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

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Simon,

On Fri, 7 Mar 2025 12:21:19 +0000
Simon Horman <horms@kernel.org> wrote:

> On Wed, Mar 05, 2025 at 03:19:31PM +0100, Maxime Chevallier 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>
> > ---
> >  net/ethtool/netlink.c | 45 ++++++++++++++++++++++++++++---------------
> >  net/ethtool/netlink.h |  1 +
> >  2 files changed, 30 insertions(+), 16 deletions(-)
> > 
> > diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
> > index 734849a57369..0815b28ba32f 100644
> > --- a/net/ethtool/netlink.c
> > +++ b/net/ethtool/netlink.c
> > @@ -578,21 +578,34 @@ 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_dev(skb, dev, ctx,
> > +						 genl_info_dump(cb));  
> 
> Hi Maxime,
> 
> ethnl_default_dump_one_dev() is called here but it doesn't exist
> until the following patch is applied, which breaks bisection.

Yeah I messed-up in my rebase and bisection broke :(

I'll send a new version in a few days, as Jakub said, let's give some
time for the netdev_lock series to move forward and go through CI, I'll
need to rebase on it at some point.

> 
> >  		rcu_read_lock();
> > -		dev_put(dev);
> > -
> > -		if (ret < 0 && ret != -EOPNOTSUPP) {
> > -			if (likely(skb->len))
> > -				ret = skb->len;
> > -			break;
> > +		netdev_put(ctx->req_info->dev, &ctx->req_info->dev_tracker);
> > +	} else {
> > +		for_each_netdev_dump(net, dev, ctx->pos_ifindex) {
> > +			dev_hold(dev);
> > +			rcu_read_unlock();
> > +
> > +			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;
> > +			}
> > +			ret = 0;
> >  		}
> > -		ret = 0;
> >  	}
> >  	rcu_read_unlock();
> >    
> 
> ...
> 
> > diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
> > index ec6ab5443a6f..4db27182741f 100644
> > --- a/net/ethtool/netlink.h
> > +++ b/net/ethtool/netlink.h
> > @@ -388,6 +388,7 @@ struct ethnl_request_ops {
> >  	unsigned int		req_info_size;
> >  	unsigned int		reply_data_size;
> >  	bool			allow_nodev_do;
> > +	bool			allow_pernetdev_dump;  
> 
> nit: allow_pernetdev_dump should also be added to the Kernel doc for
>      struct ethnl_request_ops
> 
>      Flagged by ./scripts/kernel-doc -none
> 
>      There also appear to be similar minor issues with subsequent
>      patches in this series.

Ack, I'll make sure the doc is up to date and properly formatted :)

Thanks,

Maxime

> >  	u8			set_ntf_cmd;
> >  
> >  	int (*parse_request)(struct ethnl_req_info *req_info,
> > -- 
> > 2.48.1
> >