Re: [PATCH net-next v2 09/12] ethtool: rss: support dumping RSS contexts

[Joe Damato <jdamato@fastly.com>]

On Fri, Aug 02, 2024 at 09:26:21PM -0700, Jakub Kicinski wrote:
> Now that we track RSS contexts in the core we can easily dump
> them. This is a major introspection improvement, as previously
> the only way to find all contexts would be to try all ids
> (of which there may be 2^32 - 1).
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---

Thanks for doing this important and extremely useful work. I am
personally very excited to see this data available to userland.

[...]

> diff --git a/net/ethtool/rss.c b/net/ethtool/rss.c
> index 023782ca1230..62e7b6fe605d 100644
> --- a/net/ethtool/rss.c
> +++ b/net/ethtool/rss.c
> @@ -208,6 +208,139 @@ static void rss_cleanup_data(struct ethnl_reply_data *reply_base)
>  	kfree(data->indir_table);
>  }
>  
> +struct rss_nl_dump_ctx {
> +	unsigned long		ifindex;
> +	unsigned long		ctx_idx;
> +
> +	unsigned int		one_ifindex;

My apologies: I'm probably just not familiar enough with the code,
but I'm having a hard time understanding what the purpose of
one_ifindex is.

I read both ethnl_rss_dump_start and ethnl_rss_dumpit, but I'm still
not following what this is used for; it'll probably be obvious in
retrospect once you explain it, but I suppose my feedback is that a
comment or something would be really helpful :)

> +};
> +
> +static struct rss_nl_dump_ctx *rss_dump_ctx(struct netlink_callback *cb)
> +{
> +	NL_ASSERT_DUMP_CTX_FITS(struct rss_nl_dump_ctx);
> +
> +	return (struct rss_nl_dump_ctx *)cb->ctx;
> +}
> +
> +int ethnl_rss_dump_start(struct netlink_callback *cb)
> +{
> +	const struct genl_info *info = genl_info_dump(cb);
> +	struct rss_nl_dump_ctx *ctx = rss_dump_ctx(cb);
> +	struct ethnl_req_info req_info = {};
> +	struct nlattr **tb = info->attrs;
> +	int ret;
> +
> +	/* Filtering by context not supported */
> +	if (tb[ETHTOOL_A_RSS_CONTEXT]) {
> +		NL_SET_BAD_ATTR(info->extack, tb[ETHTOOL_A_RSS_CONTEXT]);
> +		return -EINVAL;
> +	}
> +
> +	ret = ethnl_parse_header_dev_get(&req_info,
> +					 tb[ETHTOOL_A_RSS_HEADER],
> +					 sock_net(cb->skb->sk), cb->extack,
> +					 false);
> +	if (req_info.dev) {
> +		ctx->one_ifindex = req_info.dev->ifindex;
> +		ctx->ifindex = ctx->one_ifindex;
> +		ethnl_parse_header_dev_put(&req_info);
> +		req_info.dev = NULL;
> +	}
> +
> +	return ret;
> +}
> +
> +static int
> +rss_dump_one_ctx(struct sk_buff *skb, struct netlink_callback *cb,
> +		 struct net_device *dev, u32 rss_context)
> +{
> +	const struct genl_info *info = genl_info_dump(cb);
> +	struct rss_reply_data data = {};
> +	struct rss_req_info req = {};
> +	void *ehdr;
> +	int ret;
> +
> +	req.rss_context = rss_context;
> +
> +	ehdr = ethnl_dump_put(skb, cb, ETHTOOL_MSG_RSS_GET_REPLY);
> +	if (!ehdr)
> +		return -EMSGSIZE;
> +
> +	ret = ethnl_fill_reply_header(skb, dev, ETHTOOL_A_RSS_HEADER);
> +	if (ret < 0)
> +		goto err_cancel;
> +
> +	if (!rss_context)
> +		ret = rss_prepare_get(&req, dev, &data, info);
> +	else
> +		ret = rss_prepare_ctx(&req, dev, &data, info);
> +	if (ret)
> +		goto err_cancel;
> +
> +	ret = rss_fill_reply(skb, &req.base, &data.base);
> +	if (ret)
> +		goto err_cleanup;
> +	genlmsg_end(skb, ehdr);
> +
> +	rss_cleanup_data(&data.base);
> +	return 0;
> +
> +err_cleanup:
> +	rss_cleanup_data(&data.base);
> +err_cancel:
> +	genlmsg_cancel(skb, ehdr);
> +	return ret;
> +}
> +
> +static int
> +rss_dump_one_dev(struct sk_buff *skb, struct netlink_callback *cb,
> +		 struct net_device *dev)
> +{
> +	struct rss_nl_dump_ctx *ctx = rss_dump_ctx(cb);
> +	int ret;
> +
> +	if (!dev->ethtool_ops->get_rxfh)
> +		return 0;
> +
> +	if (!ctx->ctx_idx) {
> +		ret = rss_dump_one_ctx(skb, cb, dev, 0);
> +		if (ret)
> +			return ret;
> +		ctx->ctx_idx++;
> +	}
> +
> +	for (; xa_find(&dev->ethtool->rss_ctx, &ctx->ctx_idx,
> +		       ULONG_MAX, XA_PRESENT); ctx->ctx_idx++) {
> +		ret = rss_dump_one_ctx(skb, cb, dev, ctx->ctx_idx);
> +		if (ret)
> +			return ret;
> +	}
> +	ctx->ctx_idx = 0;
> +
> +	return 0;
> +}
> +
> +int ethnl_rss_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
> +{
> +	struct rss_nl_dump_ctx *ctx = rss_dump_ctx(cb);
> +	struct net *net = sock_net(skb->sk);
> +	struct net_device *dev;
> +	int ret = 0;
> +
> +	rtnl_lock();
> +	for_each_netdev_dump(net, dev, ctx->ifindex) {
> +		if (ctx->one_ifindex && ctx->one_ifindex != ctx->ifindex)
> +			break;
> +
> +		ret = rss_dump_one_dev(skb, cb, dev);
> +		if (ret)
> +			break;
> +	}
> +	rtnl_unlock();
> +
> +	return ret;
> +}
> +
>  const struct ethnl_request_ops ethnl_rss_request_ops = {
>  	.request_cmd		= ETHTOOL_MSG_RSS_GET,
>  	.reply_cmd		= ETHTOOL_MSG_RSS_GET_REPLY,
> -- 
> 2.45.2
>