text: /*
   * utils.c - various utility functions used in pppd.
   *
   * Copyright (c) 1999-2002 Paul Mackerras. 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. The name(s) of the authors of this software must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission.
   *
   * 3. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by Paul Mackerras
   *     <paulus@samba.org>".
   *
   * THE AUTHORS OF THIS SOFTWARE DISCLAIM ALL WARRANTIES WITH REGARD TO
   * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
   * AND FITNESS, IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
   * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
   * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
   * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  
  #define RCSID	"$Id: utils.c,v 1.24 2004/11/04 10:02:26 paulus Exp $"
  
  #include <stdio.h>
  #include <ctype.h>
  #include <stdlib.h>
  #include <string.h>
  #include <unistd.h>
  #include <signal.h>
  #include <errno.h>
  #include <fcntl.h>
  #include <syslog.h>
  #include <netdb.h>
  #include <time.h>
  #include <utmp.h>
  #include <pwd.h>
  #include <sys/param.h>
  #include <sys/types.h>
  #include <sys/wait.h>
  #include <sys/time.h>
  #include <sys/resource.h>
  #include <sys/stat.h>
  #include <sys/socket.h>
  #include <netinet/in.h>
  #ifdef SVR4
  #include <sys/mkdev.h>
  #endif
  
  #include "pppd.h"
  #include "fsm.h"
  #include "lcp.h"
  
  static const char rcsid[] = RCSID;
  
  #if defined(SUNOS4)
  extern char *strerror();
  #endif
  
  static void logit __P((int, char *, va_list));
  static void log_write __P((int, char *));
  static void vslp_printer __P((void *, char *, ...));
  static void format_packet __P((u_char *, int, void (*) (void *, char *, ...),
  			       void *));
  
  struct buffer_info {
      char *ptr;
      int len;
  };
  
  /*
   * strlcpy - like strcpy/strncpy, doesn't overflow destination buffer,
   * always leaves destination null-terminated (for len > 0).
   */
  size_t
  strlcpy(dest, src, len)
      char *dest;
      const char *src;
      size_t len;
  {
      size_t ret = strlen(src);
  
      if (len != 0) {
  	if (ret < len)
  	    strcpy(dest, src);
  	else {
  	    strncpy(dest, src, len - 1);
  	    dest[len-1] = 0;
  	}
      }
      return ret;
  }
  
  /*
   * strlcat - like strcat/strncat, doesn't overflow destination buffer,
   * always leaves destination null-terminated (for len > 0).
   */
  size_t
  strlcat(dest, src, len)
      char *dest;
      const char *src;
      size_t len;
  {
      size_t dlen = strlen(dest);
  
      return dlen + strlcpy(dest + dlen, src, (len > dlen? len - dlen: 0));
  }
  
  
  /*
   * slprintf - format a message into a buffer.  Like sprintf except we
   * also specify the length of the output buffer, and we handle
   * %m (error message), %v (visible string),
   * %q (quoted string), %t (current time) and %I (IP address) formats.
   * Doesn't do floating-point formats.
   * Returns the number of chars put into buf.
   */
  int
  slprintf __V((char *buf, int buflen, char *fmt, ...))
  {
      va_list args;
      int n;
  
  #if defined(__STDC__)
      va_start(args, fmt);
  #else
      char *buf;
      int buflen;
      char *fmt;
      va_start(args);
      buf = va_arg(args, char *);
      buflen = va_arg(args, int);
      fmt = va_arg(args, char *);
  #endif
      n = vslprintf(buf, buflen, fmt, args);
      va_end(args);
      return n;
  }
  
