Re: About IFNET_PCP_NONE

On Mon, Aug 28, 2023 at 10:25:01PM +0800, Zhenlei Huang wrote:
> 
> 
> > On Aug 28, 2023, at 3:54 PM, Konstantin Belousov <kostikbel@gmail.com> wrote:
> > 
> > On Mon, Aug 28, 2023 at 09:51:38AM +0800, Zhenlei Huang wrote:
> >> Hi Konstantin,
> >> 
> >> 
> >> I was just about going to open a PR for https://reviews.freebsd.org/D39536 and
> >> realized I might made wrong assumption.
> >> 
> >> I thought IFNET_PCP_NONE is something like IEEE8021Q_PCP_BE but I second why not
> >> use IEEE8021Q_PCP_BE but a new const IFNET_PCP_NONE.
> 
> I meant
> 
> ```
> int
> ether_output_frame(struct ifnet *ifp, struct mbuf *m)
> {
>     uint8_t pcp;
> 
>     pcp = ifp->if_pcp;
>     if (pcp != 0 /* IEEE8021Q_PCP_BE */ && ifp->if_type != IFT_L2VLAN &&
>         !ether_set_pcp(&m, ifp, pcp))
>         return (0);
> 
> ...
This is wrong.  PCP_BE is just one of the priorities, that should allowed to
be specified in the 802.1q pseudo-vlan header.

> 
> }
> ```
> 
> >> 
> >> So despite its naming IFNET_PCP_NONE, is it actually a flag to let specific interface
> >> completely bypass (disable) PCP processing?
> >> 
> >> The const IFNET_PCP_NONE is defined in sys/net/if.h with 
> >> ```
> >> #define IFNET_PCP_NONE 0xff   /* PCP disabled */
> >> ```
> > I fail to understand your question.
> > 
> > IFNET_PCP_NONE is a value that means that no 802.1q prio is inserted into
> > the packet.  Otherwise, non-vlan traffic is tagged with the priority.
> 
> Think about the following case:
> 
> 1. Set interface's PCP to IFNET_PCP_NONE, application / firewall provide per-flow PCP, should
> the traffic be tagged with the priority ?
Yes, it should, but only for packets from the specified flows.

> 
> 
> > 
> > IEEE8021Q_PCP_BE is a name of one of the priorities, it seems from my
> > code reading.
> 
> 
> Best regards,
> Zhenlei
>