cookie.h

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/* -*- C -*- */
/*
 * Copyright (c) 2019-2020 Seagate Technology LLC and/or its Affiliates
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * For any questions about this software or licensing,
 * please email opensource@seagate.com or cortx-questions@seagate.com.
 *
 */


#pragma once

#ifndef __MOTR_HA_COOKIE_H__
#define __MOTR_HA_COOKIE_H__

#include "lib/types.h"  /* bool */
#include "lib/time.h"   /* m0_time_t */

#include "lib/types_xc.h"       /* m0_uint128_xc for ha/cookie_xc.h */ /* XXX */

/*
 * m0_ha_cookie is used to check if a process at the other end of the connection
 * is still the same. A combination of PID, start time and OS uptime is used to
 * determine the process change.
 *
 * Reasons why all the fields from the structure are needed:
 * - hc_pid: it might be 2 processes started simultaneously on different CPU
 *   cores. They may get 2 different PIDs but they still may have the same start
 *   time and OS uptime;
 * - hc_time_start: after OS reboot a process may get the same PID and it can
 *   start at the same OS uptime. Start time of the process can't simply be the
 *   same after OS restart in this case;
 * - hc_uptime: if someone wants to play with system time it would be possible
 *   to get the same start time and the same PID (when the PID is reused)
 *   without OS restart. hc_uptime ensures that in this case such processes will
 *   get different m0_ha_cookie.
 * - hc_uuid: it's still possible to restart a system while playing with system
 *   time to get a process with the same m0_ha_cookie after restart. It's highly
 *   unlikely, but it's still possible. In this case UUID generator should
 *   decrease probability of getting the same m0_ha_cookie even more.
 *
 * Anyway, if we still get into the virtually impossible situation when
 * m0_ha_cookie is the same for different processes, it would either result in a
 * Motr process panic or it will become stuck. In either case HA is able to
 * handle such situation.
 *
 * TODO implement a function to get OS uptime.
 */
struct m0_ha_cookie {
        uint64_t          hc_pid;
        m0_time_t         hc_time_start;
        m0_time_t         hc_uptime;
        struct m0_uint128 hc_uuid;
};

struct m0_ha_cookie_xc {
        uint64_t          hcx_pid;
        uint64_t          hcx_time_start;
        uint64_t          hcx_uptime;
        struct m0_uint128 hcx_uuid;
} M0_XCA_RECORD M0_XCA_DOMAIN(rpc);

extern const struct m0_ha_cookie m0_ha_cookie_no_record;

/* XXX M0_BASSERT() doesn't work for _xc.h files, need to investigate why */
/*
M0_BASSERT(sizeof(((struct m0_ha_cookie_xc *)NULL)->hcx_time_start) ==
           sizeof(((struct m0_ha_cookie *)NULL)->hc_time_start));
M0_BASSERT(sizeof(((struct m0_ha_cookie_xc *)NULL)->hcx_uptime) ==
           sizeof(((struct m0_ha_cookie *)NULL)->hc_uptime));
           */

M0_INTERNAL void m0_ha_cookie_init(struct m0_ha_cookie *hc);
M0_INTERNAL void m0_ha_cookie_fini(struct m0_ha_cookie *hc);

M0_INTERNAL void m0_ha_cookie_record(struct m0_ha_cookie *hc);
M0_INTERNAL bool m0_ha_cookie_is_eq(const struct m0_ha_cookie *a,
                                    const struct m0_ha_cookie *b);

M0_INTERNAL void m0_ha_cookie_from_xc(struct m0_ha_cookie          *hc,
                                      const struct m0_ha_cookie_xc *hc_xc);
M0_INTERNAL void m0_ha_cookie_to_xc(const struct m0_ha_cookie *hc,
                                    struct m0_ha_cookie_xc    *hc_xc);

#endif /* __MOTR_HA_COOKIE_H__ */

/*
 *  Local variables:
 *  c-indentation-style: "K&R"
 *  c-basic-offset: 8
 *  tab-width: 8
 *  fill-column: 80
 *  scroll-step: 1
 *  End:
 */
/*
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