Re: [PATCH 1/5] send-crc: Add framework to allow sending packets with customized CRC.

[Ben Greear <greearb@xxxxxxxxxxxxxxx>]

On 02/07/2012 03:59 PM, Michał Mirosław wrote:
> W dniu 7 lutego 2012 21:43 użytkownik Ben Greear
> <greearb@xxxxxxxxxxxxxxx>  napisał:
> > On 02/07/2012 12:33 PM, Michał Mirosław wrote:
> > > 2012/2/7<greearb@xxxxxxxxxxxxxxx>:
> > > > From: Ben Greear<greearb@xxxxxxxxxxxxxxx>
> > > >
> > > > This is useful for testing RX handling of frames with bad
> > > > CRCs.
> > > >
> > > > Requires driver support to actually put the packet on the
> > > > wire properly.
> > >
> > > [...]
> > >
> > > I like this idea. I think that this is not a feature to have in
> > > dev->features to toggle, though. Driver either supports this or not,
> > > so it's better to put it in dev->priv_flags instead. Disabling of FCS
> > > inserting is a per-packet option in the drivers, isn't it?
> > >
> > > For one problem with toggling: if you create a socket using it and
> > > later turn off the feature, the socket will still send skbs with FCS
> > > appended.
> > For the priv-flags, is there a way to query that from user-space to
> > see if the NIC supports it?
> >
> > The pkt-socket xmit logic will throw away pkts if the NIC doesn't
> > have the feature enabled, but a few already queued might get
> > through with extra CRC appended.
> >
> > So, I'm fine with your suggestion, as long as there is some way to
> > query whether the NIC supports this feature or not...
>
> There's a way, as you implemented -EINVAL when trying to send via
> unsupporting device. :-)  Would be even better if setting SO_NO_FCS
> would fail at setsockopt() time.

Using -EINVAL for this purpose is lame even by my low standards :)

And, you don't necessarily know what device you are bound to
at setsockopt time, so I don't think I can add restrictions
there.

> priv_flags are not exposed to userspace. It should be easy to export
> them using ETHTOOL_GFEATURES as non-changeable features, if that's
> useful.

I'll poke around and see what I can figure out.

Thanks,
Ben

--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc  http://www.candelatech.com

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