Seibold <stefani@...bold.net>

This is fourth version. Changelog
 - 12.12.2010 first version
 - 15.12.2010 code cleanup suggest by Linus
 - 16.12.2010 code cleanup suggset by Pekka Enberg
 - 16.12.2010 fix comment, move setup_inode() code into get_cramfs_inode()

This patch generates a unique inode numbers for any entries in the cram file
system. For files which did not contain data's (device nodes, fifos and
sockets) the offset of the directory entry inside the cramfs plus 1 will be
used as inode number.

The + 1 for the inode will it make possible to distinguish between
a file which contains no data and files which has data, the later one has
a inode value where the lower two bits are always 0.

It also reimplement the behavoir to set the size and the number of block
to 0 for special file, which is the right value for empty files,
devices, fifos and sockets

As a little benefit it will be also more compatible which older
mkcramfs, because it will never use the cramfs_inode->offset for
creating a inode number for special files.

The patch is aginst 2.6.37-rc5

Please apply it.

Thanks,
Stefani

Signed-off-by: Stefani Seibold <stefani@...bold.net>
---
 fs/cramfs/inode.c |  110 +++++++++++++++++++++++++++++++++--------------------
 1 files changed, 69 insertions(+), 41 deletions(-)

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 32fd5fe..dfb0029 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -34,57 +34,81 @@ static const struct address_space_operations cramfs_aops;
 static DEFINE_MUTEX(read_mutex);
 
 
-/* These two macros may change in future, to provide better st_ino
-   semantics. */
-#define CRAMINO(x)	(((x)->offset && (x)->size)?(x)->offset<<2:1)
+/* These macros may change in future, to provide better st_ino semantics. */
 #define OFFSET(x)	((x)->i_ino)
 
-static void setup_inode(struct inode *inode, struct cramfs_inode * cramfs_inode)
+static unsigned long cramino(struct cramfs_inode * cino, unsigned int offset)
 {
+	if (!cino->offset)
+		return offset + 1;
+	if (!cino->size)
+		return offset + 1;
+
+	/*
+	 * The file mode test fix buggy mkcramfs implementations where
+	 * cramfs_inode->offset is set to a non zero value for entries
+	 * which did not contain data, like devices node and fifos.
+	 */
+	switch (cino->mode & S_IFMT) {
+	case S_IFREG:
+	case S_IFDIR:
+	case S_IFLNK:
+		return cino->offset << 2;
+	default:
+		break;
+	}
+	return offset + 1;
+}
+
+static struct inode *get_cramfs_inode(struct super_block *sb,
+	struct cramfs_inode * cramfs_inode, unsigned int offset)
+{
+	struct inode *inode;
 	static struct timespec zerotime;
+
+	inode = iget_locked(sb, cramino(cramfs_inode, offset));
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+	if (!(inode->i_state & I_NEW))
+		return inode;
+
+	switch (cramfs_inode->mode & S_IFMT) {
+	case S_IFREG:
+		inode->i_fop = &generic_ro_fops;
+		inode->i_data.a_ops = &cramfs_aops;
+		break;
+	case S_IFDIR:
+		inode->i_op = &cramfs_dir_inode_operations;
+		inode->i_fop = &cramfs_directory_operations;
+		break;
+	case S_IFLNK:
+		inode->i_op = &page_symlink_inode_operations;
+		inode->i_data.a_ops = &cramfs_aops;
+		break;
+	default:
+		init_special_inode(inode, cramfs_inode->mode,
+				old_decode_dev(cramfs_inode->size));
+	}
+
 	inode->i_mode = cramfs_inode->mode;
 	inode->i_uid = cramfs_inode->uid;
-	inode->i_size = cramfs_inode->size;
-	inode->i_blocks = (cramfs_inode->size - 1) / 512 + 1;
 	inode->i_gid = cramfs_inode->gid;
+
+	/* if the lower 2 bits are zero, the inode contains data */
+	if (!(inode->i_ino & 3)) {
+		inode->i_size = cramfs_inode->size;
+		inode->i_blocks = (cramfs_inode->size - 1) / 512 + 1;
+	}
+
 	/* Struct copy intentional */
 	inode->i_mtime = inode->i_atime = inode->i_ctime = zerotime;
 	/* inode->i_nlink is left 1 - arguably wrong for directories,
 	   but it's the best we can do without reading the directory
 	   contents.  1 yields the right result in GNU find, even
 	   without -noleaf option. */
-	if (S_ISREG(inode->i_mode)) {
-		inode->i_fop = &generic_ro_fops;
-		inode->i_data.a_ops = &cramfs_aops;
-	} else if (S_ISDIR(inode->i_mode)) {
-		inode->i_op = &cramfs_dir_inode_operations;
-		inode->i_fop = &cramfs_directory_operations;
-	} else if (S_ISLNK(inode->i_mode)) {
-		inode->i_op = &page_symlink_inode_operations;
-		inode->i_data.a_ops = &cramfs_aops;
-	} else {
-		init_special_inode(inode, inode->i_mode,
-			old_decode_dev(cramfs_inode->size));
-	}
-}
 
