Thanks Stephen, for the suggestion I've sent v4 of the patch, which adds the succinct description in the af_packet documentation..
On Fri, 24 Sept 2021 at 18:11, Stephen Hemminger <step...@networkplumber.org> wrote: > On Fri, 24 Sep 2021 14:44:45 +0300 > Tudor Cornea <tudor.cor...@gmail.com> wrote: > > > +Features and Limitations of the af_packet PMD > > +--------------------------------------------- > > + > > +Since the following commit, the Linux kernel strips the vlan tag > > + > > +.. code-block:: console > > + > > + commit bcc6d47903612c3861201cc3a866fb604f26b8b2 > > + Author: Jiri Pirko <jpirko@xxxxxxxxxx> > > + Date: Thu Apr 7 19:48:33 2011 +0000 > > + > > + net: vlan: make non-hw-accel rx path similar to hw-accel > > + > > +Running on such a kernel results in receiving untagged frames while > using > > +the af_packet PMD. Fortunately, the stripped information is still > available > > +for use in ``mbuf->vlan_tci``, and applications could check > ``PKT_RX_VLAN_STRIPPED``. > > + > > +However, we currently don't have a way to describe offloads which can't > be > > +disabled by PMDs, and this creates an inconsistency with the way > applications > > +expect the PMD offloads to work, and requires them to be aware of which > > +underlying driver they use. > > + > > +Since release 21.11 the af_packet PMD will implement support for the > > +``DEV_RX_OFFLOAD_VLAN_STRIP`` offload, and users can control the > desired vlan > > +stripping behavior. > > + > > +It's important to note that the default case will change. If previously, > > +the vlan tag was stripped, if the application now requires the same > behavior, > > +it will need to configure ``rxmode.offloads`` with > ``DEV_RX_OFFLOAD_VLAN_STRIP``. > > + > > +The PMD driver will re-insert the vlan tag transparently to the > application > > +if the kernel strips it, as long as the ``DEV_RX_OFFLOAD_VLAN_STRIP`` > is not > > +enabled. > > This seems like the wrong place for this text. > It is not a new feature, it is a bug fix. > > If you want to describe it as an enhancement, the text should be succinct > and describe > the situation from user point of view. Something like: > > Af_packet PMD now works with VLAN's on Linux > >
