Re: [PATCH 09/15] xfs: simplify buffer I/O submission

[Christoph Hellwig <hch@lst.de>]

On Mon, Jan 06, 2025 at 10:42:24PM -0800, Darrick J. Wong wrote:
> So I guess b_io_remaining was the count of in-flight bios?

Yes.  Plus a bias of 1 for the submitting context so that the
completion isn't run until all bios are submitted.

> And making a
> chain of bios basically just moves all that to the bio layer, so all
> xfs_buf needs to know is whether or not a bio is in progress, right?

Yes.

> Eerrugh, I spent quite a while trying to wrap my head around the old
> code when I was writing the in-memory xfs_buf support.  This is much
> less weird to look at...
> 
> > +	for (map = 0; map < bp->b_map_count - 1; map++) {
> 
> ...but why isn't this "map < bp->b_map_count"?

Because the final ("main") bio is submitted outside the loop as the
loop body chains the ones before to it.  I guess this should go into
a comment to confuse the readers a little less.