From: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Subject: Re: [tpmdd-devel] [PATCH] tpm: remove chip_num parameter from
 in-kernel API
Date: Tue, 24 Oct 2017 23:26:52 +0530
Message-ID: <CANc+2y523PgF_-ynp2xuor_2RUGLFhnK14F-Wf5i5hwRDmk_Fw@mail.gmail.com>
References: <20171023123817.18559-1-jarkko.sakkinen@linux.intel.com>
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Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Stefan Berger <stefanb@linux.vnet.ibm.com>,
        linux-integrity@vger.kernel.org,
        David Howells <dhowells@redhat.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "open list:INTEGRITY MEASUREMENT ARCHITECTURE IMA"
        <linux-ima-user@lists.sourceforge.net>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        open list <linux-kernel@vger.kernel.org>,
        linux-security-module@vger.kernel.org,
        "moderated list:TPM DEVICE DRIVER"
        <tpmdd-devel@lists.sourceforge.net>,
        "open list:KEYS-TRUSTED" <keyrings@vger.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
        <linux-crypto@vger.kernel.org>,
        James Morris <james.l.morris@oracle.com>,
        Matt Mackall <mpm@selenic.com>,
        "open list:INTEGRITY MEASUREMENT ARCHITECTURE IMA"
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
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Hi Jason,

On 24 October 2017 at 23:16, Jason Gunthorpe
<jgunthorpe@obsidianresearch.com> wrote:
> On Tue, Oct 24, 2017 at 09:44:30PM +0530, PrasannaKumar Muralidharan wrote:
>
>> I am wondering why it is wrong. Isn't the chip id valid till it is
>> unregistered? If so the rfc is correct. Please explain, may be I am
>> missing something.
>
> The lifetime is a bit complicated, but the general rule in the kernel
> for things like this it to use pointers, not ids, and certainly not
> string ids.
>
> For that patch it could just use container_of to get the chip..
>
> Jason

hwrng requires a unique name for every device. In that patch
"tpm-rng-<chip_num>" is used. chip_num is nothing but dev->dev_num.
This way more than 1 tpm chip can be used as rng provider.
tpm_get_random uses chip_num as its parameter. This is why
chip->dev_num was used.

Is that reasoning correct?

Please feel free to correct me if I am wrong.

Thanks,
PrasannaKumar