/*      $NetBSD: pidlock.c,v 1.17 2020/03/30 08:24:36 ryo Exp $ */

/*
 * Copyright 1996, 1997 by Curt Sampson <cjs@NetBSD.org>.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: pidlock.c,v 1.17 2020/03/30 08:24:36 ryo Exp $");
#endif /* LIBC_SCCS and not lint */

#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <util.h>
#include <paths.h>

/*
 * Create a lockfile. Return 0 when locked, -1 on error.
 */
int
pidlock(const char *lockfile, int flags, pid_t *locker, const char *info)
{
        char    tempfile[MAXPATHLEN];
        char    hostname[MAXHOSTNAMELEN + 1];
        pid_t   pid2 = -1;
        struct  stat st;
        ssize_t n;
        int     f = -1, savee;
        char    s[256];
        char    *p;
        size_t  len;

        _DIAGASSERT(lockfile != NULL);
        /* locker may be NULL */
        /* info may be NULL */


        if (gethostname(hostname, sizeof(hostname)))
                return -1;
        hostname[sizeof(hostname) - 1] = '\0';

        /* avoid '/' in hostname, as it may contain arbitrary characters */
        for (p = hostname; *p != '\0'; p++) {
                if (*p == '/')
                        *p = '_';
        }

        /*
         * Build a path to the temporary file.
         * We use the path with the PID and hostname appended.
         * XXX This is not thread safe.
         */
        if (snprintf(tempfile, sizeof(tempfile), "%s.%d.%s", lockfile,
            (int) getpid(), hostname) >= (int)sizeof(tempfile))  {
                errno = ENAMETOOLONG;
                return -1;
        }

        /* Open it, write pid, hostname, info. */
        if ((f = open(tempfile, O_WRONLY|O_CREAT|O_TRUNC, 0600)) == -1)
                goto out;

        (void)snprintf(s, sizeof(s), "%10d\n", getpid());       /* pid */
        if (write(f, s, (size_t)11) != 11)
                goto out;

        if ((flags & PIDLOCK_USEHOSTNAME))  {           /* hostname */
                len = strlen(hostname);
                if ((size_t)write(f, hostname, len) != len
                    || write(f, "\n", (size_t)1) != 1)
                        goto out;
        }
        if (info)  {                                    /* info */
                if (!(flags & PIDLOCK_USEHOSTNAME))  {
                        /* write blank line because there's no hostname */
                        if (write(f, "\n", (size_t)1) != 1)
                                goto out;
                }
                len = strlen(info);
                if ((size_t)write(f, info, len) != len ||
                    write(f, "\n", (size_t)1) != 1)
                        goto out;
        }
        (void)close(f);
        f = -1;

        /* Hard link the temporary file to the real lock file. */
        /* This is an atomic operation. */
lockfailed:
        while (link(tempfile, lockfile) == -1)  {
                if (errno != EEXIST)
                        goto out;
                /* Find out who has this lockfile. */
                if ((f = open(lockfile, O_RDONLY, 0)) != -1)  {
                        if ((n = read(f, s, (size_t)11)) == -1)
                                goto out;
                        if (n == 0) {
                                errno = EINVAL;
                                goto out;
                        }
                        pid2 = atoi(s);
                        if ((n = read(f, s, sizeof(s) - 2)) == -1)
                                goto out;
                        if (n == 0)
                                *s = '\0';
                        s[sizeof(s) - 1] = '\0';
                        if ((p = strchr(s, '\n')) != NULL)
                                *p = '\0';
                        (void)close(f);
                        f = -1;

                        if ((flags & PIDLOCK_USEHOSTNAME) == 0 ||
                            strcmp(s, hostname) == 0)  {
                                if (kill(pid2, 0) == -1 && errno == ESRCH)  {
                                        /* process doesn't exist */
                                        (void)unlink(lockfile);
                                        continue;
                                }
                        }
                }
                if (flags & PIDLOCK_NONBLOCK)  {
                        if (locker)
                                *locker = pid2;
                        errno = EWOULDBLOCK;
                        goto out;
                } else
                        sleep(5);
        }
        /*
         * Check to see that we really were successful (in case we're
         * using NFS) by making sure that something really is linked
         * to our tempfile (reference count is two).
         */
        if (stat(tempfile, &st) == -1)
                goto out;
        if (st.st_nlink != 2)
                goto lockfailed;

        (void)unlink(tempfile);
        if (locker)
                *locker = getpid();     /* return this process's PID on lock */
        errno = 0;
        return 0;
out:
        savee = errno;
        if (f != -1)
                (void)close(f);
        (void)unlink(tempfile);
        errno = savee;
        return -1;
}

static int
checktty(const char *tty)
{
        char    ttyfile[MAXPATHLEN];
        struct stat sb;

        (void)strlcpy(ttyfile, _PATH_DEV, sizeof(ttyfile));
        (void)strlcat(ttyfile, tty, sizeof(ttyfile));

        /* make sure the tty exists */
        if (stat(ttyfile, &sb) == -1)
                return -1;
        if (!S_ISCHR(sb.st_mode))  {
                errno = EFTYPE;
                return -1;
        }
        return 0;
}

#define LOCKPATH        "/var/spool/lock/LCK.."

static char *
makelock(char *buf, size_t bufsiz, const char *tty)
{
        (void)strlcpy(buf, LOCKPATH, bufsiz);
        (void)strlcat(buf, tty, bufsiz);
        return buf;
}

/*ARGSUSED*/
int
ttylock(const char *tty, int flags, pid_t *locker)
{
        char    lockfile[MAXPATHLEN];

        _DIAGASSERT(tty != NULL);

        if (checktty(tty) != 0)
                return -1;

        /* do the lock */
        return pidlock(makelock(lockfile, sizeof(lockfile), tty),
            flags, locker, 0);
}

int
ttyunlock(const char *tty)
{
        char    lockfile[MAXPATHLEN];

        _DIAGASSERT(tty != NULL);

        if (checktty(tty) != 0)
                return -1;

        /* remove the lock */
        return unlink(makelock(lockfile, sizeof(lockfile), tty));
}