[PATCH] provide a default super_block_operations

A little cleanup suggested by Chris Mason or Al Viro.

Quite a number of codepaths are testing whether a superblock has a
non-null ->s_op pointer.  We can remove all those by making sure that
all superblocks have a valid ->s_op.

fs/buffer.c

@@ -219,11 +219,10 @@ int fsync_super(struct super_block *sb)
 	sync_inodes_sb(sb, 0);
 	DQUOT_SYNC(sb);
 	lock_super(sb);
-	if (sb->s_dirt && sb->s_op && sb->s_op->write_super)
+	if (sb->s_dirt && sb->s_op->write_super)
 		sb->s_op->write_super(sb);
-	if (sb->s_op && sb->s_op->sync_fs) {
+	if (sb->s_op->sync_fs)
 		sb->s_op->sync_fs(sb, 1);
-	}
 	unlock_super(sb);
 	sync_blockdev(sb->s_bdev);
 	sync_inodes_sb(sb, 1);
@@ -281,7 +280,7 @@ int file_fsync(struct file *filp, struct dentry *dentry, int datasync)
 	/* sync the superblock to buffers */
 	sb = inode->i_sb;
 	lock_super(sb);
-	if (sb->s_op && sb->s_op->write_super)
+	if (sb->s_op->write_super)
 		sb->s_op->write_super(sb);
 	unlock_super(sb);
 

fs/fs-writeback.c

@@ -57,7 +57,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 	 * dirty the inode itself
 	 */
 	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
-		if (sb->s_op && sb->s_op->dirty_inode)
+		if (sb->s_op->dirty_inode)
 			sb->s_op->dirty_inode(inode);
 	}
 
@@ -101,8 +101,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 
 static void write_inode(struct inode *inode, int sync)
 {
-	if (inode->i_sb->s_op && inode->i_sb->s_op->write_inode &&
-			!is_bad_inode(inode))
+	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
 		inode->i_sb->s_op->write_inode(inode, sync);
 }
 

fs/inode.c

@@ -225,7 +225,7 @@ void clear_inode(struct inode *inode)
 		BUG();
 	wait_on_inode(inode);
 	DQUOT_DROP(inode);
-	if (inode->i_sb && inode->i_sb->s_op && inode->i_sb->s_op->clear_inode)
+	if (inode->i_sb && inode->i_sb->s_op->clear_inode)
 		inode->i_sb->s_op->clear_inode(inode);
 	if (inode->i_bdev)
 		bd_forget(inode);
@@ -937,7 +937,7 @@ void generic_delete_inode(struct inode *inode)
 
 	security_inode_delete(inode);
 
-	if (op && op->delete_inode) {
+	if (op->delete_inode) {
 		void (*delete)(struct inode *) = op->delete_inode;
 		if (!is_bad_inode(inode))
 			DQUOT_INIT(inode);

fs/open.c

@@ -29,7 +29,7 @@ int vfs_statfs(struct super_block *sb, struct statfs *buf)
 
 	if (sb) {
 		retval = -ENOSYS;
-		if (sb->s_op && sb->s_op->statfs) {
+		if (sb->s_op->statfs) {
 			memset(buf, 0, sizeof(struct statfs));
 			retval = security_sb_statfs(sb);
 			if (retval)

fs/super.c

@@ -49,6 +49,8 @@ spinlock_t sb_lock = SPIN_LOCK_UNLOCKED;
 static struct super_block *alloc_super(void)
 {
 	struct super_block *s = kmalloc(sizeof(struct super_block),  GFP_USER);
+	static struct super_operations default_op;
+
 	if (s) {
 		memset(s, 0, sizeof(struct super_block));
 		if (security_sb_alloc(s)) {
@@ -72,6 +74,7 @@ static struct super_block *alloc_super(void)
 		s->s_maxbytes = MAX_NON_LFS;
 		s->dq_op = sb_dquot_ops;
 		s->s_qcop = sb_quotactl_ops;
+		s->s_op = &default_op;
 	}
 out:
 	return s;
@@ -186,14 +189,13 @@ void generic_shutdown_super(struct super_block *sb)
 		sb->s_flags &= ~MS_ACTIVE;
 		/* bad name - it should be evict_inodes() */
 		invalidate_inodes(sb);
-		if (sop) {
+
 		if (sop->write_super && sb->s_dirt)
 			sop->write_super(sb);
 		if (sop->sync_fs)
 			sop->sync_fs(sb, 1);
 		if (sop->put_super)
 			sop->put_super(sb);
-		}
 
 		/* Forget any remaining inodes */
 		if (invalidate_inodes(sb)) {
@@ -268,7 +270,7 @@ void drop_super(struct super_block *sb)
 static inline void write_super(struct super_block *sb)
 {
 	lock_super(sb);
-	if (sb->s_op && sb->s_root && sb->s_dirt)
+	if (sb->s_root && sb->s_dirt)
 		if (sb->s_op->write_super)
 			sb->s_op->write_super(sb);
 	unlock_super(sb);
@@ -309,8 +311,6 @@ void sync_filesystems(int wait)
 	spin_lock(&sb_lock);
 	for (sb = sb_entry(super_blocks.next); sb != sb_entry(&super_blocks);
 			sb = sb_entry(sb->s_list.next)) {
-		if (!sb->s_op)
-			continue;
 		if (!sb->s_op->sync_fs);
 			continue;
 		if (sb->s_flags & MS_RDONLY)
@@ -438,7 +438,7 @@ int do_remount_sb(struct super_block *sb, int flags, void *data)
 	if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY))
 		if (!fs_may_remount_ro(sb))
 			return -EBUSY;
-	if (sb->s_op && sb->s_op->remount_fs) {
+	if (sb->s_op->remount_fs) {
 		lock_super(sb);
 		retval = sb->s_op->remount_fs(sb, &flags, data);
 		unlock_super(sb);