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>

3 files changed, 17 insertions, 3 deletions

diff --git a/drivers/md/dm-log-userspace-base.c b/drivers/md/dm-log-userspace-base.c
index 31e1687e7bf6..aa2e0c374ab3 100644
--- a/drivers/md/dm-log-userspace-base.c
+++ b/drivers/md/dm-log-userspace-base.c
@@ -12,6 +12,8 @@
 
 #include "dm-log-userspace-transfer.h"
 
+#define DM_LOG_USERSPACE_VSN "1.1.0"
+
 struct flush_entry {
         int type;
         region_t region;
@@ -765,7 +767,7 @@ static int __init userspace_dirty_log_init(void)
                 return r;
         }
 
-        DMINFO("version 1.0.0 loaded");
+        DMINFO("version " DM_LOG_USERSPACE_VSN " loaded");
         return 0;
 }
 
@@ -775,7 +777,7 @@ static void __exit userspace_dirty_log_exit(void)
         dm_ulog_tfr_exit();
         mempool_destroy(flush_entry_pool);
 
-        DMINFO("version 1.0.0 unloaded");
+        DMINFO("version " DM_LOG_USERSPACE_VSN " unloaded");
         return;
 }
 
diff --git a/drivers/md/dm-log-userspace-transfer.c b/drivers/md/dm-log-userspace-transfer.c
index 075cbcf8a9f5..049eaf12aaab 100644
--- a/drivers/md/dm-log-userspace-transfer.c
+++ b/drivers/md/dm-log-userspace-transfer.c
@@ -198,6 +198,7 @@ resend:
 
         memset(tfr, 0, DM_ULOG_PREALLOCED_SIZE - sizeof(struct cn_msg));
         memcpy(tfr->uuid, uuid, DM_UUID_LEN);
+        tfr->version = DM_ULOG_REQUEST_VERSION;
         tfr->luid = luid;
         tfr->seq = dm_ulog_seq++;
 
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 */