source: vendor/current/ctdb/server/ipalloc_lcp2.c

/*
   ctdb ip takeover code

   Copyright (C) Ronnie Sahlberg  2007
   Copyright (C) Andrew Tridgell  2007
   Copyright (C) Martin Schwenke  2011

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, see <http://www.gnu.org/licenses/>.
*/

#include "replace.h"
#include "system/network.h"

#include "lib/util/debug.h"
#include "common/logging.h"

#include "protocol/protocol_api.h"

#include "server/ipalloc_private.h"

/*
 * This is the length of the longtest common prefix between the IPs.
 * It is calculated by XOR-ing the 2 IPs together and counting the
 * number of leading zeroes.  The implementation means that all
 * addresses end up being 128 bits long.
 *
 * FIXME? Should we consider IPv4 and IPv6 separately given that the
 * 12 bytes of 0 prefix padding will hurt the algorithm if there are
 * lots of nodes and IP addresses?
 */
static uint32_t ip_distance(ctdb_sock_addr *ip1, ctdb_sock_addr *ip2)
{
        uint32_t ip1_k[IP_KEYLEN];
        uint32_t *t;
        int i;
        uint32_t x;

        uint32_t distance = 0;

        memcpy(ip1_k, ip_key(ip1), sizeof(ip1_k));
        t = ip_key(ip2);
        for (i=0; i<IP_KEYLEN; i++) {
                x = ip1_k[i] ^ t[i];
                if (x == 0) {
                        distance += 32;
                } else {
                        /* Count number of leading zeroes.
                         * FIXME? This could be optimised...
                         */
                        while ((x & (1 << 31)) == 0) {
                                x <<= 1;
                                distance += 1;
                        }
                }
        }

        return distance;
}

/* Calculate the IP distance for the given IP relative to IPs on the
   given node.  The ips argument is generally the all_ips variable
   used in the main part of the algorithm.
 */
static uint32_t ip_distance_2_sum(ctdb_sock_addr *ip,
                                  struct public_ip_list *ips,
                                  int pnn)
{
        struct public_ip_list *t;
        uint32_t d;

        uint32_t sum = 0;

        for (t = ips; t != NULL; t = t->next) {
                if (t->pnn != pnn) {
                        continue;
                }

                /* Optimisation: We never calculate the distance
                 * between an address and itself.  This allows us to
                 * calculate the effect of removing an address from a
                 * node by simply calculating the distance between
                 * that address and all of the exitsing addresses.
                 * Moreover, we assume that we're only ever dealing
                 * with addresses from all_ips so we can identify an
                 * address via a pointer rather than doing a more
                 * expensive address comparison. */
                if (&(t->addr) == ip) {
                        continue;
                }

                d = ip_distance(ip, &(t->addr));
                sum += d * d;  /* Cheaper than pulling in math.h :-) */
        }

        return sum;
}

/* Return the LCP2 imbalance metric for addresses currently assigned
   to the given node.
 */
static uint32_t lcp2_imbalance(struct public_ip_list * all_ips, int pnn)
{
        struct public_ip_list *t;

        uint32_t imbalance = 0;

        for (t = all_ips; t != NULL; t = t->next) {
                if (t->pnn != pnn) {
                        continue;
                }
                /* Pass the rest of the IPs rather than the whole
                   all_ips input list.
                */
                imbalance += ip_distance_2_sum(&(t->addr), t->next, pnn);
        }

        return imbalance;
}

static bool lcp2_init(struct ipalloc_state *ipalloc_state,
                      uint32_t **lcp2_imbalances,
                      bool **rebalance_candidates)
{
        int i, numnodes;
        struct public_ip_list *t;

        numnodes = ipalloc_state->num;

        *rebalance_candidates = talloc_array(ipalloc_state, bool, numnodes);
        if (*rebalance_candidates == NULL) {
                DEBUG(DEBUG_ERR, (__location__ " out of memory\n"));
                return false;
        }
        *lcp2_imbalances = talloc_array(ipalloc_state, uint32_t, numnodes);
        if (*lcp2_imbalances == NULL) {
                DEBUG(DEBUG_ERR, (__location__ " out of memory\n"));
                return false;
        }

        for (i=0; i<numnodes; i++) {
                (*lcp2_imbalances)[i] =
                        lcp2_imbalance(ipalloc_state->all_ips, i);
                /* First step: assume all nodes are candidates */
                (*rebalance_candidates)[i] = true;
        }

