// SPDX-License-Identifier: GPL-2.0
/* Multipath TCP
 *
 * Copyright (c) 2019, Intel Corporation.
 */
#define pr_fmt(fmt) "MPTCP: " fmt

#include <linux/kernel.h>
#include <net/tcp.h>
#include <net/mptcp.h>
#include "protocol.h"

static struct workqueue_struct *pm_wq;

/* path manager command handlers */

int mptcp_pm_announce_addr(struct mptcp_sock *msk,
                           const struct mptcp_addr_info *addr)
{
        pr_debug("msk=%p, local_id=%d", msk, addr->id);

        msk->pm.local = *addr;
        WRITE_ONCE(msk->pm.addr_signal, true);
        return 0;
}

int mptcp_pm_remove_addr(struct mptcp_sock *msk, u8 local_id)
{
        return -ENOTSUPP;
}

int mptcp_pm_remove_subflow(struct mptcp_sock *msk, u8 remote_id)
{
        return -ENOTSUPP;
}

/* path manager event handlers */

void mptcp_pm_new_connection(struct mptcp_sock *msk, int server_side)
{
        struct mptcp_pm_data *pm = &msk->pm;

        pr_debug("msk=%p, token=%u side=%d", msk, msk->token, server_side);

        WRITE_ONCE(pm->server_side, server_side);
}

bool mptcp_pm_allow_new_subflow(struct mptcp_sock *msk)
{
        struct mptcp_pm_data *pm = &msk->pm;
        int ret;

        pr_debug("msk=%p subflows=%d max=%d allow=%d", msk, pm->subflows,
                 pm->subflows_max, READ_ONCE(pm->accept_subflow));

        /* try to avoid acquiring the lock below */
        if (!READ_ONCE(pm->accept_subflow))
                return false;

        spin_lock_bh(&pm->lock);
        ret = pm->subflows < pm->subflows_max;
        if (ret && ++pm->subflows == pm->subflows_max)
                WRITE_ONCE(pm->accept_subflow, false);
        spin_unlock_bh(&pm->lock);

        return ret;
}

/* return true if the new status bit is currently cleared, that is, this event
 * can be server, eventually by an already scheduled work
 */
static bool mptcp_pm_schedule_work(struct mptcp_sock *msk,
                                   enum mptcp_pm_status new_status)
{
        pr_debug("msk=%p status=%x new=%lx", msk, msk->pm.status,
                 BIT(new_status));
        if (msk->pm.status & BIT(new_status))
                return false;

        msk->pm.status |= BIT(new_status);
        if (queue_work(pm_wq, &msk->pm.work))
                sock_hold((struct sock *)msk);
        return true;
}

void mptcp_pm_fully_established(struct mptcp_sock *msk)
{
        struct mptcp_pm_data *pm = &msk->pm;

        pr_debug("msk=%p", msk);

        /* try to avoid acquiring the lock below */
        if (!READ_ONCE(pm->work_pending))
                return;

        spin_lock_bh(&pm->lock);

        if (READ_ONCE(pm->work_pending))
                mptcp_pm_schedule_work(msk, MPTCP_PM_ESTABLISHED);

        spin_unlock_bh(&pm->lock);
}

void mptcp_pm_connection_closed(struct mptcp_sock *msk)
{
        pr_debug("msk=%p", msk);
}

void mptcp_pm_subflow_established(struct mptcp_sock *msk,
                                  struct mptcp_subflow_context *subflow)
{
        struct mptcp_pm_data *pm = &msk->pm;

        pr_debug("msk=%p", msk);

        if (!READ_ONCE(pm->work_pending))
                return;

        spin_lock_bh(&pm->lock);

        if (READ_ONCE(pm->work_pending))
                mptcp_pm_schedule_work(msk, MPTCP_PM_SUBFLOW_ESTABLISHED);

        spin_unlock_bh(&pm->lock);
}

void mptcp_pm_subflow_closed(struct mptcp_sock *msk, u8 id)
{
        pr_debug("msk=%p", msk);
}

void mptcp_pm_add_addr_received(struct mptcp_sock *msk,
                                const struct mptcp_addr_info *addr)
{
        struct mptcp_pm_data *pm = &msk->pm;

        pr_debug("msk=%p remote_id=%d accept=%d", msk, addr->id,
                 READ_ONCE(pm->accept_addr));

