On Wed, Nov 23, 2022 at 6:33 AM Toke Høiland-Jørgensen [off-list ref] wrote:

Stanislav Fomichev [off-list ref] writes:

quoted

No functional changes. Boilerplate to allow stuffing more data after xdp_buff.

Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: David Ahern <redacted>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <redacted>
Cc: Anatoly Burakov <redacted>
Cc: Alexander Lobakin <redacted>
Cc: Magnus Karlsson <redacted>
Cc: Maryam Tahhan <redacted>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Signed-off-by: Stanislav Fomichev <redacted>
---
 drivers/net/ethernet/mellanox/mlx4/en_rx.c | 26 +++++++++++++---------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index 8f762fc170b3..467356633172 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -661,17 +661,21 @@ static int check_csum(struct mlx4_cqe *cqe, struct sk_buff *skb, void *va,
 #define MLX4_CQE_STATUS_IP_ANY (MLX4_CQE_STATUS_IPV4)
 #endif

+struct mlx4_xdp_buff {
+     struct xdp_buff xdp;
+};

This embedding trick works for drivers that put xdp_buff on the stack,
but mlx5 supports XSK zerocopy, which uses the xsk_buff_pool for
allocating them. This makes it a bit awkward to do the same thing there;
and since it's probably going to be fairly common to do something like
this, how about we just add a 'void *drv_priv' pointer to struct
xdp_buff that the drivers can use? The xdp_buff already takes up a full
cache line anyway, so any data stuffed after it will spill over to a new
one; so I don't think there's much difference performance-wise.

I guess the alternative is to extend xsk_buff_pool with some new
argument for xdp_buff tailroom? (so it can kmalloc(sizeof(xdp_buff) +
xdp_buff_tailroom))
But it seems messy because there is no way of knowing what the target
device's tailroom is, so it has to be a user setting :-/
I've started with a priv pointer in xdp_buff initially, it seems fine
to go back. I'll probably convert veth/mlx4 to the same mode as well
to avoid having different approaches in different places..

I'll send my patch to add support to mlx5 (using the drv_priv pointer
approach) separately.

Saw them, thanks! Will include them in v3+.