coda: add bdi backing to mount session

This ensures that dirty data gets flushed properly.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/linux/coda_psdev.h

@@ -1,6 +1,7 @@
 #ifndef __CODA_PSDEV_H
 #define __CODA_PSDEV_H
 
+#include <linux/backing-dev.h>
 #include <linux/magic.h>
 
 #define CODA_PSDEV_MAJOR 67
@@ -17,6 +18,7 @@ struct venus_comm {
 	struct list_head    vc_processing;
 	int                 vc_inuse;
 	struct super_block *vc_sb;
+	struct backing_dev_info bdi;
 };