// SPDX-License-Identifier: GPL-2.0-or-later
/* Handle vlserver selection and rotation.
 *
 * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include "internal.h"
#include "afs_vl.h"

/*
 * Begin an operation on a volume location server.
 */
bool afs_begin_vlserver_operation(struct afs_vl_cursor *vc, struct afs_cell *cell,
                                  struct key *key)
{
        static atomic_t debug_ids;

        memset(vc, 0, sizeof(*vc));
        vc->cell = cell;
        vc->key = key;
        vc->cumul_error.error = -EDESTADDRREQ;
        vc->nr_iterations = -1;

        if (signal_pending(current)) {
                vc->cumul_error.error = -EINTR;
                vc->flags |= AFS_VL_CURSOR_STOP;
                return false;
        }

        vc->debug_id = atomic_inc_return(&debug_ids);
        return true;
}

/*
 * Begin iteration through a server list, starting with the last used server if
 * possible, or the last recorded good server if not.
 */
static bool afs_start_vl_iteration(struct afs_vl_cursor *vc)
{
        struct afs_cell *cell = vc->cell;
        unsigned int dns_lookup_count;

        if (cell->dns_source == DNS_RECORD_UNAVAILABLE ||
            cell->dns_expiry <= ktime_get_real_seconds()) {
                dns_lookup_count = smp_load_acquire(&cell->dns_lookup_count);
                set_bit(AFS_CELL_FL_DO_LOOKUP, &cell->flags);
                afs_queue_cell(cell, afs_cell_trace_queue_dns);

                if (cell->dns_source == DNS_RECORD_UNAVAILABLE) {
                        if (wait_var_event_interruptible(
                                    &cell->dns_lookup_count,
                                    smp_load_acquire(&cell->dns_lookup_count)
                                    != dns_lookup_count) < 0) {
                                vc->cumul_error.error = -ERESTARTSYS;
                                return false;
                        }
                }

                /* Status load is ordered after lookup counter load */
                if (cell->dns_status == DNS_LOOKUP_GOT_NOT_FOUND) {
                        pr_warn("No record of cell %s\n", cell->name);
                        vc->cumul_error.error = -ENOENT;
                        return false;
                }

                if (cell->dns_source == DNS_RECORD_UNAVAILABLE) {
                        vc->cumul_error.error = -EDESTADDRREQ;
                        return false;
                }
        }

        read_lock(&cell->vl_servers_lock);
        vc->server_list = afs_get_vlserverlist(
                rcu_dereference_protected(cell->vl_servers,
                                          lockdep_is_held(&cell->vl_servers_lock)));
        read_unlock(&cell->vl_servers_lock);
        if (!vc->server_list->nr_servers)
                return false;

        vc->untried_servers = (1UL << vc->server_list->nr_servers) - 1;
        vc->server_index = -1;
        return true;
}

/*
 * Select the vlserver to use.  May be called multiple times to rotate
 * through the vlservers.
 */
bool afs_select_vlserver(struct afs_vl_cursor *vc)
{
        struct afs_addr_list *alist = vc->alist;
        struct afs_vlserver *vlserver;
        unsigned long set, failed;
        unsigned int rtt;
        s32 abort_code = vc->call_abort_code;
        int error = vc->call_error, i;

        vc->nr_iterations++;

        _enter("VC=%x+%x,%d{%lx},%d{%lx},%d,%d",
               vc->debug_id, vc->nr_iterations, vc->server_index, vc->untried_servers,
               vc->addr_index, vc->addr_tried,
               error, abort_code);

        if (vc->flags & AFS_VL_CURSOR_STOP) {
                _leave(" = f [stopped]");
                return false;
        }

        if (vc->nr_iterations == 0)
                goto start;

        WRITE_ONCE(alist->addrs[vc->addr_index].last_error, error);

        /* Evaluate the result of the previous operation, if there was one. */
        switch (error) {
        default:
        case 0:
                /* Success or local failure.  Stop. */
                vc->cumul_error.error = error;
                vc->flags |= AFS_VL_CURSOR_STOP;
                _leave(" = f [okay/local %d]", vc->cumul_error.error);
                return false;

        case -ECONNABORTED:
                /* The far side rejected the operation on some grounds.  This
                 * might involve the server being busy or the volume having been moved.
                 */
                switch (abort_code) {
                case AFSVL_IO:
                case AFSVL_BADVOLOPER:
                case AFSVL_NOMEM:
                        /* The server went weird. */
                        afs_prioritise_error(&vc->cumul_error, -EREMOTEIO, abort_code);
                        //write_lock(&vc->cell->vl_servers_lock);
                        //vc->server_list->weird_mask |= 1 << vc->server_index;
                        //write_unlock(&vc->cell->vl_servers_lock);
                        goto next_server;

