Re: [PATCH net-next v10 02/13] rtnetlink: Pack newlink() params into struct

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Xiao Liang <shaw.leon@gmail.com>
Date: Wed, 19 Feb 2025 20:50:28 +0800
> There are 4 net namespaces involved when creating links:
> 
>  - source netns - where the netlink socket resides,
>  - target netns - where to put the device being created,
>  - link netns - netns associated with the device (backend),
>  - peer netns - netns of peer device.
> 
> Currently, two nets are passed to newlink() callback - "src_net"
> parameter and "dev_net" (implicitly in net_device). They are set as
> follows, depending on netlink attributes in the request.
> 
>  +------------+-------------------+---------+---------+
>  | peer netns | IFLA_LINK_NETNSID | src_net | dev_net |
>  +------------+-------------------+---------+---------+
>  |            | absent            | source  | target  |
>  | absent     +-------------------+---------+---------+
>  |            | present           | link    | link    |
>  +------------+-------------------+---------+---------+
>  |            | absent            | peer    | target  |
>  | present    +-------------------+---------+---------+
>  |            | present           | peer    | link    |
>  +------------+-------------------+---------+---------+
> 
> When IFLA_LINK_NETNSID is present, the device is created in link netns
> first and then moved to target netns. This has some side effects,
> including extra ifindex allocation, ifname validation and link events.
> These could be avoided if we create it in target netns from
> the beginning.
> 
> On the other hand, the meaning of src_net parameter is ambiguous. It
> varies depending on how parameters are passed. It is the effective
> link (or peer netns) by design, but some drivers ignore it and use
> dev_net instead.
> 
> To provide more netns context for drivers, this patch packs existing
> newlink() parameters, along with the source netns, link netns and peer
> netns, into a struct. The old "src_net" is renamed to "net" to avoid
> confusion with real source netns, and will be deprecated later. The use
> of src_net are converted to params->net trivially.
> 
> Signed-off-by: Xiao Liang <shaw.leon@gmail.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>