election.c
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election.c
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	/*
	* Copyright 2004-2018 Andrew Beekhof <andrew@beekhof.net>
	*
	* This source code is licensed under the GNU Lesser General Public License
	* version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
	*/

	#include <crm_internal.h>

	#include <sys/time.h>
	#include <sys/resource.h>

	#include <crm/msg_xml.h>
	#include <crm/common/xml.h>

	#include <crm/common/mainloop.h>
	#include <crm/cluster/internal.h>
	#include <crm/cluster/election.h>
	#include <crm/crm.h>

	#define STORM_INTERVAL 2 /* in seconds */

	struct election_s {
	enum election_result state;
	guint count; // How many times local node has voted
	char *name; // Descriptive name for this election
	char *uname; // Local node's name
	GSourceFunc cb; // Function to call if election is won
	GHashTable *voted; // Key = node name, value = how node voted
	mainloop_timer_t *timeout; // When to abort if all votes not received
	};

	static void election_complete(election_t *e)
	{
	e->state = election_won;

	if(e->cb) {
	e->cb(e);
	}

	election_reset(e);
	}

	static gboolean election_timer_cb(gpointer user_data)
	{
	election_t *e = user_data;

	crm_info("%s timed out, declaring local node as winner", e->name);
	election_complete(e);
	return FALSE;
	}

	enum election_result
	election_state(election_t *e)
	{
	if(e) {
	return e->state;
	}
	return election_error;
	}

	/*!
	* \brief Create a new election object
	*
	* Every node that wishes to participate in an election must create an election
	* object. Typically, this should be done once, at start-up. A caller should
	* only create a single election object.
	*
	* \param[in] name Label for election (for logging)
	* \param[in] uname Local node's name
	* \param[in] period_ms How long to wait for all peers to vote
	* \param[in] cb Function to call if local node wins election
	*
	* \return Newly allocated election object on success, NULL on error
	* \note The caller is responsible for freeing the returned value using
	* election_fini().
	*/
	election_t *
	election_init(const char name, const char uname, guint period_ms, GSourceFunc cb)
	{
	election_t *e = NULL;

	static guint count = 0;

	CRM_CHECK(uname != NULL, return NULL);

	e = calloc(1, sizeof(election_t));
	if (e == NULL) {
	crm_perror(LOG_CRIT, "Cannot create election");
	return NULL;
	}

	e->uname = strdup(uname);
	if (e->uname == NULL) {
	crm_perror(LOG_CRIT, "Cannot create election");
	free(e);
	return NULL;
	}

	e->name = name? crm_strdup_printf("election-%s", name)
	: crm_strdup_printf("election-%u", count++);
	e->cb = cb;
	e->timeout = mainloop_timer_add(e->name, period_ms, FALSE,
	election_timer_cb, e);
	crm_trace("Created %s", e->name);
	return e;
	}

	/*!
	* \brief Disregard any previous vote by specified peer
	*
	* This discards any recorded vote from a specified peer. Election users should
	* call this whenever a voting peer becomes inactive.
	*
	* \param[in] e Election object
	* \param[in] uname Name of peer to disregard
	*/
	void
	election_remove(election_t e, const char uname)
	{
	if(e && uname && e->voted) {
	crm_trace("Discarding %s (no-)vote from lost peer %s", e->name, uname);
	g_hash_table_remove(e->voted, uname);
	}
	}

	/*!
	* \brief Stop election timer and disregard all votes
	*
	* \param[in] e Election object
	*/
	void
	election_reset(election_t *e)
	{
	if (e != NULL) {
	crm_trace("Resetting election %s", e->name);
	mainloop_timer_stop(e->timeout);
	if (e->voted) {
	crm_trace("Destroying voted cache with %d members", g_hash_table_size(e->voted));
	g_hash_table_destroy(e->voted);
	e->voted = NULL;
	}
	}
	}

	/*!
	* \brief Free an election object
	*
	* Free all memory associated with an election object, stopping its
	* election timer (if running).
	*
	* \param[in] e Election object
	*/
	void
	election_fini(election_t *e)
	{
	if(e) {
	election_reset(e);
	crm_trace("Destroying %s", e->name);
	mainloop_timer_del(e->timeout);
	free(e->uname);
	free(e->name);
	free(e);
	}
	}

	static void
	election_timeout_start(election_t *e)
	{
	if(e) {
	mainloop_timer_start(e->timeout);
	}
	}

