ocfs2: Negotiate locking protocol versions.

Currently, when ocfs2 nodes connect via TCP, they advertise their
compatibility level.  If the versions do not match, two nodes cannot speak
to each other and they disconnect. As a result, this provides no forward or
backwards compatibility.

This patch implements a simple protocol negotiation at the dlm level by
introducing a major/minor version number scheme for entities that
communicate.  Specifically, o2dlm has a major/minor version for interaction
with o2dlm on other nodes, and ocfs2 itself has a major/minor version for
interacting with the filesystem on other nodes.

This will allow rolling upgrades of ocfs2 clusters when changes to the
locking or network protocols can be done in a backwards compatible manner.
In those cases, only the minor number is changed and the negotatied protocol
minor is returned from dlm join. In the far less likely event that a
required protocol change makes backwards compatibility impossible, we simply
bump the major number.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

1 files changed, 23 insertions, 1 deletions

diff --git a/fs/ocfs2/dlm/dlmcommon.h b/fs/ocfs2/dlm/dlmcommon.h
index e90b92f9ece..9843ee17ea2 100644
--- a/fs/ocfs2/dlm/dlmcommon.h
+++ b/fs/ocfs2/dlm/dlmcommon.h
@@ -142,6 +142,12 @@ struct dlm_ctxt
 	spinlock_t work_lock;
 	struct list_head dlm_domain_handlers;
 	struct list_head	dlm_eviction_callbacks;
+
+	/* The filesystem specifies this at domain registration.  We
+	 * cache it here to know what to tell other nodes. */
+	struct dlm_protocol_version fs_locking_proto;
+	/* This is the inter-dlm communication version */
+	struct dlm_protocol_version dlm_locking_proto;
 };
 
 static inline struct hlist_head *dlm_lockres_hash(struct dlm_ctxt *dlm, unsigned i)
@@ -589,10 +595,24 @@ struct dlm_proxy_ast
 #define DLM_PROXY_AST_MAX_LEN  (sizeof(struct dlm_proxy_ast)+DLM_LVB_LEN)
 
 #define DLM_MOD_KEY (0x666c6172)
-enum dlm_query_join_response {
+enum dlm_query_join_response_code {
 	JOIN_DISALLOW = 0,
 	JOIN_OK,
 	JOIN_OK_NO_MAP,
+	JOIN_PROTOCOL_MISMATCH,
+};
+
+union dlm_query_join_response {
+	u32 intval;
+	struct {
+		u8 code;	/* Response code.  dlm_minor and fs_minor
+				   are only valid if this is JOIN_OK */
+		u8 dlm_minor;	/* The minor version of the protocol the
+				   dlm is speaking. */
+		u8 fs_minor;	/* The minor version of the protocol the
+				   filesystem is speaking. */
+		u8 reserved;
+	} packet;
 };
 
 struct dlm_lock_request
@@ -633,6 +653,8 @@ struct dlm_query_join_request
 	u8 node_idx;
 	u8 pad1[2];
 	u8 name_len;
+	struct dlm_protocol_version dlm_proto;
+	struct dlm_protocol_version fs_proto;
 	u8 domain[O2NM_MAX_NAME_LEN];
 	u8 node_map[BITS_TO_BYTES(O2NM_MAX_NODES)];
 };