Re: [tpmdd-devel] [PATCH] tpm: remove chip_num parameter from in-kernel API

From: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Stefan Berger <stefanb@linux.vnet.ibm.com>,
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	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>,
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	linux-security-module@vger.kernel.org,
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	<tpmdd-devel@lists.sourceforge.net>,
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	James Morris <james.l.morris@oracle.com>,
	Matt Mackall <mpm@selenic.com>open list:INTEGRITY MEASUREMENT
	ARCHITECTURE IMA
Subject: Re: [tpmdd-devel] [PATCH] tpm: remove chip_num parameter from in-kernel API
Date: Tue, 24 Oct 2017 23:26:52 +0530	[thread overview]
Message-ID: <CANc+2y523PgF_-ynp2xuor_2RUGLFhnK14F-Wf5i5hwRDmk_Fw@mail.gmail.com> (raw)
In-Reply-To: <20171024174637.GB1806@obsidianresearch.com>

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