	/*!
	* \brief Stop an election's timer, if running
	*
	* \param[in] e Election object
	*/
	void
	election_timeout_stop(election_t *e)
	{
	if(e) {
	mainloop_timer_stop(e->timeout);
	}
	}

	/*!
	* \brief Change an election's timeout (restarting timer if running)
	*
	* \param[in] e Election object
	* \param[in] period New timeout
	*/
	void
	election_timeout_set_period(election_t *e, guint period)
	{
	if(e) {
	mainloop_timer_set_period(e->timeout, period);
	} else {
	crm_err("No election defined");
	}
	}

	static int
	crm_uptime(struct timeval *output)
	{
	static time_t expires = 0;
	static struct rusage info;

	time_t tm_now = time(NULL);

	if (expires < tm_now) {
	int rc = 0;

	info.ru_utime.tv_sec = 0;
	info.ru_utime.tv_usec = 0;
	rc = getrusage(RUSAGE_SELF, &info);

	output->tv_sec = 0;
	output->tv_usec = 0;

	if (rc < 0) {
	crm_perror(LOG_ERR, "Could not calculate the current uptime");
	expires = 0;
	return -1;
	}

	crm_debug("Current CPU usage is: %lds, %ldus", (long)info.ru_utime.tv_sec,
	(long)info.ru_utime.tv_usec);
	}

	expires = tm_now + STORM_INTERVAL; /* N seconds after the last _access_ */
	output->tv_sec = info.ru_utime.tv_sec;
	output->tv_usec = info.ru_utime.tv_usec;

	return 1;
	}

	static int
	crm_compare_age(struct timeval your_age)
	{
	struct timeval our_age;

	crm_uptime(&our_age); /* If an error occurred, our_age will be compared as {0,0} */

	if (our_age.tv_sec > your_age.tv_sec) {
	crm_debug("Win: %ld vs %ld (seconds)", (long)our_age.tv_sec, (long)your_age.tv_sec);
	return 1;
	} else if (our_age.tv_sec < your_age.tv_sec) {
	crm_debug("Lose: %ld vs %ld (seconds)", (long)our_age.tv_sec, (long)your_age.tv_sec);
	return -1;
	} else if (our_age.tv_usec > your_age.tv_usec) {
	crm_debug("Win: %ld.%06ld vs %ld.%06ld (usec)",
	(long)our_age.tv_sec, (long)our_age.tv_usec, (long)your_age.tv_sec, (long)your_age.tv_usec);
	return 1;
	} else if (our_age.tv_usec < your_age.tv_usec) {
	crm_debug("Lose: %ld.%06ld vs %ld.%06ld (usec)",
	(long)our_age.tv_sec, (long)our_age.tv_usec, (long)your_age.tv_sec, (long)your_age.tv_usec);
	return -1;
	}

	return 0;
	}

	/*!
	* \brief Start a new election by offering local node's candidacy
	*
	* Broadcast a "vote" election message containing the local node's ID,
	* (incremented) election counter, and uptime, and start the election timer.
	*
	* \param[in] e Election object
	* \note Any nodes agreeing to the candidacy will send a "no-vote" reply, and if
	* all active peers do so, or if the election times out, the local node
	* wins the election. (If we lose to any peer vote, we will stop the
	* timer, so a timeout means we did not lose -- either some peer did not
	* vote, or we did not call election_check() in time.)
	*/
	void
	election_vote(election_t *e)
	{
	struct timeval age;
	xmlNode *vote = NULL;
	crm_node_t *our_node;

	if (e == NULL) {
	crm_trace("Election vote requested, but no election available");
	return;
	}

	our_node = crm_get_peer(0, e->uname);
	if ((our_node == NULL) \|\| (crm_is_peer_active(our_node) == FALSE)) {
	crm_trace("Cannot vote in %s yet: local node not connected to cluster",
	e->name);
	return;
	}

	election_reset(e);
	e->state = election_in_progress;
	vote = create_request(CRM_OP_VOTE, NULL, NULL, CRM_SYSTEM_CRMD, CRM_SYSTEM_CRMD, NULL);

	e->count++;
	crm_xml_add(vote, F_CRM_ELECTION_OWNER, our_node->uuid);
	crm_xml_add_int(vote, F_CRM_ELECTION_ID, e->count);

	crm_uptime(&age);
	crm_xml_add_int(vote, F_CRM_ELECTION_AGE_S, age.tv_sec);
	crm_xml_add_int(vote, F_CRM_ELECTION_AGE_US, age.tv_usec);

	send_cluster_message(NULL, crm_msg_crmd, vote, TRUE);
	free_xml(vote);

	crm_debug("Started %s round %d", e->name, e->count);
	election_timeout_start(e);
	return;
	}

