/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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/types.h>
#include <sys/stat.h>
#include <sys/uio.h>

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#include "ttymsg.h"

/*
 * Display the contents of a uio structure on a terminal.  If shout is
 * non-zero, do so even if the terminal has messages disabled.  Used by
 * wall(1), syslogd(8), and talkd(8).  Forks and finishes in child if
 * write would block, waiting up to timeout seconds.  Various "normal"
 * errors are ignored (exclusive-use, lack of permission, etc.).
 */
int
ttymsg(struct iovec *iov, int iovcnt, const char *tty, int timeout,
    bool shout)
{
        struct iovec localiov[TTYMSG_IOV_MAX];
        struct stat sb;
        ssize_t wret;
        size_t resid;
        int cnt, dd, fd, serrno;
        int forked;

        forked = 0;
        if (iovcnt > (int)(sizeof(localiov) / sizeof(localiov[0]))) {
                errno = EFBIG;
                return (-1);
        }

        dd = open(_PATH_DEV, O_SEARCH | O_DIRECTORY);
        if (dd < 0)
                return (-1);
        fd = openat(dd, tty, O_WRONLY | O_NONBLOCK | O_RESOLVE_BENEATH);
        if (fd < 0) {
                serrno = errno;
                close(dd);
                /*
                 * open will fail on slip lines or exclusive-use lines
                 * if not running as root; not an error.
                 */
                if (serrno == EBUSY || serrno == EACCES)
                        return (0);
                errno = serrno;
                return (-1);
        }
        close(dd);
        if (!shout) {
                if (fstat(fd, &sb) != 0) {
                        serrno = errno;
                        close(fd);
                        errno = serrno;
                        return (-1);
                }
                if ((sb.st_mode & S_IWGRP) == 0) {
                        close(fd);
                        return (0);
                }
        }

        for (cnt = 0, resid = 0; cnt < iovcnt; ++cnt)
                resid += iov[cnt].iov_len;

        do {
                wret = writev(fd, iov, iovcnt);
                if (wret >= 0) {
                        resid -= wret;
                        if (iov != localiov) {
                                bcopy(iov, localiov,
                                    iovcnt * sizeof(struct iovec));
                                iov = localiov;
                        }
                        while ((size_t)wret >= iov->iov_len) {
                                wret -= iov->iov_len;
                                ++iov;
                                --iovcnt;
                        }
                        if (wret) {
                                iov->iov_base = (char *)iov->iov_base + wret;
                                iov->iov_len -= wret;
                        }
                        continue;
                }
                if (errno == EWOULDBLOCK) {
                        int cpid;

                        if (forked) {
                                (void) close(fd);
                                _exit(1);
                        }
                        cpid = fork();
                        if (cpid < 0) {
                                serrno = errno;
                                (void) close(fd);
                                errno = serrno;
                                return (-1);
                        }
                        if (cpid) {     /* parent */
                                (void) close(fd);
                                return (0);
                        }
                        forked++;
                        /* wait at most timeout seconds */
                        (void) signal(SIGALRM, SIG_DFL);
                        (void) signal(SIGTERM, SIG_DFL); /* XXX */
                        (void) sigsetmask(0);
                        (void) alarm((u_int)timeout);
                        (void) fcntl(fd, F_SETFL, 0);   /* clear O_NONBLOCK */
                        continue;
                }
                /*
                 * We get ENODEV on a slip line if we're running as root,
                 * and EIO if the line just went away.
                 */
                serrno = errno;
                if (serrno == ENODEV || serrno == EIO)
                        break;
                (void) close(fd);
                if (forked)
                        _exit(1);
                errno = serrno;
                return (-1);
        } while (resid > 0);

        (void) close(fd);
        if (forked)
                _exit(0);
        return (0);
}