vfs: get rid of 'struct dcache_hash_bucket' abstraction

It's a useless abstraction for 'hlist_bl_head', and it doesn't actually
help anything - quite the reverse. All the users end up having to know
about the hlist_bl_head details anyway, using 'struct hlist_bl_node *'
etc. So it just makes the code look confusing.

And the cost of it is extra '&b->head' syntactic noise, but more
importantly it spuriously makes the hash table dentry list look
different from the per-superblock DCACHE_DISCONNECTED dentry list.

As a result, the code ended up using ad-hoc locking for one case and
special helper functions for what is really another totally identical
case in the very same function.

Make it all look and work the same.

Signed-off-by: Linus Torvalds <[e-mail]>

fs/dcache.c

···
 static unsigned int d_hash_mask __read_mostly;
 static unsigned int d_hash_shift __read_mostly;
 
-struct dcache_hash_bucket {
-	struct hlist_bl_head head;
-};
-static struct dcache_hash_bucket *dentry_hashtable __read_mostly;
+static struct hlist_bl_head *dentry_hashtable __read_mostly;
 
-static inline struct dcache_hash_bucket *d_hash(struct dentry *parent,
+static inline struct hlist_bl_head *d_hash(struct dentry *parent,
 					unsigned long hash)
 {
 	hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
···
 	return dentry_hashtable + (hash & D_HASHMASK);
 }
 
-static inline void spin_lock_bucket(struct dcache_hash_bucket *b)
+static inline void spin_lock_bucket(struct hlist_bl_head *b)
 {
-	bit_spin_lock(0, (unsigned long *)&b->head.first);
+	bit_spin_lock(0, (unsigned long *)&b->first);
 }
 
-static inline void spin_unlock_bucket(struct dcache_hash_bucket *b)
+static inline void spin_unlock_bucket(struct hlist_bl_head *b)
 {
-	__bit_spin_unlock(0, (unsigned long *)&b->head.first);
+	__bit_spin_unlock(0, (unsigned long *)&b->first);
 }
 
 /* Statistics gathering. */
···
 void __d_drop(struct dentry *dentry)
 {
 	if (!(dentry->d_flags & DCACHE_UNHASHED)) {
+		struct hlist_bl_head *b;
 		if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED)) {
-			bit_spin_lock(0,
-				(unsigned long *)&dentry->d_sb->s_anon.first);
+			b = &dentry->d_sb->s_anon;
+			spin_lock_bucket(b);
 			dentry->d_flags |= DCACHE_UNHASHED;
 			hlist_bl_del_init(&dentry->d_hash);
-			__bit_spin_unlock(0,
-				(unsigned long *)&dentry->d_sb->s_anon.first);
+			spin_unlock_bucket(b);
 		} else {
-			struct dcache_hash_bucket *b;
+			struct hlist_bl_head *b;
 			b = d_hash(dentry->d_parent, dentry->d_name.hash);
 			spin_lock_bucket(b);
 			/*
···
 	unsigned int len = name->len;
 	unsigned int hash = name->hash;
 	const unsigned char *str = name->name;
-	struct dcache_hash_bucket *b = d_hash(parent, hash);
+	struct hlist_bl_head *b = d_hash(parent, hash);
 	struct hlist_bl_node *node;
 	struct dentry *dentry;
 
···
 	 *
 	 * See Documentation/filesystems/path-lookup.txt for more details.
 	 */
-	hlist_bl_for_each_entry_rcu(dentry, node, &b->head, d_hash) {
+	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
 		struct inode *i;
 		const char *tname;
 		int tlen;
···
 	unsigned int len = name->len;
 	unsigned int hash = name->hash;
 	const unsigned char *str = name->name;
-	struct dcache_hash_bucket *b = d_hash(parent, hash);
+	struct hlist_bl_head *b = d_hash(parent, hash);
 	struct hlist_bl_node *node;
 	struct dentry *found = NULL;
 	struct dentry *dentry;
···
 	 */
 	rcu_read_lock();
 	
-	hlist_bl_for_each_entry_rcu(dentry, node, &b->head, d_hash) {
+	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
 		const char *tname;
 		int tlen;
 
···
 }
 EXPORT_SYMBOL(d_delete);
 
-static void __d_rehash(struct dentry * entry, struct dcache_hash_bucket *b)
+static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
 {
 	BUG_ON(!d_unhashed(entry));
 	spin_lock_bucket(b);
  	entry->d_flags &= ~DCACHE_UNHASHED;
-	hlist_bl_add_head_rcu(&entry->d_hash, &b->head);
+	hlist_bl_add_head_rcu(&entry->d_hash, b);
 	spin_unlock_bucket(b);
 }
 
···
 
 	dentry_hashtable =
 		alloc_large_system_hash("Dentry cache",
-					sizeof(struct dcache_hash_bucket),
+					sizeof(struct hlist_bl_head),
 					dhash_entries,
 					13,
 					HASH_EARLY,
···
 					0);
 
 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
-		INIT_HLIST_BL_HEAD(&dentry_hashtable[loop].head);
+		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
 }
 
 static void __init dcache_init(void)
···
 
 	dentry_hashtable =
 		alloc_large_system_hash("Dentry cache",
-					sizeof(struct dcache_hash_bucket),
+					sizeof(struct hlist_bl_head),
 					dhash_entries,
 					13,
 					0,
···
 					0);
 
 	for (loop = 0; loop < (1 << d_hash_shift); loop++)
-		INIT_HLIST_BL_HEAD(&dentry_hashtable[loop].head);
+		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
 }
 
 /* SLAB cache for __getname() consumers */