  /*
   * vslprintf - like slprintf, takes a va_list instead of a list of args.
   */
  #define OUTCHAR(c)	(buflen > 0? (--buflen, *buf++ = (c)): 0)
  
  int
  vslprintf(buf, buflen, fmt, args)
      char *buf;
      int buflen;
      char *fmt;
      va_list args;
  {
      int c, i, n;
      int width, prec, fillch;
      int base, len, neg, quoted;
      unsigned long val = 0;
      char *str, *f, *buf0;
      unsigned char *p;
      char num[32];
      time_t t;
      u_int32_t ip;
      static char hexchars[] = "0123456789abcdef";
      struct buffer_info bufinfo;
  
      buf0 = buf;
      --buflen;
      while (buflen > 0) {
  	for (f = fmt; *f != '%' && *f != 0; ++f)
  	    ;
  	if (f > fmt) {
  	    len = f - fmt;
  	    if (len > buflen)
  		len = buflen;
  	    memcpy(buf, fmt, len);
  	    buf += len;
  	    buflen -= len;
  	    fmt = f;
  	}
  	if (*fmt == 0)
  	    break;
  	c = *++fmt;
  	width = 0;
  	prec = -1;
  	fillch = ' ';
  	if (c == '0') {
  	    fillch = '0';
  	    c = *++fmt;
  	}
  	if (c == '*') {
  	    width = va_arg(args, int);
  	    c = *++fmt;
  	} else {
  	    while (isdigit(c)) {
  		width = width * 10 + c - '0';
  		c = *++fmt;
  	    }
  	}
  	if (c == '.') {
  	    c = *++fmt;
  	    if (c == '*') {
  		prec = va_arg(args, int);
  		c = *++fmt;
  	    } else {
  		prec = 0;
  		while (isdigit(c)) {
  		    prec = prec * 10 + c - '0';
  		    c = *++fmt;
  		}
  	    }
  	}
  	str = 0;
  	base = 0;
  	neg = 0;
  	++fmt;
  	switch (c) {
  	case 'l':
  	    c = *fmt++;
  	    switch (c) {
  	    case 'd':
  		val = va_arg(args, long);
  		if (val < 0) {
  		    neg = 1;
  		    val = -val;
  		}
  		base = 10;
  		break;
  	    case 'u':
  		val = va_arg(args, unsigned long);
  		base = 10;
  		break;
  	    default:
  		*buf++ = '%'; --buflen;
  		*buf++ = 'l'; --buflen;
  		--fmt;		/* so %lz outputs %lz etc. */
  		continue;
  	    }
  	    break;
  	case 'd':
  	    i = va_arg(args, int);
  	    if (i < 0) {
  		neg = 1;
  		val = -i;
  	    } else
  		val = i;
  	    base = 10;
  	    break;
  	case 'u':
  	    val = va_arg(args, unsigned int);
  	    base = 10;
  	    break;
  	case 'o':
  	    val = va_arg(args, unsigned int);
  	    base = 8;
  	    break;
  	case 'x':
  	case 'X':
  	    val = va_arg(args, unsigned int);
  	    base = 16;
  	    break;
  	case 'p':
  	    val = (unsigned long) va_arg(args, void *);
  	    base = 16;
  	    neg = 2;
  	    break;
  	case 's':
  	    str = va_arg(args, char *);
  	    break;
  	case 'c':
  	    num[0] = va_arg(args, int);
  	    num[1] = 0;
  	    str = num;
  	    break;
  	case 'm':
  	    str = strerror(errno);
  	    break;
  	case 'I':
  	    ip = va_arg(args, u_int32_t);
  	    ip = ntohl(ip);
  	    slprintf(num, sizeof(num), "%d.%d.%d.%d", (ip >> 24) & 0xff,
  		     (ip >> 16) & 0xff, (ip >> 8) & 0xff, ip & 0xff);
  	    str = num;
  	    break;
  #if 0	/* not used, and breaks on S/390, apparently */
  	case 'r':
  	    f = va_arg(args, char *);
  #ifndef __powerpc__
