Subject: Re: [PATCH net v3 09/11] net: core: add ignore flag to netdev_adjacent structure

From: Jakub Kicinski <[email-masked]>
Date: Fri, 20 Sep 2019 16:55:04 -0700

On Mon, 16 Sep 2019 22:48:00 +0900, Taehee Yoo wrote:
> In order to link an adjacent node, netdev_upper_dev_link() is used
> and in order to unlink an adjacent node, netdev_upper_dev_unlink() is used.
> unlink operation does not fail, but link operation can fail.
> 
> In order to exchange adjacent nodes, we should unlink an old adjacent
> node first. then, link a new adjacent node.
> If link operation is failed, we should link an old adjacent node again.
> But this link operation can fail too.
> It eventually breaks the adjacent link relationship.
> 
> This patch adds an ignore flag into the netdev_adjacent structure.
> If this flag is set, netdev_upper_dev_link() ignores an old adjacent
> node for a moment.
> So we can skip unlink operation before link operation.
> 
> Signed-off-by: Taehee Yoo <[email-masked]>

Could this perhaps be achieved by creating prepare, commit, and abort
helpers? That would make the API look slightly more canonical.

netdev_adjacent_change_prepare(old, new, dev)
netdev_adjacent_change_commit(old, new, dev)
netdev_adjacent_change_abort(old, new, dev)

The current naming makes the operation a little harder to follow if one
is just reading the vxlan code.

Please let me know if I didn't read the code closely enough to
understand why that's not fitting here.

> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 5bb5756129af..4506810c301b 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -4319,6 +4319,10 @@ int netdev_master_upper_dev_link(struct net_device *dev,
>  				 struct netlink_ext_ack *extack);
>  void netdev_upper_dev_unlink(struct net_device *dev,
>  			     struct net_device *upper_dev);
> +void netdev_adjacent_dev_disable(struct net_device *upper_dev,
> +				 struct net_device *lower_dev);
> +void netdev_adjacent_dev_enable(struct net_device *upper_dev,
> +				struct net_device *lower_dev);
>  void netdev_adjacent_rename_links(struct net_device *dev, char *oldname);
>  void *netdev_lower_dev_get_private(struct net_device *dev,
>  				   struct net_device *lower_dev);