netdev - Re: [ovs-dev] [Xen-devel] Re: [PATCH] ethtool: ETHTOOL_SFEATURES: remove NETIF_F

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Date:	Sun, 29 May 2011 11:38:49 +0200
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Jesse Gross <jesse@...ira.com>
Cc:	Ian Campbell <Ian.Campbell@...rix.com>, dev@...nvswitch.org,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	xen-api@...ts.xensource.com,
	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [ovs-dev] [Xen-devel] Re: [PATCH] ethtool: ETHTOOL_SFEATURES:
 remove NETIF_F_COMPAT return

On Sat, May 28, 2011 at 10:31:03AM -0700, Jesse Gross wrote:
> 2011/5/28 Ian Campbell <Ian.Campbell@...rix.com>:
> > On Sat, 2011-05-28 at 08:35 +0100, Michał Mirosław wrote:
> >> On Sat, May 28, 2011 at 12:25:55AM +0100, Ben Hutchings wrote:
> >> > On Fri, 2011-05-27 at 18:34 +0200, Michał Mirosław wrote:
> >> > > On Fri, May 27, 2011 at 04:45:50PM +0100, Ben Hutchings wrote:
> >> > > > On Fri, 2011-05-27 at 17:28 +0200, Michał Mirosław wrote:
> >> > [...]
> >> > > > >      (note: ETHTOOL_S{SG,...} are not ever going away)
> >> > > > >    - causes NETIF_F_* to be an ABI
> >> > > > If feature flag numbers are not stable then what is the point of
> >> > > > /sys/class/net/<name>/features?  Also, I'm not aware that features have
> >> > > > ever been renumbered in the past.
> >> > > Since no NETIF_F_* were exported earlier, I assume /sys/class/net/*/features
> >> > > is a debugging aid. What is it used for besides that?
> >> > xen-api <https://github.com/xen-org/xen-api> uses it in
> >> > scripts/InterfaceReconfigureVswitch.py.  Though it doesn't seem to be
> >> > used for a particularly good reason...
> >> Look like it should use ETHTOOL_GFLAGS instead for netdev_has_vlan_accel().
> ETHTOOL_GFLAGS didn't expose the vlan acceleration flags until 2.6.37,
> which is why /sys/class/net was used instead.

https://github.com/xen-org/xen-api/commit/78b8078e6ae3cf48179859bed6350bb326987546

The commit using it was introduced after 2.6.37 kernel was released and uses
undocumented acccess path to the bits in question. What is the kernel patch
this commit is referring to?

Best Regards,
Michał Mirosław
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