                default:
                        afs_prioritise_error(&vc->cumul_error, error, abort_code);
                        goto failed;
                }

        case -ERFKILL:
        case -EADDRNOTAVAIL:
        case -ENETUNREACH:
        case -EHOSTUNREACH:
        case -EHOSTDOWN:
        case -ECONNREFUSED:
        case -ETIMEDOUT:
        case -ETIME:
                _debug("no conn %d", error);
                afs_prioritise_error(&vc->cumul_error, error, 0);
                goto iterate_address;

        case -ECONNRESET:
                _debug("call reset");
                afs_prioritise_error(&vc->cumul_error, error, 0);
                vc->flags |= AFS_VL_CURSOR_RETRY;
                goto next_server;

        case -EOPNOTSUPP:
                _debug("notsupp");
                goto next_server;
        }

restart_from_beginning:
        _debug("restart");
        if (vc->call_responded &&
            vc->addr_index != vc->alist->preferred &&
            test_bit(alist->preferred, &vc->addr_tried))
                WRITE_ONCE(alist->preferred, vc->addr_index);
        afs_put_addrlist(alist, afs_alist_trace_put_vlrotate_restart);
        alist = vc->alist = NULL;

        afs_put_vlserverlist(vc->cell->net, vc->server_list);
        vc->server_list = NULL;
        if (vc->flags & AFS_VL_CURSOR_RETRIED)
                goto failed;
        vc->flags |= AFS_VL_CURSOR_RETRIED;
start:
        _debug("start");
        ASSERTCMP(alist, ==, NULL);

        if (!afs_start_vl_iteration(vc))
                goto failed;

        error = afs_send_vl_probes(vc->cell->net, vc->key, vc->server_list);
        if (error < 0) {
                afs_prioritise_error(&vc->cumul_error, error, 0);
                goto failed;
        }

pick_server:
        _debug("pick [%lx]", vc->untried_servers);
        ASSERTCMP(alist, ==, NULL);

        error = afs_wait_for_vl_probes(vc->server_list, vc->untried_servers);
        if (error < 0) {
                afs_prioritise_error(&vc->cumul_error, error, 0);
                goto failed;
        }

        /* Pick the untried server with the lowest RTT. */
        vc->server_index = vc->server_list->preferred;
        if (test_bit(vc->server_index, &vc->untried_servers))
                goto selected_server;

        vc->server_index = -1;
        rtt = UINT_MAX;
        for (i = 0; i < vc->server_list->nr_servers; i++) {
                struct afs_vlserver *s = vc->server_list->servers[i].server;

                if (!test_bit(i, &vc->untried_servers) ||
                    !test_bit(AFS_VLSERVER_FL_RESPONDING, &s->flags))
                        continue;
                if (s->probe.rtt <= rtt) {
                        vc->server_index = i;
                        rtt = s->probe.rtt;
                }
        }

        if (vc->server_index == -1)
                goto no_more_servers;

selected_server:
        _debug("use %d", vc->server_index);
        __clear_bit(vc->server_index, &vc->untried_servers);

        /* We're starting on a different vlserver from the list.  We need to
         * check it, find its address list and probe its capabilities before we
         * use it.
         */
        vlserver = vc->server_list->servers[vc->server_index].server;
        vc->server = vlserver;

        _debug("USING VLSERVER: %s", vlserver->name);

        read_lock(&vlserver->lock);
        alist = rcu_dereference_protected(vlserver->addresses,
                                          lockdep_is_held(&vlserver->lock));
        vc->alist = afs_get_addrlist(alist, afs_alist_trace_get_vlrotate_set);
        read_unlock(&vlserver->lock);

        vc->addr_tried = 0;
        vc->addr_index = -1;

iterate_address:
        /* Iterate over the current server's address list to try and find an
         * address on which it will respond to us.
         */
        set = READ_ONCE(alist->responded);
        failed = READ_ONCE(alist->probe_failed);
        vc->addr_index = READ_ONCE(alist->preferred);

        _debug("%lx-%lx-%lx,%d", set, failed, vc->addr_tried, vc->addr_index);

        set &= ~(failed | vc->addr_tried);

        if (!set)
                goto next_server;

        if (!test_bit(vc->addr_index, &set))
                vc->addr_index = __ffs(set);

        set_bit(vc->addr_index, &vc->addr_tried);
        vc->alist = alist;

