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Miller" , Paolo Abeni , sdf@fomichev.me, kernel-team@cloudflare.com, arthur@arthurfabre.com Subject: Re: [PATCH bpf-next V2 1/7] net: xdp: Add xdp_rx_meta structure In-Reply-To: (Jesper Dangaard Brouer's message of "Thu, 17 Jul 2025 16:40:47 +0200") References: <175146824674.1421237.18351246421763677468.stgit@firesoul> <175146829944.1421237.13943404585579626611.stgit@firesoul> <87v7nrdvi8.fsf@cloudflare.com> Date: Fri, 18 Jul 2025 12:33:16 +0200 Message-ID: <871pqdeqkz.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Thu, Jul 17, 2025 at 04:40 PM +02, Jesper Dangaard Brouer wrote: > On 17/07/2025 11.19, Jakub Sitnicki wrote: >> On Wed, Jul 02, 2025 at 04:58 PM +02, Jesper Dangaard Brouer wrote: >>> From: Lorenzo Bianconi >>> >>> Introduce the `xdp_rx_meta` structure to serve as a container for XDP RX >>> hardware hints within XDP packet buffers. Initially, this structure will >>> accommodate `rx_hash` and `rx_vlan` metadata. (The `rx_timestamp` hint will >>> get stored in `skb_shared_info`). >>> >>> A key design aspect is making this metadata accessible both during BPF >>> program execution (via `struct xdp_buff`) and later if an `struct >>> xdp_frame` is materialized (e.g., for XDP_REDIRECT). >>> To achieve this: >>> - The `struct xdp_frame` embeds an `xdp_rx_meta` field directly for >>> storage. >>> - The `struct xdp_buff` includes an `xdp_rx_meta` pointer. This pointer >>> is initialized (in `xdp_prepare_buff`) to point to the memory location >>> within the packet buffer's headroom where the `xdp_frame`'s embedded >>> `rx_meta` field would reside. >>> >>> This setup allows BPF kfuncs, operating on `xdp_buff`, to populate the >>> metadata in the precise location where it will be found if an `xdp_frame` >>> is subsequently created. >>> >>> The availability of this metadata storage area within the buffer is >>> indicated by the `XDP_FLAGS_META_AREA` flag in `xdp_buff->flags` (and >>> propagated to `xdp_frame->flags`). This flag is only set if sufficient >>> headroom (at least `XDP_MIN_HEADROOM`, currently 192 bytes) is present. >>> Specific hints like `XDP_FLAGS_META_RX_HASH` and `XDP_FLAGS_META_RX_VLAN` >>> will then denote which types of metadata have been populated into the >>> `xdp_rx_meta` structure. >>> >>> This patch is a step for enabling the preservation and use of XDP RX >>> hints across operations like XDP_REDIRECT. >>> >>> Signed-off-by: Lorenzo Bianconi >>> Signed-off-by: Jesper Dangaard Brouer >>> --- >>> include/net/xdp.h | 57 +++++++++++++++++++++++++++++++++++------------ >>> net/core/xdp.c | 1 + >>> net/xdp/xsk_buff_pool.c | 4 ++- >>> 3 files changed, 47 insertions(+), 15 deletions(-) >>> >>> diff --git a/include/net/xdp.h b/include/net/xdp.h >>> index b40f1f96cb11..f52742a25212 100644 >>> --- a/include/net/xdp.h >>> +++ b/include/net/xdp.h >>> @@ -71,11 +71,31 @@ struct xdp_txq_info { >>> struct net_device *dev; >>> }; >>> +struct xdp_rx_meta { >>> + struct xdp_rx_meta_hash { >>> + u32 val; >>> + u32 type; /* enum xdp_rss_hash_type */ >>> + } hash; >>> + struct xdp_rx_meta_vlan { >>> + __be16 proto; >>> + u16 tci; >>> + } vlan; >>> +}; >>> + >>> +/* Storage area for HW RX metadata only available with reasonable headroom >>> + * available. Less than XDP_PACKET_HEADROOM due to Intel drivers. >>> + */ >>> +#define XDP_MIN_HEADROOM 192 >>> + >>> enum xdp_buff_flags { >>> XDP_FLAGS_HAS_FRAGS = BIT(0), /* non-linear xdp buff */ >>> XDP_FLAGS_FRAGS_PF_MEMALLOC = BIT(1), /* xdp paged memory is under >>> * pressure >>> */ >>> + XDP_FLAGS_META_AREA = BIT(2), /* storage area available */ >> Idea: Perhaps this could be called *HW*_META_AREA to differentiate from >> the existing custom metadata area: >> > > I agree, that calling it META_AREA can easily be misunderstood and confused with > metadata or data_meta. > > What do you think about renaming this to "hints" ? > E.g. XDP_FLAGS_HINTS_AREA > or XDP_FLAGS_HINTS_AVAIL > > And also renaming XDP_FLAGS_META_RX_* to > e.g XDP_FLAGS_META_RX_HASH -> XDP_FLAGS_HINT_RX_HASH > or XDP_FLAGS_HW_HINT_RX_HASH Any name that doesn't lean on the already overloaded "metadata" term is a better alternative, in my mind :-)