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>

2 files changed, 120 insertions, 108 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 7fdf6a7b7436..0daf255b7bf9 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -22,76 +22,103 @@
 #include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/security.h>
+#include <linux/hash.h>
 #include "sysfs.h"
 
 DEFINE_MUTEX(sysfs_mutex);
 DEFINE_SPINLOCK(sysfs_assoc_lock);
 
+#define to_sysfs_dirent(X) rb_entry((X), struct sysfs_dirent, s_rb);
+
 static DEFINE_SPINLOCK(sysfs_ino_lock);
 static DEFINE_IDA(sysfs_ino_ida);
 
 /**
- *      sysfs_link_sibling - link sysfs_dirent into sibling list
+ *      sysfs_name_hash
+ *      @ns:   Namespace tag to hash
+ *      @name: Null terminated string to hash
+ *
+ *      Returns 31 bit hash of ns + name (so it fits in an off_t )
+ */
+static unsigned int sysfs_name_hash(const void *ns, const char *name)
+{
+        unsigned long hash = init_name_hash();
+        unsigned int len = strlen(name);
+        while (len--)
+                hash = partial_name_hash(*name++, hash);
+        hash = ( end_name_hash(hash) ^ hash_ptr( (void *)ns, 31 ) );
+        hash &= 0x7fffffffU;
+        /* Reserve hash numbers 0, 1 and INT_MAX for magic directory entries */
+        if (hash < 1)
+                hash += 2;
+        if (hash >= INT_MAX)
+                hash = INT_MAX - 1;
+        return hash;
+}
+
+static int sysfs_name_compare(unsigned int hash, const void *ns,
+        const char *name, const struct sysfs_dirent *sd)
+{
+        if (hash != sd->s_hash)
+                return hash - sd->s_hash;
+        if (ns != sd->s_ns)
+                return ns - sd->s_ns;
+        return strcmp(name, sd->s_name);
+}
+
+static int sysfs_sd_compare(const struct sysfs_dirent *left,
+                            const struct sysfs_dirent *right)
+{
+        return sysfs_name_compare(left->s_hash, left->s_ns, left->s_name,
+                                  right);
+}
+
+/**
+ *      sysfs_link_subling - link sysfs_dirent into sibling rbtree
  *      @sd: sysfs_dirent of interest
  *
- *      Link @sd into its sibling list which starts from
+ *      Link @sd into its sibling rbtree which starts from
  *      sd->s_parent->s_dir.children.
  *
  *      Locking:
  *      mutex_lock(sysfs_mutex)
+ *
+ *      RETURNS:
+ *      0 on susccess -EEXIST on failure.
  */
-static void sysfs_link_sibling(struct sysfs_dirent *sd)
+static int sysfs_link_sibling(struct sysfs_dirent *sd)
 {
-        struct sysfs_dirent *parent_sd = sd->s_parent;
-
-        struct rb_node **p;
-        struct rb_node *parent;
+        struct rb_node **node = &sd->s_parent->s_dir.children.rb_node;
+        struct rb_node *parent = NULL;
 
         if (sysfs_type(sd) == SYSFS_DIR)
-                parent_sd->s_dir.subdirs++;
-
-        p = &parent_sd->s_dir.inode_tree.rb_node;
-        parent = NULL;
-        while (*p) {
-                parent = *p;
-#define node    rb_entry(parent, struct sysfs_dirent, inode_node)
-                if (sd->s_ino < node->s_ino) {
-                        p = &node->inode_node.rb_left;
-                } else if (sd->s_ino > node->s_ino) {
-                        p = &node->inode_node.rb_right;
-                } else {
-                        printk(KERN_CRIT "sysfs: inserting duplicate inode '%lx'\n",
-                               (unsigned long) sd->s_ino);
-                        BUG();
-                }
-#undef node
-        }
-        rb_link_node(&sd->inode_node, parent, p);
-        rb_insert_color(&sd->inode_node, &parent_sd->s_dir.inode_tree);
-
-        p = &parent_sd->s_dir.name_tree.rb_node;
-        parent = NULL;
-        while (*p) {
-                int c;
-                parent = *p;
-#define node    rb_entry(parent, struct sysfs_dirent, name_node)
-                c = strcmp(sd->s_name, node->s_name);
-                if (c < 0) {
-                        p = &node->name_node.rb_left;
-                } else {
-                        p = &node->name_node.rb_right;
-                }
-#undef node
+                sd->s_parent->s_dir.subdirs++;
+
+        while (*node) {
+                struct sysfs_dirent *pos;
+                int result;
+
+                pos = to_sysfs_dirent(*node);
+                parent = *node;
+                result = sysfs_sd_compare(sd, pos);
+                if (result < 0)
+                        node = &pos->s_rb.rb_left;
+                else if (result > 0)
+                        node = &pos->s_rb.rb_right;
+                else
+                        return -EEXIST;
         }
-        rb_link_node(&sd->name_node, parent, p);
-        rb_insert_color(&sd->name_node, &parent_sd->s_dir.name_tree);
+        /* add new node and rebalance the tree */
+        rb_link_node(&sd->s_rb, parent, node);
+        rb_insert_color(&sd->s_rb, &sd->s_parent->s_dir.children);
+        return 0;
 }
 
