linux-kernel - Re: [PATCH v2] tpm: use struct tpm_chip for tpm_chip_find

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Date:   Wed, 25 Oct 2017 14:17:44 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        David Safford <safford@...ibm.com>,
        David Howells <dhowells@...hat.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:TPM DEVICE DRIVER" 
        <tpmdd-devel@...ts.sourceforge.net>,
        "open list:INTEGRITY MEASUREMENT ARCHITECTURE (IMA)" 
        <linux-ima-devel@...ts.sourceforge.net>,
        "open list:INTEGRITY MEASUREMENT ARCHITECTURE (IMA)" 
        <linux-ima-user@...ts.sourceforge.net>,
        "open list:KEYS-TRUSTED" <keyrings@...r.kernel.org>
Subject: Re: [PATCH v2] tpm: use struct tpm_chip for tpm_chip_find_get()

On Wed, Oct 25, 2017 at 10:07:46PM +0200, Jarkko Sakkinen wrote:

> The id has a nice feature that it is unique for one boot cycle you can
> even try to get a chip that has been deleted. It has the most stable
> properties in the long run.

It isn't unique, we can re-use ids them via idr_alloc(). We should
never use index inside the kernel.

> Address is a reusable identifier in one boot cycle.

It is invalid to pass in a chip for which the caller does not hold a
kref, so address is the safest argument.

Jason