        /* avoid acquiring the lock if there is no room for fouther addresses */
        if (!READ_ONCE(pm->accept_addr))
                return;

        spin_lock_bh(&pm->lock);

        /* be sure there is something to signal re-checking under PM lock */
        if (READ_ONCE(pm->accept_addr) &&
            mptcp_pm_schedule_work(msk, MPTCP_PM_ADD_ADDR_RECEIVED))
                pm->remote = *addr;

        spin_unlock_bh(&pm->lock);
}

/* path manager helpers */

bool mptcp_pm_addr_signal(struct mptcp_sock *msk, unsigned int remaining,
                          struct mptcp_addr_info *saddr)
{
        int ret = false;

        spin_lock_bh(&msk->pm.lock);

        /* double check after the lock is acquired */
        if (!mptcp_pm_should_signal(msk))
                goto out_unlock;

        if (remaining < mptcp_add_addr_len(msk->pm.local.family))
                goto out_unlock;

        *saddr = msk->pm.local;
        WRITE_ONCE(msk->pm.addr_signal, false);
        ret = true;

out_unlock:
        spin_unlock_bh(&msk->pm.lock);
        return ret;
}

int mptcp_pm_get_local_id(struct mptcp_sock *msk, struct sock_common *skc)
{
        return mptcp_pm_nl_get_local_id(msk, skc);
}

static void pm_worker(struct work_struct *work)
{
        struct mptcp_pm_data *pm = container_of(work, struct mptcp_pm_data,
                                                work);
        struct mptcp_sock *msk = container_of(pm, struct mptcp_sock, pm);
        struct sock *sk = (struct sock *)msk;

        lock_sock(sk);
        spin_lock_bh(&msk->pm.lock);

        pr_debug("msk=%p status=%x", msk, pm->status);
        if (pm->status & BIT(MPTCP_PM_ADD_ADDR_RECEIVED)) {
                pm->status &= ~BIT(MPTCP_PM_ADD_ADDR_RECEIVED);
                mptcp_pm_nl_add_addr_received(msk);
        }
        if (pm->status & BIT(MPTCP_PM_ESTABLISHED)) {
                pm->status &= ~BIT(MPTCP_PM_ESTABLISHED);
                mptcp_pm_nl_fully_established(msk);
        }
        if (pm->status & BIT(MPTCP_PM_SUBFLOW_ESTABLISHED)) {
                pm->status &= ~BIT(MPTCP_PM_SUBFLOW_ESTABLISHED);
                mptcp_pm_nl_subflow_established(msk);
        }

        spin_unlock_bh(&msk->pm.lock);
        release_sock(sk);
        sock_put(sk);
}

void mptcp_pm_data_init(struct mptcp_sock *msk)
{
        msk->pm.add_addr_signaled = 0;
        msk->pm.add_addr_accepted = 0;
        msk->pm.local_addr_used = 0;
        msk->pm.subflows = 0;
        WRITE_ONCE(msk->pm.work_pending, false);
        WRITE_ONCE(msk->pm.addr_signal, false);
        WRITE_ONCE(msk->pm.accept_addr, false);
        WRITE_ONCE(msk->pm.accept_subflow, false);
        msk->pm.status = 0;

        spin_lock_init(&msk->pm.lock);
        INIT_WORK(&msk->pm.work, pm_worker);

        mptcp_pm_nl_data_init(msk);
}

void mptcp_pm_close(struct mptcp_sock *msk)
{
        if (cancel_work_sync(&msk->pm.work))
                sock_put((struct sock *)msk);
}

void mptcp_pm_init(void)
{
        pm_wq = alloc_workqueue("pm_wq", WQ_UNBOUND | WQ_MEM_RECLAIM, 8);
        if (!pm_wq)
                panic("Failed to allocate workqueue");

        mptcp_pm_nl_init();
}