  	    n = vslprintf(buf, buflen + 1, f, va_arg(args, va_list));
  #else
  	    /* On the powerpc, a va_list is an array of 1 structure */
  	    n = vslprintf(buf, buflen + 1, f, va_arg(args, void *));
  #endif
  	    buf += n;
  	    buflen -= n;
  	    continue;
  #endif
  	case 't':
  	    time(&t);
  	    str = ctime(&t);
  	    str += 4;		/* chop off the day name */
  	    str[15] = 0;	/* chop off year and newline */
  	    break;
  	case 'v':		/* "visible" string */
  	case 'q':		/* quoted string */
  	    quoted = c == 'q';
  	    p = va_arg(args, unsigned char *);
  	    if (fillch == '0' && prec >= 0) {
  		n = prec;
  	    } else {
  		n = strlen((char *)p);
  		if (prec >= 0 && n > prec)
  		    n = prec;
  	    }
  	    while (n > 0 && buflen > 0) {
  		c = *p++;
  		--n;
  		if (!quoted && c >= 0x80) {
  		    OUTCHAR('M');
  		    OUTCHAR('-');
  		    c -= 0x80;
  		}
  		if (quoted && (c == '"' || c == '\\'))
  		    OUTCHAR('\\');
  		if (c < 0x20 || (0x7f <= c && c < 0xa0)) {
  		    if (quoted) {
  			OUTCHAR('\\');
  			switch (c) {
  			case '\t':	OUTCHAR('t');	break;
  			case '\n':	OUTCHAR('n');	break;
  			case '\b':	OUTCHAR('b');	break;
  			case '\f':	OUTCHAR('f');	break;
  			default:
  			    OUTCHAR('x');
  			    OUTCHAR(hexchars[c >> 4]);
  			    OUTCHAR(hexchars[c & 0xf]);
  			}
  		    } else {
  			if (c == '\t')
  			    OUTCHAR(c);
  			else {
  			    OUTCHAR('^');
  			    OUTCHAR(c ^ 0x40);
  			}
  		    }
  		} else
  		    OUTCHAR(c);
  	    }
  	    continue;
  	case 'P':		/* print PPP packet */
  	    bufinfo.ptr = buf;
  	    bufinfo.len = buflen + 1;
  	    p = va_arg(args, unsigned char *);
  	    n = va_arg(args, int);
  	    format_packet(p, n, vslp_printer, &bufinfo);
  	    buf = bufinfo.ptr;
  	    buflen = bufinfo.len - 1;
  	    continue;
  	case 'B':
  	    p = va_arg(args, unsigned char *);
  	    for (n = prec; n > 0; --n) {
  		c = *p++;
  		if (fillch == ' ')
  		    OUTCHAR(' ');
  		OUTCHAR(hexchars[(c >> 4) & 0xf]);
  		OUTCHAR(hexchars[c & 0xf]);
  	    }
  	    continue;
  	default:
  	    *buf++ = '%';
  	    if (c != '%')
  		--fmt;		/* so %z outputs %z etc. */
  	    --buflen;
  	    continue;
  	}
  	if (base != 0) {
  	    str = num + sizeof(num);
  	    *--str = 0;
  	    while (str > num + neg) {
  		*--str = hexchars[val % base];
  		val = val / base;
  		if (--prec <= 0 && val == 0)
  		    break;
  	    }
  	    switch (neg) {
  	    case 1:
  		*--str = '-';
  		break;
  	    case 2:
  		*--str = 'x';
  		*--str = '0';
  		break;
  	    }
  	    len = num + sizeof(num) - 1 - str;
  	} else {
  	    len = strlen(str);
  	    if (prec >= 0 && len > prec)
  		len = prec;
  	}
  	if (width > 0) {
  	    if (width > buflen)
  		width = buflen;
  	    if ((n = width - len) > 0) {
  		buflen -= n;
  		for (; n > 0; --n)
  		    *buf++ = fillch;
  	    }
  	}
  	if (len > buflen)
  	    len = buflen;
  	memcpy(buf, str, len);
  	buf += len;
  	buflen -= len;
      }
      *buf = 0;
      return buf - buf0;
  }
  
