sdiff.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

	int diff_fds[2];

	if (pipe (diff_fds) != 0)
	  perror_fatal ("pipe");

	diffpid = fork ();
	if (diffpid < 0)
	  perror_fatal ("fork failed");
	if (!diffpid)
	  {
	    signal (SIGINT, SIG_IGN);  /* in case user interrupts editor */
	    signal (SIGPIPE, SIG_DFL);

	    close (diff_fds[0]);
	    if (diff_fds[1] != STDOUT_FILENO)
	      {
		dup2 (diff_fds[1], STDOUT_FILENO);
		close (diff_fds[1]);
	      }

	    execdiff ();
	  }

	close (diff_fds[1]);
	diffout = fdopen (diff_fds[0], "r");
	if (!diffout)
	  perror_fatal ("fdopen");
      }
#endif /* HAVE_FORK */

      lf_init (&diff_filt, diffout);
      lf_init (&lfilt, left);
      lf_init (&rfilt, right);

      interact_ok = interact (&diff_filt, &lfilt, &rfilt, out);

      ck_fclose (left);
      ck_fclose (right);
      ck_fclose (out);

      {
	int wstatus;

#if ! HAVE_FORK
	wstatus = pclose (diffout);
#else
	ck_fclose (diffout);
	while (waitpid (diffpid, &wstatus, 0) < 0)
	  if (errno == EINTR)
	    checksigs ();
	  else
	    perror_fatal ("wait failed");
	diffpid = 0;
#endif

	if (tmpmade)
	  {
	    unlink (tmpname);
	    tmpmade = 0;
	  }

	if (! interact_ok)
	  exiterr ();

	if (! (WIFEXITED (wstatus) && WEXITSTATUS (wstatus) < 2))
	  fatal ("Subsidiary diff failed");

	untrapsig (0);
	checksigs ();
	exit (WEXITSTATUS (wstatus));
      }
    }
  return 0;			/* Fool -Wall . . . */
}

static void
diffarg (a)
     char const *a;
{
  static unsigned diffargs, diffargsmax;

  if (diffargs == diffargsmax)
    {
      if (! diffargsmax)
	{
	  diffargv = (char const **) xmalloc (sizeof (char));
	  diffargsmax = 8;
	}
      diffargsmax *= 2;
      diffargv = (char const **) realloc (diffargv,
					  diffargsmax * sizeof (char const *));
      if (! diffargv)
	fatal ("out of memory");
    }
  diffargv[diffargs++] = a;
}

static void
execdiff ()
{
  execvp (diffbin, (char **) diffargv);
  write (STDERR_FILENO, diffbin, strlen (diffbin));
  write (STDERR_FILENO, ": not found\n", 12);
  _exit (2);
}




/* Signal handling */

#define NUM_SIGS (sizeof (sigs) / sizeof (*sigs))
static int const sigs[] = {
#ifdef SIGHUP
       SIGHUP,
#endif
#ifdef SIGQUIT
       SIGQUIT,
#endif
#ifdef SIGTERM
       SIGTERM,
#endif
#ifdef SIGXCPU
       SIGXCPU,
#endif
#ifdef SIGXFSZ
       SIGXFSZ,
#endif
       SIGINT,
       SIGPIPE
};

/* Prefer `sigaction' if it is available, since `signal' can lose signals.  */
#if HAVE_SIGACTION
static struct sigaction initial_action[NUM_SIGS];
#define initial_handler(i) (initial_action[i].sa_handler)
#else
static RETSIGTYPE (*initial_action[NUM_SIGS]) ();
#define initial_handler(i) (initial_action[i])
#endif

static int volatile ignore_SIGINT;
static int volatile signal_received;
static int sigs_trapped;

static RETSIGTYPE
catchsig (s)
     int s;
{
#if ! HAVE_SIGACTION
  signal (s, SIG_IGN);
#endif
  if (! (s == SIGINT && ignore_SIGINT))
    signal_received = s;
}

static void
trapsigs ()
{
  int i;

#if HAVE_SIGACTION
  struct sigaction catchaction;
  bzero (&catchaction, sizeof (catchaction));
  catchaction.sa_handler = catchsig;
#ifdef SA_INTERRUPT
  /* Non-Posix BSD-style systems like SunOS 4.1.x need this
     so that `read' calls are interrupted properly.  */
  catchaction.sa_flags = SA_INTERRUPT;
#endif
  sigemptyset (&catchaction.sa_mask);
  for (i = 0;  i < NUM_SIGS;  i++)
    sigaddset (&catchaction.sa_mask, sigs[i]);
  for (i = 0;  i < NUM_SIGS;  i++)
    {
      sigaction (sigs[i], 0, &initial_action[i]);
      if (initial_handler (i) != SIG_IGN
	  && sigaction (sigs[i], &catchaction, 0) != 0)
	fatal ("signal error");
    }
#else /* ! HAVE_SIGACTION */
  for (i = 0;  i < NUM_SIGS;  i++)
    {
      initial_action[i] = signal (sigs[i], SIG_IGN);
      if (initial_handler (i) != SIG_IGN
	  && signal (sigs[i], catchsig) != SIG_IGN)
	fatal ("signal error");
    }
#endif /* ! HAVE_SIGACTION */

