/* Client connection-specific management code.
 *
 * Copyright (C) 2016 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 Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/slab.h>
#include <linux/idr.h>
#include <linux/timer.h>
#include "ar-internal.h"

/*
 * We use machine-unique IDs for our client connections.
 */
DEFINE_IDR(rxrpc_client_conn_ids);
static DEFINE_SPINLOCK(rxrpc_conn_id_lock);

/*
 * Get a connection ID and epoch for a client connection from the global pool.
 * The connection struct pointer is then recorded in the idr radix tree.  The
 * epoch is changed if this wraps.
 *
 * TODO: The IDR tree gets very expensive on memory if the connection IDs are
 * widely scattered throughout the number space, so we shall need to retire
 * connections that have, say, an ID more than four times the maximum number of
 * client conns away from the current allocation point to try and keep the IDs
 * concentrated.  We will also need to retire connections from an old epoch.
 */
static int rxrpc_get_client_connection_id(struct rxrpc_connection *conn,
					  gfp_t gfp)
{
	u32 epoch;
	int id;

	_enter("");

	idr_preload(gfp);
	spin_lock(&rxrpc_conn_id_lock);

	epoch = rxrpc_epoch;

	/* We could use idr_alloc_cyclic() here, but we really need to know
	 * when the thing wraps so that we can advance the epoch.
	 */
	if (rxrpc_client_conn_ids.cur == 0)
		rxrpc_client_conn_ids.cur = 1;
	id = idr_alloc(&rxrpc_client_conn_ids, conn,
		       rxrpc_client_conn_ids.cur, 0x40000000, GFP_NOWAIT);
	if (id < 0) {
		if (id != -ENOSPC)
			goto error;
		id = idr_alloc(&rxrpc_client_conn_ids, conn,
			       1, 0x40000000, GFP_NOWAIT);
		if (id < 0)
			goto error;
		epoch++;
		rxrpc_epoch = epoch;
	}
	rxrpc_client_conn_ids.cur = id + 1;

	spin_unlock(&rxrpc_conn_id_lock);
	idr_preload_end();

	conn->proto.epoch = epoch;
	conn->proto.cid = id << RXRPC_CIDSHIFT;
	set_bit(RXRPC_CONN_HAS_IDR, &conn->flags);
	_leave(" [CID %x:%x]", epoch, conn->proto.cid);
	return 0;

error:
	spin_unlock(&rxrpc_conn_id_lock);
	idr_preload_end();
	_leave(" = %d", id);
	return id;
}

/*
 * Release a connection ID for a client connection from the global pool.
 */
static void rxrpc_put_client_connection_id(struct rxrpc_connection *conn)
{
	if (test_bit(RXRPC_CONN_HAS_IDR, &conn->flags)) {
		spin_lock(&rxrpc_conn_id_lock);
		idr_remove(&rxrpc_client_conn_ids,
			   conn->proto.cid >> RXRPC_CIDSHIFT);
		spin_unlock(&rxrpc_conn_id_lock);
	}
}

/*
 * Destroy the client connection ID tree.
 */
void rxrpc_destroy_client_conn_ids(void)
{
	struct rxrpc_connection *conn;
	int id;

	if (!idr_is_empty(&rxrpc_client_conn_ids)) {
		idr_for_each_entry(&rxrpc_client_conn_ids, conn, id) {
			pr_err("AF_RXRPC: Leaked client conn %p {%d}\n",
			       conn, atomic_read(&conn->usage));
		}
		BUG();
	}

	idr_destroy(&rxrpc_client_conn_ids);
}

/*
 * Allocate a client connection.  The caller must take care to clear any
 * padding bytes in *cp.
 */
static struct rxrpc_connection *
rxrpc_alloc_client_connection(struct rxrpc_conn_parameters *cp, gfp_t gfp)
{
	struct rxrpc_connection *conn;
	int ret;

