From fbffad1d5196fe2d3bec7a40a1ec209218fb6bda Mon Sep 17 00:00:00 2001
From: Zach Brown <zab@versity.com>
Date: Fri, 25 Oct 2019 11:34:49 -0700
Subject: [PATCH] scoutfs: add initial lock write_version

We need a way to compare two items in different log btrees and learn
which is the most recent.  Each time we grant a new write lock we give
it a larger write version.  Items store the version of the lock they're
written under.  Readers can now easily see which item is newer.

This is a trivial initial implementation which is not consistent across
unmount or server failover.   We'll need to recover the greatest
write_version from locks during recovery and from log trees as the
server starts up.

Signed-off-by: Zach Brown <zab@versity.com>
---
 kmod/src/format.h      | 1 +
 kmod/src/lock.c        | 1 +
 kmod/src/lock.h        | 5 +++--
 kmod/src/lock_server.c | 8 ++++++++
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/kmod/src/format.h b/kmod/src/format.h
index a167c5cc..cb804c4e 100644
--- a/kmod/src/format.h
+++ b/kmod/src/format.h
@@ -726,6 +726,7 @@ struct scoutfs_net_extent_list {
 
 struct scoutfs_net_lock {
 	struct scoutfs_key key;
+	__le64 write_version;
 	__u8 old_mode;
 	__u8 new_mode;
 } __packed;
diff --git a/kmod/src/lock.c b/kmod/src/lock.c
index 6397d573..c491ed22 100644
--- a/kmod/src/lock.c
+++ b/kmod/src/lock.c
@@ -587,6 +587,7 @@ int scoutfs_lock_grant_response(struct super_block *sb,
 
 	lock->request_pending = 0;
 	lock->mode = nl->new_mode;
+	lock->write_version = le64_to_cpu(nl->write_version);
 
 	if (lock_count_match_exists(nl->new_mode, lock->waiters))
 		extend_grace(sb, lock);
diff --git a/kmod/src/lock.h b/kmod/src/lock.h
index f61bbe70..a6f8a688 100644
--- a/kmod/src/lock.h
+++ b/kmod/src/lock.h
@@ -11,8 +11,8 @@
 #define SCOUTFS_LOCK_NR_MODES		SCOUTFS_LOCK_INVALID
 
 /*
- * A few fields (start, end, refresh_gen, granted_mode) are referenced
- * by code outside lock.c.
+ * A few fields (start, end, refresh_gen, write_version, granted_mode)
+ * are referenced by code outside lock.c.
  */
 struct scoutfs_lock {
 	struct super_block *sb;
@@ -21,6 +21,7 @@ struct scoutfs_lock {
 	struct rb_node node;
 	struct rb_node range_node;
 	u64 refresh_gen;
+	u64 write_version;
 	struct list_head lru_head;
 	wait_queue_head_t waitq;
 	struct work_struct shrink_work;
diff --git a/kmod/src/lock_server.c b/kmod/src/lock_server.c
index 5c393038..2199bb23 100644
--- a/kmod/src/lock_server.c
+++ b/kmod/src/lock_server.c
@@ -494,6 +494,8 @@ static int process_waiting_requests(struct super_block *sb,
 	struct client_lock_entry *req_tmp;
 	struct client_lock_entry *gr;
 	struct client_lock_entry *gr_tmp;
+	static atomic64_t write_version = ATOMIC64_INIT(0);
+	u64 wv;
 	int ret;
 
 	BUG_ON(!mutex_is_locked(&snode->mutex));
@@ -544,6 +546,12 @@ static int process_waiting_requests(struct super_block *sb,
 			nl.old_mode = SCOUTFS_LOCK_NULL;
 		}
 
+		if (nl.new_mode == SCOUTFS_LOCK_WRITE ||
+		    nl.new_mode == SCOUTFS_LOCK_WRITE_ONLY) {
+			wv = atomic64_inc_return(&write_version);
+			nl.write_version = cpu_to_le64(wv);
+		}
+
 		ret = scoutfs_server_lock_response(sb, req->rid,
 						   req->net_id, &nl);
 		if (ret)