/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/conf.h>
#include <sys/fcntl.h>
#include <sys/filio.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/snoop.h>
#include <sys/sx.h>
#include <sys/systm.h>
#include <sys/tty.h>
#include <sys/uio.h>

static struct cdev      *snp_dev;
static MALLOC_DEFINE(M_SNP, "snp", "tty snoop device");

/* XXX: should be mtx, but TTY can be locked by Giant. */
#if 0
static struct mtx       snp_register_lock;
MTX_SYSINIT(snp_register_lock, &snp_register_lock,
    "tty snoop registration", MTX_DEF);
#define SNP_LOCK()      mtx_lock(&snp_register_lock)
#define SNP_UNLOCK()    mtx_unlock(&snp_register_lock)
#else
static struct sx        snp_register_lock;
SX_SYSINIT(snp_register_lock, &snp_register_lock,
    "tty snoop registration");
#define SNP_LOCK()      sx_xlock(&snp_register_lock)
#define SNP_UNLOCK()    sx_xunlock(&snp_register_lock)
#endif

#define SNPGTYY_32DEV   _IOR('T', 89, uint32_t)

/*
 * There is no need to have a big input buffer. In most typical setups,
 * we won't inject much data into the TTY, because users can't type
 * really fast.
 */
#define SNP_INPUT_BUFSIZE       16
/*
 * The output buffer has to be really big. Right now we don't support
 * any form of flow control, which means we lost any data we can't
 * accept. We set the output buffer size to about twice the size of a
 * pseudo-terminal/virtual console's output buffer.
 */
#define SNP_OUTPUT_BUFSIZE      16384

static d_open_t         snp_open;
static d_read_t         snp_read;
static d_write_t        snp_write;
static d_ioctl_t        snp_ioctl;
static d_poll_t         snp_poll;

static struct cdevsw snp_cdevsw = {
        .d_version      = D_VERSION,
        .d_open         = snp_open,
        .d_read         = snp_read,
        .d_write        = snp_write,
        .d_ioctl        = snp_ioctl,
        .d_poll         = snp_poll,
        .d_name         = "snp",
};

static th_getc_capture_t        snp_getc_capture;

static struct ttyhook snp_hook = {
        .th_getc_capture        = snp_getc_capture,
};

/*
 * Per-instance structure.
 *
 * List of locks
 * (r)  locked by snp_register_lock on assignment
 * (t)  locked by tty_lock
 */
struct snp_softc {
        struct tty      *snp_tty;       /* (r) TTY we're snooping. */
        struct ttyoutq  snp_outq;       /* (t) Output queue. */
        struct cv       snp_outwait;    /* (t) Output wait queue. */
        struct selinfo  snp_outpoll;    /* (t) Output polling. */
};

static void
snp_dtor(void *data)
{
        struct snp_softc *ss = data;
        struct tty *tp;

        tp = ss->snp_tty;
        if (tp != NULL) {
                tty_lock(tp);
                ttyoutq_free(&ss->snp_outq);
                ttyhook_unregister(tp);
                ss->snp_tty = NULL;
        }

        cv_destroy(&ss->snp_outwait);
        free(ss, M_SNP);
}

/*
 * Snoop device node routines.
 */

static int
snp_open(struct cdev *dev, int flag, int mode, struct thread *td)
{
        struct snp_softc *ss;

        /* Allocate per-snoop data. */
        ss = malloc(sizeof(struct snp_softc), M_SNP, M_WAITOK|M_ZERO);
        cv_init(&ss->snp_outwait, "snp out");

        devfs_set_cdevpriv(ss, snp_dtor);

        return (0);
}

static int
snp_read(struct cdev *dev, struct uio *uio, int flag)
{
        int error, oresid = uio->uio_resid;
        struct snp_softc *ss;
        struct tty *tp;

        if (uio->uio_resid == 0)
                return (0);

        error = devfs_get_cdevpriv((void **)&ss);
        if (error != 0)
                return (error);

        tp = ss->snp_tty;
        if (tp == NULL || tty_gone(tp))
                return (EIO);

        tty_lock(tp);
        for (;;) {
                error = ttyoutq_read_uio(&ss->snp_outq, tp, uio);
                if (error != 0 || uio->uio_resid != oresid)
                        break;

                /* Wait for more data. */
                if (flag & O_NONBLOCK) {
                        error = EWOULDBLOCK;
                        break;
                }
                error = cv_wait_sig(&ss->snp_outwait, tty_getlock(tp));
                if (error != 0)
                        break;
                if (tty_gone(tp)) {
                        error = EIO;
                        break;
                }
        }
        tty_unlock(tp);

        return (error);
}

static int
snp_write(struct cdev *dev, struct uio *uio, int flag)
{
        struct snp_softc *ss;
        struct tty *tp;
        int error, len;
        char in[SNP_INPUT_BUFSIZE];

        error = devfs_get_cdevpriv((void **)&ss);
        if (error != 0)
                return (error);

        tp = ss->snp_tty;
        if (tp == NULL || tty_gone(tp))
                return (EIO);

        while (uio->uio_resid > 0) {
                /* Read new data. */
                len = imin(uio->uio_resid, sizeof in);
                error = uiomove(in, len, uio);
                if (error != 0)
                        return (error);

                tty_lock(tp);

