[Tarantool-patches] [PATCH v2 1/5] replication: introduce ballot.can_lead

[Vladislav Shpilevoy via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

The flag tells whether the sender has election mode 'candidate' or
'manual'.

The new field during bootstrap will help to avoid selecting a
'voter' as a master. Voters can't write, they are unable to boot
themselves nor register others.

@TarantoolBot document
Title: New field - IPROTO_BALLOT_CAN_LEAD
It is sent as a part of `IPROTO_BALLOT (0x29)`. The field is a
boolean flag which is true if the sender has `election_mode` in
its config `'manual'` or `'candidate'`.

During bootstrap the nodes able to become a leader are preferred
over the nodes configured as `'voter'`.

The field key is `0x07`.
---
 src/box/box.cc             |  3 +++
 src/box/iproto_constants.h |  1 +
 src/box/xrow.c             | 14 ++++++++++++--
 src/box/xrow.h             |  2 ++
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index eeb57b04e..800f4d76f 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -2881,6 +2881,9 @@ void
 box_process_vote(struct ballot *ballot)
 {
 	ballot->is_ro_cfg = cfg_geti("read_only") != 0;
+	enum election_mode mode = box_check_election_mode();
+	ballot->can_lead = mode == ELECTION_MODE_CANDIDATE ||
+			   mode == ELECTION_MODE_MANUAL;
 	ballot->is_anon = replication_anon;
 	ballot->is_ro = is_ro_summary;
 	ballot->is_booted = is_box_configured;
diff --git a/src/box/iproto_constants.h b/src/box/iproto_constants.h
index 137bee9da..ea7290da6 100644
--- a/src/box/iproto_constants.h
+++ b/src/box/iproto_constants.h
@@ -168,6 +168,7 @@ enum iproto_ballot_key {
 	IPROTO_BALLOT_IS_RO = 0x04,
 	IPROTO_BALLOT_IS_ANON = 0x05,
 	IPROTO_BALLOT_IS_BOOTED = 0x06,
+	IPROTO_BALLOT_CAN_LEAD = 0x07,
 };
 
 #define bit(c) (1ULL<<IPROTO_##c)
diff --git a/src/box/xrow.c b/src/box/xrow.c
index 16cb2484c..cffaee0a5 100644
--- a/src/box/xrow.c
+++ b/src/box/xrow.c
@@ -459,7 +459,9 @@ iproto_reply_vote(struct obuf *out, const struct ballot *ballot,
 		mp_sizeof_uint(UINT32_MAX) +
 		mp_sizeof_vclock_ignore0(&ballot->vclock) +
 		mp_sizeof_uint(UINT32_MAX) +
-		mp_sizeof_vclock_ignore0(&ballot->gc_vclock);
+		mp_sizeof_vclock_ignore0(&ballot->gc_vclock) +
+		mp_sizeof_uint(IPROTO_BALLOT_CAN_LEAD) +
+		mp_sizeof_bool(ballot->can_lead);
 
 	char *buf = obuf_reserve(out, max_size);
 	if (buf == NULL) {
@@ -471,7 +473,7 @@ iproto_reply_vote(struct obuf *out, const struct ballot *ballot,
 	char *data = buf + IPROTO_HEADER_LEN;
 	data = mp_encode_map(data, 1);
 	data = mp_encode_uint(data, IPROTO_BALLOT);
-	data = mp_encode_map(data, 6);
+	data = mp_encode_map(data, 7);
 	data = mp_encode_uint(data, IPROTO_BALLOT_IS_RO_CFG);
 	data = mp_encode_bool(data, ballot->is_ro_cfg);
 	data = mp_encode_uint(data, IPROTO_BALLOT_IS_RO);
@@ -484,6 +486,8 @@ iproto_reply_vote(struct obuf *out, const struct ballot *ballot,
 	data = mp_encode_vclock_ignore0(data, &ballot->vclock);
 	data = mp_encode_uint(data, IPROTO_BALLOT_GC_VCLOCK);
 	data = mp_encode_vclock_ignore0(data, &ballot->gc_vclock);
+	data = mp_encode_uint(data, IPROTO_BALLOT_CAN_LEAD);
+	data = mp_encode_bool(data, ballot->can_lead);
 	size_t size = data - buf;
 	assert(size <= max_size);
 
@@ -1362,6 +1366,7 @@ int
 xrow_decode_ballot(struct xrow_header *row, struct ballot *ballot)
 {
 	ballot->is_ro_cfg = false;
+	ballot->can_lead = false;
 	ballot->is_ro = false;
 	ballot->is_anon = false;
 	ballot->is_booted = true;
@@ -1434,6 +1439,11 @@ xrow_decode_ballot(struct xrow_header *row, struct ballot *ballot)
 				goto err;
 			ballot->is_booted = mp_decode_bool(&data);
 			break;
+		case IPROTO_BALLOT_CAN_LEAD:
+			if (mp_typeof(*data) != MP_BOOL)
+				goto err;
+			ballot->can_lead = mp_decode_bool(&data);
+			break;
 		default:
 			mp_next(&data);
 		}
diff --git a/src/box/xrow.h b/src/box/xrow.h
index 9f61bfd47..000cd6b88 100644
--- a/src/box/xrow.h
+++ b/src/box/xrow.h
@@ -368,6 +368,8 @@ xrow_encode_auth(struct xrow_header *row, const char *salt, size_t salt_len,
 struct ballot {
 	/** Set if the instance is configured in read-only mode. */
 	bool is_ro_cfg;
+	/** Set if the instance can become a Raft leader. */
+	bool can_lead;
 	/**
 	 * A flag whether the instance is anonymous, not having an
 	 * ID, and not going to request it.
-- 
2.24.3 (Apple Git-128)