ANDROID: sdcardfs: support direct-IO (DIO) operations

This comes from the wrapfs
commit 2e346c83b26e ("Wrapfs: support direct-IO (DIO) operations")

Signed-off-by: Li Mengyang <li.mengyang@stonybrook.edu>
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Bug: 34133558
Change-Id: I3fd779c510ab70d56b1d918f99c20421b524cdc4

fs/sdcardfs/mmap.c

@@ -84,27 +84,14 @@ static int sdcardfs_page_mkwrite(struct vm_area_struct *vma,
 static ssize_t sdcardfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 {
 	/*
-     * 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.
+	 * This function should never be called directly.  We need it
+	 * to exist, to get past a check in open_check_o_direct(),
+	 * which is called from do_last().
 	 */
-	printk(KERN_INFO "%s, operation is not supported\n", __func__);
-	return 0;
+	return -EINVAL;
 }
 
-/*
- * 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,
 };
 

fs/sdcardfs/sdcardfs.h

@@ -29,6 +29,7 @@
 #include <linux/dcache.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/aio.h>
 #include <linux/mm.h>
 #include <linux/mount.h>
 #include <linux/namei.h>