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/*
Copyright (C) 2005 Juliusz Chroboczek
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; see the file COPYING. If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/time.h>
#ifdef _WIN32
#include <windows.h>
#include <io.h>
#endif
int sloppy_atomic_create(const char *p)
{
int fd;
fd = open(p, O_WRONLY | O_EXCL | O_CREAT, 0666);
if(fd < 0)
return -1;
close(fd);
return 1;
}
#ifdef _WIN32
int atomic_create(const char *p)
{
return sloppy_atomic_create(p);
}
#else
static int careful_atomic_create(const char *p)
{
/* O_EXCL is not available over NFSv2, and even under NFSv3, it is
broken on many systems. The following protocol is provably
safe assuming that:
- creation of hard links is atomic;
- stat hits the server rather than working from the cache.
*/
static char hostname[65] = {'\0'};
int fd, rc, saved_errno;
#define FILENAME_SIZE (11 + 15 + 8 + 1)
char *filename;
char *lastslash;
int dirlen;
struct timeval now;
struct stat sb;
if(hostname[0] == '\0') {
char *c;
int i;
/* POSIX guarantees 65 is enough. */
rc = gethostname(hostname, 65);
if(rc < 0 || rc >= 65) {
fprintf(stderr, "Error reading hostname when locking.\n");
strcpy(hostname, "kremvax");
}
c = strchr(hostname, '.');
if(c != NULL)
*c = '\0';
hostname[15] = '\0';
/* clean up a few possible nasty characters folks might put in their hostname */
for (i=0;i<15;i++)
if (hostname[i] == ':' || hostname[i] == '/' || hostname[i] == '\\')
hostname[i] = '-';
}
lastslash = strrchr(p, '/');
dirlen = lastslash ? lastslash - p + 1 : 0;
filename = malloc(dirlen + FILENAME_SIZE);
if(filename == NULL)
return -1;
if(dirlen > 0)
memcpy(filename, p, dirlen);
filename[dirlen] = '\0';
gettimeofday(&now, NULL);
rc = snprintf(filename + dirlen, FILENAME_SIZE, "darcs_lock_%s%04x%04x",
hostname, ((unsigned)getpid()) & 0xFFFF,
((unsigned)(now.tv_usec ^ (now.tv_usec >> 16))) & 0xFFFF);
if(rc < 0 || rc >= FILENAME_SIZE) {
fprintf(stderr, "Error writing to lock filename (%d)\n",
rc < 0 ? errno : 0);
goto fail2;
}
fd = open(filename, O_WRONLY | O_EXCL | O_CREAT, 0666);
if(fd < 0)
goto fail2;
/* Paranoia: should cause the client to flush its metadata cache. */
rc = close(fd);
if(rc < 0) {
fprintf(stderr, "Error closing file %s. (%d)\n", filename, errno);
goto fail;
}
rc = link(filename, p);
if(rc >= 0)
goto success;
else if(errno == EPERM || errno == EOPNOTSUPP) {
/* Linux returns EPERM when making hard links on filesystems
that don't support them. */
/* It seems that MacOS returns EOPNOTSUPP on filesystems that
don't support hard links. */
unlink(filename);
free(filename);
return sloppy_atomic_create(p);
} else if(errno != EEXIST && errno != EIO)
goto fail;
/* The link may still have been successful if we're running over
UDP and got EEXIST or EIO. Check the file's link count. */
rc = stat(filename, &sb);
if(rc < 0) {
goto fail;
}
if(sb.st_nlink != 2) {
errno = EEXIST;
goto fail;
}
success:
unlink(filename);
free(filename);
return 1;
fail:
saved_errno = errno;
unlink(filename);
errno = saved_errno;
fail2:
free(filename);
return -1;
}
int atomic_create(const char *p)
{
static int sloppy = -1;
if(sloppy < 0) {
char *s = getenv("DARCS_SLOPPY_LOCKS");
sloppy = (s != NULL);
}
if(sloppy)
return sloppy_atomic_create(p);
else
return careful_atomic_create(p);
}
#endif
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