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From: schaefer@bgsuvax.UUCP (Stephen Schaefer)
Newsgroups: net.unix-wizards
Subject: Re: Script Hanging
Message-ID: <72@bgsuvax.UUCP>
Date: Tue, 13-May-86 15:24:40 EDT
Article-I.D.: bgsuvax.72
Posted: Tue May 13 15:24:40 1986
Date-Received: Fri, 16-May-86 06:24:21 EDT
Organization: Bowling Green State University,OH
Lines: 133

I suppose I  should be quicker  with my "f"  key.  Here are   fixes to
three  different  problems   with script,  building  from  the    code
distributed with 4.2BSD:

% rlog script.c
RCS file:        RCS/script.c,v;   Working file:    script.c
head:            1.5
locks:           root: 1.5;  strict
access list:   
symbolic names:
comment leader:  " * "
total revisions: 5;    selected revisions: 5
description:
As received from Berkeley.
----------------------------
revision 1.5        locked by: root;       
date: 86/05/13 15:07:58;  author: root;  state: Exp;  lines added/del: 3/0
Disable the following, which CBREAK was not passing through as desired:
t_flushc (toggles throwing away output), t_lnextc (quotes characters -
I hope nothing needs this now), and ^M (which was being translated to
^J on input, to ^M^J on output).  I hope I haven't missed anything...
----------------------------
revision 1.4        
date: 86/01/28 16:53:17;  author: root;  state: Exp;  lines added/del: 13/1
Changed real terminal mode to CBREAK while running, setting the
real terminals interrupt generating characters undefined.  All
this to handle control-s/control-q.
----------------------------
revision 1.3        
date: 85/12/10 17:17:28;  author: root;  state: Exp;  lines added/del: 13/5
Problem: script would open /dev/ptyXX for which it did not have
suitable permissions on the corresponding /dev/ttyXX.
Fix: in getmaster(), try the next line if /dev/ttyXX does not have
suitable permissions, as returned by stat(2).
----------------------------
revision 1.2        
date: 85/12/05 14:02:48;  author: root;  state: Exp;  lines added/del: 15/6
Problem: script would occasionally hang when exiting its subshell.
Caused by a race condition when the script child performed a "read"
system call, which either would or would not return <=0 when the shell
child died.
Fix: changed the routing which handles the SIGCHLD signal in the script
child to perform proper cleanup - named "finish2".
----------------------------
revision 1.1        
date: 85/12/05 13:55:54;  author: root;  state: Exp;  
Initial revision
=============================================================================

% rcsdiff -r1.1 script.c
RCS file: RCS/script.c,v
retrieving revision 1.1
diff  -r1.1 script.c
15a16,18
> #define READ_PERM 4
> #define WRITE_PERM 2
> 
24a28
> int	finish2();
75c79,80
< 		f = fork();
---
> 		(void) signal(SIGCHLD, finish2);
> 	    	f = fork();
109a115,125
> finish2()
> {
> 	time_t tvec;
> 
> 	tvec = time((time_t *)0);
> 	fprintf(fscript,"\nscript done on %s", ctime(&tvec));
> 	(void) fclose(fscript);
> 	(void) close(master);
> 	exit(0);
> }
> 
126,130c142
< 	tvec = time((time_t *)0);
< 	fprintf(fscript,"\nscript done on %s", ctime(&tvec));
< 	(void) fclose(fscript);
< 	(void) close(master);
< 	exit(0);
---
> 	finish2();
156a169,170
> 	struct tchars tbuf;
> 	struct ltchars lbuf;
159c173
< 	sbuf.sg_flags |= RAW;
---
> 	sbuf.sg_flags |= CBREAK;
160a175
> 	sbuf.sg_flags &= ~CRMOD;
161a177,186
> 	tbuf = tc;
> 	tbuf.t_intrc = -1;
> 	tbuf.t_quitc = -1;
> 	ioctl(0, TIOCSETC, (char *)&tbuf);
> 	lbuf = lc;
> 	lbuf.t_suspc = -1;
> 	lbuf.t_dsuspc = -1;
> 	lbuf.t_flushc = -1;
> 	lbuf.t_lnextc = -1;
> 	ioctl(0, TIOCSLTC, (char *)&lbuf);
174a200,201
> 	ioctl(0, TIOCSETC, (char *)&tc);
> 	ioctl(0, TIOCSLTC, (char *)&lc);
184a212
> 	line[strlen("/dev/")] = 't';
186,189c214
< 		line[strlen("/dev/pty")] = c;
< 		line[strlen("/dev/ptyp")] = '0';
< 		if (stat(line, &stb) < 0)
< 			break;
---
> 		line[strlen("/dev/tty")] = c;
191c216,222
< 			line[strlen("/dev/ptyp")] = "0123456789abcdef"[i];
---
> 			line[strlen("/dev/ttyp")] = "0123456789abcdef"[i];
> 			if (stat(line, &stb) < 0)   /* does line exist? */
> 			        continue;
> 			if (((READ_PERM | WRITE_PERM) & (stb.st_mode)) !=
> 			    (READ_PERM | WRITE_PERM))  /* protected? */
> 			        continue;
> 			line[strlen("/dev/")] = 'p';
200a232
> 			line[strlen("/dev/")] = 't';
-- 
Stephen P. Schaefer
Systems Programmer
schaefer@bgsu
...!cbosgd!osu-eddie!bgsuvax!schaefer