// SPDX-License-Identifier: GPL-2.0
/*
 *     SUCS NET3:
 *
 *     Generic stream handling routines. These are generic for most
 *     protocols. Even IP. Tonight 8-).
 *     This is used because TCP, LLC (others too) layer all have mostly
 *     identical sendmsg() and recvmsg() code.
 *     So we (will) share it here.
 *
 *     Authors:        Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *                     (from old tcp.c code)
 *                     Alan Cox <alan@lxorguk.ukuu.org.uk> (Borrowed comments 8-))
 */

#include <linux/module.h>
#include <linux/sched/signal.h>
#include <linux/net.h>
#include <linux/signal.h>
#include <linux/tcp.h>
#include <linux/wait.h>
#include <net/sock.h>

/**
 * sk_stream_write_space - stream socket write_space callback.
 * @sk: pointer to the socket structure
 *
 * This function is invoked when there's space available in the socket's
 * send buffer for writing. It first checks if the socket is writable,
 * clears the SOCK_NOSPACE flag indicating that memory for writing
 * is now available, wakes up any processes waiting for write operations
 * and sends asynchronous notifications if needed.
 */
void sk_stream_write_space(struct sock *sk)
{
        struct socket *sock = sk->sk_socket;
        struct socket_wq *wq;

        if (__sk_stream_is_writeable(sk, 1) && sock) {
                clear_bit(SOCK_NOSPACE, &sock->flags);

                rcu_read_lock();
                wq = rcu_dereference(sk->sk_wq);
                if (skwq_has_sleeper(wq))
                        wake_up_interruptible_poll(&wq->wait, EPOLLOUT |
                                                EPOLLWRNORM | EPOLLWRBAND);
                if (wq && wq->fasync_list && !(sk->sk_shutdown & SEND_SHUTDOWN))
                        sock_wake_async(wq, SOCK_WAKE_SPACE, POLL_OUT);
                rcu_read_unlock();
        }
}

/**
 * sk_stream_wait_connect - Wait for a socket to get into the connected state
 * @sk: sock to wait on
 * @timeo_p: for how long to wait
 *
 * Must be called with the socket locked.
 */
int sk_stream_wait_connect(struct sock *sk, long *timeo_p)
{
        DEFINE_WAIT_FUNC(wait, woken_wake_function);
        struct task_struct *tsk = current;
        int done;

        do {
                int err = sock_error(sk);
                if (err)
                        return err;
                if ((1 << sk->sk_state) & ~(TCPF_SYN_SENT | TCPF_SYN_RECV))
                        return -EPIPE;
                if (!*timeo_p)
                        return -EAGAIN;
                if (signal_pending(tsk))
                        return sock_intr_errno(*timeo_p);

                add_wait_queue(sk_sleep(sk), &wait);
                sk->sk_write_pending++;
                done = sk_wait_event(sk, timeo_p,
                                     !READ_ONCE(sk->sk_err) &&
                                     !((1 << READ_ONCE(sk->sk_state)) &
                                       ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)), &wait);
                remove_wait_queue(sk_sleep(sk), &wait);
                sk->sk_write_pending--;
        } while (!done);
        return done < 0 ? done : 0;
}
EXPORT_SYMBOL(sk_stream_wait_connect);

/**
 * sk_stream_closing - Return 1 if we still have things to send in our buffers.
 * @sk: socket to verify
 */
static int sk_stream_closing(const struct sock *sk)
{
        return (1 << READ_ONCE(sk->sk_state)) &
               (TCPF_FIN_WAIT1 | TCPF_CLOSING | TCPF_LAST_ACK);
}

void sk_stream_wait_close(struct sock *sk, long timeout)
{
        if (timeout) {
                DEFINE_WAIT_FUNC(wait, woken_wake_function);

                add_wait_queue(sk_sleep(sk), &wait);

                do {
                        if (sk_wait_event(sk, &timeout, !sk_stream_closing(sk), &wait))
                                break;
                } while (!signal_pending(current) && timeout);

                remove_wait_queue(sk_sleep(sk), &wait);
        }
}
EXPORT_SYMBOL(sk_stream_wait_close);

/**
 * sk_stream_wait_memory - Wait for more memory for a socket
 * @sk: socket to wait for memory
 * @timeo_p: for how long
 */
int sk_stream_wait_memory(struct sock *sk, long *timeo_p)
{
        int ret, err = 0;
        long vm_wait = 0;
        long current_timeo = *timeo_p;
        DEFINE_WAIT_FUNC(wait, woken_wake_function);

        if (sk_stream_memory_free(sk))
                current_timeo = vm_wait = get_random_u32_below(HZ / 5) + 2;

        add_wait_queue(sk_sleep(sk), &wait);

        while (1) {
                sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);

                if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
                        goto do_error;
                if (!*timeo_p)
                        goto do_eagain;
                if (signal_pending(current))
                        goto do_interrupted;
                sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
                if (sk_stream_memory_free(sk) && !vm_wait)
                        break;

                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
                sk->sk_write_pending++;
                ret = sk_wait_event(sk, &current_timeo, READ_ONCE(sk->sk_err) ||
                                    (READ_ONCE(sk->sk_shutdown) & SEND_SHUTDOWN) ||
                                    (sk_stream_memory_free(sk) && !vm_wait),
                                    &wait);
                sk->sk_write_pending--;
                if (ret < 0)
                        goto do_error;

                if (vm_wait) {
                        vm_wait -= current_timeo;
                        current_timeo = *timeo_p;
                        if (current_timeo != MAX_SCHEDULE_TIMEOUT &&
                            (current_timeo -= vm_wait) < 0)
                                current_timeo = 0;
                        vm_wait = 0;
                }
                *timeo_p = current_timeo;
        }
out:
        if (!sock_flag(sk, SOCK_DEAD))
                remove_wait_queue(sk_sleep(sk), &wait);
        return err;

do_error:
        err = -EPIPE;
        goto out;
do_eagain:
        /* Make sure that whenever EAGAIN is returned, EPOLLOUT event can
         * be generated later.
         * When TCP receives ACK packets that make room, tcp_check_space()
         * only calls tcp_new_space() if SOCK_NOSPACE is set.
         */
        set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
        err = -EAGAIN;
        goto out;
do_interrupted:
        err = sock_intr_errno(*timeo_p);
        goto out;
}
EXPORT_SYMBOL(sk_stream_wait_memory);

int sk_stream_error(struct sock *sk, int flags, int err)
{
        if (err == -EPIPE)
                err = sock_error(sk) ? : -EPIPE;
        if (err == -EPIPE && !(flags & MSG_NOSIGNAL))
                send_sig(SIGPIPE, current, 0);
        return err;
}
EXPORT_SYMBOL(sk_stream_error);

void sk_stream_kill_queues(struct sock *sk)
{
        /* First the read buffer. */
        __skb_queue_purge(&sk->sk_receive_queue);

        /* Next, the error queue.
         * We need to use queue lock, because other threads might
         * add packets to the queue without socket lock being held.
         */
        skb_queue_purge(&sk->sk_error_queue);

        /* Next, the write queue. */
        WARN_ON_ONCE(!skb_queue_empty(&sk->sk_write_queue));

        /* Account for returned memory. */
        sk_mem_reclaim_final(sk);

        WARN_ON_ONCE(sk->sk_wmem_queued);

        /* It is _impossible_ for the backlog to contain anything
         * when we get here.  All user references to this socket
         * have gone away, only the net layer knows can touch it.
         */
}
EXPORT_SYMBOL(sk_stream_kill_queues);