	_enter("");

	conn = rxrpc_alloc_connection(gfp);
	if (!conn) {
		_leave(" = -ENOMEM");
		return ERR_PTR(-ENOMEM);
	}

	conn->params		= *cp;
	conn->out_clientflag	= RXRPC_CLIENT_INITIATED;
	conn->state		= RXRPC_CONN_CLIENT;

	ret = rxrpc_get_client_connection_id(conn, gfp);
	if (ret < 0)
		goto error_0;

	ret = rxrpc_init_client_conn_security(conn);
	if (ret < 0)
		goto error_1;

	ret = conn->security->prime_packet_security(conn);
	if (ret < 0)
		goto error_2;

	write_lock(&rxrpc_connection_lock);
	list_add_tail(&conn->link, &rxrpc_connections);
	write_unlock(&rxrpc_connection_lock);

	/* We steal the caller's peer ref. */
	cp->peer = NULL;
	rxrpc_get_local(conn->params.local);
	key_get(conn->params.key);

	_leave(" = %p", conn);
	return conn;

error_2:
	conn->security->clear(conn);
error_1:
	rxrpc_put_client_connection_id(conn);
error_0:
	kfree(conn);
	_leave(" = %d", ret);
	return ERR_PTR(ret);
}

/*
 * find a connection for a call
 * - called in process context with IRQs enabled
 */
int rxrpc_connect_call(struct rxrpc_call *call,
		       struct rxrpc_conn_parameters *cp,
		       struct sockaddr_rxrpc *srx,
		       gfp_t gfp)
{
	struct rxrpc_connection *conn, *candidate = NULL;
	struct rxrpc_local *local = cp->local;
	struct rb_node *p, **pp, *parent;
	long diff;
	int chan;

	DECLARE_WAITQUEUE(myself, current);

	_enter("{%d,%lx},", call->debug_id, call->user_call_ID);

	cp->peer = rxrpc_lookup_peer(cp->local, srx, gfp);
	if (!cp->peer)
		return -ENOMEM;

	if (!cp->exclusive) {
		/* Search for a existing client connection unless this is going
		 * to be a connection that's used exclusively for a single call.
		 */
		_debug("search 1");
		spin_lock(&local->client_conns_lock);
		p = local->client_conns.rb_node;
		while (p) {
			conn = rb_entry(p, struct rxrpc_connection, client_node);

#define cmp(X) ((long)conn->params.X - (long)cp->X)
			diff = (cmp(peer) ?:
				cmp(key) ?:
				cmp(security_level));
			if (diff < 0)
				p = p->rb_left;
			else if (diff > 0)
				p = p->rb_right;
			else
				goto found_extant_conn;
		}
		spin_unlock(&local->client_conns_lock);
	}

	/* We didn't find a connection or we want an exclusive one. */
	_debug("get new conn");
	candidate = rxrpc_alloc_client_connection(cp, gfp);
	if (!candidate) {
		_leave(" = -ENOMEM");
		return -ENOMEM;
	}

	if (cp->exclusive) {
		/* Assign the call on an exclusive connection to channel 0 and
		 * don't add the connection to the endpoint's shareable conn
		 * lookup tree.
		 */
		_debug("exclusive chan 0");
		conn = candidate;
		atomic_set(&conn->avail_chans, RXRPC_MAXCALLS - 1);
		spin_lock(&conn->channel_lock);
		chan = 0;
		goto found_channel;
	}

	/* We need to redo the search before attempting to add a new connection
	 * lest we race with someone else adding a conflicting instance.
	 */
	_debug("search 2");
	spin_lock(&local->client_conns_lock);

	pp = &local->client_conns.rb_node;
	parent = NULL;
	while (*pp) {
		parent = *pp;
		conn = rb_entry(parent, struct rxrpc_connection, client_node);

		diff = (cmp(peer) ?:
			cmp(key) ?:
			cmp(security_level));
		if (diff < 0)
			pp = &(*pp)->rb_left;
		else if (diff > 0)
			pp = &(*pp)->rb_right;
		else
			goto found_extant_conn;
	}