                /* Driver could have abandoned the TTY in the mean time. */
                if (tty_gone(tp)) {
                        tty_unlock(tp);
                        return (ENXIO);
                }

                /*
                 * Deliver data to the TTY. Ignore errors for now,
                 * because we shouldn't bail out when we're running
                 * close to the watermarks.
                 */
                ttydisc_rint_simple(tp, in, len);
                ttydisc_rint_done(tp);

                tty_unlock(tp);
        }

        return (0);
}

static int
snp_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int flags,
    struct thread *td)
{
        struct snp_softc *ss;
        struct tty *tp;
        int error;

        error = devfs_get_cdevpriv((void **)&ss);
        if (error != 0)
                return (error);

        switch (cmd) {
        case SNPSTTY:
                /* Bind TTY to snoop instance. */
                SNP_LOCK();
                tp = ss->snp_tty;
                if (tp != NULL) {
                        if (*(int *)data == -1) {
                                tty_lock(tp);
                                ss->snp_tty = NULL;
                                ttyoutq_free(&ss->snp_outq);
                                ttyhook_unregister(tp);
                                error = 0;
                        } else {
                                error = EBUSY;
                        }
                        SNP_UNLOCK();
                        return (error);
                }
                /*
                 * XXXRW / XXXJA: no capability check here.
                 */
                error = ttyhook_register(&ss->snp_tty, td->td_proc,
                    *(int *)data, &snp_hook, ss);
                SNP_UNLOCK();
                if (error != 0)
                        return (error);

                /* Now that went okay, allocate a buffer for the queue. */
                tp = ss->snp_tty;
                tty_lock(tp);
                ttyoutq_setsize(&ss->snp_outq, tp, SNP_OUTPUT_BUFSIZE);
                tty_unlock(tp);

                return (0);
        case SNPGTTY:
                /* Obtain device number of associated TTY. */
                if (ss->snp_tty == NULL)
                        *(dev_t *)data = NODEV;
                else
                        *(dev_t *)data = tty_udev(ss->snp_tty);
                return (0);
        case SNPGTYY_32DEV:
                if (ss->snp_tty == NULL)
                        *(uint32_t *)data = -1;
                else
                        *(uint32_t *)data = tty_udev(ss->snp_tty); /* trunc */
                return (0);
        case FIONREAD:
                tp = ss->snp_tty;
                if (tp != NULL) {
                        tty_lock(tp);
                        if (tty_gone(tp))
                                *(int *)data = SNP_TTYCLOSE;
                        else
                                *(int *)data = ttyoutq_bytesused(&ss->snp_outq);
                        tty_unlock(tp);
                } else {
                        *(int *)data = SNP_DETACH;
                }
                return (0);
        default:
                return (ENOTTY);
        }
}

static int
snp_poll(struct cdev *dev, int events, struct thread *td)
{
        struct snp_softc *ss;
        struct tty *tp;
        int revents;

        if (devfs_get_cdevpriv((void **)&ss) != 0)
                return (events &
                    (POLLHUP|POLLIN|POLLRDNORM|POLLOUT|POLLWRNORM));

        revents = 0;

        if (events & (POLLIN | POLLRDNORM)) {
                tp = ss->snp_tty;
                if (tp != NULL) {
                        tty_lock(tp);
                        if (ttyoutq_bytesused(&ss->snp_outq) > 0)
                                revents |= events & (POLLIN | POLLRDNORM);
                        tty_unlock(tp);
                }
        }

        if (revents == 0)
                selrecord(td, &ss->snp_outpoll);

        return (revents);
}

/*
 * TTY hook events.
 */

static int
snp_modevent(module_t mod, int type, void *data)
{

        switch (type) {
        case MOD_LOAD:
                snp_dev = make_dev(&snp_cdevsw, 0,
                    UID_ROOT, GID_WHEEL, 0600, "snp");
                return (0);
        case MOD_UNLOAD:
                /* XXX: Make existing users leave. */
                destroy_dev(snp_dev);
                return (0);
        default:
                return (EOPNOTSUPP);
        }
}

static void
snp_getc_capture(struct tty *tp, const void *buf, size_t len)
{
        struct snp_softc *ss = ttyhook_softc(tp);

        ttyoutq_write(&ss->snp_outq, buf, len);

        cv_broadcast(&ss->snp_outwait);
        selwakeup(&ss->snp_outpoll);
}

static moduledata_t snp_mod = {
        "snp",
        snp_modevent,
        NULL
};

DECLARE_MODULE(snp, snp_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);