netdev - Re: [PATCH 1/2] xfrm: add SA information to the offloaded packet

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Message-ID: <Zyx/ueeoeBdq/FXj@moon.secunet.de>
Date: Thu, 7 Nov 2024 09:52:09 +0100
From: Antony Antony <antony.antony@...unet.com>
To: Feng Wang <wangfe@...gle.com>
CC: <antony.antony@...unet.com>, Leon Romanovsky <leon@...nel.org>,
	<netdev@...r.kernel.org>, <steffen.klassert@...unet.com>
Subject: Re: [PATCH 1/2] xfrm: add SA information to the offloaded packet

On Wed, Nov 06, 2024 at 16:14:36 -0800, Feng Wang wrote:
> Antony brought out an important function xfrm_lookup_with_ifid(), this
> function returns the next dst_entry.
> 
> The xfrm_lookup_with_ifid() function utilizes xfrm_sk_policy_lookup()

would the output packet, looked up using xfrm_lookup_with_ifid ,
match xfrm policy with "offload packet" set?
When lookup is in the xfrm device.

ip xfrm policy .... offload packet dev <if-name>

> to find a matching policy based on the given if_id. The if_id checking
> is handled in it.
> Once the policy is found, xfrm_resolve_and_create_bundle() determines
> the correct Security Association (SA) and associates it with the
> destination entry (dst->xfrm).

If the output packet got this far, dst is set in skb?
And when the packet reach the driver dst = skb_dst(skb);
dst->xfrm is the state?
If this is the case  why add state to skb as your patch proose?
May be I am missing something in the packet path.

> This SA information is then passed directly to the driver. Since the
> kernel has already performed the necessary if_id checks for policy,
> there's no need for the driver to duplicate this effort.

Is this how packet offload would work? My guess was in packet offload
policy look happens in the driver.