netdev - Re: [PATCH net-next] filter: add MOD operation

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Date:	Sat, 8 Sep 2012 20:31:13 +0000
From:	George Bakos <gbakos@...inista.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Andi Kleen <ak@...ux.intel.com>, Jay Schulist <jschlst@...ba.org>,
	netdev@...r.kernel.org, tcpdump-workers@...ts.tcpdump.org
Subject: Re: [PATCH net-next] filter: add MOD operation

Here's a patch to libpcap-1.3 to test against. I still need to
include changes to man pages.

g

On Sat, 08 Sep 2012 10:03:35 +0200
Eric Dumazet <eric.dumazet@...il.com> wrote:

> From: Eric Dumazet <edumazet@...gle.com>
> 
> On Fri, 2012-09-07 at 20:03 -0700, Andi Kleen wrote:
> > On Fri, Sep 07, 2012 at 07:49:10AM +0000, George Bakos wrote:
> > > Gents,
> > > Any fundamental reason why the following (, etc.) shouldn't be
> > > included in net/core/filter.c?
> > > 
> > >                 case BPF_S_ALU_MOD_X:
> > >                         if (X == 0)
> > >                                 return 0;
> > >                         A %= X;
> > >                         continue;
> > 
> > Copying netdev.
> > 
> > In principle no reason against it, but you may need to update
> > the various BPF JITs too that Linux now has too.
> 
> Hi Andi, thanks for the forward
> 
> In recent commit ffe06c17afbb was added ALU_XOR_X,
> so we could add ALU_MOD_X as well.
> 
> ALU_MOD_K is a bit more complex as we cant use an ancillary, and must
> instead use a new BPF_OP code :
> 
> /* alu/jmp fields */
> #define BPF_OP(code)    ((code) & 0xf0)
> #define         BPF_ADD         0x00
> #define         BPF_SUB         0x10
> #define         BPF_MUL         0x20
> #define         BPF_DIV         0x30
> #define         BPF_OR          0x40
> #define         BPF_AND         0x50
> #define         BPF_LSH         0x60
> #define         BPF_RSH         0x70
> #define         BPF_NEG         0x80
> 
> So I guess we could use
> 
> #define         BPF_MOD         0x90
> 
> About the various arches JIT, there is no hurry :
> We can update them later.
> 
> At JIT 'compile' time, if we find a not yet handled instruction, we fall
> back to the net/core/filter.c interpreter.
> 
> If the following patch is accepted, I'll do the x86 part as a followup.
> 
> Thanks !
> 
> [PATCH net-next] filter: add MOD operation
> 
> Add a new ALU opcode, to compute a modulus.
> 
> Commit ffe06c17afbbb used an ancillary to implement XOR_X,
> but here we reserve one of the available ALU opcode to implement both
> MOD_X and MOD_K
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Suggested-by: George Bakos <gbakos@...inista.org>
> Cc: Jay Schulist <jschlst@...ba.org>
> Cc: Jiri Pirko <jpirko@...hat.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> ---
>  include/linux/filter.h |    4 ++++
>  net/core/filter.c      |   15 +++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 82b0135..3cf5fd5 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -74,6 +74,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
>  #define         BPF_LSH         0x60
>  #define         BPF_RSH         0x70
>  #define         BPF_NEG         0x80
> +#define		BPF_MOD		0x90
> +
>  #define         BPF_JA          0x00
>  #define         BPF_JEQ         0x10
>  #define         BPF_JGT         0x20
> @@ -196,6 +198,8 @@ enum {
>  	BPF_S_ALU_MUL_K,
>  	BPF_S_ALU_MUL_X,
>  	BPF_S_ALU_DIV_X,
> +	BPF_S_ALU_MOD_K,
> +	BPF_S_ALU_MOD_X,
>  	BPF_S_ALU_AND_K,
>  	BPF_S_ALU_AND_X,
>  	BPF_S_ALU_OR_K,
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 907efd2..fbe3a8d 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -167,6 +167,14 @@ unsigned int sk_run_filter(const struct sk_buff *skb,
>  		case BPF_S_ALU_DIV_K:
>  			A = reciprocal_divide(A, K);
>  			continue;
> +		case BPF_S_ALU_MOD_X:
> +			if (X == 0)
> +				return 0;
> +			A %= X;
> +			continue;
> +		case BPF_S_ALU_MOD_K:
> +			A %= K;
> +			continue;
>  		case BPF_S_ALU_AND_X:
>  			A &= X;
>  			continue;
> @@ -469,6 +477,8 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
>  		[BPF_ALU|BPF_MUL|BPF_K]  = BPF_S_ALU_MUL_K,
>  		[BPF_ALU|BPF_MUL|BPF_X]  = BPF_S_ALU_MUL_X,
>  		[BPF_ALU|BPF_DIV|BPF_X]  = BPF_S_ALU_DIV_X,
> +		[BPF_ALU|BPF_MOD|BPF_K]  = BPF_S_ALU_MOD_K,
> +		[BPF_ALU|BPF_MOD|BPF_X]  = BPF_S_ALU_MOD_X,
>  		[BPF_ALU|BPF_AND|BPF_K]  = BPF_S_ALU_AND_K,
>  		[BPF_ALU|BPF_AND|BPF_X]  = BPF_S_ALU_AND_X,
>  		[BPF_ALU|BPF_OR|BPF_K]   = BPF_S_ALU_OR_K,
> @@ -531,6 +541,11 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
>  				return -EINVAL;
>  			ftest->k = reciprocal_value(ftest->k);
>  			break;
> +		case BPF_S_ALU_MOD_K:
> +			/* check for division by zero */
> +			if (ftest->k == 0)
> +				return -EINVAL;
> +			break;
>  		case BPF_S_LD_MEM:
>  		case BPF_S_LDX_MEM:
>  		case BPF_S_ST:
> 
> 


-- 

View attachment "libpcap-1.3.0-with-modulus.patch" of type "text/x-patch" (4453 bytes)