Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry

From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Sumit Garg <sumit.garg@linaro.org>
Cc: Jerome Forissier <jerome@forissier.org>,
	Maxim Uvarov <maxim.uvarov@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Arnd Bergmann <arnd@linaro.org>,
	"tee-dev @ lists . linaro . org" <tee-dev@lists.linaro.org>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	linux-integrity@vger.kernel.org, peterhuewe@gmx.de
Subject: Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry
Date: Thu, 25 Jun 2020 16:31:42 -0700	[thread overview]
Message-ID: <1593127902.13253.11.camel@HansenPartnership.com> (raw)
In-Reply-To: <CAFA6WYMF+JjrB9Cx9TdgDzMeQSvPZfMNapzD-MH4ALVoUoo1sQ@mail.gmail.com>

On Thu, 2020-06-25 at 19:54 +0530, Sumit Garg wrote:
> On Wed, 24 Jun 2020 at 20:51, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
> > 
> > On Wed, 2020-06-24 at 16:17 +0530, Sumit Garg wrote:
> > > Apologies for delay in my reply as I was busy with some other
> > > stuff.
> > > 
> > > On Fri, 19 Jun 2020 at 20:30, James Bottomley
> > > <James.Bottomley@hansenpartnership.com> wrote:
> > 
> > [...]
> > > > it's about consistency with what the kernel types mean.  When
> > > > some checker detects your using little endian operations on a
> > > > big endian structure (like in the prink for instance) they're
> > > > going to keep emailing you about it.
> > > 
> > > As mentioned above, using different terminology is meant to cause
> > > more confusion than just difference in endianness which is
> > > manageable inside TEE.
> > > 
> > > And I think it's safe to say that the kernel implements UUID in
> > > big endian format and thus uses %pUb whereas OP-TEE implements
> > > UUID in little endian format and thus uses %pUl.
> > 
> > So what I think you're saying is that if we still had uuid_be and
> > uuid_le you'd use uuid_le, because that's exactly the structure
> > described in the docs.  But because we renamed
> > 
> > uuid_be -> uuid_t
> > uuid_le -> guid_t
> > 
> > You can't use guid_t as a kernel type because it has the wrong
> > name?
> 
> Isn't the rename commit description [1] pretty clear about which is
> the true UUID type from Linux point of view?

I don't think the kernel code takes a position on eternal verity, just
on logical or arithmetic truth.  We just have to deal with both LE and
BE UUIDs so we have appropriate types for them and the LE type is now
named guid_t.  They're both equally correct to use provided the use
case matches the designed one. So does the name really matter?  If we
did

#define uuid_le_t guid_t

would you be happy? (not that the kernel cares about karmic emotional
states either ...)

James