Re: [PATCH v5 08/14] platform/x86: dell-smbios: Add a sysfs interface for SMBIOS tokens

[Greg KH]

On Sat, Oct 07, 2017 at 11:56:04AM +0000, Mario.Limonciello@xxxxxxxx wrote:
> > -----Original Message-----
> > From: Greg KH [mailto:greg@xxxxxxxxx]
> > Sent: Saturday, October 7, 2017 1:54 AM
> > To: Limonciello, Mario <Mario_Limonciello@xxxxxxxx>
> > Cc: dvhart@xxxxxxxxxxxxx; Andy Shevchenko <andy.shevchenko@xxxxxxxxx>;
> > LKML <linux-kernel@xxxxxxxxxxxxxxx>; platform-driver-x86@xxxxxxxxxxxxxxx;
> > Andy Lutomirski <luto@xxxxxxxxxx>; quasisec@xxxxxxxxxx;
> > pali.rohar@xxxxxxxxx; rjw@xxxxxxxxxxxxx; mjg59@xxxxxxxxxx; hch@xxxxxx
> > Subject: Re: [PATCH v5 08/14] platform/x86: dell-smbios: Add a sysfs interface for
> > SMBIOS tokens
> > 
> > On Fri, Oct 06, 2017 at 11:59:52PM -0500, Mario Limonciello wrote:
> > > Currently userspace tools can access system tokens via the dcdbas
> > > kernel module and a SMI call that will cause the platform to execute
> > > SMM code.
> > >
> > > With a goal in mind of deprecating the dcdbas kernel module a different
> > > method for accessing these tokens from userspace needs to be created.
> > >
> > > This is intentionally marked to only be readable as root as it can
> > > contain sensitive information about the platform's configuration.
> > >
> > > MAINTAINERS was missing for this driver.  Add myself and Pali to
> > > maintainers list for it.
> > >
> > > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxxx>
> > > ---
> > >  .../ABI/testing/sysfs-platform-dell-smbios         | 16 ++++++
> > >  MAINTAINERS                                        |  7 +++
> > >  drivers/platform/x86/dell-smbios.c                 | 64 ++++++++++++++++++++++
> > >  3 files changed, 87 insertions(+)
> > >  create mode 100644 Documentation/ABI/testing/sysfs-platform-dell-smbios
> > >
> > > diff --git a/Documentation/ABI/testing/sysfs-platform-dell-smbios
> > b/Documentation/ABI/testing/sysfs-platform-dell-smbios
> > > new file mode 100644
> > > index 000000000000..d97f4bd5bd91
> > > --- /dev/null
> > > +++ b/Documentation/ABI/testing/sysfs-platform-dell-smbios
> > > @@ -0,0 +1,16 @@
> > > +What:		/sys/devices/platform/<platform>/tokens
> > > +Date:		November 2017
> > > +KernelVersion:	4.15
> > > +Contact:	"Mario Limonciello" <mario.limonciello@xxxxxxxx>
> > > +Description:
> > > +		A read-only description of Dell platform tokens
> > > +		available on the machine.
> > > +
> > > +		The tokens will be displayed in the following
> > > +		machine readable format with each token on a
> > > +		new line:
> > > +
> > > +		ID	Location	value
> > > +
> > > +		For example token:
> > > +		5	5	3
> > 
> > That's more than "one value per file" which is what sysfs requires, so
> > this isn't acceptable, sorry.
> 
> What's more acceptable to you to relay this information?  
> Binary sysfs attribute and export the structure format in a uapi?

binary sysfs apis are for passing "raw" data to/from firmware/hardware
to userspace, without the  kernel knowing anything about the structure
or format of the data.  Putting the format in a structure in a uapi
header kind of defeats that purpose :)

> or a collection of sysfs files?
> Eg:
> tokens/$x/id
> tokens/$x/location
> tokens/$s/value
> 
> I'm guessing the latter is the better way to go.

Good guess :)

thanks,

greg k-h