netdev - Re: [PATCH net-next v7 11/16] netkit: Add netkit notifier to check for unregistering devices

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Message-ID: <7dc69b9f-0b48-4818-9689-fa22a98fad22@blackwall.org>
Date: Mon, 19 Jan 2026 16:22:44 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org
Cc: bpf@...r.kernel.org, kuba@...nel.org, davem@...emloft.net,
 pabeni@...hat.com, willemb@...gle.com, sdf@...ichev.me,
 john.fastabend@...il.com, martin.lau@...nel.org, jordan@...fe.io,
 maciej.fijalkowski@...el.com, magnus.karlsson@...el.com, dw@...idwei.uk,
 toke@...hat.com, yangzhenze@...edance.com, wangdongdong.6@...edance.com
Subject: Re: [PATCH net-next v7 11/16] netkit: Add netkit notifier to check
 for unregistering devices

On 15/01/2026 10:25, Daniel Borkmann wrote:
> Add a netdevice notifier in netkit to watch for NETDEV_UNREGISTER events.
> If the target device is indeed NETREG_UNREGISTERING and previously leased
> a queue to a netkit device, then collect the related netkit devices and
> batch-unregister_netdevice_many() them.
> 
> If this would not be done, then the netkit device would hold a reference
> on the physical device preventing it from going away. However, in case of
> both io_uring zero-copy as well as AF_XDP this situation is handled
> gracefully and the allocated resources are torn down.
> 
> In the case where mentioned infra is used through netkit, the applications
> have a reference on netkit, and netkit in turn holds a reference on the
> physical device. In order to have netkit release the reference on the
> physical device, we need such watcher to then unregister the netkit ones.
> 
> This is generally quite similar to the dependency handling in case of
> tunnels (e.g. vxlan bound to a underlying netdev) where the tunnel device
> gets removed along with the physical device.
> 
>    # ip a
>    [...]
>    4: enp10s0f0np0: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN group default qlen 1000
>        link/ether e8:eb:d3:a3:43:f6 brd ff:ff:ff:ff:ff:ff
>        inet 10.0.0.2/24 scope global enp10s0f0np0
>           valid_lft forever preferred_lft forever
>    [...]
>    8: nk@...E: <BROADCAST,MULTICAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 1000
>        link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
>    [...]
> 
>    # rmmod mlx5_ib
>    # rmmod mlx5_core
> 
>    [  309.261822] mlx5_core 0000:0a:00.0 mlx5_0: Port: 1 Link DOWN
>    [  344.235236] mlx5_core 0000:0a:00.1: E-Switch: Unload vfs: mode(LEGACY), nvfs(0), necvfs(0), active vports(0)
>    [  344.246948] mlx5_core 0000:0a:00.1: E-Switch: Disable: mode(LEGACY), nvfs(0), necvfs(0), active vports(0)
>    [  344.463754] mlx5_core 0000:0a:00.1: E-Switch: Disable: mode(LEGACY), nvfs(0), necvfs(0), active vports(0)
>    [  344.770155] mlx5_core 0000:0a:00.1: E-Switch: cleanup
>    [  345.345709] mlx5_core 0000:0a:00.0: E-Switch: Unload vfs: mode(LEGACY), nvfs(0), necvfs(0), active vports(0)
>    [  345.357524] mlx5_core 0000:0a:00.0: E-Switch: Disable: mode(LEGACY), nvfs(0), necvfs(0), active vports(0)
>    [  350.995989] mlx5_core 0000:0a:00.0: E-Switch: Disable: mode(LEGACY), nvfs(0), necvfs(0), active vports(0)
>    [  351.574396] mlx5_core 0000:0a:00.0: E-Switch: cleanup
> 
>    # ip a
>    [...]
>    [ both enp10s0f0np0 and nk gone ]
>    [...]
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Co-developed-by: David Wei <dw@...idwei.uk>
> Signed-off-by: David Wei <dw@...idwei.uk>
> ---
>   drivers/net/netkit.c      | 57 ++++++++++++++++++++++++++++++++++++++-
>   include/linux/netdevice.h |  6 +++++
>   2 files changed, 62 insertions(+), 1 deletion(-)
> 

Reviewed-by: Nikolay Aleksandrov <razor@...ckwall.org>