        _debug("VL address %d/%d", vc->addr_index, alist->nr_addrs);

        vc->call_responded = false;
        _leave(" = t %pISpc", rxrpc_kernel_remote_addr(alist->addrs[vc->addr_index].peer));
        return true;

next_server:
        _debug("next");
        ASSERT(alist);
        if (vc->call_responded &&
            vc->addr_index != alist->preferred &&
            test_bit(alist->preferred, &vc->addr_tried))
                WRITE_ONCE(alist->preferred, vc->addr_index);
        afs_put_addrlist(alist, afs_alist_trace_put_vlrotate_next);
        alist = vc->alist = NULL;
        goto pick_server;

no_more_servers:
        /* That's all the servers poked to no good effect.  Try again if some
         * of them were busy.
         */
        if (vc->flags & AFS_VL_CURSOR_RETRY)
                goto restart_from_beginning;

        for (i = 0; i < vc->server_list->nr_servers; i++) {
                struct afs_vlserver *s = vc->server_list->servers[i].server;

                if (test_bit(AFS_VLSERVER_FL_RESPONDING, &s->flags))
                        vc->cumul_error.responded = true;
                afs_prioritise_error(&vc->cumul_error, READ_ONCE(s->probe.error),
                                     s->probe.abort_code);
        }

failed:
        if (alist) {
                if (vc->call_responded &&
                    vc->addr_index != alist->preferred &&
                    test_bit(alist->preferred, &vc->addr_tried))
                        WRITE_ONCE(alist->preferred, vc->addr_index);
                afs_put_addrlist(alist, afs_alist_trace_put_vlrotate_fail);
                alist = vc->alist = NULL;
        }
        vc->flags |= AFS_VL_CURSOR_STOP;
        _leave(" = f [failed %d]", vc->cumul_error.error);
        return false;
}

/*
 * Dump cursor state in the case of the error being EDESTADDRREQ.
 */
static void afs_vl_dump_edestaddrreq(const struct afs_vl_cursor *vc)
{
        struct afs_cell *cell = vc->cell;
        static int count;
        int i;

        if (!IS_ENABLED(CONFIG_AFS_DEBUG_CURSOR) || count > 3)
                return;
        count++;

        rcu_read_lock();
        pr_notice("EDESTADDR occurred\n");
        pr_notice("CELL: %s err=%d\n", cell->name, cell->error);
        pr_notice("DNS: src=%u st=%u lc=%x\n",
                  cell->dns_source, cell->dns_status, cell->dns_lookup_count);
        pr_notice("VC: ut=%lx ix=%u ni=%hu fl=%hx err=%hd\n",
                  vc->untried_servers, vc->server_index, vc->nr_iterations,
                  vc->flags, vc->cumul_error.error);
        pr_notice("VC: call  er=%d ac=%d r=%u\n",
                  vc->call_error, vc->call_abort_code, vc->call_responded);

        if (vc->server_list) {
                const struct afs_vlserver_list *sl = vc->server_list;
                pr_notice("VC: SL nr=%u ix=%u\n",
                          sl->nr_servers, sl->index);
                for (i = 0; i < sl->nr_servers; i++) {
                        const struct afs_vlserver *s = sl->servers[i].server;
                        pr_notice("VC: server %s+%hu fl=%lx E=%hd\n",
                                  s->name, s->port, s->flags, s->probe.error);
                        if (s->addresses) {
                                const struct afs_addr_list *a =
                                        rcu_dereference(s->addresses);
                                pr_notice("VC:  - nr=%u/%u/%u pf=%u\n",
                                          a->nr_ipv4, a->nr_addrs, a->max_addrs,
                                          a->preferred);
                                pr_notice("VC:  - R=%lx F=%lx\n",
                                          a->responded, a->probe_failed);
                                if (a == vc->alist)
                                        pr_notice("VC:  - current\n");
                        }
                }
        }

        pr_notice("AC: t=%lx ax=%u\n", vc->addr_tried, vc->addr_index);
        rcu_read_unlock();
}

/*
 * Tidy up a volume location server cursor and unlock the vnode.
 */
int afs_end_vlserver_operation(struct afs_vl_cursor *vc)
{
        struct afs_net *net = vc->cell->net;

        _enter("VC=%x+%x", vc->debug_id, vc->nr_iterations);

        switch (vc->cumul_error.error) {
        case -EDESTADDRREQ:
        case -EADDRNOTAVAIL:
        case -ENETUNREACH:
        case -EHOSTUNREACH:
                afs_vl_dump_edestaddrreq(vc);
                break;
        }

        if (vc->alist) {
                if (vc->call_responded &&
                    vc->addr_index != vc->alist->preferred &&
                    test_bit(vc->alist->preferred, &vc->addr_tried))
                        WRITE_ONCE(vc->alist->preferred, vc->addr_index);
                afs_put_addrlist(vc->alist, afs_alist_trace_put_vlrotate_end);
                vc->alist = NULL;
        }
        afs_put_vlserverlist(net, vc->server_list);
        return vc->cumul_error.error;
}