linux-kernel - Re: [PATCH 1/2] hw_random: core updates to allow more efficient drivers

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Message-Id: <200911282035.26847.rusty@rustcorp.com.au>
Date:	Sat, 28 Nov 2009 20:35:26 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Ian Molton <ian.molton@...labora.co.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] hw_random: core updates to allow more efficient drivers

On Thu, 26 Nov 2009 11:33:23 am Matt Mackall wrote:
> On Thu, 2009-11-26 at 00:25 +0000, Ian Molton wrote:
> >  #define PFX			RNG_MODULE_NAME ": "
> >  #define RNG_MISCDEV_MINOR	183 /* official */
> > +#define RNG_BUFFSIZE		64
> 
> How about just:
> 
> static u8 rng_buffer[RNG_BUFFSIZE] __cacheline_aligned;
> 
> And lose all the kmalloc and kfree code? The memory use will be smaller,
> even when the buffer isn't needed.

And might as well just #defube RNG_BUFFSIZE SMP_CACHE_BYTES (or use
SMP_CACHE_BYTES here and sizeof() elsewhere).

> > +		if (!data_avail) {
> > +			bytes_read = rng_get_data(current_rng, rng_buffer,
> > +				RNG_BUFFSIZE, !(filp->f_flags & O_NONBLOCK));
> 
> No need to pass rng_buffer to the helper as there's only one with global
> scope.

Naah, I like the separation; it matches the rest of the kernel and means we
can get funky with buffer management in 10 years time when we rewrite this
again.

Thanks,
Rusty.
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