  /*
   * vslp_printer - used in processing a %P format
   */
  static void
  vslp_printer __V((void *arg, char *fmt, ...))
  {
      int n;
      va_list pvar;
      struct buffer_info *bi;
  
  #if defined(__STDC__)
      va_start(pvar, fmt);
  #else
      void *arg;
      char *fmt;
      va_start(pvar);
      arg = va_arg(pvar, void *);
      fmt = va_arg(pvar, char *);
  #endif
  
      bi = (struct buffer_info *) arg;
      n = vslprintf(bi->ptr, bi->len, fmt, pvar);
      va_end(pvar);
  
      bi->ptr += n;
      bi->len -= n;
  }
  
  #ifdef unused
  /*
   * log_packet - format a packet and log it.
   */
  
  void
  log_packet(p, len, prefix, level)
      u_char *p;
      int len;
      char *prefix;
      int level;
  {
  	init_pr_log(prefix, level);
  	format_packet(p, len, pr_log, &level);
  	end_pr_log();
  }
  #endif /* unused */
  
  /*
   * format_packet - make a readable representation of a packet,
   * calling `printer(arg, format, ...)' to output it.
   */
  static void
  format_packet(p, len, printer, arg)
      u_char *p;
      int len;
      void (*printer) __P((void *, char *, ...));
      void *arg;
  {
      int i, n;
      u_short proto;
      struct protent *protp;
  
      if (len >= PPP_HDRLEN && p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
  	p += 2;
  	GETSHORT(proto, p);
  	len -= PPP_HDRLEN;
  	for (i = 0; (protp = protocols[i]) != NULL; ++i)
  	    if (proto == protp->protocol)
  		break;
  	if (protp != NULL) {
  	    printer(arg, "[%s", protp->name);
  	    n = (*protp->printpkt)(p, len, printer, arg);
  	    printer(arg, "]");
  	    p += n;
  	    len -= n;
  	} else {
  	    for (i = 0; (protp = protocols[i]) != NULL; ++i)
  		if (proto == (protp->protocol & ~0x8000))
  		    break;
  	    if (protp != 0 && protp->data_name != 0) {
  		printer(arg, "[%s data]", protp->data_name);
  		if (len > 8)
  		    printer(arg, "%.8B ...", p);
  		else
  		    printer(arg, "%.*B", len, p);
  		len = 0;
  	    } else
  		printer(arg, "[proto=0x%x]", proto);
  	}
      }
  
      if (len > 32)
  	printer(arg, "%.32B ...", p);
      else
  	printer(arg, "%.*B", len, p);
  }
  
  /*
   * init_pr_log, end_pr_log - initialize and finish use of pr_log.
   */
  
  static char line[256];		/* line to be logged accumulated here */
  static char *linep;		/* current pointer within line */
  static int llevel;		/* level for logging */
  
  void
  init_pr_log(prefix, level)
       char *prefix;
       int level;
  {
  	linep = line;
  	if (prefix != NULL) {
  		strlcpy(line, prefix, sizeof(line));
  		linep = line + strlen(line);
  	}
  	llevel = level;
  }
  
  void
  end_pr_log()
  {
  	if (linep != line) {
  		*linep = 0;
  		log_write(llevel, line);
  	}
  }
  
  /*
   * pr_log - printer routine for outputting to syslog
   */
  void
  pr_log __V((void *arg, char *fmt, ...))
  {
  	int l, n;
  	va_list pvar;
  	char *p, *eol;
  	char buf[256];
  
  #if defined(__STDC__)
  	va_start(pvar, fmt);
  #else
  	void *arg;
  	char *fmt;
  	va_start(pvar);
  	arg = va_arg(pvar, void *);
  	fmt = va_arg(pvar, char *);
  #endif
  
  	n = vslprintf(buf, sizeof(buf), fmt, pvar);
  	va_end(pvar);
  
  	p = buf;
  	eol = strchr(buf, '\n');
  	if (linep != line) {
  		l = (eol == NULL)? n: eol - buf;
  		if (linep + l < line + sizeof(line)) {
  			if (l > 0) {
  				memcpy(linep, buf, l);
  				linep += l;
  			}
  			if (eol == NULL)
  				return;
  			p = eol + 1;
  			eol = strchr(p, '\n');
  		}
  		*linep = 0;
  		log_write(llevel, line);
  		linep = line;
  	}
  
  	while (eol != NULL) {
  		*eol = 0;
  		log_write(llevel, p);
  		p = eol + 1;
  		eol = strchr(p, '\n');
  	}
  
