netdev - Re: [PATCH net-next 5/8] net: bpf: add neq jump operations to bpf machine

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Date:	Mon, 31 Dec 2012 19:25:49 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 5/8] net: bpf: add neq jump operations to bpf
 machine

On Mon, 2012-12-31 at 14:59 +0100, Daniel Borkmann wrote:
> This patch adds jump operations for neq (!=) that compare A
> with K resp. X in order to facilitate filter programming with
> conditional jumps, since currently only eq (==) is present in
> the BPF machine. For user-space filter programming / compilers,
> it might be good to also have this complementary operation.
> They don't need to be as ancillary, since they fit into the
> instruction encoding directly. Follow-up BPF JIT patches are
> welcomed.
> 
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> ---
>  include/linux/filter.h      |  2 ++
>  include/uapi/linux/filter.h |  1 +
>  net/core/filter.c           | 14 ++++++++++++++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 36630bc..256c01f 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -105,6 +105,8 @@ enum {
>  	BPF_S_JMP_JA,
>  	BPF_S_JMP_JEQ_K,
>  	BPF_S_JMP_JEQ_X,
> +	BPF_S_JMP_JNEQ_K,
> +	BPF_S_JMP_JNEQ_X,
>  	BPF_S_JMP_JGE_K,
>  	BPF_S_JMP_JGE_X,
>  	BPF_S_JMP_JGT_K,
> diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
> index 3ebcc2e..d909a6f 100644
> --- a/include/uapi/linux/filter.h
> +++ b/include/uapi/linux/filter.h
> @@ -80,6 +80,7 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
>  #define         BPF_JSET        0x40
>  #define         BPF_JLT         0x50
>  #define         BPF_JLE         0x60
> +#define         BPF_JNEQ        0x70
>  
>  #define BPF_SRC(code)   ((code) & 0x08)
>  #define         BPF_K           0x00
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 2122eba..b360fb3 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -228,6 +228,9 @@ unsigned int sk_run_filter(const struct sk_buff *skb,
>  		case BPF_S_JMP_JEQ_K:
>  			fentry += (A == K) ? fentry->jt : fentry->jf;
>  			continue;
> +		case BPF_S_JMP_JNEQ_K:
> +			fentry += (A != K) ? fentry->jt : fentry->jf;
> +			continue;
>  		case BPF_S_JMP_JSET_K:
>  			fentry += (A & K) ? fentry->jt : fentry->jf;
>  			continue;

This makes no sense at all to me, it seems kernel bloat.

The JNE instruction already exists.

You only have to take the JEQ (jt,jf) and swap the jt/jf targets.



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