ceph: add LAZYIO ioctl to mark a file description for lazy consistency

Allow an application to mark a file descriptor for lazy file consistency
semantics, allowing buffered reads and writes when multiple clients are
accessing the same file.

Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/ioctl.h

@@ -37,4 +37,6 @@ struct ceph_ioctl_dataloc {
 #define CEPH_IOC_GET_DATALOC _IOWR(CEPH_IOCTL_MAGIC, 3,	\
 				   struct ceph_ioctl_dataloc)
 
+#define CEPH_IOC_LAZYIO _IO(CEPH_IOCTL_MAGIC, 4)
+
 #endif