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Subject: Re: [9front] [PATCH] Unmount to remove sharp devices.
Reply-To: 9front@9front.org
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Great work on this moody.  I have some (hopefully helpful) questions
below.


Quoth Jacob Moody <moody@mail.posixcafe.org>:
> Another iteration.
> To state all of what this does:
> 
> A process can remove access to a driver through writing
> 
> chdev [ 0! ] devmask
> 
> to /dev/drivers. This is tied to the processes namegroup,
> and is inherited on both RFCNAMEG and RFNAMEG. In order to provide
> all the knobs RFNOMNT does, blocking 'M' is interpreted to block all mounting.
> 
> Support for this new operation has been added to namespace files,
> along with a matching chdev(1). /lib/namespace.ftp has been updated
> to use chdev.
> ...
> --- /tmp/diff100000711164
> +++ b/rc/bin/chdev
> @@ -1,0 +1,3 @@
> +#!/bin/rc
> +
> +echo chdev $* >> '#c/drivers'
> ...
> --- /tmp/diff100000711170
> +++ b/sys/man/1/chdev
> @@ -1,0 +1,93 @@
> +.TH CHDEV 1
> +.SH NAME
> +chdev \- change kernel driver access
> +.SH SYNOPSIS
> +.B chdev
> +[ 0! ] \f2devmask\fP...

> --- a/sys/src/9/port/dev.c
> +++ b/sys/src/9/port/dev.c
> @@ -31,6 +31,74 @@
>  }
> 
>  void
> +devmask(Pgrp *pgrp, char *devs)
> +{
> +	int i, t, w;
> +	int invert;
> +	char *p;
> +	Rune r;
> +	u64int mask[nelem(pgrp->notallowed)];
> +
> +	
> +	invert = 1;
> +	switch(*devs){
> +	case '!':
> +		memset(mask, 0, sizeof mask);
> +		devs++;
> +		invert--;
> +		break;
> +	case '0':
> +		devs = "";
> +	default:
> +		memset(mask, 0xFF, sizeof mask);
> +		break;
> +	}		
> +
> +	w = sizeof mask[0] * 8;
> +	for(p = devs; *p != '\0';){
> +		p += chartorune(&r, p);
> +		t = devno(r, 1);
> +		if(t == -1)
> +			continue;
> +		if(invert)
> +			mask[t/w] &= ~(1<<t%w);
> +		else
> +			mask[t/w] |= 1<<t%w;
> +	}

What happens if '!!!' is the prefix?  Should the '!' set invert = 0
explicitly instead of invert--?  Does '!0' allow access to all
drivers?