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attrd_elections.c
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/*
* Copyright 2013-2024 the Pacemaker project contributors
*
* The version control history for this file may have further details.
*
* This source code is licensed under the GNU General Public License version 2
* or later (GPLv2+) WITHOUT ANY WARRANTY.
*/
#include <crm_internal.h>
#include <crm/cluster.h>
#include <crm/cluster/election_internal.h>
#include <crm/common/xml.h>
#include "pacemaker-attrd.h"
static char *peer_writer = NULL;
static election_t *writer = NULL;
static gboolean
attrd_election_cb(gpointer user_data)
{
attrd_declare_winner();
/* Update the peers after an election */
attrd_peer_sync(NULL);
/* After winning an election, update the CIB with the values of all
* attributes as the winner knows them.
*/
attrd_write_attributes(attrd_write_all);
return G_SOURCE_REMOVE;
}
void
attrd_election_init(void)
{
writer = election_init(PCMK__VALUE_ATTRD, attrd_cluster->uname, 120000,
attrd_election_cb);
}
void
attrd_election_fini(void)
{
election_fini(writer);
}
void
attrd_start_election_if_needed(void)
{
if ((peer_writer == NULL)
&& (election_state(writer) != election_in_progress)
&& !attrd_shutting_down(false)) {
crm_info("Starting an election to determine the writer");
election_vote(writer);
}
}
bool
attrd_election_won(void)
{
return (election_state(writer) == election_won);
}
void
attrd_handle_election_op(const crm_node_t *peer, xmlNode *xml)
{
enum election_result rc = 0;
enum election_result previous = election_state(writer);
crm_xml_add(xml, PCMK__XA_SRC, peer->uname);
// Don't become writer if we're shutting down
rc = election_count_vote(writer, xml, !attrd_shutting_down(false));
switch(rc) {
case election_start:
crm_debug("Unsetting writer (was %s) and starting new election",
peer_writer? peer_writer : "unset");
free(peer_writer);
peer_writer = NULL;
election_vote(writer);
break;
case election_lost:
/* The election API should really distinguish between "we just lost
* to this peer" and "we already lost previously, and we are
* discarding this vote for some reason", but it doesn't.
*
* In the first case, we want to tentatively set the peer writer to
* this peer, even though another peer may eventually win (which we
* will learn via attrd_check_for_new_writer()), so
* attrd_start_election_if_needed() doesn't start a new election.
*
* Approximate a test for that case as best as possible.
*/
if ((peer_writer == NULL) || (previous != election_lost)) {
pcmk__str_update(&peer_writer, peer->uname);
crm_debug("Election lost, presuming %s is writer for now",
peer_writer);
}
break;
case election_in_progress:
election_check(writer);
break;
default:
crm_info("Ignoring election op from %s due to error", peer->uname);
break;
}
}
bool
attrd_check_for_new_writer(const crm_node_t *peer, const xmlNode *xml)
{
int peer_state = 0;
crm_element_value_int(xml, PCMK__XA_ATTR_WRITER, &peer_state);
if (peer_state == election_won) {
if ((election_state(writer) == election_won)
&& !pcmk__str_eq(peer->uname, attrd_cluster->uname, pcmk__str_casei)) {
crm_notice("Detected another attribute writer (%s), starting new election",
peer->uname);
election_vote(writer);
} else if (!pcmk__str_eq(peer->uname, peer_writer, pcmk__str_casei)) {
crm_notice("Recorded new attribute writer: %s (was %s)",
peer->uname, (peer_writer? peer_writer : "unset"));
pcmk__str_update(&peer_writer, peer->uname);
}
}
return (peer_state == election_won);
}
void
attrd_declare_winner(void)
{
crm_notice("Recorded local node as attribute writer (was %s)",
(peer_writer? peer_writer : "unset"));
pcmk__str_update(&peer_writer, attrd_cluster->uname);
}
void
attrd_remove_voter(const crm_node_t *peer)
{
election_remove(writer, peer->uname);
if (peer_writer && pcmk__str_eq(peer->uname, peer_writer, pcmk__str_casei)) {
free(peer_writer);
peer_writer = NULL;
crm_notice("Lost attribute writer %s", peer->uname);
/* Clear any election dampening in effect. Otherwise, if the lost writer
* had just won, the election could fizzle out with no new writer.
*/
election_clear_dampening(writer);
/* If the writer received attribute updates during its shutdown, it will
* not have written them to the CIB. Ensure we get a new writer so they
* are written out. This means that every node that sees the writer
* leave will start a new election, but that's better than losing
* attributes.
*/
attrd_start_election_if_needed();
/* If an election is in progress, we need to call election_check(), in case
* this lost peer is the only one that hasn't voted, otherwise the election
* would be pending until it's timed out.
*/
} else if (election_state(writer) == election_in_progress) {
crm_debug("Checking election status upon loss of voter %s", peer->uname);
election_check(writer);
}
}
void
attrd_xml_add_writer(xmlNode *xml)
{
crm_xml_add_int(xml, PCMK__XA_ATTR_WRITER, election_state(writer));
}

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