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

[Matt Mackall <mpm@selenic.com>]

On Thu, 2009-11-26 at 00:25 +0000, Ian Molton wrote:
> 	This patch implements a new method by which hw_random hardware drivers
> can pass data to the core more efficiently, using a shared buffer.
> 
> The old methods have been retained as a compatability layer until all the
> drivers have been updated.
> 
> Signed-off-by: Ian Molton <ian.molton@collabora.co.uk>
> ---
>  drivers/char/hw_random/core.c |  120 ++++++++++++++++++++++++++---------------
>  include/linux/hw_random.h     |    9 ++-
>  2 files changed, 82 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 1573aeb..e179afd 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -47,12 +47,14 @@
>  #define RNG_MODULE_NAME		"hw_random"
>  #define PFX			RNG_MODULE_NAME ": "
>  #define RNG_MISCDEV_MINOR	183 /* official */
> +#define RNG_BUFFSIZE		64
>  
> 
>  static struct hwrng *current_rng;
>  static LIST_HEAD(rng_list);
>  static DEFINE_MUTEX(rng_mutex);
> -
> +static u8 *rng_buffer;

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.

> +		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.

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