  	/* assumes sizeof(buf) <= sizeof(line) */
  	l = buf + n - p;
  	if (l > 0) {
  		memcpy(line, p, n);
  		linep = line + l;
  	}
  }
  
  /*
   * print_string - print a readable representation of a string using
   * printer.
   */
  void
  print_string(p, len, printer, arg)
      char *p;
      int len;
      void (*printer) __P((void *, char *, ...));
      void *arg;
  {
      int c;
  
      printer(arg, "\"");
      for (; len > 0; --len) {
  	c = *p++;
  	if (' ' <= c && c <= '~') {
  	    if (c == '\\' || c == '"')
  		printer(arg, "\\");
  	    printer(arg, "%c", c);
  	} else {
  	    switch (c) {
  	    case '\n':
  		printer(arg, "\\n");
  		break;
  	    case '\r':
  		printer(arg, "\\r");
  		break;
  	    case '\t':
  		printer(arg, "\\t");
  		break;
  	    default:
  		printer(arg, "\\%.3o", c);
  	    }
  	}
      }
      printer(arg, "\"");
  }
  
  /*
   * logit - does the hard work for fatal et al.
   */
  static void
  logit(level, fmt, args)
      int level;
      char *fmt;
      va_list args;
  {
      int n;
      char buf[1024];
  
      n = vslprintf(buf, sizeof(buf), fmt, args);
      log_write(level, buf);
  }
  
  static void
  log_write(level, buf)
      int level;
      char *buf;
  {
      syslog(level, "%s", buf);
      if (log_to_fd >= 0 && (level != LOG_DEBUG || debug)) {
  	int n = strlen(buf);
  
  	if (n > 0 && buf[n-1] == '\n')
  	    --n;
  	if (write(log_to_fd, buf, n) != n
  	    || write(log_to_fd, "\n", 1) != 1)
  	    log_to_fd = -1;
      }
  }
  
  /*
   * fatal - log an error message and die horribly.
   */
  void
  fatal __V((char *fmt, ...))
  {
      va_list pvar;
  
  #if defined(__STDC__)
      va_start(pvar, fmt);
  #else
      char *fmt;
      va_start(pvar);
      fmt = va_arg(pvar, char *);
  #endif
  
      logit(LOG_ERR, fmt, pvar);
      va_end(pvar);
  
      die(1);			/* as promised */
  }
  
  /*
   * error - log an error message.
   */
  void
  error __V((char *fmt, ...))
  {
      va_list pvar;
  
  #if defined(__STDC__)
      va_start(pvar, fmt);
  #else
      char *fmt;
      va_start(pvar);
      fmt = va_arg(pvar, char *);
  #endif
  
      logit(LOG_ERR, fmt, pvar);
      va_end(pvar);
      ++error_count;
  }
  
  /*
   * warn - log a warning message.
   */
  void
  warn __V((char *fmt, ...))
  {
      va_list pvar;
  
  #if defined(__STDC__)
      va_start(pvar, fmt);
  #else
      char *fmt;
      va_start(pvar);
      fmt = va_arg(pvar, char *);
  #endif
  
      logit(LOG_WARNING, fmt, pvar);
      va_end(pvar);
  }
  
  /*
   * notice - log a notice-level message.
   */
  void
  notice __V((char *fmt, ...))
  {
      va_list pvar;
  
  #if defined(__STDC__)
      va_start(pvar, fmt);
  #else
      char *fmt;
      va_start(pvar);
      fmt = va_arg(pvar, char *);
  #endif
  
      logit(LOG_NOTICE, fmt, pvar);
      va_end(pvar);
  }
  
  /*
   * info - log an informational message.
   */
  void
  info __V((char *fmt, ...))
  {
      va_list pvar;
  
