linux-kernel - Re: [PATCH] tpm: Move Linux RNG connection to hwrng

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Message-ID: <20171025193707.GA998@obsidianresearch.com>
Date:   Wed, 25 Oct 2017 13:37:07 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        linux-integrity@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        "open list:KEYS-TRUSTED" <keyrings@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        James Morris <james.l.morris@...cle.com>,
        Matt Mackall <mpm@...enic.com>,
        David Safford <safford@...ibm.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH] tpm: Move Linux RNG connection to hwrng

On Wed, Oct 25, 2017 at 08:58:17PM +0200, Jarkko Sakkinen wrote:
> On Wed, Oct 25, 2017 at 08:15:09PM +0530, PrasannaKumar Muralidharan wrote:
> > > +       if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
> > > +               return 0;
> > 
> > Can #ifndef CONFIG_HW_RANDOM_TPM be used instead? That way an if
> > condition can be avoided.
> 
> Nope. There is no reason to avoid the if-condition. Compiler will take
> care of it. IS_ENABLED() macro is available just for the purpose Jason
> is using it.
> 
> > > +       char tpm_hwrng_name[64];
> > > +       struct hwrng tpm_hwrng;
> > > +
> > 
> > Can this also be put inside the #ifdef?
> 
> Yes. It should be inside #ifdef.

Then we need #idefs in the .c code, IS_ENABLED is not enough :\ I
don't think the few bytes matters enough to bother.

Jason