	/*!
	* \brief Check whether local node has won an election
	*
	* If all known peers have sent no-vote messages, stop the election timer, set
	* the election state to won, and call any registered win callback.
	*
	* \param[in] e Election object
	*
	* \return TRUE if local node has won, FALSE otherwise
	* \note If all known peers have sent no-vote messages, but the election owner
	* does not call this function, the election will not be won (and the
	* callback will not be called) until the election times out.
	* \note This should be called when election_count_vote() returns
	* \c election_in_progress.
	*/
	bool
	election_check(election_t *e)
	{
	int voted_size = 0;
	int num_members = 0;

	if(e == NULL) {
	crm_trace("Election check requested, but no election available");
	return FALSE;
	}
	if (e->voted == NULL) {
	crm_trace("%s check requested, but no votes received yet", e->name);
	return FALSE;
	}

	voted_size = g_hash_table_size(e->voted);
	num_members = crm_active_peers();

	/* in the case of #voted > #members, it is better to
	* wait for the timeout and give the cluster time to
	* stabilize
	*/
	if (voted_size >= num_members) {
	/* we won and everyone has voted */
	election_timeout_stop(e);
	if (voted_size > num_members) {
	GHashTableIter gIter;
	const crm_node_t *node;
	char *key = NULL;

	crm_warn("Received too many votes in %s", e->name);
	g_hash_table_iter_init(&gIter, crm_peer_cache);
	while (g_hash_table_iter_next(&gIter, NULL, (gpointer *) & node)) {
	if (crm_is_peer_active(node)) {
	crm_warn("* expected vote: %s", node->uname);
	}
	}

	g_hash_table_iter_init(&gIter, e->voted);
	while (g_hash_table_iter_next(&gIter, (gpointer *) & key, NULL)) {
	crm_warn("* actual vote: %s", key);
	}

	}

	crm_info("%s won by local node", e->name);
	election_complete(e);
	return TRUE;

	} else {
	crm_debug("%s still waiting on %d of %d votes",
	e->name, num_members - voted_size, num_members);
	}

	return FALSE;
	}

	#define LOSS_DAMPEN 2 /* in seconds */

	struct vote {
	const char *op;
	const char *from;
	const char *version;
	const char *election_owner;
	int election_id;
	struct timeval age;
	};

	/*!
	* \brief Unpack an election message
	*
	* \param[in] e Election object
	* \param[in] message Election message XML
	* \param[out] vote Parsed fields from message
	*
	* \return TRUE if election message and election are valid, FALSE otherwise
	* \note The parsed struct's pointer members are valid only for the lifetime of
	* the message argument.
	*/
	static bool
	parse_election_message(election_t e, xmlNode message, struct vote *vote)
	{
	CRM_CHECK(message && vote, return FALSE);

	vote->election_id = -1;
	vote->age.tv_sec = -1;
	vote->age.tv_usec = -1;

	vote->op = crm_element_value(message, F_CRM_TASK);
	vote->from = crm_element_value(message, F_CRM_HOST_FROM);
	vote->version = crm_element_value(message, F_CRM_VERSION);
	vote->election_owner = crm_element_value(message, F_CRM_ELECTION_OWNER);

	crm_element_value_int(message, F_CRM_ELECTION_ID, &(vote->election_id));

	if ((vote->op == NULL) \|\| (vote->from == NULL) \|\| (vote->version == NULL)
	\|\| (vote->election_owner == NULL) \|\| (vote->election_id < 0)) {

	crm_warn("Invalid %s message from %s in %s ",
	(vote->op? vote->op : "election"),
	(vote->from? vote->from : "unspecified node"),
	(e? e->name : "election"));
	return FALSE;
	}

	// Op-specific validation

	if (crm_str_eq(vote->op, CRM_OP_VOTE, TRUE)) {
	// Only vote ops have uptime
	crm_element_value_timeval(message, F_CRM_ELECTION_AGE_S,
	F_CRM_ELECTION_AGE_US, &(vote->age));
	if ((vote->age.tv_sec < 0) \|\| (vote->age.tv_usec < 0)) {
	crm_warn("Cannot count %s %s from %s because it is missing uptime",
	(e? e->name : "election"), vote->op, vote->from);
	return FALSE;
	}

