netdev - RE: rtnetlink and many VFs

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Date:	Thu, 21 Apr 2011 10:50:35 -0700
From:	"Rose, Gregory V" <gregory.v.rose@...el.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	sf-linux-drivers <linux-net-drivers@...arflare.com>
Subject: RE: rtnetlink and many VFs

> -----Original Message-----
> From: Ben Hutchings [mailto:bhutchings@...arflare.com]
> Sent: Thursday, April 21, 2011 10:40 AM
> To: Rose, Gregory V
> Cc: David Miller; netdev; sf-linux-drivers
> Subject: RE: rtnetlink and many VFs
> 
> On Thu, 2011-04-21 at 10:02 -0700, Rose, Gregory V wrote:
> > > -----Original Message-----
> > > From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org]
> > > On Behalf Of Ben Hutchings
> > > Sent: Thursday, April 21, 2011 7:36 AM
> > > To: David Miller
> > > Cc: netdev; sf-linux-drivers
> > > Subject: rtnetlink and many VFs
> > >
> >
> > As more VFs become possible it really needs a fix.  I was thinking
> > about something along the lines of this:
> >
> > # ip link show eth(x) vf (n)
> >
> > Where eth(x) is the physical function that owns the VFs and (n) is the
> > specific VF you want information for.  That way one could easily
> > script something that loops through the VFs and gets the information
> > for each.  This really becomes necessary when we start adding
> > additional MAC and VLAN filters for each VF that need to be displayed.
> > In that case you can only show a few VFs before you run out of space.
> 
> I think that what 'ip link show' is doing now seems to be perfectly
> valid.  It allocates a 16K buffer which would be enough if netlink
> didn't apply this PAGE_SIZE limit to single messages.

Ah, I hadn't seen that it was allocating 16K, that would then be enough for 128 VFs but in the future would not be enough for 40Gig (or higher speed) devices that might support two or 4 times that many VFs.  I still feel like eventually the number of VFs will outgrow the capability of a single message to handle, especially when VFs will have the capability of having multiple MAC address and VLAN filters assigned to them.  And it seems orthogonal to me to mirror the 'ip link set eth(x) vf (n)' syntax with a 'ip link show eth(x) vf (n)' syntax.

That's just me though.

> 
> It is certainly a bug.  rtnetlink is the currently favoured API for
> querying and configuring network device settings, but there are now
> valid device settings that cannot be queried.

I'll look into just fixing the bug for now and reserve (at least what I consider to be) future improvements for later.

- Greg