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

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Message-ID: <20260126194359.461f908b@kernel.org>
Date: Mon, 26 Jan 2026 19:43:59 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Bobby Eshleman <bobbyeshleman@...il.com>
Cc: Stanislav Fomichev <stfomichev@...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 Mon, 26 Jan 2026 19:06:49 -0800 Bobby Eshleman wrote:
> > > Then, if the dmabuf count encoding space is exhausted, the socket would
> > > have to wait until the user returns all of the tokens from one of the
> > > dmabufs and frees the ID (or err out is another option).
> > > 
> > > This wouldn't change adding a field to the socket, we'd have to add one
> > > or two more for allocating the dmabuf ID and fetching the dmabuf with
> > > it. But it does fix the single binding thing.  
> > 
> > I think the bigger problem (than space exhaustion) is that we'd also
> > have some understanding of permissions. If an application guesses 
> > the binding ID of another app it can mess up its buffers. ENOBUENO..  
> 
> I was thinking it would be per-socket, effectively:
> 
> sk->sk_devmem_info.bindings[binding_id_from_token(token)]
> 
> So sockets could only access those that they have already recv'd on.

Ah, missed that the array would be per socket. I guess it'd have to be
reusing the token xarray otherwise we're taking up even more space in
the socket struct? Dunno.