mandatory.c

APUE(第二版)的随书源代码,与第一版的代码相比增加了一些章节的代码(详见第二版的说明)

#include	<sys/types.h>
#include	<sys/stat.h>
#include	<sys/wait.h>
#include	<errno.h>
#include	<fcntl.h>
#include	"ourhdr.h"
int
main(void)
{
	int				fd;
	pid_t			pid;
	char			buff[5];
	struct stat		statbuf;
	if ( (fd = open("templock", O_RDWR | O_CREAT | O_TRUNC,
												FILE_MODE)) < 0)
		err_sys("open error");
	if (write(fd, "abcdef", 6) != 6)
		err_sys("write error");

		/* turn on set-group-ID and turn off group-execute */
	if (fstat(fd, &statbuf) < 0)
		err_sys("fstat error");
	if (fchmod(fd, (statbuf.st_mode & ~S_IXGRP) | S_ISGID) < 0)
		err_sys("fchmod error");

	TELL_WAIT();
	if ( (pid = fork()) < 0) {
		err_sys("fork error");

	} else if (pid > 0) {	/* parent */
				/* write lock entire file */
		if (write_lock(fd, 0, SEEK_SET, 0) < 0)
			err_sys("write_lock error");
		TELL_CHILD(pid);

		if (waitpid(pid, NULL, 0) < 0)
			err_sys("waitpid error");

	} else {				/* child */
		WAIT_PARENT();		/* wait for parent to set lock */

		set_fl(fd, O_NONBLOCK);

			/* first let's see what error we get if region is locked */
		if (read_lock(fd, 0, SEEK_SET, 0) != -1)	/* no wait */
			err_sys("child: read_lock succeeded");
		printf("read_lock of already-locked region returns %d\n", errno);

			/* now try to read the mandatory locked file */
		if (lseek(fd, 0, SEEK_SET) == -1)
			err_sys("lseek error");
		if (read(fd, buff, 2) < 0)
			err_ret("read failed (mandatory locking works)");
		else
			printf("read OK (no mandatory locking), buff = %2.2s\n", buff);
	}
	exit(0);
}