  #if defined(__STDC__)
      va_start(pvar, fmt);
  #else
      char *fmt;
      va_start(pvar);
      fmt = va_arg(pvar, char *);
  #endif
  
      logit(LOG_INFO, fmt, pvar);
      va_end(pvar);
  }
  
  /*
   * dbglog - log a debug message.
   */
  void
  dbglog __V((char *fmt, ...))
  {
      va_list pvar;
  
  #if defined(__STDC__)
      va_start(pvar, fmt);
  #else
      char *fmt;
      va_start(pvar);
      fmt = va_arg(pvar, char *);
  #endif
  
      logit(LOG_DEBUG, fmt, pvar);
      va_end(pvar);
  }
  
  /*
   * dump_packet - print out a packet in readable form if it is interesting.
   * Assumes len >= PPP_HDRLEN.
   */
  void
  dump_packet(const char *tag, unsigned char *p, int len)
  {
      int proto;
  
      if (!debug)
  	return;
  
      /*
       * don't print LCP echo request/reply packets if debug <= 1
       * and the link is up.
       */
      proto = (p[2] << 8) + p[3];
      if (debug <= 1 && unsuccess == 0 && proto == PPP_LCP
  	&& len >= PPP_HDRLEN + HEADERLEN) {
  	unsigned char *lcp = p + PPP_HDRLEN;
  	int l = (lcp[2] << 8) + lcp[3];
  
  	if ((lcp[0] == ECHOREQ || lcp[0] == ECHOREP)
  	    && l >= HEADERLEN && l <= len - PPP_HDRLEN)
  	    return;
      }
  
      dbglog("%s %P", tag, p, len);
  }
  
  /*
   * complete_read - read a full `count' bytes from fd,
   * unless end-of-file or an error other than EINTR is encountered.
   */
  ssize_t
  complete_read(int fd, void *buf, size_t count)
  {
  	size_t done;
  	ssize_t nb;
  	char *ptr = buf;
  
  	for (done = 0; done < count; ) {
  		nb = read(fd, ptr, count - done);
  		if (nb < 0) {
  			if (errno == EINTR)
  				continue;
  			return -1;
  		}
  		if (nb == 0)
  			break;
  		done += nb;
  		ptr += nb;
  	}
  	return done;
  }
  
  /* Procedures for locking the serial device using a lock file. */
  #ifndef LOCK_DIR
  #ifdef __linux__
  #define LOCK_DIR	"/var/lock"
  #else
  #ifdef SVR4
  #define LOCK_DIR	"/var/spool/locks"
  #else
  #define LOCK_DIR	"/var/spool/lock"
  #endif
  #endif
  #endif /* LOCK_DIR */
  
  static char lock_file[MAXPATHLEN];
  
  /*
   * lock - create a lock file for the named device
   */
  int
  lock(dev)
      char *dev;
  {
  #ifdef LOCKLIB
      int result;
  
      result = mklock (dev, (void *) 0);
      if (result == 0) {
  	strlcpy(lock_file, dev, sizeof(lock_file));
  	return 0;
      }
  
      if (result > 0)
          notice("Device %s is locked by pid %d", dev, result);
      else
  	error("Can't create lock file %s", lock_file);
      return -1;
  
  #else /* LOCKLIB */
  
      char lock_buffer[12];
      int fd, pid, n;
  
  #ifdef SVR4
      struct stat sbuf;
  
      if (stat(dev, &sbuf) < 0) {
  	error("Can't get device number for %s: %m", dev);
  	return -1;
      }
      if ((sbuf.st_mode & S_IFMT) != S_IFCHR) {
  	error("Can't lock %s: not a character device", dev);
  	return -1;
      }
      slprintf(lock_file, sizeof(lock_file), "%s/LK.%03d.%03d.%03d",
  	     LOCK_DIR, major(sbuf.st_dev),
  	     major(sbuf.st_rdev), minor(sbuf.st_rdev));
  #else
      char *p;
      char lockdev[MAXPATHLEN];
  
