Re: [PATCH v18 05/10] xbitmap: add more operations

From: Wei Wang
Date: Thu Dec 07 2017 - 06:59:31 EST


On 12/03/2017 09:50 AM, Tetsuo Handa wrote:
Matthew Wilcox wrote:
On Fri, Dec 01, 2017 at 03:09:08PM +0000, Wang, Wei W wrote:
On Friday, December 1, 2017 9:02 PM, Tetsuo Handa wrote:
If start == end is legal,

for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) {

makes this loop do nothing because 10 < 10 is false.
How about "start <= end "?
Don't ask Tetsuo for his opinion, write some userspace code that uses it.

Please be sure to prepare for "end == -1UL" case, for "start < end" will become
true when "start = (start | (IDA_BITMAP_BITS - 1)) + 1" made "start == 0" due to
overflow.

I think there is one more corner case with this API: searching for bit "1" from [0, ULONG_MAX] while no bit is set in the range, there appear to be no possible value that we can return (returning "end + 1" will be "ULONG_MAX + 1", which is 0)
I plan to make the "end" be exclusive of the searching, that is, [start, end), and return "end" if no such bit is found.

For cases like [16, 16), returning 16 doesn't mean bit 16 is 1 or 0, it simply means there is no bits to search in the given range, since 16 is exclusive.

Please let me know if you have a different thought.

Best,
Wei