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From: futagami@nttspl.ntt.junet (Toshitsugu Futagami)
Newsgroups: net.unix
Subject: The problem of "read" system call
Message-ID: <140@nttspl.ntt.junet>
Date: Thu, 13-Mar-86 17:14:08 EST
Article-I.D.: nttspl.140
Posted: Thu Mar 13 17:14:08 1986
Date-Received: Sun, 16-Mar-86 09:42:43 EST
Distribution: net
Organization: NTT Software Production Technology Labs., Japan
Lines: 96


Dear Sirs:

	Our VAX-11/750 stops on the point of "read" in the following program.
This process remains the status "D" of process runnability and we cannot kill
the process. We find that it often stops after reading a tape mark. 

	Is it a bug of 4.2BSD? Or our mt equipment has any troubles? If you can,
please run this program and tell me the result.

	If you know anything, please tell me them, wouldn't you? Thank you.

+--------+---------+---------+---------+---------+---------+---------+---------+
| NTT			      Toshitsugu Futagami			   NTT |
| NTT	      ( NTT Software Production Technology Labs. JAPAN)		   NTT |
| NTT			JUNET:  futagami@nttspl.ntt.junet		   NTT |
| NTT			UUCP :  ..!kddlab!nttlab!nttspl!futagami	   NTT |
| NTT			PHONE:  ( 0422 ) 59 - 3518			   NTT |
+--------+---------+---------+---------+---------+---------+---------+---------+

---------------------------------------------------------------
#include <ctype.h>
#include <sys/param.h>
#include <sys/file.h>
#include <sys/mtio.h>
#include <sys/ioctl.h>
#include <stdio.h>
main()
{
	int  i,mfd;
	int  r;
        int  k;
	char buf[4100];
	struct mtop mtbl;
	
        k=1;
	if ((mfd=open("/dev/rmt12",O_RDONLY,00777)) == -1) {
		printf("open err\n");
		exit();
	}
	while(1) {
		r = read(mfd,buf,4100);
		if ( r == -1) {
			printf("read err\n"); 
			exit();
		}
		if (r == 0) {
			printf("<TM>\n");
			if (close(mfd) == -1) { 
				printf("close err\n");
				exit();
			}
			if ((mfd=open("/dev/rmt12",O_RDONLY,00777)) == -1) {
				printf("open err\n");
				exit();
			}
			r = read(mfd,buf,4100);
			if (r == -1) {
				printf("read err\n");
				exit();
			}
			if (r == 0) { 
				printf("<TM>\n");
				if (close(mfd) == -1) {
					printf("close err\n");
					exit();
				}
				break;
			}
			for (i=0;i<r;i++) 
				putchar(buf[i]);
			printf("<EOB>\n");
			continue;
		}
		for (i=0;i<r;i++) 
			putchar(buf[i]);
		printf("<EOB>\n");
		continue;
	}
	printf("<fin>\n");
	if ((mfd=open("/dev/rmt12",O_RDONLY,00777)) == -1) {
		printf("open err\n");
		exit();
	}
	mtbl.mt_op = MTREW;
	mtbl.mt_count = 1;
	if (ioctl(mfd, MTIOCTOP, &mtbl) == -1) {
	  printf("ioctl error\n");
	  exit();
	}
	if (close(mfd) == -1) {
		printf("close err\n");
		exit();
	}
}
---------------------------------------------------------------