	/* The second search also failed; simply add the new connection with
	 * the new call in channel 0.  Note that we need to take the channel
	 * lock before dropping the client conn lock.
	 */
	_debug("new conn");
	set_bit(RXRPC_CONN_IN_CLIENT_CONNS, &candidate->flags);
	rb_link_node(&candidate->client_node, parent, pp);
	rb_insert_color(&candidate->client_node, &local->client_conns);
attached:
	conn = candidate;
	candidate = NULL;

	atomic_set(&conn->avail_chans, RXRPC_MAXCALLS - 1);
	spin_lock(&conn->channel_lock);
	spin_unlock(&local->client_conns_lock);
	chan = 0;

found_channel:
	_debug("found chan");
	call->conn	= conn;
	call->channel	= chan;
	call->epoch	= conn->proto.epoch;
	call->cid	= conn->proto.cid | chan;
	call->call_id	= ++conn->channels[chan].call_counter;
	conn->channels[chan].call_id = call->call_id;
	rcu_assign_pointer(conn->channels[chan].call, call);

	_net("CONNECT call %d on conn %d", call->debug_id, conn->debug_id);

	spin_unlock(&conn->channel_lock);
	rxrpc_put_peer(cp->peer);
	cp->peer = NULL;
	_leave(" = %p {u=%d}", conn, atomic_read(&conn->usage));
	return 0;

	/* We found a potentially suitable connection already in existence.  If
	 * we can reuse it (ie. its usage count hasn't been reduced to 0 by the
	 * reaper), discard any candidate we may have allocated, and try to get
	 * a channel on this one, otherwise we have to replace it.
	 */
found_extant_conn:
	_debug("found conn");
	if (!rxrpc_get_connection_maybe(conn)) {
		set_bit(RXRPC_CONN_IN_CLIENT_CONNS, &candidate->flags);
		rb_replace_node(&conn->client_node,
				&candidate->client_node,
				&local->client_conns);
		clear_bit(RXRPC_CONN_IN_CLIENT_CONNS, &conn->flags);
		goto attached;
	}

	spin_unlock(&local->client_conns_lock);

	rxrpc_put_connection(candidate);

	if (!atomic_add_unless(&conn->avail_chans, -1, 0)) {
		if (!gfpflags_allow_blocking(gfp)) {
			rxrpc_put_connection(conn);
			_leave(" = -EAGAIN");
			return -EAGAIN;
		}

		add_wait_queue(&conn->channel_wq, &myself);
		for (;;) {
			set_current_state(TASK_INTERRUPTIBLE);
			if (atomic_add_unless(&conn->avail_chans, -1, 0))
				break;
			if (signal_pending(current))
				goto interrupted;
			schedule();
		}
		remove_wait_queue(&conn->channel_wq, &myself);
		__set_current_state(TASK_RUNNING);
	}

	/* The connection allegedly now has a free channel and we can now
	 * attach the call to it.
	 */
	spin_lock(&conn->channel_lock);

	for (chan = 0; chan < RXRPC_MAXCALLS; chan++)
		if (!conn->channels[chan].call)
			goto found_channel;
	BUG();

interrupted:
	remove_wait_queue(&conn->channel_wq, &myself);
	__set_current_state(TASK_RUNNING);
	rxrpc_put_connection(conn);
	rxrpc_put_peer(cp->peer);
	cp->peer = NULL;
	_leave(" = -ERESTARTSYS");
	return -ERESTARTSYS;
}

/*
 * Remove a client connection from the local endpoint's tree, thereby removing
 * it as a target for reuse for new client calls.
 */
void rxrpc_unpublish_client_conn(struct rxrpc_connection *conn)
{
	struct rxrpc_local *local = conn->params.local;

	spin_lock(&local->client_conns_lock);
	if (test_and_clear_bit(RXRPC_CONN_IN_CLIENT_CONNS, &conn->flags))
		rb_erase(&conn->client_node, &local->client_conns);
	spin_unlock(&local->client_conns_lock);

	rxrpc_put_client_connection_id(conn);
}