	} else if (!crm_str_eq(vote->op, CRM_OP_NOVOTE, TRUE)) {
	crm_info("Cannot process %s message from %s because %s is not a known election op",
	(e? e->name : "election"), vote->from, vote->op);
	return FALSE;
	}

	// Election validation

	if (e == NULL) {
	crm_info("Cannot count %s from %s because no election available",
	vote->op, vote->from);
	return FALSE;
	}

	/* If the membership cache is NULL, we REALLY shouldn't be voting --
	* the question is how we managed to get here.
	*/
	if (crm_peer_cache == NULL) {
	crm_info("Cannot count %s %s from %s because no peer information available",
	e->name, vote->op, vote->from);
	return FALSE;
	}
	return TRUE;
	}

	static void
	record_vote(election_t e, struct vote vote)
	{
	char *voter_copy = NULL;
	char *vote_copy = NULL;

	CRM_ASSERT(e && vote && vote->from && vote->op);
	if (e->voted == NULL) {
	e->voted = crm_str_table_new();
	}

	voter_copy = strdup(vote->from);
	vote_copy = strdup(vote->op);
	CRM_ASSERT(voter_copy && vote_copy);

	g_hash_table_replace(e->voted, voter_copy, vote_copy);
	}

	static void
	send_no_vote(crm_node_t peer, struct vote vote)
	{
	// @TODO probably shouldn't hardcode CRM_SYSTEM_CRMD and crm_msg_crmd

	xmlNode *novote = create_request(CRM_OP_NOVOTE, NULL, vote->from,
	CRM_SYSTEM_CRMD, CRM_SYSTEM_CRMD, NULL);

	crm_xml_add(novote, F_CRM_ELECTION_OWNER, vote->election_owner);
	crm_xml_add_int(novote, F_CRM_ELECTION_ID, vote->election_id);

	send_cluster_message(peer, crm_msg_crmd, novote, TRUE);
	free_xml(novote);
	}

	/*!
	* \brief Process an election message (vote or no-vote) from a peer
	*
	* \param[in] e Election object
	* \param[in] vote Election message XML from peer
	* \param[in] can_win Whether to consider the local node eligible for winning
	*
	* \return Election state after new vote is considered
	* \note If the peer message is a vote, and we prefer the peer to win, this will
	* send a no-vote reply to the peer.
	* \note The situations "we lost to this vote" from "this is a late no-vote
	* after we've already lost" both return election_lost. If a caller needs
	* to distinguish them, it should save the current state before calling
	* this function, and then compare the result.
	*/
	enum election_result
	election_count_vote(election_t e, xmlNode message, bool can_win)
	{
	int log_level = LOG_INFO;
	gboolean done = FALSE;
	gboolean we_lose = FALSE;
	const char *reason = "unknown";
	bool we_are_owner = FALSE;
	crm_node_t our_node = NULL, your_node = NULL;
	time_t tm_now = time(NULL);
	struct vote vote;

	// @TODO these should be in election_t
	static int election_wins = 0;
	static time_t expires = 0;
	static time_t last_election_loss = 0;

	CRM_CHECK(message != NULL, return election_error);
	if (parse_election_message(e, message, &vote) == FALSE) {
	return election_error;
	}

	your_node = crm_get_peer(0, vote.from);
	our_node = crm_get_peer(0, e->uname);
	we_are_owner = (our_node != NULL)
	&& crm_str_eq(our_node->uuid, vote.election_owner, TRUE);

	if(can_win == FALSE) {
	reason = "Not eligible";
	we_lose = TRUE;

	} else if (our_node == NULL \|\| crm_is_peer_active(our_node) == FALSE) {
	reason = "We are not part of the cluster";
	log_level = LOG_ERR;
	we_lose = TRUE;

	} else if (we_are_owner && (vote.election_id != e->count)) {
	log_level = LOG_TRACE;
	reason = "Superseded";
	done = TRUE;

	} else if (your_node == NULL \|\| crm_is_peer_active(your_node) == FALSE) {
	/* Possibly we cached the message in the FSA queue at a point that it wasn't */
	reason = "Peer is not part of our cluster";
	log_level = LOG_WARNING;
	done = TRUE;

