[sheepdog] [PATCH v2] sheep: let gateway node exit in a case of gateway only cluster

[Hitoshi Mitake]

When a cluster has gateway nodes only, it means the gateway nodes
doesn't contribute to I/O of VMs. So this patch simply let them exit
and avoid the below recovery issue.

Related issue:
https://bugs.launchpad.net/sheepdog-project/+bug/1327037

Cc: duron800 at qq.com
Cc: Yang Zhang <3100100878 at zju.edu.cn>
Cc: long <nxtxiaolong at gmail.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
---
 sheep/group.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

v2: remove needless logging

diff --git a/sheep/group.c b/sheep/group.c
index 095b7c5..5dc3284 100644
--- a/sheep/group.c
+++ b/sheep/group.c
@@ -1151,6 +1151,18 @@ main_fn void sd_accept_handler(const struct sd_node *joined,
 	}
 }
 
+static bool is_gateway_only_cluster(const struct rb_root *nroot)
+{
+	struct sd_node *n;
+
+	rb_for_each_entry(n, nroot, rb) {
+		if (n->space)
+			return false;
+	}
+
+	return true;
+}
+
 main_fn void sd_leave_handler(const struct sd_node *left,
 			      const struct rb_root *nroot, size_t nr_nodes)
 {
@@ -1177,6 +1189,11 @@ main_fn void sd_leave_handler(const struct sd_node *left,
 	old_vnode_info = main_thread_get(current_vnode_info);
 	main_thread_set(current_vnode_info, alloc_vnode_info(nroot));
 	if (sys->cinfo.status == SD_STATUS_OK) {
+		if (is_gateway_only_cluster(nroot)) {
+			sd_info("only gateway nodes are remaining, exiting");
+			exit(0);
+		}
+
 		ret = inc_and_log_epoch();
 		if (ret != 0)
 			panic("cannot log current epoch %d", sys->cinfo.epoch);
-- 
1.9.1