 /**
- *      sysfs_unlink_sibling - unlink sysfs_dirent from sibling list
+ *      sysfs_unlink_sibling - unlink sysfs_dirent from sibling rbtree
  *      @sd: sysfs_dirent of interest
  *
- *      Unlink @sd from its sibling list which starts from
+ *      Unlink @sd from its sibling rbtree which starts from
  *      sd->s_parent->s_dir.children.
  *
  *      Locking:
@@ -102,8 +129,7 @@ static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
         if (sysfs_type(sd) == SYSFS_DIR)
                 sd->s_parent->s_dir.subdirs--;
 
-        rb_erase(&sd->inode_node, &sd->s_parent->s_dir.inode_tree);
-        rb_erase(&sd->name_node, &sd->s_parent->s_dir.name_tree);
+        rb_erase(&sd->s_rb, &sd->s_parent->s_dir.children);
 }
 
 /**
@@ -402,6 +428,7 @@ void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
 int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 {
         struct sysfs_inode_attrs *ps_iattr;
+        int ret;
 
         if (!!sysfs_ns_type(acxt->parent_sd) != !!sd->s_ns) {
                 WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
@@ -410,12 +437,12 @@ int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
                 return -EINVAL;
         }
 
-        if (sysfs_find_dirent(acxt->parent_sd, sd->s_ns, sd->s_name))
-                return -EEXIST;
-
+        sd->s_hash = sysfs_name_hash(sd->s_ns, sd->s_name);
         sd->s_parent = sysfs_get(acxt->parent_sd);
 
-        sysfs_link_sibling(sd);
+        ret = sysfs_link_sibling(sd);
+        if (ret)
+                return ret;
 
         /* Update timestamps on the parent */
         ps_iattr = acxt->parent_sd->s_iattr;
@@ -565,8 +592,8 @@ struct sysfs_dirent *sysfs_find_dirent(struct sysfs_dirent *parent_sd,
                                        const void *ns,
                                        const unsigned char *name)
 {
-        struct rb_node *p = parent_sd->s_dir.name_tree.rb_node;
-        struct sysfs_dirent *found = NULL;
+        struct rb_node *node = parent_sd->s_dir.children.rb_node;
+        unsigned int hash;
 
         if (!!sysfs_ns_type(parent_sd) != !!ns) {
                 WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
@@ -575,33 +602,21 @@ struct sysfs_dirent *sysfs_find_dirent(struct sysfs_dirent *parent_sd,
                 return NULL;
         }
 
-        while (p) {
-                int c;
-#define node    rb_entry(p, struct sysfs_dirent, name_node)
-                c = strcmp(name, node->s_name);
-                if (c < 0) {
-                        p = node->name_node.rb_left;
-                } else if (c > 0) {
-                        p = node->name_node.rb_right;
-                } else {
-                        found = node;
-                        p = node->name_node.rb_left;
-                }
-#undef node
-        }
-
-        if (found) {
-                while (found->s_ns != ns) {
-                        p = rb_next(&found->name_node);
-                        if (!p)
-                                return NULL;
-                        found = rb_entry(p, struct sysfs_dirent, name_node);
-                        if (strcmp(name, found->s_name))
-                                return NULL;
-                }
+        hash = sysfs_name_hash(ns, name);
+        while (node) {
+                struct sysfs_dirent *sd;
+                int result;
+
+                sd = to_sysfs_dirent(node);
+                result = sysfs_name_compare(hash, ns, name, sd);
+                if (result < 0)
+                        node = node->rb_left;
+                else if (result > 0)
+                        node = node->rb_right;
+                else
+                        return sd;
         }
-
-        return found;
+        return NULL;
 }
 
