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Date:   Sat, 7 Oct 2017 11:56:04 +0000
From:   <Mario.Limonciello@...l.com>
To:     <greg@...ah.com>
CC:     <dvhart@...radead.org>, <andy.shevchenko@...il.com>,
        <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <luto@...nel.org>,
        <quasisec@...gle.com>, <pali.rohar@...il.com>, <rjw@...ysocki.net>,
        <mjg59@...gle.com>, <hch@....de>
Subject: RE: [PATCH v5 08/14] platform/x86: dell-smbios: Add a sysfs interface
 for SMBIOS tokens

> -----Original Message-----
> From: Greg KH [mailto:greg@...ah.com]
> Sent: Saturday, October 7, 2017 1:54 AM
> To: Limonciello, Mario <Mario_Limonciello@...l.com>
> Cc: dvhart@...radead.org; Andy Shevchenko <andy.shevchenko@...il.com>;
> LKML <linux-kernel@...r.kernel.org>; platform-driver-x86@...r.kernel.org;
> Andy Lutomirski <luto@...nel.org>; quasisec@...gle.com;
> pali.rohar@...il.com; rjw@...ysocki.net; mjg59@...gle.com; hch@....de
> 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@...l.com>
> > ---
> >  .../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@...l.com>
> > +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?

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.

> 
> > +static ssize_t tokens_show(struct device *dev,
> > +			   struct device_attribute *attr, char *buf)
> > +{
> > +	size_t off = 0;
> > +	int to_print;
> > +	int i;
> > +
> > +	to_print = min(da_num_tokens, (int)(PAGE_SIZE - 1) / 15);
> > +	for (i = 0; i < to_print; i++) {
> > +		off += scnprintf(buf+off, PAGE_SIZE-off, "%04x\t%04x\t%04x\n",
> > +		da_tokens[i].tokenID, da_tokens[i].location,
> > +		da_tokens[i].value);
> 
> Huge hint, if you are checking for the max size of the buffer for sysfs,
> something is really wrong, and you need to redo your design.
> 
> thanks,
> 
> greg k-h

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