Re: [PATCH 5/7] iomap: write iomap validity checks

[Christoph Hellwig <hch@infradead.org>]

On Thu, Nov 03, 2022 at 11:35:15AM +1100, Dave Chinner wrote:
> My first thought was to make this a page op, but I ended up deciding
> against that because it isn't operating on the folio at all.
> Perhaps I misunderstood what "page_ops" was actually intended for,
> because it seems that the existing hooks are to allow the filesystem
> to wrap per-folio operations with an external context, not to
> perform iomap-specific per-folio operations.
> 
> I guess if I read "pageops" as "operations to perform on each folio
> in an operation",

Yes, that was the idea behind it.  iomap_ops is really just the
iteration, and I've still not given up on the plan from willy to
merge the two ops into a single next iterator eventually.

So basic idea is iomap_ops - complete generic iterator, that
just returns and finishes of an iomap.

iomap_page_ops - callbacks for each folio (used to be page)

> then validating the iomap is not stale once the
> folio is locked could be considered a page op. I think we could
> probably make that work for writeback, too, because we have the
> folio locked when we call ->map_blocks....

.. and then separate ops for users of iomap, like the writeback code
with iomap_writeback_ops.