/* AFS server record management
 *
 * Copyright (C) 2002, 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * 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
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/sched.h>
#include <linux/slab.h>
#include "internal.h"

static unsigned afs_server_timeout = 10;        /* server timeout in seconds */

static void afs_reap_server(struct work_struct *);

/* tree of all the servers, indexed by IP address */
static struct rb_root afs_servers = RB_ROOT;
static DEFINE_RWLOCK(afs_servers_lock);

/* LRU list of all the servers not currently in use */
static LIST_HEAD(afs_server_graveyard);
static DEFINE_SPINLOCK(afs_server_graveyard_lock);
static DECLARE_DELAYED_WORK(afs_server_reaper, afs_reap_server);

/*
 * install a server record in the master tree
 */
static int afs_install_server(struct afs_server *server)
{
        struct afs_server *xserver;
        struct rb_node **pp, *p;
        int ret;

        _enter("%p", server);

        write_lock(&afs_servers_lock);

        ret = -EEXIST;
        pp = &afs_servers.rb_node;
        p = NULL;
        while (*pp) {
                p = *pp;
                _debug("- consider %p", p);
                xserver = rb_entry(p, struct afs_server, master_rb);
                if (server->addr.s_addr < xserver->addr.s_addr)
                        pp = &(*pp)->rb_left;
                else if (server->addr.s_addr > xserver->addr.s_addr)
                        pp = &(*pp)->rb_right;
                else
                        goto error;
        }

        rb_link_node(&server->master_rb, p, pp);
        rb_insert_color(&server->master_rb, &afs_servers);
        ret = 0;

error:
        write_unlock(&afs_servers_lock);
        return ret;
}

/*
 * allocate a new server record
 */
static struct afs_server *afs_alloc_server(struct afs_cell *cell,
                                           const struct in_addr *addr)
{
        struct afs_server *server;

        _enter("");

        server = kzalloc(sizeof(struct afs_server), GFP_KERNEL);
        if (server) {
                atomic_set(&server->usage, 1);
                server->cell = cell;

                INIT_LIST_HEAD(&server->link);
                INIT_LIST_HEAD(&server->grave);
                init_rwsem(&server->sem);
                spin_lock_init(&server->fs_lock);
                server->fs_vnodes = RB_ROOT;
                server->cb_promises = RB_ROOT;
                spin_lock_init(&server->cb_lock);
                init_waitqueue_head(&server->cb_break_waitq);
                INIT_DELAYED_WORK(&server->cb_break_work,
                                  afs_dispatch_give_up_callbacks);

                memcpy(&server->addr, addr, sizeof(struct in_addr));
                server->addr.s_addr = addr->s_addr;
        }

        _leave(" = %p{%d}", server, atomic_read(&server->usage));
        return server;
}

/*
 * get an FS-server record for a cell
 */
struct afs_server *afs_lookup_server(struct afs_cell *cell,
                                     const struct in_addr *addr)
{
        struct afs_server *server, *candidate;

        _enter("%p,%pI4", cell, &addr->s_addr);

        /* quick scan of the list to see if we already have the server */
        read_lock(&cell->servers_lock);

        list_for_each_entry(server, &cell->servers, link) {
                if (server->addr.s_addr == addr->s_addr)
                        goto found_server_quickly;
        }
        read_unlock(&cell->servers_lock);

        candidate = afs_alloc_server(cell, addr);
        if (!candidate) {
                _leave(" = -ENOMEM");
                return ERR_PTR(-ENOMEM);
        }

        write_lock(&cell->servers_lock);

        /* check the cell's server list again */
        list_for_each_entry(server, &cell->servers, link) {
                if (server->addr.s_addr == addr->s_addr)
                        goto found_server;
        }

        _debug("new");
        server = candidate;
        if (afs_install_server(server) < 0)
                goto server_in_two_cells;

        afs_get_cell(cell);
        list_add_tail(&server->link, &cell->servers);

        write_unlock(&cell->servers_lock);
        _leave(" = %p{%d}", server, atomic_read(&server->usage));
        return server;

        /* found a matching server quickly */
found_server_quickly:
        _debug("found quickly");
        afs_get_server(server);
        read_unlock(&cell->servers_lock);
no_longer_unused:
        if (!list_empty(&server->grave)) {
                spin_lock(&afs_server_graveyard_lock);
                list_del_init(&server->grave);
                spin_unlock(&afs_server_graveyard_lock);
        }
        _leave(" = %p{%d}", server, atomic_read(&server->usage));
        return server;

        /* found a matching server on the second pass */
found_server:
        _debug("found");
        afs_get_server(server);
        write_unlock(&cell->servers_lock);
        kfree(candidate);
        goto no_longer_unused;

