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Date:      Thu, 12 Jun 2008 10:06:05 -0700
From:      "Jack Vogel" <jfvogel@gmail.com>
To:        "CZUCZY Gergely" <phoemix@harmless.hu>
Cc:        pyunyh@gmail.com, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>
Subject:   Re: Vlan EVENT patch
Message-ID:  <2a41acea0806121006r23936007x5acf1fa9e302a94d@mail.gmail.com>
In-Reply-To: <20080612092621.61b44529@twoflower.in.publishing.hu>
References:  <2a41acea0806100951x1142edc6qc872d3810c2bd467@mail.gmail.com> <20080611073313.GF3529@cdnetworks.co.kr> <2a41acea0806110952n2851415dyf3b3213249779bf1@mail.gmail.com> <20080612000943.GA7250@cdnetworks.co.kr> <48508708.50903@errno.com> <2a41acea0806112048g60084f72o4391701ba242442@mail.gmail.com> <20080612040452.GE7250@cdnetworks.co.kr> <20080612092621.61b44529@twoflower.in.publishing.hu>

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On Thu, Jun 12, 2008 at 12:26 AM, CZUCZY Gergely <phoemix@harmless.hu> wrote:
> On Thu, 12 Jun 2008 13:04:52 +0900
> Pyun YongHyeon <pyunyh@gmail.com> wrote:
>
>> On Wed, Jun 11, 2008 at 08:48:58PM -0700, Jack Vogel wrote:
>>  > On Wed, Jun 11, 2008 at 7:16 PM, Sam Leffler <sam@errno.com> wrote:
>>  > > [trimming cc list to reduce spamage]
>>  > >
>>  > > Pyun YongHyeon wrote:
>>  > >>
>>  > >> 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@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.
>>  > >
>>  > > Sounds like there needs to be a h/w vlan assist capability bit that
>>  > > controls this in the driver.  Then you'd have a way to disable via
>>  > > ifconfig w/ a trivial mod.
>>  >
>>  > I don't want to create stuff in ifconfig when I'm not convinced
>>  > of the need. If there were, as he says, 'buggy hardware', specifically
>>  > buggy Intel hardware, then either our drivers would have had special
>>  > errata or workarounds in it for that, but none of the OS drivers have
>>  > any special code for issues involving VFTA (the filter) or other VLAN
>>  > controlling components that I am aware of.
>>  >
>>  > If there are other network drivers that are buggy in this regard then why
>>  > encumber the generic interface due to that, let the drivers deal with it,
>>  > via sysctl or something of the sort.
>>  >
>>  > There are enough real cases of hardware problems we need to address in
>>  > code that I don't just want to modify code on the mere theoretical
>>  > possibility of such.
>>  >
>>  > How bout this, we put the change into HEAD, I add support as I've planned
>>  > into the em and igb drivers, and then we let them get tested, if a real
>>  > problem comes up, THEN we worry about adding special case code, how's that?
>>  >
>>
>> Please go ahead. I don't have any objections on it.
>> I just thought it would be better to show a flag to indicate
>> hardware VLAN filtering is active in ifconfig(8) and have user
>> disable this feature in some rare cases.
>>
>>  > Regards,
>>  >
>>  > Jack
>
> I don't know whether it's a policy or not in FreeBSD, but I also agree with the
> opinion, that a flag should show up in the ifconfig output indicating that
> hardware filtering is being done on that interface. It helps the administrator
> to clarify how the hardware is working, which features of the hardware are in
> use, and also, they can be disabled.
> Disabling features is important. Sometimes the code is messed up, the hardware
> is messed up, or neither are messed up, but they are unable to work together.
> In these cases the feature could be disabled without hacking the source, which
> is a clean solution. FreeBSD has design, and prefers clean solutions as I see.
> I understand, that you _currently_ have no troubles and problems with your code
> and hardware, but there are unforseen cases out there,  lots of other hardware
> then intel's, and to quote Douglas N. Adams, "expect the unexpected".
>
> So, it won't hurt if it shows up in ifconfig, and it can be controlled, but
> definitely helps our job, the administrators'.

OK, if people feel strongly about this, and someone wants to implement the
code in ifconfig I'll go along with it.

Jack



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