Subject: Re: SYSFS "errors"

From: Mauro Carvalho Chehab <[email-masked]>
Date: Tue, 19 Feb 2013 11:14:40 -0300

Em Tue, 19 Feb 2013 14:58:07 +0100
Hannes Reinecke <[email-masked]> escreveu:

> On 02/19/2013 02:50 PM, Borislav Petkov wrote:
> > On Tue, Feb 19, 2013 at 03:38:09PM +0200, Felipe Balbi wrote:
> >> because changing the permission will cause the same issue:
> >
> > Actually, I take that back. Mauro's patch will already create the file
> > anyway:
> >
> > 	if (mci->set_sdram_scrub_rate || mci->get_sdram_scrub_rate)
> >
> > Adjusting the permissions is simply the last missing piece to this patch
> > to make the interface to userspace 100% coherent.
> >
> > --
> > From: Mauro Carvalho Chehab <[email-masked]>
> > Date: Tue, 19 Feb 2013 09:16:10 -0300
> > Subject: [PATCH] EDAC: only create sdram_scrub_rate where supported
> >
> > Currently, sdram_scrub_rate sysfs node is created even if the device
> > doesn't support get/set the scub rate. Change the logic to only
> > create this device node when the operation is supported.
> >
> > If only read or only write is supported, it will keep returning -ENODEV
> > just like before.
> >
> > Reported-by: Felipe Balbi <[email-masked]>
> > Signed-off-by: Mauro Carvalho Chehab <[email-masked]>
> > ---
> >   drivers/edac/edac_mc_sysfs.c | 21 +++++++++++++++++++--
> >   1 file changed, 19 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/edac/edac_mc_sysfs.c b/drivers/edac/edac_mc_sysfs.c
> > index 0ca1ca71157f..5a788e60ff67 100644
> > --- a/drivers/edac/edac_mc_sysfs.c
> > +++ b/drivers/edac/edac_mc_sysfs.c
> > @@ -7,7 +7,7 @@
> >    *
> >    * Written Doug Thompson <[email-masked]> www.softwarebitmaker.com
> >    *
> > - * (c) 2012 - Mauro Carvalho Chehab <[email-masked]>
> > + * (c) 2012-2013 - Mauro Carvalho Chehab <[email-masked]>
> >    *	The entire API were re-written, and ported to use struct device
> >    *
> >    */
> > @@ -878,7 +878,6 @@ static struct attribute *mci_attrs[] = {
> >   	&dev_attr_ce_noinfo_count.attr,
> >   	&dev_attr_ue_count.attr,
> >   	&dev_attr_ce_count.attr,
> > -	&dev_attr_sdram_scrub_rate.attr,
> >   	&dev_attr_max_location.attr,
> >   	NULL
> >   };
> > @@ -1012,6 +1011,23 @@ int edac_create_sysfs_mci_device(struct mem_ctl_info *mci)
> >   		return err;
> >   	}
> >
> > +	if (mci->set_sdram_scrub_rate || mci->get_sdram_scrub_rate) {
> > +		umode_t mode = 0;
> > +
> > +		if (mci->get_sdram_scrub_rate)
> > +			mode = S_IRUGO;
> > +
> > +		if (mci->set_sdram_scrub_rate)
> > +			mode |= S_IWUSR;
> > +
> > +		dev_attr_sdram_scrub_rate.attr.mode = mode;
> > +
> > +		err = device_create_file(&mci->dev, &dev_attr_sdram_scrub_rate);
> > +		if (err) {
> > +			edac_dbg(1, "failure: create sdram_scrub_rate\n");
> > +			goto fail2;
> > +		}
> > +	}
> >   	/*
> >   	 * Create the dimm/rank devices
> >   	 */
> > @@ -1056,6 +1072,7 @@ fail:
> >   			continue;
> >   		device_unregister(&dimm->dev);
> >   	}
> > +fail2:
> >   	device_unregister(&mci->dev);
> >   	bus_unregister(&mci->bus);
> >   	kfree(mci->bus.name);
> >
> And of course you all know that creating sysfs attributes via 
> 'device_create_file' opens all sort of funny race conditions, 
> especially when checking these attributes from udev ...

Yes, we know that, but this subsystem has already lots of other
attributes created via device_create_file(). It used to be a
lot worse than that, as, on a very recent past (before Kernel 3.5),
those attributes were created via sysfs_create_file().

There's not much that can be done to avoid it on this subsystem.

> 
> Please consider adding a default attribute which return '-EINVAL' or 
> somesuch when the function pointers are not set.
> But _not_ adding it via device_create_file(). That's evil.

This thread started with Felipe's complain about it returning -ENOSYS ;)
when this feature is not supported.

Regards,
Mauro