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

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Message-ID: <aXGib0OcNdHTLyZN@mini-arch>
Date: Wed, 21 Jan 2026 20:07:11 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
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 01/21, Jakub Kicinski wrote:
> On Wed, 21 Jan 2026 19:25:27 -0800 Bobby Eshleman wrote:
> > > > That is correct, neither is true. If the two sockets share a binding the
> > > > kernel doesn't care which socket received the token or which one
> > > > returned it. No token <> socket association. There is no
> > > > queued-but-not-read race either. If any tokens are not returned, as long
> > > > as all of the binding references are eventually released and all sockets
> > > > that used the binding are closed, then all references will be accounted
> > > > for and everything cleaned up.  
> > >
> > > Naming is hard, but I wonder whether the whole feature wouldn't be
> > > better referred to as something to do with global token accounting
> > > / management? AUTORELEASE makes sense but seems like focusing on one
> > > particular side effect.  
> > 
> > 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?