netdev - Re: [PATCH bpf-next] bpf: remove useless variable

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Date:   Fri, 14 Dec 2018 17:03:02 +0000
From:   Martin Lau <kafai@...com>
To:     Andrea Claudi <aclaudi@...hat.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "sbrivio@...hat.com" <sbrivio@...hat.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH bpf-next] bpf: remove useless variable

On Thu, Dec 13, 2018 at 10:44:57PM +0100, Andrea Claudi wrote:
> bytes is initialized to end - start at the beginning of this function,
> and is never changed. Remove it making the code a bit more readable.
> 
> Suggested-by: Stefano Brivio <sbrivio@...hat.com>
> Signed-off-by: Andrea Claudi <aclaudi@...hat.com>
The change looks correct.
I found the original code more intuitive to read though.
Daniel/John, thoughts?

> ---
>  net/core/filter.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index aa274679965d..f31a0de14216 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2170,8 +2170,8 @@ static const struct bpf_func_proto bpf_msg_cork_bytes_proto = {
>  BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
>  	   u32, end, u64, flags)
>  {
> -	u32 len = 0, offset = 0, copy = 0, poffset = 0, bytes = end - start;
>  	u32 first_sge, last_sge, i, shift, bytes_sg_total;
> +	u32 len = 0, offset = 0, copy = 0, poffset = 0;
>  	struct scatterlist *sge;
>  	u8 *raw, *to, *from;
>  	struct page *page;
> @@ -2196,7 +2196,7 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
>  	/* The start may point into the sg element so we need to also
>  	 * account for the headroom.
>  	 */
> -	bytes_sg_total = start - offset + bytes;
> +	bytes_sg_total = end - offset;
>  	if (!msg->sg.copy[i] && bytes_sg_total <= len)
>  		goto out;
>  
> @@ -2279,7 +2279,7 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
>  		      msg->sg.end - shift;
>  out:
>  	msg->data = sg_virt(&msg->sg.data[first_sge]) + start - offset;
> -	msg->data_end = msg->data + bytes;
> +	msg->data_end = msg->data + end - start;
>  	return 0;
>  }
>  
> -- 
> 2.19.2
>