Fixed MTP to work with TWRP

fs/sdcardfs/mmap.c

@@ -0,0 +1,81 @@
+/*
+ * fs/sdcardfs/mmap.c
+ *
+ * Copyright (c) 2013 Samsung Electronics Co. Ltd
+ *   Authors: Daeho Jeong, Woojoong Lee, Seunghwan Hyun, 
+ *               Sunghwan Yun, Sungjong Seo
+ *                      
+ * This program has been developed as a stackable file system based on
+ * the WrapFS which written by 
+ *
+ * Copyright (c) 1998-2011 Erez Zadok
+ * Copyright (c) 2009     Shrikar Archak
+ * Copyright (c) 2003-2011 Stony Brook University
+ * Copyright (c) 2003-2011 The Research Foundation of SUNY
+ *
+ * This file is dual licensed.  It may be redistributed and/or modified
+ * under the terms of the Apache 2.0 License OR version 2 of the GNU
+ * General Public License.
+ */
+
+#include "sdcardfs.h"
+
+static int sdcardfs_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	int err;
+	struct file *file, *lower_file;
+	const struct vm_operations_struct *lower_vm_ops;
+	struct vm_area_struct lower_vma;
+
+	memcpy(&lower_vma, vma, sizeof(struct vm_area_struct));
+	file = lower_vma.vm_file;
+	lower_vm_ops = SDCARDFS_F(file)->lower_vm_ops;
+	BUG_ON(!lower_vm_ops);
+
+	lower_file = sdcardfs_lower_file(file);
+	/*
+	 * XXX: vm_ops->fault may be called in parallel.  Because we have to
+	 * resort to temporarily changing the vma->vm_file to point to the
+	 * lower file, a concurrent invocation of sdcardfs_fault could see a
+	 * different value.  In this workaround, we keep a different copy of
+	 * the vma structure in our stack, so we never expose a different
+	 * value of the vma->vm_file called to us, even temporarily.  A
+	 * better fix would be to change the calling semantics of ->fault to
+	 * take an explicit file pointer.
+	 */
+	lower_vma.vm_file = lower_file;
+	err = lower_vm_ops->fault(&lower_vma, vmf);
+	return err;
+}
+
+static ssize_t sdcardfs_direct_IO(int rw, struct kiocb *iocb,
+			      struct iov_iter *iter, loff_t offset)
+{
+	/* 
+	 * This function returns zero on purpose in order to support direct IO.
+	 * __dentry_open checks a_ops->direct_IO and returns EINVAL if it is null.
+	 * 
+	 * However, this function won't be called by certain file operations 
+	 * including generic fs functions.  * reads and writes are delivered to 
+	 * the lower file systems and the direct IOs will be handled by them. 
+	 * 
+	 * NOTE: exceptionally, on the recent kernels (since Linux 3.8.x), 
+	 * swap_writepage invokes this function directly. 
+	 */ 
+	printk(KERN_INFO "%s, operation is not supported\n", __func__);
+	return 0;
+}
+
+/*
+ * XXX: the default address_space_ops for sdcardfs is empty.  We cannot set
+ * our inode->i_mapping->a_ops to NULL because too many code paths expect
+ * the a_ops vector to be non-NULL.
+ */
+const struct address_space_operations sdcardfs_aops = {
+	/* empty on purpose */
+	.direct_IO	= sdcardfs_direct_IO,
+};
+
+const struct vm_operations_struct sdcardfs_vm_ops = {
+	.fault		= sdcardfs_fault,
+};