From: Ben Hutchings <redacted>
Date: Sat, 02 Aug 2014 14:56:22 +0100

How about adding a generic operation for independent tunables:

struct ethtool_get_tunable {
	u32	cmd;
	u32	id;
	u64	value, min, max;
};

struct ethtool_set_tunable {
	u32	cmd;
	u32	id;
	u64	value;
};

	int (*get_tunable)(struct net_device *, struct ethtool_get_tunable *);
	int (*set_tunable)(struct net_device *, const struct ethtool_set_tunable *);

The id to name mapping could be provided either through a stringset or
macros in <uapi/linux/ethtool.h>.  And perhaps we could split the id
space to allow for driver-specific tunables (while strongly discouraging
those for in-tree drivers).

That would certainly work, and another approach would be that we could
also create a tunable namespace of sorts.

struct ethtool_tunable {
	u32	cmd;
	u32	len;
	u32	data[];
};

#define ETHTOOL_GTUNABLE	x
#define ETHTOOL_STUNABLE	y

...

#define ETHTOOL_TUNABLE_COPYBREAK	0x00000001	/* u32 */

etc.

I understand the reason to gravitate towards stringset, in that it would
minimize the amount of code needed in the ethtool utility itself.