🚀 go-pugleaf

In article <PERF.89Oct16173540@osiris.efd.lth.se> perf@efd.lth.se (Per Foreby) writes:
< Facts: Bash 1.03, Sun3 SunOS 4.0.3.
< 
< Since we have over 1100 users (yp) username completion takes some
< time. If I break while the completion is running, I get an error the
< next time I try a completion:
< 
< 	bash$ ls ~per<M-?>   			< takes about 30 sec >
< 	~perf  ~perh  ~pers
< 	bash$ ls ~per<M-?><^C>   		< break after a few seconds >
< 	bash$ ls ~per				< try again >
< 	free: Called with already freed block argument
< 	mailing bug report...
< 
< If I put all users in my local /etc/passwd, I can't reproduce the
< problem.

Congratulations, you have a slightly different version of what I call
the YP vs. vfork(2) bug.  The problem is that the yp routines (used in
the Sun getpw* routines) are closing and re-opening a socket to the yp
server only when they think they need to (which is only correct _some_
of the time).  I found it because one of these cases is when the pid
chages (i.e. after a fork() or vfork()).  The problem is that vfork()
shares the data fork of the child and the parent until the child
exec()s, and the child must be very careful not to mess with the data
of the parent gratitiously.  (Actually, I have many flames on the
existance of vfork().  It is a hack that should never have been done.
The creaters did not think hard enough about the real problem.).

Bash doesn't have a vfork() (or at least, it didn't the last time I
looked, which was a while ago (if you are thinking of adding it,
DON'T!  -- it will get you in too much trouble)).  On the other hand,
interupting things in the middle will have the same effect, as far as
the getpw* routines are concerned.

The fix is (in the end) relatively easy.  What Mat Landau ended up
doing to tcsh was to put a call to fix_yp_bugs() before the first and
after the last of a series of calls to getpw*.  This seems to have
fixed the bug nicely.  Be careful, though.  Too many calls to this and
your performance will drop, as the YP routines have to make a new
socket after each call to fix_yp_bugs.

   #ifdef YPBUGS

   fix_yp_bugs()
   {
       char *mydomain;

       /*
	* PWP: The previous version assumed that yp domain was the same as the
	* internet name domain.  This isn't allways true.
	* (Thanks to Mat Landau <mlandau@bbn.com> for the original version
	* of this.)
	*/
       if (yp_get_default_domain(&mydomain) == 0) { /* if we got a name */
	   yp_unbind(mydomain);
       }	
   }

   #endif /* YPBUGS */

For example, the following routine is used in tcsh to get the next
entry from the current list of files or users:

   char *
   getentry (dir_fd, looking_for_lognames)
   DIR *dir_fd;
   {
       extern struct passwd *getpwent ();
       register struct passwd *pw;

       register struct direct *dirp;
       /* extern struct direct *readdir(); */

       if (looking_for_lognames) {	/* Is it login names we want? */
   #ifdef YPBUGS
	   pw = getpwent();
	   if (pw == NULL) {
	       fix_yp_bugs();
	       return (NULL);
	   }
   #else
	   if ((pw = getpwent ()) == NULL)
	       return (NULL);
   #endif
	   return (pw -> pw_name);
       } else {				/* It's a dir entry we want */
	   if (dirp = readdir (dir_fd))
	       return (dirp -> d_name);
	   return (NULL);
       }
   }

Happy hacking,

	-- Paul Placeway <PPlaceway@bbn.com>
	   Am I a wizard?  Are you qualified to judge?  Does it really
	   matter in the end?  "What I am is what I am, are you what
	   you are or what?" -- E.B.