netdev - Re: [RFC PATCH 00/10] Device Memory TCP

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Date: Wed, 19 Jul 2023 13:36:59 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Mina Almasry <almasrymina@...gle.com>
Cc: David Ahern <dsahern@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>, Andy
 Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org, netdev@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org, Sumit Semwal
 <sumit.semwal@...aro.org>, Christian König
 <christian.koenig@....com>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Jesper
 Dangaard Brouer <hawk@...nel.org>, Ilias Apalodimas
 <ilias.apalodimas@...aro.org>, Arnd Bergmann <arnd@...db.de>, Willem de
 Bruijn <willemdebruijn.kernel@...il.com>, Shuah Khan <shuah@...nel.org>
Subject: Re: [RFC PATCH 00/10] Device Memory TCP

On Wed, 19 Jul 2023 08:10:58 -0700 Mina Almasry wrote:
> From Jakub and David's comments it sounds (if I understood correctly),
> you'd like to tie the dma-buf bind/unbind functions to the lifetime of
> a netlink socket, rather than a struct file like I was thinking. That
> does sound cleaner, but I'm not sure how. Can you link me to any
> existing code examples? Or rough pointers to any existing code?

I don't have a strong preference whether the lifetime is bound to 
the socket or not. My main point was that if we're binding lifetimes
to processes, it should be done via netlink sockets, not special-
-purpose FDs. Inevitably more commands and info will be needed and
we'll start reinventing the uAPI wheel which is Netlink.

Currently adding state to netlink sockets is a bit raw. You can create
an Xarray which stores the per socket state using socket's portid
(genl_info->snd_portid) and use netlink_register_notifier() to get
notifications when sockets are closed.