fcntl_lock.c

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/* test whether fcntl locking works on this system */

#if defined(HAVE_UNISTD_H)
#include <unistd.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>

#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif

#ifdef HAVE_SYS_FCNTL_H
#include <sys/fcntl.h>
#endif

#ifdef HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif

#include <errno.h>

#define DATA "conftest.fcntl"

#ifndef SEEK_SET
#define SEEK_SET 0
#endif

/* lock a byte range in a open file */
int main(int argc, char *argv[])
{
	struct flock lock;
	int fd, ret, status=1;
	pid_t pid;
	char *testdir = NULL;

	testdir = getenv("TESTDIR");
	if (testdir) chdir(testdir);

	alarm(10);

	if (!(pid=fork())) {
		sleep(2);
		fd = open(DATA, O_RDONLY);

		if (fd == -1) {
			fprintf(stderr,"ERROR: failed to open %s (errno=%d)\n", 
				DATA, (int)errno);
			exit(1);
		}

		lock.l_type = F_WRLCK;
		lock.l_whence = SEEK_SET;
		lock.l_start = 0;
		lock.l_len = 4;
		lock.l_pid = getpid();
		
		lock.l_type = F_WRLCK;
		
		/* check if a lock applies */
		ret = fcntl(fd,F_GETLK,&lock);

		if ((ret == -1) ||
		    (lock.l_type == F_UNLCK)) {
			fprintf(stderr,"ERROR: lock test failed (ret=%d errno=%d)\n", ret, (int)errno);
			exit(1);
		} else {
			exit(0);
		}
	}

	unlink(DATA);
	fd = open(DATA, O_RDWR|O_CREAT|O_EXCL, 0600);

	if (fd == -1) {
		fprintf(stderr,"ERROR: failed to open %s (errno=%d)\n", 
			DATA, (int)errno);
		exit(1);
	}

	lock.l_type = F_WRLCK;
	lock.l_whence = SEEK_SET;
	lock.l_start = 0;
	lock.l_len = 4;
	lock.l_pid = getpid();

	/* set a 4 byte write lock */
	fcntl(fd,F_SETLK,&lock);

	waitpid(pid, &status, 0);

	unlink(DATA);

#if defined(WIFEXITED) && defined(WEXITSTATUS)
    if(WIFEXITED(status)) {
        status = WEXITSTATUS(status);
    } else {
        status = 1;
    }
#else /* defined(WIFEXITED) && defined(WEXITSTATUS) */
	status = (status == 0) ? 0 : 1;
#endif /* defined(WIFEXITED) && defined(WEXITSTATUS) */

	if (status) {
		fprintf(stderr,"ERROR: lock test failed with status=%d\n", 
			status);
	}

	exit(status);
}