        /* 2nd step: if a node has IPs assigned then it must have been
         * healthy before, so we remove it from consideration.  This
         * is overkill but is all we have because we don't maintain
         * state between takeover runs.  An alternative would be to
         * keep state and invalidate it every time the recovery master
         * changes.
         */
        for (t = ipalloc_state->all_ips; t != NULL; t = t->next) {
                if (t->pnn != -1) {
                        (*rebalance_candidates)[t->pnn] = false;
                }
        }

        /* 3rd step: if a node is forced to re-balance then
           we allow failback onto the node */
        if (ipalloc_state->force_rebalance_nodes == NULL) {
                return true;
        }
        for (i = 0;
             i < talloc_array_length(ipalloc_state->force_rebalance_nodes);
             i++) {
                uint32_t pnn = ipalloc_state->force_rebalance_nodes[i];
                if (pnn >= numnodes) {
                        DEBUG(DEBUG_ERR,
                              (__location__ "unknown node %u\n", pnn));
                        continue;
                }

                DEBUG(DEBUG_NOTICE,
                      ("Forcing rebalancing of IPs to node %u\n", pnn));
                (*rebalance_candidates)[pnn] = true;
        }

        return true;
}

/* Allocate any unassigned addresses using the LCP2 algorithm to find
 * the IP/node combination that will cost the least.
 */
static void lcp2_allocate_unassigned(struct ipalloc_state *ipalloc_state,
                                     uint32_t *lcp2_imbalances)
{
        struct public_ip_list *t;
        int dstnode, numnodes;

        int minnode;
        uint32_t mindsum, dstdsum, dstimbl, minimbl;
        struct public_ip_list *minip;

        bool should_loop = true;
        bool have_unassigned = true;

        numnodes = ipalloc_state->num;

        while (have_unassigned && should_loop) {
                should_loop = false;

                DEBUG(DEBUG_DEBUG,(" ----------------------------------------\n"));
                DEBUG(DEBUG_DEBUG,(" CONSIDERING MOVES (UNASSIGNED)\n"));

                minnode = -1;
                mindsum = 0;
                minip = NULL;

                /* loop over each unassigned ip. */
                for (t = ipalloc_state->all_ips; t != NULL ; t = t->next) {
                        if (t->pnn != -1) {
                                continue;
                        }

                        for (dstnode = 0; dstnode < numnodes; dstnode++) {
                                /* only check nodes that can actually takeover this ip */
                                if (!can_node_takeover_ip(ipalloc_state,
                                                          dstnode,
                                                          t)) {
                                        /* no it couldnt   so skip to the next node */
                                        continue;
                                }

                                dstdsum = ip_distance_2_sum(&(t->addr),
                                                            ipalloc_state->all_ips,
                                                            dstnode);
                                dstimbl = lcp2_imbalances[dstnode] + dstdsum;
                                DEBUG(DEBUG_DEBUG,
                                      (" %s -> %d [+%d]\n",
                                       ctdb_sock_addr_to_string(ipalloc_state,
                                                                &(t->addr)),
                                       dstnode,
                                       dstimbl - lcp2_imbalances[dstnode]));


                                if ((minnode == -1) || (dstdsum < mindsum)) {
                                        minnode = dstnode;
                                        minimbl = dstimbl;
                                        mindsum = dstdsum;
                                        minip = t;
                                        should_loop = true;
                                }
                        }
                }

                DEBUG(DEBUG_DEBUG,(" ----------------------------------------\n"));

                /* If we found one then assign it to the given node. */
                if (minnode != -1) {
                        minip->pnn = minnode;
                        lcp2_imbalances[minnode] = minimbl;
                        DEBUG(DEBUG_INFO,(" %s -> %d [+%d]\n",
                                          ctdb_sock_addr_to_string(
                                                  ipalloc_state,
                                                  &(minip->addr)),
                                          minnode,
                                          mindsum));
                }

