[PATCH] dcache: Add helper d_hash_and_lookup

It is very common to hash a dentry and then to call lookup.  If we take fs
specific hash functions into account the full hash logic can get ugly.
Further full_name_hash as an inline function is almost 100 bytes on x86 so
having a non-inline choice in some cases can measurably decrease code size.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/dcache.c

@@ -1100,6 +1100,32 @@ struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
  	return found;
 }
 
+/**
+ * d_hash_and_lookup - hash the qstr then search for a dentry
+ * @dir: Directory to search in
+ * @name: qstr of name we wish to find
+ *
+ * On hash failure or on lookup failure NULL is returned.
+ */
+struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
+{
+	struct dentry *dentry = NULL;
+
+	/*
+	 * Check for a fs-specific hash function. Note that we must
+	 * calculate the standard hash first, as the d_op->d_hash()
+	 * routine may choose to leave the hash value unchanged.
+	 */
+	name->hash = full_name_hash(name->name, name->len);
+	if (dir->d_op && dir->d_op->d_hash) {
+		if (dir->d_op->d_hash(dir, name) < 0)
+			goto out;
+	}
+	dentry = d_lookup(dir, name);
+out:
+	return dentry;
+}
+
 /**
  * d_validate - verify dentry provided from insecure source
  * @dentry: The dentry alleged to be valid child of @dparent
@@ -1616,26 +1642,12 @@ ino_t find_inode_number(struct dentry *dir, struct qstr *name)
 	struct dentry * dentry;
 	ino_t ino = 0;
 
-	/*
-	 * Check for a fs-specific hash function. Note that we must
-	 * calculate the standard hash first, as the d_op->d_hash()
-	 * routine may choose to leave the hash value unchanged.
-	 */
-	name->hash = full_name_hash(name->name, name->len);
-	if (dir->d_op && dir->d_op->d_hash)
-	{
-		if (dir->d_op->d_hash(dir, name) != 0)
-			goto out;
-	}
-
-	dentry = d_lookup(dir, name);
-	if (dentry)
-	{
+	dentry = d_hash_and_lookup(dir, name);
+	if (dentry) {
 		if (dentry->d_inode)
 			ino = dentry->d_inode->i_ino;
 		dput(dentry);
 	}
-out:
 	return ino;
 }
 

include/linux/dcache.h

@@ -275,6 +275,7 @@ extern void d_move(struct dentry *, struct dentry *);
 /* appendix may either be NULL or be used for transname suffixes */
 extern struct dentry * d_lookup(struct dentry *, struct qstr *);
 extern struct dentry * __d_lookup(struct dentry *, struct qstr *);
+extern struct dentry * d_hash_and_lookup(struct dentry *, struct qstr *);
 
 /* validate "insecure" dentry pointer */
 extern int d_validate(struct dentry *, struct dentry *);