netdev - Re: [ethtool PATCH 4/4] v5 Add RX packet classification interface

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Date:	Wed, 04 May 2011 00:34:44 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Dimitris Michailidis <dm@...lsio.com>
Cc:	Alexander Duyck <alexander.h.duyck@...el.com>, davem@...emloft.net,
	jeffrey.t.kirsher@...el.com, netdev@...r.kernel.org
Subject: Re: [ethtool PATCH 4/4] v5 Add RX packet classification interface

On Tue, 2011-05-03 at 16:23 -0700, Dimitris Michailidis wrote:
> On 05/03/2011 09:12 AM, Alexander Duyck wrote:
[...]
> > +int rxclass_rule_ins(int fd, struct ifreq *ifr,
> > +		     struct ethtool_rx_flow_spec *fsp)
> > +{
> > +	struct ethtool_rxnfc nfccmd;
> > +	__u32 loc = fsp->location;
> > +	int err;
> > +
> > +	/*
> > +	 * if location is unspecified pull rules from device
> > +	 * and allocate a free rule for our use
> > +	 */
> > +	if (loc == RX_CLS_LOC_UNSPEC) {
> > +		/* init table of available rules */
> > +		err = rmgr_init(fd, ifr);
> > +		if (err < 0)
> > +			return err;
> > +
> > +		/* verify rule location */
> > +		err = rmgr_add(fsp);
> > +		if (err < 0)
> > +			return err;
> > +
> > +		/* cleanup table and free resources */
> > +		rmgr_cleanup();
> > +	}
> 
> This logic where ethtool tries to select a filter slot when a user provides 
> RX_CLS_LOC_UNSPEC does not work in general.  It assumes that all slots are 
> equal and a new filter can go into any available slot. But a device may have 
> restrictions on where a filter may go that ethtool doesn't know.

I agree.  And if filter lookup is largely hash-based (as it is in
Solarflare hardware) the user will also find it very difficult to
specify the right location!

> I mentioned during a previous review that for cxgb4 some filters require a 
> slot number that is a multiple of 4.  There are some other constraints as 
> well depending on the type of filter being added. For such a device ethtool 
> doesn't know enough to handle RX_CLS_LOC_UNSPEC correctly.
>
> I think RX_CLS_LOC_UNSPEC should be passed to the driver, where there is 
> enough knowledge to pick an appropriate slot.  So I'd remove the
> 
>      if (loc == RX_CLS_LOC_UNSPEC)
> 
> block above, let the driver pick a slot, and then pass the selected location 
> back for ethtool to report.

But first we have to specify this in the ethtool API.  So please propose
a patch to ethtool.h.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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