I don't think this works correctly. b_io_tracking is a circular buffer of size BUF_TRACKING_SIZE; b_io_tcnt is an index into b_io_tracking, mod BUF_TRACKING_SIZE.

Either way: the point of the loop is to walk the entire circular buffer and no more. This change breaks that.

Maybe instead: j <= min(bp->b_io_tcnt + 1, BUF_TRACKING_SIZE)? That would still break output near where b_io_tcnt wraps at 4 billion, but at least it would be fairly unlikely.

Or keep the existing iteration, but check for and skip NULL values? That's straightforward.

I prefer one trace per line, similar to stack frames in backtraces. Why mash it all together?

You're right; I've reworked it to just check for NULLs instead.

Mostly to conserve the screen space; it's somewhat annoying when you do "show lockedbufs" and then realize you can't stop the output by pressing 'q' - for some reason it then just stops paging and decides to display everything, and the console output can take a few minutes.

Still, just checking for NULL improves things a lot, so I've just dropped this part of the diff.