      if ((p = strstr(dev, "dev/")) != NULL) {
  	dev = p + 4;
  	strncpy(lockdev, dev, MAXPATHLEN-1);
  	lockdev[MAXPATHLEN-1] = 0;
  	while ((p = strrchr(lockdev, '/')) != NULL) {
  	    *p = '_';
  	}
  	dev = lockdev;
      } else
  	if ((p = strrchr(dev, '/')) != NULL)
  	    dev = p + 1;
  
      slprintf(lock_file, sizeof(lock_file), "%s/LCK..%s", LOCK_DIR, dev);
  #endif
  
      while ((fd = open(lock_file, O_EXCL | O_CREAT | O_RDWR, 0644)) < 0) {
  	if (errno != EEXIST) {
  	    error("Can't create lock file %s: %m", lock_file);
  	    break;
  	}
  
  	/* Read the lock file to find out who has the device locked. */
  	fd = open(lock_file, O_RDONLY, 0);
  	if (fd < 0) {
  	    if (errno == ENOENT) /* This is just a timing problem. */
  		continue;
  	    error("Can't open existing lock file %s: %m", lock_file);
  	    break;
  	}
  #ifndef LOCK_BINARY
  	n = read(fd, lock_buffer, 11);
  #else
  	n = read(fd, &pid, sizeof(pid));
  #endif /* LOCK_BINARY */
  	close(fd);
  	fd = -1;
  	if (n <= 0) {
  	    error("Can't read pid from lock file %s", lock_file);
  	    break;
  	}
  
  	/* See if the process still exists. */
  #ifndef LOCK_BINARY
  	lock_buffer[n] = 0;
  	pid = atoi(lock_buffer);
  #endif /* LOCK_BINARY */
  	if (pid == getpid())
  	    return 1;		/* somebody else locked it for us */
  	if (pid == 0
  	    || (kill(pid, 0) == -1 && errno == ESRCH)) {
  	    if (unlink (lock_file) == 0) {
  		notice("Removed stale lock on %s (pid %d)", dev, pid);
  		continue;
  	    }
  	    warn("Couldn't remove stale lock on %s", dev);
  	} else
  	    notice("Device %s is locked by pid %d", dev, pid);
  	break;
      }
  
      if (fd < 0) {
  	lock_file[0] = 0;
  	return -1;
      }
  
      pid = getpid();
  #ifndef LOCK_BINARY
      slprintf(lock_buffer, sizeof(lock_buffer), "%10d\n", pid);
      write (fd, lock_buffer, 11);
  #else
      write(fd, &pid, sizeof (pid));
  #endif
      close(fd);
      return 0;
  
  #endif
  }
  
  /*
   * relock - called to update our lockfile when we are about to detach,
   * thus changing our pid (we fork, the child carries on, and the parent dies).
   * Note that this is called by the parent, with pid equal to the pid
   * of the child.  This avoids a potential race which would exist if
   * we had the child rewrite the lockfile (the parent might die first,
   * and another process could think the lock was stale if it checked
   * between when the parent died and the child rewrote the lockfile).
   */
  int
  relock(pid)
      int pid;
  {
  #ifdef LOCKLIB
      /* XXX is there a way to do this? */
      return -1;
  #else /* LOCKLIB */
  
      int fd;
      char lock_buffer[12];
  
      if (lock_file[0] == 0)
  	return -1;
      fd = open(lock_file, O_WRONLY, 0);
      if (fd < 0) {
  	error("Couldn't reopen lock file %s: %m", lock_file);
  	lock_file[0] = 0;
  	return -1;
      }
  
  #ifndef LOCK_BINARY
      slprintf(lock_buffer, sizeof(lock_buffer), "%10d\n", pid);
      write (fd, lock_buffer, 11);
  #else
      write(fd, &pid, sizeof(pid));
  #endif /* LOCK_BINARY */
      close(fd);
      return 0;
  
  #endif /* LOCKLIB */
  }
  
  /*
   * unlock - remove our lockfile
   */
  void
  unlock()
  {
      if (lock_file[0]) {
  #ifdef LOCKLIB
  	(void) rmlock(lock_file, (void *) 0);
  #else
  	unlink(lock_file);
  #endif
  	lock_file[0] = 0;
      }
  }
  
  