Re: [PATCH net-next v2 12/18] xdp: add generic xdp_build_skb_from_buff()

Maciej Fijalkowski
2024-10-17T12:34:50Z

On Tue, Oct 15, 2024 at 04:53:44PM +0200, Alexander Lobakin wrote:
> The code which builds an skb from an &xdp_buff keeps multiplying itself
> around the drivers with almost no changes. Let's try to stop that by
> adding a generic function.
> There's __xdp_build_skb_from_frame() already, so just convert it to take
> &xdp_buff instead, while making the original one a wrapper. The original
> one always took an already allocated skb, allow both variants here -- if
> no skb passed, which is expected when calling from a driver, pick one via
> napi_build_skb().
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> ---
> include/net/xdp.h | 1 +
> net/core/xdp.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 56 insertions(+)
>
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 19d2b283b845..83e3f4648caa 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -330,6 +330,7 @@ xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
> void xdp_warn(const char *msg, const char *func, const int line);
> #define XDP_WARN(msg) xdp_warn(msg, __func__, __LINE__)
>
> +struct sk_buff *xdp_build_skb_from_buff(const struct xdp_buff *xdp);
> struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp);
> struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
> struct sk_buff *skb,
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index b1b426a9b146..9dc103a09b5c 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -624,6 +624,61 @@ int xdp_alloc_skb_bulk(void **skbs, int n_skb, gfp_t gfp)
> }
> EXPORT_SYMBOL_GPL(xdp_alloc_skb_bulk);
>
> +/**
> + * xdp_build_skb_from_buff - create an skb from an &xdp_buff
> + * @xdp: &xdp_buff to convert to an skb
> + *
> + * Perform common operations to create a new skb to pass up the stack from
> + * an &xdp_buff: allocate an skb head from the NAPI percpu cache, initialize
> + * skb data pointers and offsets, set the recycle bit if the buff is PP-backed,
> + * Rx queue index, protocol and update frags info.
> + *
> + * Return: new &sk_buff on success, %NULL on error.
> + */
> +struct sk_buff *xdp_build_skb_from_buff(const struct xdp_buff *xdp)
> +{
> + const struct xdp_rxq_info *rxq = xdp->rxq;
> + const struct skb_shared_info *sinfo;
> + struct sk_buff *skb;
> + u32 nr_frags = 0;
> + int metalen;
> +
> + if (unlikely(xdp_buff_has_frags(xdp))) {
> + sinfo = xdp_get_shared_info_from_buff(xdp);
> + nr_frags = sinfo->nr_frags;
> + }
> +
> + skb = napi_build_skb(xdp->data_hard_start, xdp->frame_sz);
> + if (unlikely(!skb))
> + return NULL;
> +
> + skb_reserve(skb, xdp->data - xdp->data_hard_start);
> + __skb_put(skb, xdp->data_end - xdp->data);
> +
> + metalen = xdp->data - xdp->data_meta;
> + if (metalen > 0)
> + skb_metadata_set(skb, metalen);
> +
> + if (is_page_pool_compiled_in() && rxq->mem.type == MEM_TYPE_PAGE_POOL)
> + skb_mark_for_recycle(skb);
> +
> + skb_record_rx_queue(skb, rxq->queue_index);
> +
> + if (unlikely(nr_frags)) {
> + u32 ts;

nit: spell out truesize? ts confuse my brain with timestamp TBH

> +
> + ts = sinfo->xdp_frags_truesize ? : nr_frags * xdp->frame_sz;
> + xdp_update_skb_shared_info(skb, nr_frags,
> + sinfo->xdp_frags_size, ts,
> + xdp_buff_is_frag_pfmemalloc(xdp));
> + }
> +
> + skb->protocol = eth_type_trans(skb, rxq->dev);

could we leave this out to be set by drivers? i see in ice for example
netdev ptr is retrieved in different ways here.

> +
> + return skb;
> +}
> +EXPORT_SYMBOL_GPL(xdp_build_skb_from_buff);
> +
> struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
> struct sk_buff *skb,
> struct net_device *dev)
> --
> 2.46.2
>