linux-kernel - Re: [PATCH net-next v3] xdp: Add helpers for head length, headroom, and metadata length

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Message-ID: <20250507171829.3e8f8a76@kernel.org>
Date: Wed, 7 May 2025 17:18:29 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jesper Dangaard Brouer <hawk@...nel.org>
Cc: Jon Kohler <jon@...anix.com>, Willem de Bruijn
 <willemdebruijn.kernel@...il.com>, Zvi Effron <zeffron@...tgames.com>,
 Stanislav Fomichev <stfomichev@...il.com>, Jason Wang
 <jasowang@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo
 Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Daniel
 Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>,
 Simon Horman <horms@...nel.org>, "netdev@...r.kernel.org"
 <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "bpf@...r.kernel.org"
 <bpf@...r.kernel.org>, Jacob Keller <jacob.e.keller@...el.com>
Subject: Re: [PATCH net-next v3] xdp: Add helpers for head length, headroom,
 and metadata length

On Wed, 7 May 2025 22:58:33 +0200 Jesper Dangaard Brouer wrote:
> > There is a neat hint from Lorenzo’s change in bpf.h for bpf_xdp_get_buff_len()
> > that talks about both linear and paged length. Also, xdp_buff_flags’s
> > XDP_FLAGS_HAS_FRAGS says non-linear xdp buff.
> > 
> > Taking those hints, what about:
> > xdp_linear_len() == xdp->data_end - xdp->data
> > xdp_paged_len() == sinfo->xdp_frags_size
> > xdp_get_buff_len() == xdp_linear_len() + xdp_paged_len()
> 
> I like xdp_linear_len() as it is descriptive/clear.

FWIW I don't feel strongly but my very weak preference would be 
not to merge this. I already know I'll be looking at the definitions
every time. Is it obvious to everyone in this thread whether "headroom"
includes the metadata length? It's not obvious to me. But the patch
seems quite popular so 🤷️