netdev - Re: [PATCH net-next] net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)

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Message-ID: <20160618061650.GA17882@u54ee753d2d1854bda401.ant.amazon.com>
Date:	Fri, 17 Jun 2016 23:16:51 -0700
From:	Matt Wilson <msw@...n.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Benjamin Poirier <benjamin.poirier@...il.com>,
	Netanel Belgazal <netanel@...apurnalabs.com>,
	netdev@...r.kernel.org, davem@...emloft.net,
	linux-kernel@...r.kernel.org, zorik@...apurnalabs.com,
	saeed@...apurnalabs.com, alex@...apurnalabs.com,
	aliguori@...zon.com, antoine.tenart@...e-electrons.com
Subject: Re: [PATCH net-next] net: ena: Add a driver for Amazon Elastic
 Network Adapters (ENA)

On Thu, Jun 16, 2016 at 07:06:52PM +0100, Ben Hutchings wrote:
> On Thu, 2016-06-16 at 10:55 -0700, Benjamin Poirier wrote:
> > On 2016/06/13 11:46, Netanel Belgazal wrote:
> [...]
> > > +static ssize_t ena_show_small_copy_len(struct device *dev,
> > > +				       struct device_attribute *attr, char *buf)
> > > +{
> > > +	struct ena_adapter *adapter = dev_get_drvdata(dev);
> > > +
> > > +	return sprintf(buf, "%d\n", adapter->small_copy_len);
> > > +}
> > > +
> > > +static DEVICE_ATTR(small_copy_len, S_IRUGO | S_IWUSR, ena_show_small_copy_len,
> > > +		   ena_store_small_copy_len);
> > 
> > This is what many other drivers call (rx_)copybreak. Perhaps it's time
> > to add it to ethtool as well?
> [...]
> 
> There is the 'tunable' ethtool API for random parameters like
> rx_copybreak.  The ethtool utility doesn't support it yet, though.

So I started implementing proper support for this in ethtool in a
generic way (retrieving the string set, parsing generically, etc), but
it seems that the implementation isn't quite as complete as one would
like. You said [1] that the kernel returns the type of each tunable,
but I don't see this implemented anywhere.

The string set also includes "Unspec", which is of dubious value.

I think that something tunable specific is going to need to be added
apart from ETHTOOL_GSTRINGS to provide ethtool the needed type
information.

--msw

[1] http://thread.gmane.org/gmane.linux.network/367058/focus=376701