 /**
@@ -804,9 +819,9 @@ static void __sysfs_remove_dir(struct sysfs_dirent *dir_sd)
 
         pr_debug("sysfs %s: removing dir\n", dir_sd->s_name);
         sysfs_addrm_start(&acxt, dir_sd);
-        pos = rb_first(&dir_sd->s_dir.inode_tree);
+        pos = rb_first(&dir_sd->s_dir.children);
         while (pos) {
-                struct sysfs_dirent *sd = rb_entry(pos, struct sysfs_dirent, inode_node);
+                struct sysfs_dirent *sd = to_sysfs_dirent(pos);
                 pos = rb_next(pos);
                 if (sysfs_type(sd) != SYSFS_DIR)
                         sysfs_remove_one(&acxt, sd);
@@ -919,38 +934,36 @@ static int sysfs_dir_release(struct inode *inode, struct file *filp)
 }
 
 static struct sysfs_dirent *sysfs_dir_pos(const void *ns,
-        struct sysfs_dirent *parent_sd, ino_t ino, struct sysfs_dirent *pos)
+        struct sysfs_dirent *parent_sd, loff_t hash, struct sysfs_dirent *pos)
 {
         if (pos) {
                 int valid = !(pos->s_flags & SYSFS_FLAG_REMOVED) &&
                         pos->s_parent == parent_sd &&
-                        ino == pos->s_ino;
+                        hash == pos->s_hash;
                 sysfs_put(pos);
                 if (!valid)
                         pos = NULL;
         }
-        if (!pos && (ino > 1) && (ino < INT_MAX)) {
-                struct rb_node *p = parent_sd->s_dir.inode_tree.rb_node;
-                while (p) {
-#define node    rb_entry(p, struct sysfs_dirent, inode_node)
-                        if (ino < node->s_ino) {
-                                pos = node;
-                                p = node->inode_node.rb_left;
-                        } else if (ino > node->s_ino) {
-                                p = node->inode_node.rb_right;
-                        } else {
-                                pos = node;
+        if (!pos && (hash > 1) && (hash < INT_MAX)) {
+                struct rb_node *node = parent_sd->s_dir.children.rb_node;
+                while (node) {
+                        pos = to_sysfs_dirent(node);
+
+                        if (hash < pos->s_hash)
+                                node = node->rb_left;
+                        else if (hash > pos->s_hash)
+                                node = node->rb_right;
+                        else
                                 break;
-                        }
-#undef node
                 }
         }
+        /* Skip over entries in the wrong namespace */
         while (pos && pos->s_ns != ns) {
-                struct rb_node *p = rb_next(&pos->inode_node);
-                if (!p)
+                struct rb_node *node = rb_next(&pos->s_rb);
+                if (!node)
                         pos = NULL;
                 else
-                        pos = rb_entry(p, struct sysfs_dirent, inode_node);
+                        pos = to_sysfs_dirent(node);
         }
         return pos;
 }
@@ -960,11 +973,11 @@ static struct sysfs_dirent *sysfs_dir_next_pos(const void *ns,
 {
         pos = sysfs_dir_pos(ns, parent_sd, ino, pos);
         if (pos) do {
-                struct rb_node *p = rb_next(&pos->inode_node);
-                if (!p)
+                struct rb_node *node = rb_next(&pos->s_rb);
+                if (!node)
                         pos = NULL;
                 else
-                        pos = rb_entry(p, struct sysfs_dirent, inode_node);
+                        pos = to_sysfs_dirent(node);
         } while (pos && pos->s_ns != ns);
         return pos;
 }
@@ -1006,7 +1019,7 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
                 len = strlen(name);
                 ino = pos->s_ino;
                 type = dt_type(pos);
-                filp->f_pos = ino;
+                filp->f_pos = pos->s_hash;
                 filp->private_data = sysfs_get(pos);
 
                 mutex_unlock(&sysfs_mutex);
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;