source: trunk/athena/bin/syncupdate/syncupdate.c @ 16689

/* Copyright 1999 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

static const char rcsid[] = "$Id: syncupdate.c,v 1.3 2001-10-23 01:43:24 amb Exp $";

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#ifndef S_IAMB
#define S_IAMB 0x1FF    /* Access bits part of struct stat st_mode field */
#endif

static void copy(const char *source, const char *tempfile);
static void open_and_sync(const char *filename);
static void usage(void);

int main(int argc, char **argv)
{
  int c;
  const char *tempfile = NULL, *source, *dest;

  while ((c = getopt(argc, argv, "c:")) != EOF)
    {
      switch (c)
        {
        case 'c':
          tempfile = optarg;
          break;
        case '?':
          usage();
        }
    }
  argc -= optind;
  argv += optind;
  if (argc != 2)
    usage();
  source = argv[0];
  dest = argv[1];

  /* Set up for the move. */
  if (tempfile)
    {
      copy(source, tempfile);
      source = tempfile;
    }
  else
    open_and_sync(source);

  if (rename(source, dest) == -1)
    {
      fprintf(stderr, "syncupdate: can't rename %s to %s: %s\n",
              source, dest, strerror(errno));
      exit(1);
    }

  exit(0);
}

static void copy(const char *source, const char *tempfile)
{
  int sfd, tfd, count, pos, n;
  struct stat statbuf;
  unsigned char buf[8192];

  /* Open the source file and get its status information. */
  sfd = open(source, O_RDONLY, 0);
  if (sfd == -1)
    {   
      fprintf(stderr, "syncupdate: can't read %s: %s\n", source,
              strerror(errno));
      exit(1);
    }
  if (fstat(sfd, &statbuf) == -1)
    {
      fprintf(stderr, "syncupdate: can't stat %s: %s\n", source,
              strerror(errno));
      exit(1);
    }

  /* Remove, open, and set mode on the temp file. */
  if (unlink(tempfile) == -1 && errno != ENOENT)
    {
      fprintf(stderr, "syncupdate: can't remove %s: %s\n", tempfile,
              strerror(errno));
      exit(1);
    }
  tfd = open(tempfile, O_RDWR | O_CREAT | O_EXCL, 0);
  if (tfd == -1)
    {
      fprintf(stderr, "syncupdate: can't create %s: %s\n", tempfile,
              strerror(errno));
      exit(1);
    }
  if (fchmod(tfd, statbuf.st_mode & S_IAMB) == -1)
    {
      fprintf(stderr, "syncupdate: can't fchmod %s: %s\n", tempfile,
              strerror(errno));
      unlink(tempfile);
      exit(1);
    }

  /* Now copy and fsync. */
  while ((count = read(sfd, buf, sizeof(buf))) > 0)
    {
      for (pos = 0; pos < count; pos += n)
        {
          n = write(tfd, buf + pos, count - pos);
          if (n == -1)
            {
              fprintf(stderr, "syncupdate: can't write to %s: %s\n", tempfile,
                      strerror(errno));
              unlink(tempfile);
              exit(1);
            }
        }
    }
  if (count == -1)
    {
      fprintf(stderr, "syncupdate: can't read from %s: %s\n", source,
              strerror(errno));
    }

  if (fsync(tfd) == -1)
    {
      fprintf(stderr, "syncupdate: can't fsync %s: %s\n", tempfile,
              strerror(errno));
      unlink(tempfile);
      exit(1);
    }

  close(sfd);
  close(tfd);
}

static void open_and_sync(const char *filename)
{
  int fd;

  fd = open(filename, O_RDWR, 0);
  if (fd == -1)
    {
      fprintf(stderr, "syncupdate: can't open %s: %s\n", filename,
              strerror(errno));
      exit(1);
    }

  if (fsync(fd) == -1)
    {
      fprintf(stderr, "syncupdate: can't fsync %s: %s\n", filename,
              strerror(errno));
      exit(1);
    }

  close(fd);
}

static void usage(void)
{
  fprintf(stderr, "Usage: syncupdate [-c tempfile] source dest\n");
  exit(1);
}