net: reject PTP periodic output requests with unsupported flags

Commit 823eb2a3c4 ("PTP: add support for one-shot output") introduced
a new flag for the PTP periodic output request ioctl. This flag is not
currently supported by any driver.

Fix all drivers which implement the periodic output request ioctl to
explicitly reject any request with flags they do not understand. This
ensures that the driver does not accidentally misinterpret the
PTP_PEROUT_ONE_SHOT flag, or any new flag introduced in the future.

This is important for forward compatibility: if a new flag is
introduced, the driver should reject requests to enable the flag until
the driver has actually been modified to support the flag in question.

Cc: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Christopher Hall <christopher.s.hall@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/igb/igb_ptp.c

@@ -551,6 +551,10 @@ static int igb_ptp_feature_enable_i210(struct ptp_clock_info *ptp,
 		return 0;
 
 	case PTP_CLK_REQ_PEROUT:
+		/* Reject requests with unsupported flags */
+		if (rq->perout.flags)
+			return -EOPNOTSUPP;
+
 		if (on) {
 			pin = ptp_find_pin(igb->ptp_clock, PTP_PF_PEROUT,
 					   rq->perout.index);