On Mon, Jun 20, 2011 at 2:16 PM, Ben Hutchings
[off-list ref] wrote:

On Mon, 2011-06-20 at 21:14 +0200, Michał Mirosław wrote:
[...]

quoted

@@ -125,19 +131,26 @@ static int ethtool_set_features(struct net_device *dev, void __user *useraddr)

      if (copy_from_user(features, useraddr, sizeof(features)))
              return -EFAULT;

-     if (features[0].valid & ~NETIF_F_ETHTOOL_BITS)
+     /* I wonder if the compiler will be smart enough to loop-unroll
+      * and optimize this... (no worries if not) --mq */
+     for (i = ETHTOOL_DEV_FEATURE_WORDS; i-- > 0; ) {
+             valid = (valid << 32)|features[i].valid;
+             wanted = (wanted << 32)|features[i].requested;
+     }

[...]

I don't know (or care) about optimisation of this, but I would expect
gcc to complain about shifting a 32-bit value by 32 bits.  I suggest you
write this as:

       for (i = 0; i < ETHTOOL_DEV_FEATURE_WORDS; ++i) {
               valid |= (netdev_features_t)features[i].valid << 32 *i;
               wanted |= (netdev_features_t)features[i].requested << 32 *i;

It's a valid point but this type of typecast or similar usage would
imply that netdev_feature_t is an int of XXX bits. That's not opaque
and would hinder the way you can abstract the feature type.

--mahesh..

       }

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.

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