vfs: split __lookup_hash

Split __lookup_hash into two component functions:

 lookup_dcache - tries cached lookup, returns whether real lookup is needed
 lookup_real - calls i_op->lookup

This eliminates code duplication between d_alloc_and_lookup() and
d_inode_lookup().
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1054,53 +1054,65 @@ static void follow_dotdot(struct nameidata *nd)
 }
 
 /*
- * Allocate a dentry with name and parent, and perform a parent
- * directory ->lookup on it. Returns the new dentry, or ERR_PTR
- * on error. parent->d_inode->i_mutex must be held. d_lookup must
- * have verified that no child exists while under i_mutex.
+ * This looks up the name in dcache, possibly revalidates the old dentry and
+ * allocates a new one if not found or not valid.  In the need_lookup argument
+ * returns whether i_op->lookup is necessary.
+ *
+ * dir->d_inode->i_mutex must be held
  */
-static struct dentry *d_alloc_and_lookup(struct dentry *parent,
-				struct qstr *name, struct nameidata *nd)
+static struct dentry *lookup_dcache(struct qstr *name, struct dentry *dir,
+				    struct nameidata *nd, bool *need_lookup)
 {
-	struct inode *inode = parent->d_inode;
 	struct dentry *dentry;
-	struct dentry *old;
+	int error;
 
-	/* Don't create child dentry for a dead directory. */
-	if (unlikely(IS_DEADDIR(inode)))
-		return ERR_PTR(-ENOENT);
+	*need_lookup = false;
+	dentry = d_lookup(dir, name);
+	if (dentry) {
+		if (d_need_lookup(dentry)) {
+			*need_lookup = true;
+		} else if (dentry->d_flags & DCACHE_OP_REVALIDATE) {
+			error = d_revalidate(dentry, nd);
+			if (unlikely(error <= 0)) {
+				if (error < 0) {
+					dput(dentry);
+					return ERR_PTR(error);
+				} else if (!d_invalidate(dentry)) {
+					dput(dentry);
+					dentry = NULL;
+				}
+			}
+		}
+	}
 
-	dentry = d_alloc(parent, name);
+	if (!dentry) {
+		dentry = d_alloc(dir, name);
 		if (unlikely(!dentry))
 			return ERR_PTR(-ENOMEM);
 
-	old = inode->i_op->lookup(inode, dentry, nd);
-	if (unlikely(old)) {
-		dput(dentry);
-		dentry = old;
+		*need_lookup = true;
 	}
 	return dentry;
 }
 
 /*
- * We already have a dentry, but require a lookup to be performed on the parent
- * directory to fill in d_inode. Returns the new dentry, or ERR_PTR on error.
- * parent->d_inode->i_mutex must be held. d_lookup must have verified that no
- * child exists while under i_mutex.
+ * Call i_op->lookup on the dentry.  The dentry must be negative but may be
+ * hashed if it was pouplated with DCACHE_NEED_LOOKUP.
+ *
+ * dir->d_inode->i_mutex must be held
  */
-static struct dentry *d_inode_lookup(struct dentry *parent, struct dentry *dentry,
+static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
 				  struct nameidata *nd)
 {
-	struct inode *inode = parent->d_inode;
 	struct dentry *old;
 
 	/* Don't create child dentry for a dead directory. */
-	if (unlikely(IS_DEADDIR(inode))) {
+	if (unlikely(IS_DEADDIR(dir))) {
 		dput(dentry);
 		return ERR_PTR(-ENOENT);
 	}
 
-	old = inode->i_op->lookup(inode, dentry, nd);
+	old = dir->i_op->lookup(dir, dentry, nd);
 	if (unlikely(old)) {
 		dput(dentry);
 		dentry = old;
@@ -1111,46 +1123,14 @@ static struct dentry *d_inode_lookup(struct dentry *parent, struct dentry *dentr
 static struct dentry *__lookup_hash(struct qstr *name,
 		struct dentry *base, struct nameidata *nd)
 {
+	bool need_lookup;
 	struct dentry *dentry;
 
-	/*
-	 * Don't bother with __d_lookup: callers are for creat as
-	 * well as unlink, so a lot of the time it would cost
-	 * a double lookup.
-	 */
-	dentry = d_lookup(base, name);
-
-	if (dentry && d_need_lookup(dentry)) {
-		/*
-		 * __lookup_hash is called with the parent dir's i_mutex already
-		 * held, so we are good to go here.
-		 */
-		return d_inode_lookup(base, dentry, nd);
-	}
-
-	if (dentry && (dentry->d_flags & DCACHE_OP_REVALIDATE)) {
-		int status = d_revalidate(dentry, nd);
-		if (unlikely(status <= 0)) {
-			/*
-			 * The dentry failed validation.
-			 * If d_revalidate returned 0 attempt to invalidate
-			 * the dentry otherwise d_revalidate is asking us
-			 * to return a fail status.
-			 */
-			if (status < 0) {
-				dput(dentry);
-				return ERR_PTR(status);
-			} else if (!d_invalidate(dentry)) {
-				dput(dentry);
-				dentry = NULL;
-			}
-		}
-	}
-
-	if (!dentry)
-		dentry = d_alloc_and_lookup(base, name, nd);
-
+	dentry = lookup_dcache(name, base, nd, &need_lookup);
+	if (!need_lookup)
 		return dentry;
+
+	return lookup_real(base->d_inode, dentry, nd);
 }
 
 /*