Re: /proc/residual (CONFIG_PREP_PROCRESIDUAL)

[Tom Rini <trini@kernel.crashing.org>]

On Wed, Jan 30, 2002 at 08:47:46PM +0000, Leigh Brown wrote:

> On Tue, 29 Jan 2002, Tom Rini wrote:
>
> > On Tue, Jan 29, 2002 at 09:47:02PM +0000, Leigh Brown wrote:
> >
> > > On Tue, 29 Jan 2002 hollis@austin.ibm.com wrote:
> > >
> > > > On Tue, Jan 29, 2002 at 04:08:43PM +0000, Leigh Brown wrote:
> [...]
> > > > > 2. Remove #ifdef __KERNEL__ from header file for use space utility
> > > >
> > > > This encourages user applications to include kernel header files, which has
> > > > been deemed ungood. I believe there should be many lengthy threads on the
> > > > subject in the lkml archives, but more practically speaking Paul has said he'd
> > > > be perfectly happy if all kernel headers were completely protected from user
> > > > space.
> > >
> > > Surely that can't be true.  What about asm/errno.h?  I thought you just
> > > put #ifdef __KERNEL__ around stuff you don't want to export to user space.
> > > In the case of asm/residual.h it all needs to be exported to user space.
> > > The alternative is to simply clone the file, which seems a bit silly.
> >
> > There's a few legacy files which unfortunatly can't be clamped down on.
> > In general you are supposed to copy the file and be done with it.  In
> > fact, if I ever wanted to read the residual image from my PReP box
> > (usually off) on my x86 (which I'm typing on right now), I'd need to do
> > this anyways since x86 won't have '<asm/residual.h>'.
>
> That's a fairly contrived example but I'm not going to argue.  I'm
> amending lsresidual to use a local copy of any kernel headers it needs
> (plus making it endian safe so that you really can see your residual data
> on your x86 box :-)

heh.  Well the better example is stuff like atomic ops, which on some
arches can only be done in kernel-space. :)

> > > > > 4. Only create entry if residual size > 0 'coz what you can't see won't
> > > > >    hurt you + eliminate chance of people wondering why they are getting an
> > > > >    error trying to read it.
> > > >
> > > > I don't like that, because it leaves you wondering if you compiled in residual
> > > > support at all... I'd much rather have it be 0 length.
> > >
> > > Okay.  I think the best behaviour is to simply return 0 bytes if there
> > > is no residual data and let lsresidual interpret that as being no
> > > residual data.
> >
> > If we don't have any residual data, shouldn't we be returning a 0 byte
> > file anyhow?  I didn't explicitly test this, but in the original version
> > I got from Sven/Hollis, no residual data gave me an empty
> > /proc/residual.
>
> The original may have, but the one you posted doesn't:
>
> +static int prep_residual_open(struct inode * inode, struct file * file)
> +{
> +	if (res->ResidualLength == 0) {
> +		return -ENOENT;
> +	}
> +	DPRINTK("/proc/residual opened\n");
> +	MOD_INC_USE_COUNT;
> +	return 0;
> +}
>
> The above will cause the open to fail if no residual data is present.
> I've attached an updated version of my patch that has the required
> behaviour (based on what you and Hollis have said).

Er, I think this is the desired output.  dd, et al will give an empty
file and things checking more througly will/can give a proper error msg.
Sorry for the confusion :)

--
Tom Rini (TR1265)
http://gate.crashing.org/~trini/

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