	} else if (crm_str_eq(vote.op, CRM_OP_NOVOTE, TRUE)
	\|\| crm_str_eq(vote.from, e->uname, TRUE)) {
	/* Receiving our own broadcast vote, or a no-vote from peer, is a vote
	* for us to win
	*/
	if (!we_are_owner) {
	crm_warn("Cannot count %s round %d %s from %s because we are not election owner (%s)",
	e->name, vote.election_id, vote.op, vote.from,
	vote.election_owner);
	return election_error;
	}
	if (e->state != election_in_progress) {
	// Should only happen if we already lost
	crm_debug("Not counting %s round %d %s from %s because no election in progress",
	e->name, vote.election_id, vote.op, vote.from);
	return e->state;
	}
	record_vote(e, &vote);
	reason = "Recorded";
	done = TRUE;

	} else {
	// A peer vote requires a comparison to determine which node is better
	int age_result = crm_compare_age(vote.age);
	int version_result = compare_version(vote.version, CRM_FEATURE_SET);

	if (version_result < 0) {
	reason = "Version";
	we_lose = TRUE;

	} else if (version_result > 0) {
	reason = "Version";

	} else if (age_result < 0) {
	reason = "Uptime";
	we_lose = TRUE;

	} else if (age_result > 0) {
	reason = "Uptime";

	} else if (strcasecmp(e->uname, vote.from) > 0) {
	reason = "Host name";
	we_lose = TRUE;

	} else {
	reason = "Host name";
	}
	}

	if (expires < tm_now) {
	election_wins = 0;
	expires = tm_now + STORM_INTERVAL;

	} else if (done == FALSE && we_lose == FALSE) {
	int peers = 1 + g_hash_table_size(crm_peer_cache);
	static bool wrote_blackbox = FALSE; // @TODO move to election_t

	/* If every node has to vote down every other node, thats N*(N-1) total elections
	* Allow some leeway before _really_ complaining
	*/
	election_wins++;
	if (election_wins > (peers * peers)) {
	crm_warn("%s election storm detected: %d wins in %d seconds",
	e->name, election_wins, STORM_INTERVAL);
	election_wins = 0;
	expires = tm_now + STORM_INTERVAL;
	if (wrote_blackbox == FALSE) {
	/* It's questionable whether a black box (from every node in the
	* cluster) would be truly helpful in diagnosing an election
	* storm. It's also highly doubtful a production environment
	* would get multiple election storms from distinct causes, so
	* saving one blackbox per process lifetime should be
	* sufficient. Alternatives would be to save a timestamp of the
	* last blackbox write instead of a boolean, and write a new one
	* if some amount of time has passed; or to save a storm count,
	* write a blackbox on every Nth occurrence.
	*/
	crm_write_blackbox(0, NULL);
	}
	}
	}

	if (done) {
	do_crm_log(log_level + 1,
	"Processed %s round %d %s (current round %d) from %s (%s)",
	e->name, vote.election_id, vote.op, e->count, vote.from,
	reason);
	return e->state;

	} else if (we_lose == FALSE) {
	if (last_election_loss == 0
	\|\| tm_now - last_election_loss > (time_t) LOSS_DAMPEN) {

	do_crm_log(log_level, "%s round %d (owner node ID %s) pass: %s from %s (%s)",
	e->name, vote.election_id, vote.election_owner, vote.op,
	vote.from, reason);

	last_election_loss = 0;
	election_timeout_stop(e);

	/* Start a new election by voting down this, and other, peers */
	e->state = election_start;
	return e->state;
	} else {
	char *loss_time = ctime(&last_election_loss);

	if (loss_time) {
	// Show only HH:MM:SS
	loss_time += 11;
	loss_time[8] = '\0';
	}
	crm_info("Ignoring %s round %d (owner node ID %s) pass vs %s because we lost less than %ds ago at %s",
	e->name, vote.election_id, vote.election_owner, vote.from,
	LOSS_DAMPEN, (loss_time? loss_time : "unknown"));
	}
	}

	last_election_loss = tm_now;

	do_crm_log(log_level, "%s round %d (owner node ID %s) lost: %s from %s (%s)",
	e->name, vote.election_id, vote.election_owner, vote.op,
	vote.from, reason);

	election_reset(e);
	send_no_vote(your_node, &vote);
	e->state = election_lost;
	return e->state;
	}

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