> +i.e. at a high level how iomap does write iter is [1]::
> + user IO
> + loop for file IO range
> + loop for each mapped extent
> + if (buffered) {
> + loop for each page/folio {
> + instantiate page cache
> + copy data to/from page cache
> + update page cache state
> + }
> + } else { /* direct IO */
> + loop for each bio {
> + pack user pages into bio
> + submit bio
> + }
> + }
> + }
> + }
This would probably be easier to follow (and match the actual code)
with two separate flows for buffered vs direct I/O.
The loop for each bio in direct I/O is also not wrong, but maybe a
bit confusing as we really map over a pinned memory range. The code
just has a little optimization to directly place that into a bio.
> +Guideline for filesystem conversion to iomap
> +=============================================
Maybe split this into a separate file?
