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>

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;
 }
 

drivers/md/dm-log-userspace-transfer.c

@@ -198,6 +198,7 @@ int dm_consult_userspace(const char *uuid, uint64_t luid, int request_type,
 
 	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++;
 

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 */