cvs commit: src/sys/dev/fxp if_fxp.c if_fxpvar.h

[Yar Tikhiy]

On Tue, May 25, 2004 at 09:47:57PM +0300, Ruslan Ermilov wrote:
> On Tue, May 25, 2004 at 09:34:59PM +0400, Yar Tikhiy wrote:
> > On Tue, May 25, 2004 at 07:42:51PM +0300, Ruslan Ermilov wrote:
> > > On Tue, May 25, 2004 at 07:49:46AM -0700, Yar Tikhiy wrote:
> > > > yar         2004/05/25 07:49:46 PDT
> > > > 
> > > >   FreeBSD src repository
> > > > 
> > > >   Modified files:
> > > >     sys/dev/fxp          if_fxp.c if_fxpvar.h 
> > > >   Log:
> > > >   Teach fxp(4) to control VLAN_MTU in the hardware.
> > > >   Now reception of extended frames can be toggled
> > > >   through ioctl(SIOCSIFCAP).
> > > >   
> > > >   The card will also receive extended frames when
> > > >   in promiscuous mode.
> > > >   
> > > >   Revision  Changes    Path
> > > >   1.209     +16 -8     src/sys/dev/fxp/if_fxp.c
> > > >   1.30      +1 -0      src/sys/dev/fxp/if_fxpvar.h
> > > > 
> > > This change also made VLAN_MTU disabled by default, what was
> > > the reason to do it?
> > 
> > I disabled it so that the interface won't violate without need
> > the Ethernet standard WRT the upper limit on frame size.
> > 
> What clause and in which of many 802 standards do you refer to?

I refer to 802.3.  AFAIK it hasn't been a long time since it relaxed
the limit to allow for VLAN-tagged frames (search for
maxUntaggedFrameSize.)  And a lot of implementations still stick to
the older 1518-byte limit.

> > vlan(4) will enable VLAN_MTU on an fxp interace as soon as a vlan
> > interface is attached to it.
> > 
> vlan(4) may not be the only consumer of VLAN capable frames.
> For example, I have ng_vlan(4) connected to ng_ether(4) node,
> and doing VLAN processing here, and this change will break
> the existing and working config.  I can survive, but it sounds
> against POLA to me.

IMHO ng_vlan(4) is young enough to implement VLAN_MTU control instead
of relying on the old behaviour of VLAN_MTU, which resulted from bugs
I've been fixing recently.

ng_vlan(4) could send a control command to ng_ether(4) instructing
the latter to increment the VLAN counter on the Ethernet interface
and toggle VLAN_MTU on if the counter value became equal to 1.

Another way I see is to drop automatic fiddling with VLAN_MTU in
the first place and implement an option for ifconfig(8) so that a
user/admin can control the capability WRT a particular case, e.g.,
disable it if a NIC displays erroneous behaviour in long frame mode.

-- 
Yar