        /* found a server that seems to be in two cells */
server_in_two_cells:
        write_unlock(&cell->servers_lock);
        kfree(candidate);
        printk(KERN_NOTICE "kAFS: Server %pI4 appears to be in two cells\n",
               addr);
        _leave(" = -EEXIST");
        return ERR_PTR(-EEXIST);
}

/*
 * look up a server by its IP address
 */
struct afs_server *afs_find_server(const struct in_addr *_addr)
{
        struct afs_server *server = NULL;
        struct rb_node *p;
        struct in_addr addr = *_addr;

        _enter("%pI4", &addr.s_addr);

        read_lock(&afs_servers_lock);

        p = afs_servers.rb_node;
        while (p) {
                server = rb_entry(p, struct afs_server, master_rb);

                _debug("- consider %p", p);

                if (addr.s_addr < server->addr.s_addr) {
                        p = p->rb_left;
                } else if (addr.s_addr > server->addr.s_addr) {
                        p = p->rb_right;
                } else {
                        afs_get_server(server);
                        goto found;
                }
        }

        server = NULL;
found:
        read_unlock(&afs_servers_lock);
        ASSERTIFCMP(server, server->addr.s_addr, ==, addr.s_addr);
        _leave(" = %p", server);
        return server;
}

/*
 * destroy a server record
 * - removes from the cell list
 */
void afs_put_server(struct afs_server *server)
{
        if (!server)
                return;

        _enter("%p{%d}", server, atomic_read(&server->usage));

        _debug("PUT SERVER %d", atomic_read(&server->usage));

        ASSERTCMP(atomic_read(&server->usage), >, 0);

        if (likely(!atomic_dec_and_test(&server->usage))) {
                _leave("");
                return;
        }

        afs_flush_callback_breaks(server);

        spin_lock(&afs_server_graveyard_lock);
        if (atomic_read(&server->usage) == 0) {
                list_move_tail(&server->grave, &afs_server_graveyard);
                server->time_of_death = get_seconds();
                schedule_delayed_work(&afs_server_reaper,
                                      afs_server_timeout * HZ);
        }
        spin_unlock(&afs_server_graveyard_lock);
        _leave(" [dead]");
}

/*
 * destroy a dead server
 */
static void afs_destroy_server(struct afs_server *server)
{
        _enter("%p", server);

        ASSERTIF(server->cb_break_head != server->cb_break_tail,
                 delayed_work_pending(&server->cb_break_work));

        ASSERTCMP(server->fs_vnodes.rb_node, ==, NULL);
        ASSERTCMP(server->cb_promises.rb_node, ==, NULL);
        ASSERTCMP(server->cb_break_head, ==, server->cb_break_tail);
        ASSERTCMP(atomic_read(&server->cb_break_n), ==, 0);

        afs_put_cell(server->cell);
        kfree(server);
}

/*
 * reap dead server records
 */
static void afs_reap_server(struct work_struct *work)
{
        LIST_HEAD(corpses);
        struct afs_server *server;
        unsigned long delay, expiry;
        time_t now;

        now = get_seconds();
        spin_lock(&afs_server_graveyard_lock);

        while (!list_empty(&afs_server_graveyard)) {
                server = list_entry(afs_server_graveyard.next,
                                    struct afs_server, grave);

                /* the queue is ordered most dead first */
                expiry = server->time_of_death + afs_server_timeout;
                if (expiry > now) {
                        delay = (expiry - now) * HZ;
                        if (!schedule_delayed_work(&afs_server_reaper, delay)) {
                                cancel_delayed_work(&afs_server_reaper);
                                schedule_delayed_work(&afs_server_reaper,
                                                      delay);
                        }
                        break;
                }

                write_lock(&server->cell->servers_lock);
                write_lock(&afs_servers_lock);
                if (atomic_read(&server->usage) > 0) {
                        list_del_init(&server->grave);
                } else {
                        list_move_tail(&server->grave, &corpses);
                        list_del_init(&server->link);
                        rb_erase(&server->master_rb, &afs_servers);
                }
                write_unlock(&afs_servers_lock);
                write_unlock(&server->cell->servers_lock);
        }

        spin_unlock(&afs_server_graveyard_lock);

        /* now reap the corpses we've extracted */
        while (!list_empty(&corpses)) {
                server = list_entry(corpses.next, struct afs_server, grave);
                list_del(&server->grave);
                afs_destroy_server(server);
        }
}

/*
 * discard all the server records for rmmod
 */
void __exit afs_purge_servers(void)
{
        afs_server_timeout = 0;
        cancel_delayed_work(&afs_server_reaper);
        schedule_delayed_work(&afs_server_reaper, 0);
}