sysfs: count subdirectories

sysfs: count subdirectories

This patch introduces a subdirectory counter for each sysfs directory.

Without the patch, sysfs_refresh_inode would walk all entries of the directory
to calculate the number of subdirectories.

This patch improves time of "ls -la /sys/block" when there are 10000 block
devices from 9 seconds to 0.19 seconds.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/dir.c

@@ -47,6 +47,9 @@ static void sysfs_link_sibling(struct sysfs_dirent *sd)
 
 	BUG_ON(sd->s_sibling);
 
+	if (sysfs_type(sd) == SYSFS_DIR)
+		parent_sd->s_dir.subdirs++;
+
 	/* Store directory entries in order by ino.  This allows
 	 * readdir to properly restart without having to add a
 	 * cursor into the s_dir.children list.
@@ -73,6 +76,9 @@ static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
 {
 	struct sysfs_dirent **pos;
 
+	if (sysfs_type(sd) == SYSFS_DIR)
+		sd->s_parent->s_dir.subdirs--;
+
 	for (pos = &sd->s_parent->s_dir.children; *pos;
 	     pos = &(*pos)->s_sibling) {
 		if (*pos == sd) {

fs/sysfs/inode.c

@@ -202,18 +202,6 @@ 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;
@@ -230,7 +218,7 @@ static void sysfs_refresh_inode(struct sysfs_dirent *sd, struct inode *inode)
 	}
 
 	if (sysfs_type(sd) == SYSFS_DIR)
-		inode->i_nlink = sysfs_count_nlink(sd);
+		inode->i_nlink = sd->s_dir.subdirs + 2;
 }
 
 int sysfs_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)

fs/sysfs/sysfs.h

@@ -19,6 +19,8 @@ struct sysfs_elem_dir {
 	struct kobject		*kobj;
 	/* children list starts here and goes through sd->s_sibling */
 	struct sysfs_dirent	*children;
+
+	unsigned long		subdirs;
 };
 
 struct sysfs_elem_symlink {