Subject: Re: SYSFS "errors"

From: Mauro Carvalho Chehab <[email-masked]>
Date: Tue, 19 Feb 2013 07:03:10 -0300

Em Mon, 18 Feb 2013 23:44:05 +0100
Borislav Petkov <[email-masked]> escreveu:

> On Mon, Feb 18, 2013 at 02:26:18PM -0800, Greg KH wrote:
> > I don't know, it depends on if userspace can handle this properly or
> > not. What tools rely on this sysfs file? WHat happens when they get a
> > non-number in the file?

The thing with "sdram_scrub_rate" is that this is not supported by any
userspace application I know. I suspect that this is used by userspace
scripts. So, we'll never know in advance what behavior those scripts would
expect.

> 
> I'm not aware of any, frankly speaking.
> 
> If there are any, those tools should be able to handle the -ENODEV
> they get. Now, if this gets changed this way, the read would succeed
> but they'll have to parse the returned value and see that it is not an
> integer.
> 
> So I don't know either.
> 
> But my gut feeling says to stay concervative and not touch this code -
> we don't know what uses it and how much we would break by "fixing" it.
> The current situation is not that big of a deal IMVHO and I'd be willing
> to accept the small inconcistency versus possibly breaking userspace.

I remember I saw some discussions about it in the past at bluesmoke ML,
saying that -ENODEV is the expected behavior when this is not supported.

Changing from -ENODEV to "N/A" will break anything that would be relying
on the previous behavior. So, I think that such change will for sure break
userspace.

If we're willing to change it, not creating the "sdram_scrub_rate" sysfs 
node is less likely to affect userspace.

Regards,
Mauro