dax: unify ext2/4_{dax,}_file_operations

The original dax patchset split the ext2/4_file_operations because of the
two NULL splice_read/splice_write in the dax case.

In the vfs if splice_read/splice_write are NULL we then call
default_splice_read/write.

What we do here is make generic_file_splice_read aware of IS_DAX() so the
original ext2/4_file_operations can be used as is.

For write it appears that iter_file_splice_write is just fine.  It uses
the regular f_op->write(file,..) or new_sync_write(file, ...).

Signed-off-by: Boaz Harrosh <boaz@plexistor.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext2/file.c

@@ -109,24 +109,6 @@ const struct file_operations ext2_file_operations = {
 	.splice_write	= iter_file_splice_write,
 };
 
-#ifdef CONFIG_FS_DAX
-const struct file_operations ext2_dax_file_operations = {
-	.llseek		= generic_file_llseek,
-	.read		= new_sync_read,
-	.write		= new_sync_write,
-	.read_iter	= generic_file_read_iter,
-	.write_iter	= generic_file_write_iter,
-	.unlocked_ioctl = ext2_ioctl,
-#ifdef CONFIG_COMPAT
-	.compat_ioctl	= ext2_compat_ioctl,
-#endif
-	.mmap		= ext2_file_mmap,
-	.open		= dquot_file_open,
-	.release	= ext2_release_file,
-	.fsync		= ext2_fsync,
-};
-#endif
-
 const struct inode_operations ext2_file_inode_operations = {
 #ifdef CONFIG_EXT2_FS_XATTR
 	.setxattr	= generic_setxattr,