linux-kernel - Re: [EXTERNAL] Re: [PATCH net 3/3] net: ti: icssg-prueth: Add AF

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Message-ID: <04ff4911-de4b-4d68-b72f-f03915baa9c9@ti.com>
Date: Thu, 6 Feb 2025 19:31:23 +0530
From: "Malladi, Meghana" <m-malladi@...com>
To: Ido Schimmel <idosch@...sch.org>
CC: <rogerq@...nel.org>, <danishanwar@...com>, <pabeni@...hat.com>,
        <kuba@...nel.org>, <edumazet@...gle.com>, <davem@...emloft.net>,
        <andrew+netdev@...n.ch>, <bpf@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, <robh@...nel.org>,
        <matthias.schiffer@...tq-group.com>, <dan.carpenter@...aro.org>,
        <rdunlap@...radead.org>, <diogo.ivo@...mens.com>,
        <schnelle@...ux.ibm.com>, <glaroque@...libre.com>,
        <john.fastabend@...il.com>, <hawk@...nel.org>, <daniel@...earbox.net>,
        <ast@...nel.org>, <srk@...com>, Vignesh Raghavendra
	<vigneshr@...com>
Subject: Re: [EXTERNAL] Re: [PATCH net 3/3] net: ti: icssg-prueth: Add AF_XDP
 support



On 2/5/2025 11:16 PM, Ido Schimmel wrote:
> On Tue, Feb 04, 2025 at 11: 25: 39PM +0530, Malladi, Meghana wrote: > On 
> 1/23/2025 10: 55 PM, Ido Schimmel wrote: > > XDP program could have 
> changed the packet length, but driver seems to be > > This will be true 
> given, emac->xdp_prog
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> On Tue, Feb 04, 2025 at 11:25:39PM +0530, Malladi, Meghana wrote:
>> On 1/23/2025 10:55 PM, Ido Schimmel wrote:
>> > XDP program could have changed the packet length, but driver seems to be
>> 
>> This will be true given, emac->xdp_prog is not NULL. What about when XDP is
>> not enabled ?
> 
> I don't understand the question. My point is that the packet doesn't
> necessarily look the same after XDP ran.
> 

emac_rx_packet() is a common function for both XDP and non-XDP use 
cases. XDP will only run when emac->xdp_prog is not NULL. I understand 
that when XDP ran, it can change the contents of the packet hence it is 
advisable to use "xdp_build_skb_from_buff(const struct xdp_buff *xdp)", 
but for cases when xdp doesn't run - the xdp struct has junk/zero value 
which cannot be converted into some valid skb. But I think I will do 
something like this:

if (emac->xdp_prog)
	xdp_build_skb_from_buff(xdp);
else
	skb = napi_build_skb(pa, PAGE_SIZE);

Hope this will address your comment.

>> 
>> > building the skb using original length read from the descriptor.
>> > Consider using xdp_build_skb_from_buff()
>> > 
>> 
>