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>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index b8a6bddf0727..7e75b6fd8d45 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -336,4 +336,9 @@ enum {
  */
 #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 */