                /* There might be a better way but at least this is clear. */
                have_unassigned = false;
                for (t = ipalloc_state->all_ips; t != NULL; t = t->next) {
                        if (t->pnn == -1) {
                                have_unassigned = true;
                        }
                }
        }

        /* We know if we have an unassigned addresses so we might as
         * well optimise.
         */
        if (have_unassigned) {
                for (t = ipalloc_state->all_ips; t != NULL; t = t->next) {
                        if (t->pnn == -1) {
                                DEBUG(DEBUG_WARNING,
                                      ("Failed to find node to cover ip %s\n",
                                       ctdb_sock_addr_to_string(ipalloc_state,
                                                                &t->addr)));
                        }
                }
        }
}

/* LCP2 algorithm for rebalancing the cluster.  Given a candidate node
 * to move IPs from, determines the best IP/destination node
 * combination to move from the source node.
 */
static bool lcp2_failback_candidate(struct ipalloc_state *ipalloc_state,
                                    int srcnode,
                                    uint32_t *lcp2_imbalances,
                                    bool *rebalance_candidates)
{
        int dstnode, mindstnode, numnodes;
        uint32_t srcimbl, srcdsum, dstimbl, dstdsum;
        uint32_t minsrcimbl, mindstimbl;
        struct public_ip_list *minip;
        struct public_ip_list *t;

        /* Find an IP and destination node that best reduces imbalance. */
        srcimbl = 0;
        minip = NULL;
        minsrcimbl = 0;
        mindstnode = -1;
        mindstimbl = 0;

        numnodes = ipalloc_state->num;

        DEBUG(DEBUG_DEBUG,(" ----------------------------------------\n"));
        DEBUG(DEBUG_DEBUG,(" CONSIDERING MOVES FROM %d [%d]\n",
                           srcnode, lcp2_imbalances[srcnode]));

        for (t = ipalloc_state->all_ips; t != NULL; t = t->next) {
                /* Only consider addresses on srcnode. */
                if (t->pnn != srcnode) {
                        continue;
                }

                /* What is this IP address costing the source node? */
                srcdsum = ip_distance_2_sum(&(t->addr),
                                            ipalloc_state->all_ips,
                                            srcnode);
                srcimbl = lcp2_imbalances[srcnode] - srcdsum;

                /* Consider this IP address would cost each potential
                 * destination node.  Destination nodes are limited to
                 * those that are newly healthy, since we don't want
                 * to do gratuitous failover of IPs just to make minor
                 * balance improvements.
                 */
                for (dstnode = 0; dstnode < numnodes; dstnode++) {
                        if (!rebalance_candidates[dstnode]) {
                                continue;
                        }

                        /* only check nodes that can actually takeover this ip */
                        if (!can_node_takeover_ip(ipalloc_state, dstnode,
                                                  t)) {
                                /* no it couldnt   so skip to the next node */
                                continue;
                        }

                        dstdsum = ip_distance_2_sum(&(t->addr),
                                                    ipalloc_state->all_ips,
                                                    dstnode);
                        dstimbl = lcp2_imbalances[dstnode] + dstdsum;
                        DEBUG(DEBUG_DEBUG,(" %d [%d] -> %s -> %d [+%d]\n",
                                           srcnode, -srcdsum,
                                           ctdb_sock_addr_to_string(
                                                   ipalloc_state, &(t->addr)),
                                           dstnode, dstdsum));

                        if ((dstimbl < lcp2_imbalances[srcnode]) &&
                            (dstdsum < srcdsum) &&                      \
                            ((mindstnode == -1) ||                              \
                             ((srcimbl + dstimbl) < (minsrcimbl + mindstimbl)))) {

