[Sheepdog] [PATCH v2] sheep: need not read many copies of bitmap

[yaohaiting.wujue at gmail.com]

From: HaiTing Yao <wujue.yht at taobao.com>

Node maybe need read all of the bitmaps when the epoch is not zero. This
perhaps occurs when we restart the shutdown cluster or join one once
existed node.

Usually, node need not read many copies of bitmap. If the cluster status
is OK and the node status is waiting for format, node just need read one
bitamp.

Signed-off-by: HaiTing Yao <wujue.yht at taobao.com>
---
 sheep/group.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)

changes from v1
Sometimes node only need read one copy of bitmap, and sometimes it
need read all of copies of bitmap. I added some comments to make it
more clear. 

diff --git a/sheep/group.c b/sheep/group.c
index c7fd387..d7ceae7 100644
--- a/sheep/group.c
+++ b/sheep/group.c
@@ -720,9 +720,17 @@ static void __sd_join(struct event_struct *cevent)
 	if (sys_stat_ok())
 		return;
 
-	get_vdi_bitmap_from_sd_list();
-	for (i = 0; i < w->member_list_entries; i++)
-		get_vdi_bitmap_from(w->member_list + i);
+	/*
+	* If a new comer try to join the running cluster, it only need read
+	* one copy of bitmap from the first member.
+	*/
+	if (sys_stat_wait_format())
+		get_vdi_bitmap_from(w->member_list);
+	else {
+		get_vdi_bitmap_from_sd_list();
+		for (i = 0; i < w->member_list_entries; i++)
+			get_vdi_bitmap_from(w->member_list + i);
+	}
 }
 
 static void __sd_leave(struct event_struct *cevent)
-- 
1.7.1