[PATCH 4/4] md/raid5-cache: adjust the write position of the empty block and mark it as a checkpoint

[JackieLiu <liuyun01@kylinos.cn>]

When recovery is complete, we write an empty block and record his
position first, then make the data-only stripes rewritten done,
the location of the empty block as the last checkpoint position
to write into the super block. And we should update last_checkpoint
to this empty block position.

------------------------------------------------------------------
|  old log       | empty block | data only stripes | invalid log |
------------------------------------------------------------------
^                ^                                 ^
|                |- log->last_checkpoint           |- log->log_start
|                |- log->last_cp_seq               |- log->next_checkpoint
|- log->seq=n    |- log->seq=10+n

At the same time, if there is no data-only stripes, this scene may appear,
| meta1 | meta2 | meta3 |
meta 1 is valid, meta 2 is invalid. meta 3 could be valid. so we should 
The solution is we create a new meta in meta2 with its seq == meta1's 
seq + 10 and let superblock points to meta2. 

Reviewed-by: Zhengyuan Liu <liuzhengyuan@kylinos.cn>
Signed-off-by: JackieLiu <liuyun01@kylinos.cn>
---
 drivers/md/raid5-cache.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 9e72180..20594f7 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -2072,7 +2072,6 @@ r5c_recovery_rewrite_data_only_stripes(struct r5l_log *log,
 		return -ENOMEM;
 	}
 
-	ctx->seq += 10;
 	list_for_each_entry_safe(sh, next, &ctx->cached_list, lru) {
 		struct r5l_meta_block *mb;
 		int i;
@@ -2132,6 +2131,7 @@ static int r5l_recovery_log(struct r5l_log *log)
 	struct mddev *mddev = log->rdev->mddev;
 	struct r5l_recovery_ctx ctx;
 	int ret;
+	sector_t pos;
 
 	ctx.pos = log->last_checkpoint;
 	ctx.seq = log->last_cp_seq;
@@ -2149,6 +2149,10 @@ static int r5l_recovery_log(struct r5l_log *log)
 	if (ret)
 		return ret;
 
+	pos = ctx.pos;
+	r5l_log_write_empty_meta_block(log, ctx.pos, (ctx.seq += 10));
+	ctx.pos = r5l_ring_add(log, ctx.pos, BLOCK_SECTORS);
+
 	if ((ctx.data_only_stripes == 0) && (ctx.data_parity_stripes == 0))
 		pr_debug("md/raid:%s: starting from clean shutdown\n",
 			 mdname(mddev));
@@ -2167,9 +2171,9 @@ static int r5l_recovery_log(struct r5l_log *log)
 
 	log->log_start = ctx.pos;
 	log->next_checkpoint = ctx.pos;
+	log->last_checkpoint = pos;
 	log->seq = ctx.seq;
-	r5l_log_write_empty_meta_block(log, ctx.pos, ctx.seq);
-	r5l_write_super(log, ctx.pos);
+	r5l_write_super(log, pos);
 	return 0;
 }
 
-- 
2.7.4