Use ecryptfs_dentry_to_lower_path in a couple of places

There are two places in ecryptfs that benefit from using
ecryptfs_dentry_to_lower_path() instead of separate calls to
ecryptfs_dentry_to_lower() and ecryptfs_dentry_to_lower_mnt().  Both
sites use fewer instructions and less stack (determined by examining
objdump output).
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

fs/ecryptfs/file.c

@@ -49,7 +49,7 @@ static ssize_t ecryptfs_read_update_atime(struct kiocb *iocb,
 				unsigned long nr_segs, loff_t pos)
 {
 	ssize_t rc;
-	struct path lower;
+	struct path *path;
 	struct file *file = iocb->ki_filp;
 
 	rc = generic_file_aio_read(iocb, iov, nr_segs, pos);
@@ -60,9 +60,8 @@ static ssize_t ecryptfs_read_update_atime(struct kiocb *iocb,
 	if (-EIOCBQUEUED == rc)
 		rc = wait_on_sync_kiocb(iocb);
 	if (rc >= 0) {
-		lower.dentry = ecryptfs_dentry_to_lower(file->f_path.dentry);
-		lower.mnt = ecryptfs_dentry_to_lower_mnt(file->f_path.dentry);
-		touch_atime(&lower);
+		path = ecryptfs_dentry_to_lower_path(file->f_path.dentry);
+		touch_atime(path);
 	}
 	return rc;
 }

fs/ecryptfs/main.c

@@ -120,16 +120,15 @@ static int ecryptfs_init_lower_file(struct dentry *dentry,
 				    struct file **lower_file)
 {
 	const struct cred *cred = current_cred();
-	struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
-	struct vfsmount *lower_mnt = ecryptfs_dentry_to_lower_mnt(dentry);
+	struct path *path = ecryptfs_dentry_to_lower_path(dentry);
 	int rc;
 
-	rc = ecryptfs_privileged_open(lower_file, lower_dentry, lower_mnt,
+	rc = ecryptfs_privileged_open(lower_file, path->dentry, path->mnt,
 				      cred);
 	if (rc) {
 		printk(KERN_ERR "Error opening lower file "
 		       "for lower_dentry [0x%p] and lower_mnt [0x%p]; "
-		       "rc = [%d]\n", lower_dentry, lower_mnt, rc);
+		       "rc = [%d]\n", path->dentry, path->mnt, rc);
 		(*lower_file) = NULL;
 	}
 	return rc;