[PATCH 3/7] sysfs: Keep an nlink count on sysfs directories.

["Eric W. Biederman" <ebiederm@xmission.com>]

From: Eric W. Biederman <ebiederm@aristanetworks.com>

On large directories sysfs_count_nlinks can be a significant
bottleneck, so keep a count in sysfs_dirent.  If we exceed
the maximum number of directory entries we can store return
nlink of 1.  An nlink of 1 matches what reiserfs does in
this case, and it let's find and similar utlities know that
we have a the directory nlink can not be used for optimization
purposes.

Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
---
 fs/sysfs/dir.c   |   20 ++++++++++++++++++++
 fs/sysfs/inode.c |   15 +--------------
 fs/sysfs/mount.c |    1 +
 fs/sysfs/sysfs.h |    1 +
 4 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 5c4703d..1c364be 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -359,6 +359,7 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
 	sd->s_name = name;
 	sd->s_mode = mode;
 	sd->s_flags = type;
+	sd->s_nlink = type == SYSFS_DIR? 2:1;
 
 	return sd;
 
@@ -392,6 +393,23 @@ void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
 	mutex_lock(&sysfs_mutex);
 }
 
+static void sysfs_dir_inc_nlink(struct sysfs_dirent *sd)
+{
+	/* If we overflow force nlink to be 1 */
+	if (sd->s_nlink > 1) {
+		sd->s_nlink++;
+		if (sd->s_nlink == 0)
+			sd->s_nlink = 1;
+	}
+}
+
+static void sysfs_dir_dec_nlink(struct sysfs_dirent *sd)
+{
+	/* Don't decrement if we overflowed an increment */
+	if (sd->s_nlink != 1)
+		sd->s_nlink--;
+}
+
 /**
  *	__sysfs_add_one - add sysfs_dirent to parent without warning
  *	@acxt: addrm context to use
@@ -420,6 +438,7 @@ int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 		return -EEXIST;
 
 	sd->s_parent = sysfs_get(acxt->parent_sd);
+	sysfs_dir_inc_nlink(sd->s_parent);
 
 	sysfs_link_sibling(sd);
 
@@ -512,6 +531,7 @@ void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 
 	BUG_ON(sd->s_flags & SYSFS_FLAG_REMOVED);
 
+	sysfs_dir_dec_nlink(sd->s_parent);
 	sysfs_unlink_sibling(sd);
 
 	/* Update timestamps on the parent */
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 104cbc1..f0172b3 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -201,18 +201,6 @@ static inline void set_inode_attr(struct inode * inode, struct iattr * iattr)
 	inode->i_ctime = iattr->ia_ctime;
 }
 
-static int sysfs_count_nlink(struct sysfs_dirent *sd)
-{
-	struct sysfs_dirent *child;
-	int nr = 0;
-
-	for (child = sd->s_dir.children; child; child = child->s_sibling)
-		if (sysfs_type(child) == SYSFS_DIR)
-			nr++;
-
-	return nr + 2;
-}
-
 static void sysfs_refresh_inode(struct sysfs_dirent *sd, struct inode *inode)
 {
 	struct sysfs_inode_attrs *iattrs = sd->s_iattr;
@@ -228,8 +216,7 @@ static void sysfs_refresh_inode(struct sysfs_dirent *sd, struct inode *inode)
 					    iattrs->ia_secdata_len);
 	}
 
-	if (sysfs_type(sd) == SYSFS_DIR)
-		inode->i_nlink = sysfs_count_nlink(sd);
+	inode->i_nlink = sd->s_nlink;
 }
 
 int sysfs_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 4974995..372a32c 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -37,6 +37,7 @@ struct sysfs_dirent sysfs_root = {
 	.s_count	= ATOMIC_INIT(1),
 	.s_flags	= SYSFS_DIR,
 	.s_mode		= S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,
+	.s_nlink	= 2,
 	.s_ino		= 1,
 };
 
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 0417805..85d5c6c 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -67,6 +67,7 @@ struct sysfs_dirent {
 
 	unsigned int		s_flags;
 	unsigned short		s_mode;
+	unsigned short		s_nlink;
 	ino_t			s_ino;
 	struct sysfs_inode_attrs *s_iattr;
 };
-- 
1.6.5.2.143.g8cc62