Subject: Re: [net-next v3 1/6] net: dcb: add new pcp selector to app object

From: Petr Machata <[email-masked]>
Date: Wed, 26 Oct 2022 12:11:08 +0200

Daniel Machon <[email-masked]> writes:

> Add new PCP selector for the 8021Qaz APP managed object.
>
> As the PCP selector is not part of the 8021Qaz standard, a new non-std
> extension attribute DCB_ATTR_DCB_APP has been introduced. Also two
> helper functions to translate between selector and app attribute type
> has been added. The new selector has been given a value of 255, to
> minimize the risk of future overlap of std- and non-std attributes.
>
> The new DCB_ATTR_DCB_APP is sent alongside the ieee std attribute in the
> app table. This means that the dcb_app struct can now both contain std-
> and non-std app attributes. Currently there is no overlap between the
> selector values of the two attributes.
>
> The purpose of adding the PCP selector, is to be able to offload
> PCP-based queue classification to the 8021Q Priority Code Point table,
> see 6.9.3 of IEEE Std 802.1Q-2018.
>
> PCP and DEI is encoded in the protocol field as 8*dei+pcp, so that a
> mapping of PCP 2 and DEI 1 to priority 3 is encoded as {255, 10, 3}.
>
> Signed-off-by: Daniel Machon <[email-masked]>

>  static struct sk_buff *dcbnl_newmsg(int type, u8 cmd, u32 port, u32 seq,
>  				    u32 flags, struct nlmsghdr **nlhp)
>  {
> @@ -1116,8 +1143,9 @@ static int dcbnl_ieee_fill(struct sk_buff *skb, struct net_device *netdev)
>  	spin_lock_bh(&dcb_lock);
>  	list_for_each_entry(itr, &dcb_app_list, list) {
>  		if (itr->ifindex == netdev->ifindex) {
> -			err = nla_put(skb, DCB_ATTR_IEEE_APP, sizeof(itr->app),
> -					 &itr->app);
> +			enum ieee_attrs_app type =
> +				dcbnl_app_attr_type_get(itr->app.selector);
> +			err = nla_put(skb, type, sizeof(itr->app), &itr->app);
>  			if (err) {
>  				spin_unlock_bh(&dcb_lock);
>  				return -EMSGSIZE;
> @@ -1495,7 +1523,7 @@ static int dcbnl_ieee_set(struct net_device *netdev, struct nlmsghdr *nlh,
>  		nla_for_each_nested(attr, ieee[DCB_ATTR_IEEE_APP_TABLE], rem) {
>  			struct dcb_app *app_data;
>  
> -			if (nla_type(attr) != DCB_ATTR_IEEE_APP)
> +			if (!dcbnl_app_attr_type_validate(nla_type(attr)))
>  				continue;
>  
>  			if (nla_len(attr) < sizeof(struct dcb_app)) {
> @@ -1556,7 +1584,7 @@ static int dcbnl_ieee_del(struct net_device *netdev, struct nlmsghdr *nlh,
>  		nla_for_each_nested(attr, ieee[DCB_ATTR_IEEE_APP_TABLE], rem) {
>  			struct dcb_app *app_data;
>  
> -			if (nla_type(attr) != DCB_ATTR_IEEE_APP)
> +			if (!dcbnl_app_attr_type_validate(nla_type(attr)))
>  				continue;
>  			app_data = nla_data(attr);
>  			if (ops->ieee_delapp)

I'm missing a validation that DCB_APP_SEL_PCP is always sent in
DCB_ATTR_DCB_APP encapsulation. Wouldn't the current code permit
sending it in the IEEE encap? This should be forbidden.

And vice versa: I'm not sure we want to permit sending the standard
attributes in the DCB encap.