#if !defined(SIGCHLD) && defined(SIGCLD)
#define SIGCHLD SIGCLD
#endif
#ifdef SIGCHLD
  /* System V fork+wait does not work if SIGCHLD is ignored.  */
  signal (SIGCHLD, SIG_DFL);
#endif

  sigs_trapped = 1;
}

/* Untrap signal S, or all trapped signals if S is zero.  */
static void
untrapsig (s)
     int s;
{
  int i;

  if (sigs_trapped)
    for (i = 0;  i < NUM_SIGS;  i++)
      if ((!s || sigs[i] == s)  &&  initial_handler (i) != SIG_IGN)
#if HAVE_SIGACTION
	  sigaction (sigs[i], &initial_action[i], 0);
#else
	  signal (sigs[i], initial_action[i]);
#endif
}

/* Exit if a signal has been received.  */
static void
checksigs ()
{
  int s = signal_received;
  if (s)
    {
      cleanup ();

      /* Yield an exit status indicating that a signal was received.  */
      untrapsig (s);
      kill (getpid (), s);

      /* That didn't work, so exit with error status.  */
      exit (2);
    }
}



static void
give_help ()
{
  fprintf (stderr,"l:\tuse the left version\n");
  fprintf (stderr,"r:\tuse the right version\n");
  fprintf (stderr,"e l:\tedit then use the left version\n");
  fprintf (stderr,"e r:\tedit then use the right version\n");
  fprintf (stderr,"e b:\tedit then use the left and right versions concatenated\n");
  fprintf (stderr,"e:\tedit a new version\n");
  fprintf (stderr,"s:\tsilently include common lines\n");
  fprintf (stderr,"v:\tverbosely include common lines\n");
  fprintf (stderr,"q:\tquit\n");
}

static int
skip_white ()
{
  int c;
  for (;;)
    {
      c = getchar ();
      if (!ISSPACE (c) || c == '\n')
	break;
      checksigs ();
    }
  if (ferror (stdin))
    perror_fatal ("input error");
  return c;
}

static void
flush_line ()
{
  int c;
  while ((c = getchar ()) != '\n' && c != EOF)
    ;
  if (ferror (stdin))
    perror_fatal ("input error");
}


/* interpret an edit command */
static int
edit (left, lenl, right, lenr, outfile)
     struct line_filter *left;
     int lenl;
     struct line_filter *right;
     int lenr;
     FILE *outfile;
{
  for (;;)
    {
      int cmd0, cmd1;
      int gotcmd = 0;

      cmd1 = 0; /* Pacify `gcc -W'.  */

      while (!gotcmd)
	{
	  if (putchar ('%') != '%')
	    perror_fatal ("output error");
	  ck_fflush (stdout);

	  cmd0 = skip_white ();
	  switch (cmd0)
	    {
	    case 'l': case 'r': case 's': case 'v': case 'q':
	      if (skip_white () != '\n')
		{
		  give_help ();
		  flush_line ();
		  continue;
		}
	      gotcmd = 1;
	      break;

	    case 'e':
	      cmd1 = skip_white ();
	      switch (cmd1)
		{
		case 'l': case 'r': case 'b':
		  if (skip_white () != '\n')
		    {
		      give_help ();
		      flush_line ();
		      continue;
		    }
		  gotcmd = 1;
		  break;
		case '\n':
		  gotcmd = 1;
		  break;
		default:
		  give_help ();
		  flush_line ();
		  continue;
		}
	      break;
	    case EOF:
	      if (feof (stdin))
		{
		  gotcmd = 1;
		  cmd0 = 'q';
		  break;
		}
	      /* falls through */
	    default:
	      flush_line ();
	      /* falls through */
	    case '\n':
	      give_help ();
	      continue;
	    }
	}

      switch (cmd0)
	{
	case 'l':
	  lf_copy (left, lenl, outfile);
	  lf_skip (right, lenr);
	  return 1;
	case 'r':
	  lf_copy (right, lenr, outfile);
	  lf_skip (left, lenl);
	  return 1;
	case 's':
	  suppress_common_flag = 1;
	  break;
	case 'v':
	  suppress_common_flag = 0;
	  break;
	case 'q':
	  return 0;
	case 'e':
	  {
	    int tfd;
	    FILE *tmp;

