Provide new_anon_inode function for inodes without a default inode number, and
not on sb list. This can enable filesystems to reduce locking. "Real"
filesystems can also reduce locking by allocating anonymous inode first, then
adding it to lists after finding the inode number.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

---
 fs/anon_inodes.c   |    2 +-
 fs/inode.c         |   32 +++++++++++++++++++++++++++++++-
 fs/pipe.c          |    3 ++-
 include/linux/fs.h |    2 ++
 net/socket.c       |    3 ++-
 5 files changed, 38 insertions(+), 4 deletions(-)

Index: linux-2.6/fs/inode.c
===================================================================
--- linux-2.6.orig/fs/inode.c	2010-10-19 14:18:59.000000000 +1100
+++ linux-2.6/fs/inode.c	2010-10-19 14:19:22.000000000 +1100
@@ -219,6 +219,7 @@
 #ifdef CONFIG_QUOTA
 	memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
 #endif
+	INIT_LIST_HEAD(&inode->i_sb_list);
 	inode->i_pipe = NULL;
 	inode->i_bdev = NULL;
 	inode->i_cdev = NULL;
@@ -761,6 +762,8 @@
  */
 static void inode_sb_list_del(struct inode *inode)
 {
+	if (list_empty(&inode->i_sb_list))
+		return;
 	lg_local_lock_cpu(inode_list_lglock, inode_list_cpu(inode));
 	list_del_rcu(&inode->i_sb_list);
 	lg_local_unlock_cpu(inode_list_lglock, inode_list_cpu(inode));
@@ -819,7 +822,7 @@
  */
 static DEFINE_PER_CPU(unsigned int, last_ino);
 
-static unsigned int get_next_ino(void)
+unsigned int get_next_ino(void)
 {
 	unsigned int res;
 
@@ -838,6 +841,7 @@
 	put_cpu();
 	return res;
 }
+EXPORT_SYMBOL(get_next_ino);
 
 /**
  *	new_inode 	- obtain an inode
@@ -870,6 +874,32 @@
 }
 EXPORT_SYMBOL(new_inode);
 
+/**
+ *	new_anon_inode 	- obtain an anonymous inode
+ *	@sb: superblock
+ *
+ *	Similar to new_inode, however the inode is not given an inode
+ *	number, and is not added to the sb's list of inodes, to reduce
+ *	overheads.
+ *
+ *	A filesystem which needs an inode number must subsequently
+ *	assign one to i_ino. A filesystem which needs inodes to be on the
+ *	per-sb list (currently only used by the vfs for umount or remount)
+ *	must add the inode to that list.
+ */
+struct inode *new_anon_inode(struct super_block *sb)
+{
+	struct inode *inode;
+
+	inode = alloc_inode(sb);
+	if (inode) {
+		inode->i_ino = ULONG_MAX;
+		inode->i_state = 0;
+	}
+	return inode;
+}
+EXPORT_SYMBOL(new_anon_inode);
+
 void unlock_new_inode(struct inode *inode)
 {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
Index: linux-2.6/fs/pipe.c
===================================================================
--- linux-2.6.orig/fs/pipe.c	2010-10-19 14:18:59.000000000 +1100
+++ linux-2.6/fs/pipe.c	2010-10-19 14:19:00.000000000 +1100
@@ -948,7 +948,7 @@
 
 static struct inode * get_pipe_inode(void)
 {
-	struct inode *inode = new_inode(pipe_mnt->mnt_sb);
+	struct inode *inode = new_anon_inode(pipe_mnt->mnt_sb);
 	struct pipe_inode_info *pipe;
 
 	if (!inode)
@@ -962,6 +962,7 @@
 	pipe->readers = pipe->writers = 1;
 	inode->i_fop = &rdwr_pipefifo_fops;
 
+	inode->i_ino = get_next_ino();
 	/*
 	 * Mark the inode dirty from the very beginning,
 	 * that way it will never be moved to the dirty
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h	2010-10-19 14:18:59.000000000 +1100
+++ linux-2.6/include/linux/fs.h	2010-10-19 14:19:21.000000000 +1100
@@ -2192,11 +2192,13 @@
 extern int insert_inode_locked(struct inode *);
 extern void unlock_new_inode(struct inode *);
 
+extern unsigned int get_next_ino(void);
 extern void iget_failed(struct inode *);
 extern void end_writeback(struct inode *);
 extern void destroy_inode(struct inode *);
 extern void __destroy_inode(struct inode *);
 extern struct inode *new_inode(struct super_block *);
+extern struct inode *new_anon_inode(struct super_block *);
 extern void free_inode_nonrcu(struct inode *inode);
 extern int should_remove_suid(struct dentry *);
 extern int file_remove_suid(struct file *);
Index: linux-2.6/net/socket.c
===================================================================
--- linux-2.6.orig/net/socket.c	2010-10-19 14:18:59.000000000 +1100
+++ linux-2.6/net/socket.c	2010-10-19 14:19:19.000000000 +1100
@@ -476,13 +476,14 @@
 	struct inode *inode;
 	struct socket *sock;
 
-	inode = new_inode(sock_mnt->mnt_sb);
+	inode = new_anon_inode(sock_mnt->mnt_sb);
 	if (!inode)
 		return NULL;
 
 	sock = SOCKET_I(inode);
 
 	kmemcheck_annotate_bitfield(sock, type);
+	inode->i_ino = get_next_ino();
 	inode->i_mode = S_IFSOCK | S_IRWXUGO;
 	inode->i_uid = current_fsuid();
 	inode->i_gid = current_fsgid();
Index: linux-2.6/fs/anon_inodes.c
===================================================================
--- linux-2.6.orig/fs/anon_inodes.c	2010-10-19 14:18:58.000000000 +1100
+++ linux-2.6/fs/anon_inodes.c	2010-10-19 14:19:19.000000000 +1100
@@ -191,7 +191,7 @@
  */
 static struct inode *anon_inode_mkinode(void)
 {
-	struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
+	struct inode *inode = new_anon_inode(anon_inode_mnt->mnt_sb);
 
 	if (!inode)
 		return ERR_PTR(-ENOMEM);


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