Subject: Re: [PATCH] net: helper function for skb_shift

From: Jakub Kicinski <[email-masked]>
Date: Thu, 16 Jun 2022 09:54:55 -0700

On Thu, 16 Jun 2022 14:26:29 +0200 Richard Gobert wrote:
> Move the len fields manipulation in the skbs to a helper function.
> There is a comment specifically requesting this. This improves the
> readability of skb_shift.
> 
> Signed-off-by: Richard Gobert <[email-masked]>
> ---
>  net/core/skbuff.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 30b523fa4ad2..8a0a941915e8 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3508,6 +3508,19 @@ static int skb_prepare_for_shift(struct sk_buff *skb)
>  }
>  
>  /**
> + * skb_shift_len - Update length fields of skbs when shifting.
> + */

1) this is not a valid kdoc
2) I don't see the point unless we have another user of this helper

> +static inline void skb_shift_len(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
> +{
> +	skb->len -= shiftlen;
> +	skb->data_len -= shiftlen;
> +	skb->truesize -= shiftlen;
> +	tgt->len += shiftlen;
> +	tgt->data_len += shiftlen;
> +	tgt->truesize += shiftlen;
> +}
> +
> +/**
>   * skb_shift - Shifts paged data partially from skb to another
>   * @tgt: buffer into which tail data gets added
>   * @skb: buffer from which the paged data comes from
> @@ -3634,14 +3647,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
>  	tgt->ip_summed = CHECKSUM_PARTIAL;
>  	skb->ip_summed = CHECKSUM_PARTIAL;
>  
> -	/* Yak, is it really working this way? Some helper please? */
> -	skb->len -= shiftlen;
> -	skb->data_len -= shiftlen;
> -	skb->truesize -= shiftlen;
> -	tgt->len += shiftlen;
> -	tgt->data_len += shiftlen;
> -	tgt->truesize += shiftlen;
> -
> +	skb_shift_len(tgt, skb, shiftlen);
>  	return shiftlen;
>  }
>