/* 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));
  	} else {
  		_leave(" = NULL [nomem]");
  	}
  	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
  ",
  	       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();
  		queue_delayed_work(afs_wq, &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;
  			mod_delayed_work(afs_wq, &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;
  	mod_delayed_work(afs_wq, &afs_server_reaper, 0);
  }