/*
 * Copyright (c) 2006, 2017 Oracle and/or its affiliates. All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/in.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <linux/ipv6.h>

#include "rds_single_path.h"
#include "rds.h"
#include "loop.h"

static DEFINE_SPINLOCK(loop_conns_lock);
static LIST_HEAD(loop_conns);
static atomic_t rds_loop_unloading = ATOMIC_INIT(0);

static void rds_loop_set_unloading(void)
{
        atomic_set(&rds_loop_unloading, 1);
}

static bool rds_loop_is_unloading(struct rds_connection *conn)
{
        return atomic_read(&rds_loop_unloading) != 0;
}

/*
 * This 'loopback' transport is a special case for flows that originate
 * and terminate on the same machine.
 *
 * Connection build-up notices if the destination address is thought of
 * as a local address by a transport.  At that time it decides to use the
 * loopback transport instead of the bound transport of the sending socket.
 *
 * The loopback transport's sending path just hands the sent rds_message
 * straight to the receiving path via an embedded rds_incoming.
 */

/*
 * Usually a message transits both the sender and receiver's conns as it
 * flows to the receiver.  In the loopback case, though, the receive path
 * is handed the sending conn so the sense of the addresses is reversed.
 */
static int rds_loop_xmit(struct rds_connection *conn, struct rds_message *rm,
                         unsigned int hdr_off, unsigned int sg,
                         unsigned int off)
{
        struct scatterlist *sgp = &rm->data.op_sg[sg];
        int ret = sizeof(struct rds_header) +
                        be32_to_cpu(rm->m_inc.i_hdr.h_len);

        /* Do not send cong updates to loopback */
        if (rm->m_inc.i_hdr.h_flags & RDS_FLAG_CONG_BITMAP) {
                rds_cong_map_updated(conn->c_fcong, ~(u64) 0);
                ret = min_t(int, ret, sgp->length - conn->c_xmit_data_off);
                goto out;
        }

        BUG_ON(hdr_off || sg || off);

        rds_inc_init(&rm->m_inc, conn, &conn->c_laddr);
        /* For the embedded inc. Matching put is in loop_inc_free() */
        rds_message_addref(rm);

        rds_recv_incoming(conn, &conn->c_laddr, &conn->c_faddr, &rm->m_inc,
                          GFP_KERNEL);

        rds_send_drop_acked(conn, be64_to_cpu(rm->m_inc.i_hdr.h_sequence),
                            NULL);

        rds_inc_put(&rm->m_inc);
out:
        return ret;
}

/*
 * See rds_loop_xmit(). Since our inc is embedded in the rm, we
 * make sure the rm lives at least until the inc is done.
 */
static void rds_loop_inc_free(struct rds_incoming *inc)
{
        struct rds_message *rm = container_of(inc, struct rds_message, m_inc);

        rds_message_put(rm);
}

/* we need to at least give the thread something to succeed */
static int rds_loop_recv_path(struct rds_conn_path *cp)
{
        return 0;
}

struct rds_loop_connection {
        struct list_head loop_node;
        struct rds_connection *conn;
};

/*
 * Even the loopback transport needs to keep track of its connections,
 * so it can call rds_conn_destroy() on them on exit. N.B. there are
 * 1+ loopback addresses (127.*.*.*) so it's not a bug to have
 * multiple loopback conns allocated, although rather useless.
 */
static int rds_loop_conn_alloc(struct rds_connection *conn, gfp_t gfp)
{
        struct rds_loop_connection *lc;
        unsigned long flags;

        lc = kzalloc(sizeof(struct rds_loop_connection), gfp);
        if (!lc)
                return -ENOMEM;

        INIT_LIST_HEAD(&lc->loop_node);
        lc->conn = conn;
        conn->c_transport_data = lc;

        spin_lock_irqsave(&loop_conns_lock, flags);
        list_add_tail(&lc->loop_node, &loop_conns);
        spin_unlock_irqrestore(&loop_conns_lock, flags);

        return 0;
}

static void rds_loop_conn_free(void *arg)
{
        struct rds_loop_connection *lc = arg;
        unsigned long flags;

        rdsdebug("lc %p\n", lc);
        spin_lock_irqsave(&loop_conns_lock, flags);
        list_del(&lc->loop_node);
        spin_unlock_irqrestore(&loop_conns_lock, flags);
        kfree(lc);
}

static int rds_loop_conn_path_connect(struct rds_conn_path *cp)
{
        rds_connect_complete(cp->cp_conn);
        return 0;
}

static void rds_loop_conn_path_shutdown(struct rds_conn_path *cp)
{
}

void rds_loop_exit(void)
{
        struct rds_loop_connection *lc, *_lc;
        LIST_HEAD(tmp_list);

        rds_loop_set_unloading();
        synchronize_rcu();
        /* avoid calling conn_destroy with irqs off */
        spin_lock_irq(&loop_conns_lock);
        list_splice(&loop_conns, &tmp_list);
        INIT_LIST_HEAD(&loop_conns);
        spin_unlock_irq(&loop_conns_lock);

        list_for_each_entry_safe(lc, _lc, &tmp_list, loop_node) {
                WARN_ON(lc->conn->c_passive);
                rds_conn_destroy(lc->conn);
        }
}

static void rds_loop_kill_conns(struct net *net)
{
        struct rds_loop_connection *lc, *_lc;
        LIST_HEAD(tmp_list);

        spin_lock_irq(&loop_conns_lock);
        list_for_each_entry_safe(lc, _lc, &loop_conns, loop_node)  {
                struct net *c_net = read_pnet(&lc->conn->c_net);

                if (net != c_net)
                        continue;
                list_move_tail(&lc->loop_node, &tmp_list);
        }
        spin_unlock_irq(&loop_conns_lock);

        list_for_each_entry_safe(lc, _lc, &tmp_list, loop_node) {
                WARN_ON(lc->conn->c_passive);
                rds_conn_destroy(lc->conn);
        }
}

static void __net_exit rds_loop_exit_net(struct net *net)
{
        rds_loop_kill_conns(net);
}

static struct pernet_operations rds_loop_net_ops = {
        .exit = rds_loop_exit_net,
};

int rds_loop_net_init(void)
{
        return register_pernet_device(&rds_loop_net_ops);
}

void rds_loop_net_exit(void)
{
        unregister_pernet_device(&rds_loop_net_ops);
}

/*
 * This is missing .xmit_* because loop doesn't go through generic
 * rds_send_xmit() and doesn't call rds_recv_incoming().  .listen_stop and
 * .laddr_check are missing because transport.c doesn't iterate over
 * rds_loop_transport.
 */
struct rds_transport rds_loop_transport = {
        .xmit                   = rds_loop_xmit,
        .recv_path              = rds_loop_recv_path,
        .conn_alloc             = rds_loop_conn_alloc,
        .conn_free              = rds_loop_conn_free,
        .conn_path_connect      = rds_loop_conn_path_connect,
        .conn_path_shutdown     = rds_loop_conn_path_shutdown,
        .inc_copy_to_user       = rds_message_inc_copy_to_user,
        .inc_free               = rds_loop_inc_free,
        .t_name                 = "loopback",
        .t_type                 = RDS_TRANS_LOOP,
        .t_unloading            = rds_loop_is_unloading,
};