Date: Wed, 13 Oct 2004 19:23:07 +0300 From: Ruslan Ermilov <ru@FreeBSD.org> To: Sam Leffler <sam@errno.com> Cc: Gleb Smirnoff <glebius@FreeBSD.org> Subject: Re: Broadcom bge and 802.1Q vlan tags Message-ID: <20041013162307.GA4987@ip.net.ua> In-Reply-To: <416D4EE6.1080109@errno.com> References: <9256D57F598E6C41B288AA7DB94F29C902DFB963@pgnmail1.pgnaplikace.cz> <20041012140205.GD29433@cell.sick.ru> <416BFE30.2090308@errno.com> <20041012185129.GA86935@ip.net.ua> <416C3C77.20406@errno.com> <20041013064227.GA1338@ip.net.ua> <416D4EE6.1080109@errno.com>
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--YZ5djTAD1cGYuMQK Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Oct 13, 2004 at 08:51:02AM -0700, Sam Leffler wrote: > Ruslan Ermilov wrote: > >Hi Sam, > > > >On Tue, Oct 12, 2004 at 01:20:07PM -0700, Sam Leffler wrote: > > > >>>>This pessimizes normal traffic. > >>> > >>>m_tag_locate() doesn't look like a very expensive function. And > >>>with the "normal traffic", I don't expect to be more than one tag, > >>>no? Also, if if_nvlans > 0, this is already "pessimized". > >>> > >>> > >>> > >>>>We should look for a solution in the=20 > >>>>driver(s) to avoid sending packets up with tags when no vlans are=20 > >>>>configured. > >>>> > >>> > >>>I'd be opposed to such a change in behavior. The VLAN consumer can > >>>be not only vlan(4), it can equally be the ng_vlan(4) node, etc. > >> > >>I'm not sure what you are opposed to or why. The issue I have is that= =20 > >>m_tag_locate can be expensive if many packets have tags. The check for= =20 > >>the existence of vlans configured on the interface short-circuits this= =20 > >>work. That vlan-tagged packets may be generated when no vlans are=20 > >>configured seems wrong to me and breaks the assumption used to write th= e=20 > >>code. Changing the driver to drop the frame if ifp->if_nvlans is zero= =20 > >>seems straightforward and could probably be hidden in the existing macr= o. > >> > > > >Please take a moment and re-read what I've already said: vlan(4) is not > >the only consumer of VLAN frames: ng_vlan(4) is another such one, and I > >have a proprietary Netgraph node here that demultiplexes VLANs. If you > >start dropping VLAN frames in drivers when if_nvlans =3D=3D 0, this will= be > >a problem for me. Is that clear now? > > > > > >Cheers, >=20 > I've read what you've written but you also haven't explained why you=20 > can't signal the presence of these other entities in some way. >=20 Because these other entities don't have an access to "ifp", and can even exist on remote host (please see below). > The=20 > current mechanism to signal the presence of "interested parties" for=20 > vlan-tagged frames is ifp->if_nvlans. You are saying you have new=20 > (proprietary) code that is interested in vlans but will not use the=20 > existing mechanism. My reaction is fix your code, don't pessimize the=20 > code everyone else uses without netgraph. >=20 But ng_vlan(4) is part of the standard FreeBSD distribution, and you don't have access to "ifp" inside ng_vlan(4), because it's connected to the interface indirectly, through the ng_ether(4) node. Even worse, ng_vlan(4) may not even be connected to a local interface, for example, you can capture and tunnel all Ethernet traffic to another host, and do the VLAN processing there, FWIW. So while ifp->if_nvlans seems to be a good signalling mechamism for vlan(4), it's not suitable for ng_vlan(4) and other Netgraph code that works with VLAN. This code works now, and I'm afraid it will break if we change drivers to drop VLAN frames if if_nvlans =3D=3D 0, and I fail to see how I can make it work again after that. In other words, I want that ng_ether(4) continues to see VLAN frames even if no vlan(4) interfaces are configured, like it does now: the ng_ether processing is done in ether_input() before ether_demux() that checks for ifp->if_nvlans. OTOH, you may be right that one option would be to make ng_ether(4) increment ifp->if_nvlans, but I'm a little worried about the effect of doing this on the VLAN_OUTPUT_TAG macro (it looks safe, but I'm not sure). Cheers, --=20 Ruslan Ermilov ru@FreeBSD.org FreeBSD committer --YZ5djTAD1cGYuMQK Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (FreeBSD) iD8DBQFBbVZrqRfpzJluFF4RAlPEAJ4gyuklL7WCWLsqTJ3xXxU9Rdoe/gCcDLKJ 3UBQP/n0FKaW+ZWpHB9v7OI= =beod -----END PGP SIGNATURE----- --YZ5djTAD1cGYuMQK--
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