Re: [9fans] directly opening Plan9 devices

["Roman V. Shaposhnik" <rvs@sun.com>]

On Sat, 2009-01-03 at 17:03 -0500, erik quanstrom wrote:
> > Did you see the example I provided in the original
> > email? "rfork m" is *exactly* RFNOMNT. And it doesn't
> > seem to work for one simple reason: RFNOMNT doesn't
> > restrict bind(2).
>
> these are exceptions.  from port/chan.c:
>
> 	case '#':
> 		nomount = 1;
> 		up->genbuf[0] = '\0';
> 		n = 0;
> 		while(*name != '\0' && (*name != '/' || n < 2)){
> 			if(n >= sizeof(up->genbuf)-1)
> 				error(Efilename);
> 			up->genbuf[n++] = *name++;
> 		}
> 		up->genbuf[n] = '\0';
> 		/*
> 		 *  noattach is sandboxing.
> 		 *
> 		 *  the OK exceptions are:
> 		 *	|  it only gives access to pipes you create
> 		 *	d  this process's file descriptors
> 		 *	e  this process's environment
> 		 *  the iffy exceptions are:
> 		 *	c  time and pid, but also cons and consctl
> 		 *	p  control of your own processes (and unfortunately
> 		 *	   any others left unprotected)
> 		 */
> 		n = chartorune(&r, up->genbuf+1)+1;
> 		/* actually / is caught by parsing earlier */
> >>>>		if(utfrune("M", r))
> >>>>			error(Enoattach);
> >>>>		if(up->pgrp->noattach && utfrune("|decp", r)==nil)
> 			error(Enoattach);
> 		t = devno(r, 1);
> 		if(t == -1)
> 			error(Ebadsharp);
> 		c = devtab[t]->attach(up->genbuf+n);
> 		break;
>
> the first two indicated lines are redundant.
> i'm not so sure about any of the exceptions.

Two comments:
   0. First of all, thanks for the code snippet. I'm so used to Plan9
      having as little exceptions as possible and being very well
      documents that I sometimes forget to look for the source.
   1. This better be documented in the man pages, if you ask me.

And finally, I'd say having these exceptions is a mistake. Unless,
there's a really good reason, they break the paradigm of RFNOMNT
quite needlessly without even a hint of a benefit.

Anybody disagrees?

Thanks,
Roman.