linux-kernel - Re: [PATCH 2/3] arch/mips/net/bpf

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Date:	Thu, 17 Jul 2014 14:52:46 +0100
From:	Markos Chandras <Markos.Chandras@...tec.com>
To:	Andrey Utkin <andrey.krieger.utkin@...il.com>,
	<linux-kernel@...r.kernel.org>, <kernel-janitors@...r.kernel.org>,
	<linux-mips@...ux-mips.org>
CC:	<dborkman@...hat.com>, <ralf@...ux-mips.org>
Subject: Re: [PATCH 2/3] arch/mips/net/bpf_jit.c: fix failure check

On 07/17/2014 02:27 PM, Andrey Utkin wrote:
> static int pkt_type_offset(void) returned -1 in case of failure, and
> actual (positive) offset value in case of success. In the only instance
> of its usage, the result was saved to local "unsigned int off" variable,
>    which is used in a lot of places in the same (large) function, so
>    changing its type could cause many warnings.
> There was no signed int variable which could be just used for this case.
> There are two possibilities to resolve that: to declare temporary signed
> int variable to get the return value from pkt_type_offset(), or to
> separate return status from returned offset value. The latter approach
> was chosen, however, I am not sure which would be practically optimal.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=80371
> Reported-by: David Binderman <dcb314@...mail.com>
> Signed-off-by: Andrey Utkin <andrey.krieger.utkin@...il.com>
> ---
>  arch/mips/net/bpf_jit.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
> index b87390a..47f65d5 100644
> --- a/arch/mips/net/bpf_jit.c
> +++ b/arch/mips/net/bpf_jit.c
> @@ -770,7 +770,7 @@ static u64 jit_get_skb_w(struct sk_buff *skb, unsigned offset)
>  #else
>  #define PKT_TYPE_MAX	7
>  #endif
> -static int pkt_type_offset(void)
> +static int pkt_type_offset(unsigned int *off_arg)
>  {
>  	struct sk_buff skb_probe = {
>  		.pkt_type = ~0,
> @@ -779,8 +779,10 @@ static int pkt_type_offset(void)
>  	unsigned int off;
>  
>  	for (off = 0; off < sizeof(struct sk_buff); off++) {
> -		if (ct[off] == PKT_TYPE_MAX)
> -			return off;
> +		if (ct[off] == PKT_TYPE_MAX) {
> +			*off_arg = off;
> +			return 0;
> +		}
>  	}
>  	pr_err_once("Please fix pkt_type_offset(), as pkt_type couldn't be found\n");
>  	return -1;
> @@ -1332,9 +1334,7 @@ jmp_cmp:
>  		case BPF_ANC | SKF_AD_PKTTYPE:
>  			ctx->flags |= SEEN_SKB;
>  
> -			off = pkt_type_offset();
> -
> -			if (off < 0)
> +			if (pkt_type_offset(&off))
>  				return -1;
>  			emit_load_byte(r_tmp, r_skb, off, ctx);
>  			/* Keep only the last 3 bits */
> 
Hi,

Thanks for the patch. I would personally prefer to use a new signed int
variable, but I am fine either way.

-- 
markos
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