sysfs: Add s_hash to sysfs_dirent and order directory entries by hash

Compute a 31 bit hash of directory entries (that can fit in a signed
32bit off_t) and index the sysfs directory entries by that hash,
replacing the per directory indexes by name and by inode.  Because we
now only use a single rbtree this reduces the size of sysfs_dirent by 2
pointers.  Because we have fewer cases to deal with the code is now
simpler.

For now I use the simple hash that the dcache uses as that is easy to
use and seems simple enough.

In addition to makeing the code simpler using a hash for the file
position in readdir brings sysfs in line with other filesystems that
have non-trivial directory structures.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 5 deletions

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 7484a36ee678..2b5c923b4b90 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -20,9 +20,8 @@ struct sysfs_elem_dir {
         struct kobject          *kobj;
 
         unsigned long           subdirs;
-
-        struct rb_root          inode_tree;
-        struct rb_root          name_tree;
+        /* children rbtree starts here and goes through sd->s_rb */
+        struct rb_root          children;
 };
 
 struct sysfs_elem_symlink {
@@ -62,8 +61,7 @@ struct sysfs_dirent {
         struct sysfs_dirent     *s_parent;
         const char              *s_name;
 
-        struct rb_node          inode_node;
-        struct rb_node          name_node;
+        struct rb_node          s_rb;
 
         union {
                 struct completion       *completion;
@@ -71,6 +69,7 @@ struct sysfs_dirent {
         } u;
 
         const void              *s_ns; /* namespace tag */
+        unsigned int            s_hash; /* ns + name hash */
         union {
                 struct sysfs_elem_dir           s_dir;
                 struct sysfs_elem_symlink       s_symlink;