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Re: [PATCH 2/2] audit: shrink audit_krule by using smaller bitfields



On Tuesday, December 23, 2014 01:20:15 PM Richard Guy Briggs wrote:
> Replace five 32-bit fields with one.  Move a nearby 32-bit field to enable
> 64-bit alignment.

Are there performance impacts from handling bit fields? The syscall audit rules 
affect each syscall of each program running. Also, setting bitfields so small 
kind of boxes in any future capability enhancements.

-Steve

> Signed-off-by: Richard Guy Briggs <rgb redhat com>
> ---
>  include/linux/audit.h |   13 +++++++------
>  1 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index b481779..bd06f92 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -46,13 +46,14 @@ struct audit_tree;
>  struct sk_buff;
> 
>  struct audit_krule {
> -	u32			pflags;
> -	u32			flags;
> -	u32			listnr;
> -	u32			action;
> -	u32			mask[AUDIT_BITMASK_SIZE];
> +	u32			listnr:4,
> +				flags:5,
> +				action:2,
> +				pflags:1,
> +				field_count:7,
> +				reserved:13;
>  	u32			buflen; /* for data alloc on list rules */
> -	u32			field_count;
> +	u32			mask[AUDIT_BITMASK_SIZE];
>  	char			*filterkey; /* ties events to rules */
>  	struct audit_field	*fields;
>  	struct audit_field	*arch_f; /* quick access to arch field */


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