Re: Vlan EVENT patch

On Wed, Jun 11, 2008 at 09:52:23AM -0700, Jack Vogel wrote:
 > On Wed, Jun 11, 2008 at 12:33 AM, Pyun YongHyeon <pyunyh_at_gmail.com> wrote:
 > > On Tue, Jun 10, 2008 at 09:51:53AM -0700, Jack Vogel wrote:
 > >  > This is a small patch that Sam came up with for me, it will allow
 > >  > drivers to know
 > >  > when a vlan attaches.
 > >  >
 > >  > It is transparent to any code that doesn't want to change, but this
 > >  > will allow my
 > >  > drivers to finally utilize the vlan hardware filter (something Linux has had for
 > >  > ever but we lacked).
 > >  >
 > >
 > > Just curious, is there any rule how to use that new capability?
 > > Because drivers will receive events whenever VLAN tags are
 > > added/removed they would know how to act for these events. If
 > > promiscuous mode is on for interface, driver should not filter any
 > > VLAN tagged frames, right?
 > > If users want to disable VLAN hardware filtering feature what is
 > > best way to perform this? Introducing a new flag like
 > > IFCAP_VLAN_HWFILT or add a new sysctl that control this feature?
 > > I guess VIA Rhine III also have VLAN hardware filtering capability
 > > so it would be even better if we have a way to share common part.
 > 
 > All the patch does is have the vlan driver generate events when it attaches
 > or detaches from a NIC, there are no rules, however I can tell you what
 > I'm coding into this in the Intel drivers.
 > 
 > The way it works is the driver registers a callback for each event, I will
 > call that [igb,em,ixgbe]_register_vlan(), and unregister obviously.
 > 
 > Right now, the drivers just generically enable VLAN capability because
 > there is never a trigger to know IF and WHEN you need to do so, but
 > with this change the VLAN capability will only get turned on by the
 > registration routine.
 > 
 > Most significantly, now when the pseudo device it gives the driver
 > the VLAN tag, this will mean the driver will be able from the start
 > to use the VFTA, the hardware filter, for each vlan attach the driver
 > will add the ID into this table.
 > 
 > The unregister event will turn the table entry off, and if this is the
 > last VLAN being detached it will then disable the features.
 > 
 > Oh yes, these routines will also take care of the size change of
 > the frame due to the tag. I already have the changes in place in
 > the igb drive, and they are working great.
 > 
 > I do not understand why you think you need a flag to disable this,
 > yes it could be done, but why? If you need to do some sort of
 > debugging won't a system not using vlans and in promiscuous
 > mode do just fine?
 > 

I guess this would be the same reason why FreeBSD have a way to
disable checksum offload for buggy hardware. Diabling all hardware
VLAN assistance due to broken VLAN filtering doesn't look right.

 > It just seems to violate the whole reason for doing vlans in the
 > first place, however perhaps I am missing something? I do not
 > believe the Linux driver has some way to disable use of the table
 > but I'll double check on that.
 > 
 > Remember, this change requires NO driver changes unless they
 > wish to take advantage of the ability.

Yes.

 > 
 > Cheers,
 > 
 > Jack

Thanks.
-- 
Regards,
Pyun YongHyeon