linux-kernel - Re: [PATCH net-next v10 4/5] net: devmem: document NETDEV_A_DMABUF

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Message-ID: <20260126172646.2e5af2d4@kernel.org>
Date: Mon, 26 Jan 2026 17:26:46 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: Bobby Eshleman <bobbyeshleman@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Kuniyuki Iwashima
 <kuniyu@...gle.com>, Willem de Bruijn <willemb@...gle.com>, Neal Cardwell
 <ncardwell@...gle.com>, David Ahern <dsahern@...nel.org>, Mina Almasry
 <almasrymina@...gle.com>, Arnd Bergmann <arnd@...db.de>, Jonathan Corbet
 <corbet@....net>, Andrew Lunn <andrew+netdev@...n.ch>, Shuah Khan
 <shuah@...nel.org>, Donald Hunter <donald.hunter@...il.com>, Stanislav
 Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
 asml.silence@...il.com, matttbe@...nel.org, skhawaja@...gle.com, Bobby
 Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v10 4/5] net: devmem: document
 NETDEV_A_DMABUF_AUTORELEASE netlink attribute

On Wed, 21 Jan 2026 20:07:11 -0800 Stanislav Fomichev wrote:
> On 01/21, Jakub Kicinski wrote:
> > On Wed, 21 Jan 2026 19:25:27 -0800 Bobby Eshleman wrote:  
> > > Good point. The only real use case for autorelease=on is for backwards
> > > compatibility... so I thought maybe DEVMEM_A_DMABUF_COMPAT_TOKEN
> > > or DEVMEM_A_DMABUF_COMPAT_DONTNEED would be clearer?  
> > 
> > Hm. Maybe let's return to naming once we have consensus on the uAPI.
> > 
> > Does everyone think that pushing this via TCP socket opts still makes
> > sense, even tho in practice the TCP socket is just how we find the
> > binding?  
> 
> I'm not a fan of the existing cmsg scheme, but we already have userspace
> using it, so getting more performance out of it seems like an easy win?

I don't like:
 - the fact that we have to add the binding to a socket (extra field)
   - single socket can only serve single binding, there's no technical
     reason for this really, AFAICT, just the fact that we have a single
     pointer in the sock struct
 - the 7 levels of indentation in tcp_recvmsg_dmabuf()

I understand your argument, but as is this series feels closer to a PoC
than an easy win (the easy part should imply minor changes and no
detrimental effect on code quality IMHO).