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

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Date:	Tue, 07 Feb 2012 16:06:00 -0800
From:	Ben Greear <greearb@...delatech.com>
To:	Michał Mirosław <mirqus@...il.com>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/5] send-crc: Add framework to allow sending packets
 with customized CRC.

On 02/07/2012 03:59 PM, Michał Mirosław wrote:
> W dniu 7 lutego 2012 21:43 użytkownik Ben Greear
> <greearb@...delatech.com>  napisał:
>> On 02/07/2012 12:33 PM, Michał Mirosław wrote:
>>>
>>> 2012/2/7<greearb@...delatech.com>:
>>>>
>>>> From: Ben Greear<greearb@...delatech.com>
>>>>
>>>> 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@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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