dm log userspace: add version number to comms

This patch adds a 'version' field to the 'dm_ulog_request'
structure.

The 'version' field is taken from a portion of the unused
'padding' field in the 'dm_ulog_request' structure.  This
was done to avoid changing the size of the structure and
possibly disrupting backwards compatibility.

The version number will help notify user-space daemons
when a change has been made to the kernel/userspace
log API.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/include/linux/dm-log-userspace.h b/include/linux/dm-log-userspace.h
index 0c3c3a2110c4..eeace7d3ff15 100644
--- a/include/linux/dm-log-userspace.h
+++ b/include/linux/dm-log-userspace.h
@@ -370,6 +370,16 @@
 #define DM_ULOG_REQUEST_TYPE(request_type) \
         (DM_ULOG_REQUEST_MASK & (request_type))
 
+/*
+ * DM_ULOG_REQUEST_VERSION is incremented when there is a
+ * change to the way information is passed between kernel
+ * and userspace.  This could be a structure change of
+ * dm_ulog_request or a change in the way requests are
+ * issued/handled.  Changes are outlined here:
+ *      version 1:  Initial implementation
+ */
+#define DM_ULOG_REQUEST_VERSION 1
+
 struct dm_ulog_request {
         /*
          * The local unique identifier (luid) and the universally unique
@@ -383,8 +393,9 @@ struct dm_ulog_request {
          */
         uint64_t luid;
         char uuid[DM_UUID_LEN];
-        char padding[7];        /* Padding because DM_UUID_LEN = 129 */
+        char padding[3];        /* Padding because DM_UUID_LEN = 129 */
 
+        uint32_t version;       /* See DM_ULOG_REQUEST_VERSION */
         int32_t error;          /* Used to report back processing errors */
 
         uint32_t seq;           /* Sequence number for request */