netdev - Re: [PATCH net v3 9/9] tap: Use tun's vnet-related code

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Message-ID: <CACGkMEuPXDWHErCCdEUB7+Q0NxsAjpSH9uTvOxzuBvNeyw7_Hg@mail.gmail.com>
Date: Mon, 20 Jan 2025 08:36:32 +0800
From: Jason Wang <jasowang@...hat.com>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>, Jonathan Corbet <corbet@....net>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, kvm@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
	Yuri Benditovich <yuri.benditovich@...nix.com>, Andrew Melnychenko <andrew@...nix.com>, 
	Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com, devel@...nix.com
Subject: Re: [PATCH net v3 9/9] tap: Use tun's vnet-related code

On Fri, Jan 17, 2025 at 6:35 PM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>
> On 2025/01/17 18:23, Willem de Bruijn wrote:
> > Akihiko Odaki wrote:
> >> tun and tap implements the same vnet-related features so reuse the code.
> >>
> >> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> >> ---
> >>   drivers/net/Kconfig    |   1 +
> >>   drivers/net/Makefile   |   6 +-
> >>   drivers/net/tap.c      | 152 +++++--------------------------------------------
> >>   drivers/net/tun_vnet.c |   5 ++
> >>   4 files changed, 24 insertions(+), 140 deletions(-)
> >>
> >> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> >> index 1fd5acdc73c6..c420418473fc 100644
> >> --- a/drivers/net/Kconfig
> >> +++ b/drivers/net/Kconfig
> >> @@ -395,6 +395,7 @@ config TUN
> >>      tristate "Universal TUN/TAP device driver support"
> >>      depends on INET
> >>      select CRC32
> >> +    select TAP
> >>      help
> >>        TUN/TAP provides packet reception and transmission for user space
> >>        programs.  It can be viewed as a simple Point-to-Point or Ethernet
> >> diff --git a/drivers/net/Makefile b/drivers/net/Makefile
> >> index bb8eb3053772..2275309a97ee 100644
> >> --- a/drivers/net/Makefile
> >> +++ b/drivers/net/Makefile
> >> @@ -29,9 +29,9 @@ obj-y += mdio/
> >>   obj-y += pcs/
> >>   obj-$(CONFIG_RIONET) += rionet.o
> >>   obj-$(CONFIG_NET_TEAM) += team/
> >> -obj-$(CONFIG_TUN) += tun-drv.o
> >> -tun-drv-y := tun.o tun_vnet.o
> >> -obj-$(CONFIG_TAP) += tap.o
> >> +obj-$(CONFIG_TUN) += tun.o
> >
> > Is reversing the previous changes to tun.ko intentional?
> >
> > Perhaps the previous approach with a new CONFIG_TUN_VNET is preferable
> > over this. In particular over making TUN select TAP, a new dependency.
>
> Jason, you also commented about CONFIG_TUN_VNET for the previous
> version. Do you prefer the old approach, or the new one? (Or if you have
> another idea, please tell me.)

Ideally, if we can make TUN select TAP that would be better. But there
are some subtle differences in the multi queue implementation. We will
end up with some useless code for TUN unless we can unify the multi
queue logic. It might not be worth it to change the TUN's multi queue
logic so having a new file seems to be better.

Thanks


>
> >
> >> +obj-$(CONFIG_TAP) += tap-drv.o
> >> +tap-drv-y := tap.o tun_vnet.o
> >>   obj-$(CONFIG_VETH) += veth.o
> >>   obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
> >>   obj-$(CONFIG_VXLAN) += vxlan/
>