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

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Message-ID: <CAFA6WYOiBNQt0ZRyRxfsqW57z+O=aLqi3DTEAfZ7fGjf8UPB3Q@mail.gmail.com>
Date:   Fri, 26 Jun 2020 10:43:15 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Maxim Uvarov <maxim.uvarov@...aro.org>
Cc:     Jerome Forissier <jerome@...issier.org>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Arnd Bergmann <arnd@...aro.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@...ts.linaro.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        linux-integrity@...r.kernel.org, peterhuewe@....de
Subject: Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry

On Thu, 25 Jun 2020 at 18:22, Maxim Uvarov <maxim.uvarov@...aro.org> wrote:
>
> On Wed, 24 Jun 2020 at 18:44, Jerome Forissier <jerome@...issier.org> wrote:
> >
> >
> >
> > On 6/24/20 5:21 PM, James Bottomley 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@...senpartnership.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?
> >
> > Let me try to clear the confusion that I introduce myself I believe :-/
> > IMO:
> >
> > - optee_register_device(const uuid_t *device_uuid) *is* the correct
> > prototype.
> > - device_uuid is *guaranteed* to be BE because OP-TEE makes this
> > guarantee (it converts from its internal LE representation to BE when
> > enumerating the devices, but it doesn't matter to the kernel).
> > - Therefore %pUb is the correct format.
> >
> > I'm sorry for doubting the BE order initially. I am so used to OP-TEE
> > using LE internally, that I missed the fact that we have an explicit
> > conversion...
> >
> > Does this sound good?
> >
> > Thanks,
> > --
> > Jerome
>
> I think your description is correct. But I think this problem  would
> be solved outside of the current patchset.
> All places should use one single format (LE):

I guess you missed the point that uuid_t is implemented in BE format
in the kernel which is compliant as per RFC 4122.

> -  internal optee representation;
> -  device enumeration pta;
> -  this kernel driver which creates sysfs entry and sets
> uid_copy(&optee_device->id.uuid, device_uuid);
> -  matching function;
> -  drivers use UUID_INIT();

See carefully the implementation of UUID_INIT() which is in BE format.

-Sumit

>
> In that way everything will be consistent. But it will require
> changing other pieces, not just the kernel. While
> these patches add functionality to support current device enumeration
> in optee os.
> So I think this version is ok to be applied.
>
> Regards,
> Maxim.