	    if (tmpmade)
	      {
	        unlink (tmpname);
	        tmpmade = 0;
		free (tmpname);
	      }

	    asprintf (&tmpname, "%s/sdiff.XXXXXX",
	      getenv("TMPDIR") ?: P_tmpdir);
	    if (tmpname == NULL)
	      perror_fatal ("temporary file name");
	    tfd = mkstemp(tmpname);
	    if (tfd == -1)
	      perror_fatal ("temporary file name");
	    tmp = fdopen (tfd, "w+");
	    if (tmp == NULL)
	      perror_fatal ("temporary file name");
 
	    tmpmade = 1;

	    if (cmd1 == 'l' || cmd1 == 'b')
	      lf_copy (left, lenl, tmp);
	    else
	      lf_skip (left, lenl);

	    if (cmd1 == 'r' || cmd1 == 'b')
	      lf_copy (right, lenr, tmp);
	    else
	      lf_skip (right, lenr);

	    ck_fflush (tmp);

	    {
	      int wstatus;
#if ! HAVE_FORK
	      char *command = xmalloc (strlen (edbin) + strlen (tmpname) + 2);
	      sprintf (command, "%s %s", edbin, tmpname);
	      wstatus = system (command);
	      free (command);
#else /* HAVE_FORK */
	      pid_t pid;

	      ignore_SIGINT = 1;
	      checksigs ();

	      pid = fork ();
	      if (pid == 0)
		{
		  char const *argv[3];
		  int i = 0;

		  argv[i++] = edbin;
		  argv[i++] = tmpname;
		  argv[i++] = 0;

		  execvp (edbin, (char **) argv);
		  write (STDERR_FILENO, edbin, strlen (edbin));
		  write (STDERR_FILENO, ": not found\n", 12);
		  _exit (1);
		}

	      if (pid < 0)
		perror_fatal ("fork failed");

	      while (waitpid (pid, &wstatus, 0) < 0)
		if (errno == EINTR)
		  checksigs ();
		else
		  perror_fatal ("wait failed");

	      ignore_SIGINT = 0;
#endif /* HAVE_FORK */

	      if (wstatus != 0)
		fatal ("Subsidiary editor failed");
	    }

	    if (fseek (tmp, 0L, SEEK_SET) != 0)
	      perror_fatal ("fseek");
	    {
	      /* SDIFF_BUFSIZE is too big for a local var
		 in some compilers, so we allocate it dynamically.  */
	      char *buf = xmalloc (SDIFF_BUFSIZE);
	      size_t size;

	      while ((size = ck_fread (buf, SDIFF_BUFSIZE, tmp)) != 0)
		{
		  checksigs ();
		  ck_fwrite (buf, size, outfile);
		}
	      ck_fclose (tmp);

	      free (buf);
	    }
	    return 1;
	  }
	default:
	  give_help ();
	  break;
	}
    }
}



/* Alternately reveal bursts of diff output and handle user commands.  */
static int
interact (diff, left, right, outfile)
     struct line_filter *diff;
     struct line_filter *left;
     struct line_filter *right;
     FILE *outfile;
{
  for (;;)
    {
      char diff_help[256];
      int snarfed = lf_snarf (diff, diff_help, sizeof (diff_help));

      if (snarfed <= 0)
	return snarfed;

      checksigs ();

      switch (diff_help[0])
	{
	case ' ':
	  puts (diff_help + 1);
	  break;
	case 'i':
	  {
	    int lenl = atoi (diff_help + 1), lenr, lenmax;
	    char *p = strchr (diff_help, ',');

	    if (!p)
	      fatal (diff_help);
	    lenr = atoi (p + 1);
	    lenmax = max (lenl, lenr);

	    if (suppress_common_flag)
	      lf_skip (diff, lenmax);
	    else
	      lf_copy (diff, lenmax, stdout);

	    lf_copy (left, lenl, outfile);
	    lf_skip (right, lenr);
	    break;
	  }
	case 'c':
	  {
	    int lenl = atoi (diff_help + 1), lenr;
	    char *p = strchr (diff_help, ',');

	    if (!p)
	      fatal (diff_help);
	    lenr = atoi (p + 1);
	    lf_copy (diff, max (lenl, lenr), stdout);
	    if (! edit (left, lenl, right, lenr, outfile))
	      return 0;
	    break;
	  }
	default:
	  fatal (diff_help);
	  break;
	}
    }
}



/* temporary lossage: this is torn from gnu libc */
/* Return nonzero if DIR is an existing directory.  */
static int
diraccess (dir)
     char const *dir;
{
  struct stat buf;
  return stat (dir, &buf) == 0 && S_ISDIR (buf.st_mode);
}