dm ioctl: allow message to return data
This patch introduces enhanced message support that allows the
device-mapper core to recognise messages that are common to all devices,
and for messages to return data to userspace.
Core messages are processed by the function "message_for_md". If the
device mapper doesn't support the message, it is passed to the target
driver.
If the message returns data, the kernel sets the flag
DM_MESSAGE_OUT_FLAG.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index b8a6bdd..7e75b6f 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -336,4 +336,9 @@
*/
#define DM_SECURE_DATA_FLAG (1 << 15) /* In */
+/*
+ * If set, a message generated output data.
+ */
+#define DM_DATA_OUT_FLAG (1 << 16) /* Out */
+
#endif /* _LINUX_DM_IOCTL_H */