fuse: llseek optimize SEEK_CUR and SEEK_SET

Use generic_file_llseek() instead of open coding the seek function.

i_mutex protection is only necessary for SEEK_END (and SEEK_HOLE, SEEK_DATA), so
move SEEK_CUR and SEEK_SET out from under i_mutex.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/file.c

@@ -1555,48 +1555,16 @@ static loff_t fuse_file_llseek(struct file *file, loff_t offset, int origin)
 	loff_t retval;
 	struct inode *inode = file->f_path.dentry->d_inode;
 
-	mutex_lock(&inode->i_mutex);
-	if (origin != SEEK_CUR && origin != SEEK_SET) {
-		retval = fuse_update_attributes(inode, NULL, file, NULL);
-		if (retval)
-			goto exit;
-	}
+	/* No i_mutex protection necessary for SEEK_CUR and SEEK_SET */
+	if (origin == SEEK_CUR || origin == SEEK_SET)
+		return generic_file_llseek(file, offset, origin);
 
-	switch (origin) {
-	case SEEK_END:
-		offset += i_size_read(inode);
-		break;
-	case SEEK_CUR:
-		if (offset == 0) {
-			retval = file->f_pos;
-			goto exit;
-		}
-		offset += file->f_pos;
-		break;
-	case SEEK_DATA:
-		if (offset >= i_size_read(inode)) {
-			retval = -ENXIO;
-			goto exit;
-		}
-		break;
-	case SEEK_HOLE:
-		if (offset >= i_size_read(inode)) {
-			retval = -ENXIO;
-			goto exit;
-		}
-		offset = i_size_read(inode);
-		break;
-	}
-	retval = -EINVAL;
-	if (offset >= 0 && offset <= inode->i_sb->s_maxbytes) {
-		if (offset != file->f_pos) {
-			file->f_pos = offset;
-			file->f_version = 0;
-		}
-		retval = offset;
-	}
-exit:
+	mutex_lock(&inode->i_mutex);
+	retval = fuse_update_attributes(inode, NULL, file, NULL);
+	if (!retval)
+		retval = generic_file_llseek(file, offset, origin);
 	mutex_unlock(&inode->i_mutex);
+
 	return retval;
 }