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:

[...]

quoted

+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.