Re: [PATCH -V3 08/11] arch/powerpc: Make some of the PGTABLE_RANGE dependency explicit

Paul Mackerras [off-list ref] writes:

On Mon, Jul 09, 2012 at 06:43:38PM +0530, Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V" <redacted>

slice array size and slice mask size depend on PGTABLE_RANGE. We
can't directly include pgtable.h in these header because there is
a circular dependency. So add compile time check for these values.

Some comments below...

quoted

 struct slice_mask {
 	u16 low_slices;
 	/*
-	 * This should be derived out of PGTABLE_RANGE. For the current
-	 * max 64TB, u64 should be ok.
+	 * We do this as a union so that we can verify
+	 * SLICE_MASK_SIZE against PGTABLE_RANGE
 	 */
-	u64 high_slices;
+	union {
+		u64 high_slices;
+		unsigned char not_used[SLICE_MASK_SIZE];
+	};

Seems ugly to have to have a union just for that.  Can't we do
something like BUILD_BUG_ON(sizeof(u64) < SLICE_MASK_SIZE) instead?

Dropped the union from the patch

quoted

@@ -73,7 +73,7 @@ static struct slice_mask slice_range_to_mask(unsigned long start,
 					     unsigned long len)
 {
 	unsigned long end = start + len - 1;
-	struct slice_mask ret = { 0, 0 };
+	struct slice_mask ret = { 0, {0} };

Wouldn't { 0 } suffice?  Similarly in several places below.

Once i drop the union all these changes can be dropped.

-aneesh