-static struct inode *get_cramfs_inode(struct super_block *sb,
-				struct cramfs_inode * cramfs_inode)
-{
-	struct inode *inode;
-	if (CRAMINO(cramfs_inode) == 1) {
-		inode = new_inode(sb);
-		if (inode) {
-			inode->i_ino = 1;
-			setup_inode(inode, cramfs_inode);
-		}
-	} else {
-		inode = iget_locked(sb, CRAMINO(cramfs_inode));
-		if (inode && (inode->i_state & I_NEW)) {
-			setup_inode(inode, cramfs_inode);
-			unlock_new_inode(inode);
-		}
-	}
+	unlock_new_inode(inode);
+
 	return inode;
 }
 
@@ -265,6 +289,9 @@ static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 		printk(KERN_ERR "cramfs: root is not a directory\n");
 		goto out;
 	}
+	/* correct strange, hard-coded permissions of mkcramfs */
+	super.root.mode |= (S_IRUSR | S_IXUSR | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
+
 	root_offset = super.root.offset << 2;
 	if (super.flags & CRAMFS_FLAG_FSID_VERSION_2) {
 		sbi->size=super.size;
@@ -289,7 +316,7 @@ static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 
 	/* Set it all up.. */
 	sb->s_op = &cramfs_ops;
-	root = get_cramfs_inode(sb, &super.root);
+	root = get_cramfs_inode(sb, &super.root, 0);
 	if (!root)
 		goto out;
 	sb->s_root = d_alloc_root(root);
@@ -365,7 +392,7 @@ static int cramfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 		 */
 		namelen = de->namelen << 2;
 		memcpy(buf, name, namelen);
-		ino = CRAMINO(de);
+		ino = cramino(de, OFFSET(inode) + offset);
 		mode = de->mode;
 		mutex_unlock(&read_mutex);
 		nextoffset = offset + sizeof(*de) + namelen;
@@ -404,8 +431,9 @@ static struct dentry * cramfs_lookup(struct inode *dir, struct dentry *dentry, s
 		struct cramfs_inode *de;
 		char *name;
 		int namelen, retval;
+		int dir_off = OFFSET(dir) + offset;
 
-		de = cramfs_read(dir->i_sb, OFFSET(dir) + offset, sizeof(*de)+CRAMFS_MAXPATHLEN);
+		de = cramfs_read(dir->i_sb, dir_off, sizeof(*de)+CRAMFS_MAXPATHLEN);
 		name = (char *)(de+1);
 
 		/* Try to take advantage of sorted directories */
@@ -436,7 +464,7 @@ static struct dentry * cramfs_lookup(struct inode *dir, struct dentry *dentry, s
 		if (!retval) {
 			struct cramfs_inode entry = *de;
 			mutex_unlock(&read_mutex);
-			d_add(dentry, get_cramfs_inode(dir->i_sb, &entry));
+			d_add(dentry, get_cramfs_inode(dir->i_sb, &entry, dir_off));
 			return NULL;
 		}
 		/* else (retval < 0) */
-- 
1.7.3.3

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