linux-kernel - Re: [PATCH 3/3] cxacru: Store all device status information and report it when atm_proc

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Date:	Thu, 1 Feb 2007 10:15:31 +0100
From:	Duncan Sands <duncan.sands@...h.u-psud.fr>
To:	Andrew Morton <akpm@...l.org>
Cc:	Simon Arlott <simon@...ott.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] cxacru: Store all device status information and report it when atm_proc_read is called.

On Thursday 1 February 2007 00:39:14 you wrote:
> On Tue, 30 Jan 2007 21:30:29 +0000
> Simon Arlott <simon@...ott.org> wrote:
> 
> > +static int cxacru_proc_read(struct usbatm_data *usbatm_instance,
> > +	struct atm_dev *atm_dev, loff_t * pos, char *page)
> > +{
> > +	struct cxacru_data *instance = usbatm_instance->driver_data;
> > +	u32 *cxinf = instance->cxinf_status;
> > +	int left = *pos;
> > +
> > +	if (!left--)
> > +		return sprintf(page, "# %s\n", usbatm_instance->description);
> > +
> > +	if (!left--) {
> > +		if (cxinf[CXINF_LINE_STATUS] == 5) {
> > +			return sprintf(page, "# UP %u/%u\n",
> > +				cxinf[CXINF_DOWNSTREAM_RATE],
> > +				cxinf[CXINF_UPSTREAM_RATE]);
> > +		} else {
> > +			return sprintf(page, "# DOWN\n");
> > +		}
> > +	}
> 
> hm, how well-tested was this proc interface?  The pread() and lseek()
> behaviour might be strange.
> 
> I guess as long as it doesn't oops, hang or anything like that then it'll
> be OK.  Anyone who does anything apart from a single big-fat-read from a 
> procfile has a good chance of getting into trouble :(

All the ATM drivers seem to do it like this.  That doesn't mean they are
right of course!  But I never saw anyone complain on the ATM mailing list.
On the other hand, why does Simon want this?  If he has written a user space
tool that extracts bits from the proc file (eg: to tell users what's going
on) then he could run into trouble, depending on how he implements it.

Ciao,

Duncan.
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