netdev - Re: [PATCH net-next V1 1/2] ethtool: Support for configurable RSS hash function

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Date:	Wed, 26 Nov 2014 22:29:33 +0200
From:	Eyal perry <eyalpe@....mellanox.co.il>
To:	David Miller <davem@...emloft.net>, ben@...adent.org.uk
CC:	amirv@...lanox.com, netdev@...r.kernel.org, ogerlitz@...lanox.com,
	yevgenyp@...lanox.com, eyalpe@...lanox.com,
	Tom Lendacky <thomas.lendacky@....com>, ariel.elior@...gic.com,
	prashant@...adcom.com, mchan@...adcom.com, hariprasad@...lsio.com,
	sathya.perla@...lex.com, subbu.seetharaman@...lex.com,
	ajit.khaparde@...lex.com, jeffrey.t.kirsher@...el.com,
	jesse.brandeburg@...el.com, bruce.w.allan@...el.com,
	carolyn.wyborny@...el.com, donald.c.skidmore@...el.com,
	gregory.v.rose@...el.com, matthew.vick@...el.com,
	john.ronciak@...el.com, mitch.a.williams@...el.com,
	linux-net-drivers@...arflare.com, sshah@...arflare.com,
	sbhatewara@...are.com, pv-drivers@...are.com
Subject: Re: [PATCH net-next V1 1/2] ethtool: Support for configurable RSS
 hash function

On 11/22/2014 11:54 PM, David Miller wrote:
> From: Amir Vadai <amirv@...lanox.com>
> Date: Thu, 20 Nov 2014 16:26:49 +0200
> 
>> +	/* We require at least one supported parameter to be changed and no
>> +	 * change in any of the unsupported parameters
>> +	 */
>> +	if ((!indir && !key) || hfunc != ETH_RSS_HASH_NO_CHANGE)
>> +		return -EOPNOTSUPP;
>> +
> 
> I know it will make more work for you, but all of these driver
> implementations of this hook should:
> 
> 1) Accept hfunc of whatever hash function the chip is using,
>    not just ETH_RSS_HASH_NO_CHANGE.
> 
> 2) Provide an accurate hfunc value in the ->get() call.
Hello David, Ben, et al,
Before submitting V2, I'd like to consult you regarding the
implementation shown above. I thought of skipping the validity check
which I've described above as "We require at least one supported
parameter...", instead, I think it's better to fail the ->set() call
only in case of unsupported action requested, e.g.:
+	if (hfunc != ETH_RSS_HASH_NO_CHANGE &&
+	    hfunc != ETH_RSS_HASH_TOP)
+		return -EOPNOTSUPP;
+	if (indir)
+		/* set indirection table code ... */
+	if (key)
+		/* set hash key code ... */
The drawbacks are the change of previous behavior (only requests for at
least one change were supported), however it seems more reasonable and
makes the code much more readable.
In similar manner, for the ->get() call, remove the validity checks (as
I suggested in V1), and just protect against NULL pointer dereference, e.g:
-	if (!indir && !key)
-		return -EOPNOTSUPP;
+	if (indir)
+		/* fill in the given indirection table array */
+	if (key)
+		/* fill in the given hash key array */
+	if (hfunc)
+		*hfunc = ETH_RSS_HASH_TOP;
Please advise,
Thanks,
Eyal.

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