Re: [PATCH v19 3/7] xbitmap: add more operations

On 12/15/2017 12:29 AM, Tetsuo Handa wrote:

Wei Wang wrote:

quoted

I used the example of xb_clear_bit_range(), and xb_find_next_bit() is
the same fundamentally. Please let me know if anywhere still looks fuzzy.

I don't think it is the same for xb_find_next_bit() with set == 0.

+		if (radix_tree_exception(bmap)) {
+			unsigned long tmp = (unsigned long)bmap;
+			unsigned long ebit = bit + 2;
+
+			if (ebit >= BITS_PER_LONG)
+				continue;
+			if (set)
+				ret = find_next_bit(&tmp, BITS_PER_LONG, ebit);
+			else
+				ret = find_next_zero_bit(&tmp, BITS_PER_LONG,
+							 ebit);
+			if (ret < BITS_PER_LONG)
+				return ret - 2 + IDA_BITMAP_BITS * index;

What I'm saying is that find_next_zero_bit() will not be called if you do
"if (ebit >= BITS_PER_LONG) continue;" before calling find_next_zero_bit().

When scanning "0000000000000000000000000000000000000000000000000000000000000001",
"bit < BITS_PER_LONG - 2" case finds "0" in this word but
"bit >= BITS_PER_LONG - 2" case finds "0" in next word or segment.

I can't understand why this is correct behavior. It is too much puzzling.

OK, I'll post out a version without the exceptional path.

Best,
Wei