Re: [PATCH net-next v2 1/7] net: ethtool: netlink: Allow per-netdevice DUMP operations

[Kory Maincent <kory.maincent@bootlin.com>]

On Sat,  8 Mar 2025 16:54:33 +0100
Maxime Chevallier <maxime.chevallier@bootlin.com> wrote:

> We have a number of netlink commands in the ethnl family that may have
> multiple objects to dump even for a single net_device, including :
> 
>  - PLCA, PSE-PD, phy: one message per PHY device
>  - tsinfo: one message per timestamp source (netdev + phys)
>  - rss: One per RSS context
> 
> To get this behaviour, these netlink commands need to roll a custom
> ->dumpit().  
> 
> To prepare making per-netdev DUMP more generic in ethnl, introduce a
> member in the ethnl ops to indicate if a given command may allow
> pernetdev DUMPs (also referred to as filtered DUMPs).
> 
> Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> ---
> V2: - Rebase
>     - Fix kdoc
>     - Fix bissectabilitu by using the right function names
> 
>  net/ethtool/netlink.c | 45 ++++++++++++++++++++++++++++---------------
>  net/ethtool/netlink.h |  2 ++
>  2 files changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
> index 70834947f474..11e4122b7707 100644
> --- a/net/ethtool/netlink.c
> +++ b/net/ethtool/netlink.c
> @@ -586,21 +586,34 @@ static int ethnl_default_dumpit(struct sk_buff *skb,
>  	int ret = 0;
>  
>  	rcu_read_lock();
> -	for_each_netdev_dump(net, dev, ctx->pos_ifindex) {
> -		dev_hold(dev);
> +	if (ctx->req_info->dev) {
> +		dev = ctx->req_info->dev;
>  		rcu_read_unlock();
> -
> -		ret = ethnl_default_dump_one(skb, dev, ctx,
> genl_info_dump(cb)); -
> +		/* Filtered DUMP request targeted to a single netdev. We
> already
> +		 * hold a ref to the netdev from ->start()
> +		 */
> +		ret = ethnl_default_dump_one(skb, dev, ctx,
> +					     genl_info_dump(cb));
>  		rcu_read_lock();
> -		dev_put(dev);
> -
> -		if (ret < 0 && ret != -EOPNOTSUPP) {
> -			if (likely(skb->len))
> -				ret = skb->len;
> -			break;

You are not checking -EOPNOTSUPP, so you can return this error in the
ctx->req_info->dev condition. I am not sure about the policy but do we want to
report the EOPNOTSUPP error in the dump command instead of simply returning
nothing.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com