                                minip = t;
                                minsrcimbl = srcimbl;
                                mindstnode = dstnode;
                                mindstimbl = dstimbl;
                        }
                }
        }
        DEBUG(DEBUG_DEBUG,(" ----------------------------------------\n"));

        if (mindstnode != -1) {
                /* We found a move that makes things better... */
                DEBUG(DEBUG_INFO,
                      ("%d [%d] -> %s -> %d [+%d]\n",
                       srcnode, minsrcimbl - lcp2_imbalances[srcnode],
                       ctdb_sock_addr_to_string(ipalloc_state, &(minip->addr)),
                       mindstnode, mindstimbl - lcp2_imbalances[mindstnode]));


                lcp2_imbalances[srcnode] = minsrcimbl;
                lcp2_imbalances[mindstnode] = mindstimbl;
                minip->pnn = mindstnode;

                return true;
        }

        return false;
}

struct lcp2_imbalance_pnn {
        uint32_t imbalance;
        int pnn;
};

static int lcp2_cmp_imbalance_pnn(const void * a, const void * b)
{
        const struct lcp2_imbalance_pnn * lipa = (const struct lcp2_imbalance_pnn *) a;
        const struct lcp2_imbalance_pnn * lipb = (const struct lcp2_imbalance_pnn *) b;

        if (lipa->imbalance > lipb->imbalance) {
                return -1;
        } else if (lipa->imbalance == lipb->imbalance) {
                return 0;
        } else {
                return 1;
        }
}

/* LCP2 algorithm for rebalancing the cluster.  This finds the source
 * node with the highest LCP2 imbalance, and then determines the best
 * IP/destination node combination to move from the source node.
 */
static void lcp2_failback(struct ipalloc_state *ipalloc_state,
                          uint32_t *lcp2_imbalances,
                          bool *rebalance_candidates)
{
        int i, numnodes;
        struct lcp2_imbalance_pnn * lips;
        bool again;

        numnodes = ipalloc_state->num;

try_again:
        /* Put the imbalances and nodes into an array, sort them and
         * iterate through candidates.  Usually the 1st one will be
         * used, so this doesn't cost much...
         */
        DEBUG(DEBUG_DEBUG,("+++++++++++++++++++++++++++++++++++++++++\n"));
        DEBUG(DEBUG_DEBUG,("Selecting most imbalanced node from:\n"));
        lips = talloc_array(ipalloc_state, struct lcp2_imbalance_pnn, numnodes);
        for (i = 0; i < numnodes; i++) {
                lips[i].imbalance = lcp2_imbalances[i];
                lips[i].pnn = i;
                DEBUG(DEBUG_DEBUG,(" %d [%d]\n", i, lcp2_imbalances[i]));
        }
        qsort(lips, numnodes, sizeof(struct lcp2_imbalance_pnn),
              lcp2_cmp_imbalance_pnn);

        again = false;
        for (i = 0; i < numnodes; i++) {
                /* This means that all nodes had 0 or 1 addresses, so
                 * can't be imbalanced.
                 */
                if (lips[i].imbalance == 0) {
                        break;
                }

                if (lcp2_failback_candidate(ipalloc_state,
                                            lips[i].pnn,
                                            lcp2_imbalances,
                                            rebalance_candidates)) {
                        again = true;
                        break;
                }
        }

        talloc_free(lips);
        if (again) {
                goto try_again;
        }
}

bool ipalloc_lcp2(struct ipalloc_state *ipalloc_state)
{
        uint32_t *lcp2_imbalances;
        bool *rebalance_candidates;
        int numnodes, num_rebalance_candidates, i;
        bool ret = true;

        unassign_unsuitable_ips(ipalloc_state);

        if (!lcp2_init(ipalloc_state,
                       &lcp2_imbalances, &rebalance_candidates)) {
                ret = false;
                goto finished;
        }

        lcp2_allocate_unassigned(ipalloc_state, lcp2_imbalances);

        /* If we don't want IPs to fail back then don't rebalance IPs. */
        if (1 == ipalloc_state->no_ip_failback) {
                goto finished;
        }

        /* It is only worth continuing if we have suitable target
         * nodes to transfer IPs to.  This check is much cheaper than
         * continuing on...
         */
        numnodes = ipalloc_state->num;
        num_rebalance_candidates = 0;
        for (i=0; i<numnodes; i++) {
                if (rebalance_candidates[i]) {
                        num_rebalance_candidates++;
                }
        }
        if (num_rebalance_candidates == 0) {
                goto finished;
        }

        /* Now, try to make sure the ip adresses are evenly distributed
           across the nodes.
        */
        lcp2_failback(ipalloc_state, lcp2_imbalances, rebalance_candidates);

finished:
        return ret;
}