[PATCH v7 21/24] iomap: Restructure iomap_readpages_actor

[Matthew Wilcox]

On Thu, Feb 20, 2020 at 07:47:41AM -0800, Christoph Hellwig wrote:
> On Wed, Feb 19, 2020 at 01:01:00PM -0800, Matthew Wilcox wrote:
> > From: "Matthew Wilcox (Oracle)" <willy at infradead.org>
> > 
> > By putting the 'have we reached the end of the page' condition at the end
> > of the loop instead of the beginning, we can remove the 'submit the last
> > page' code from iomap_readpages().  Also check that iomap_readpage_actor()
> > didn't return 0, which would lead to an endless loop.
> 
> I'm obviously biassed a I wrote the original code, but I find the new
> very much harder to understand (not that the previous one was easy, this
> is tricky code..).

Agreed, I found the original code hard to understand.  I think this is
easier because now cur_page doesn't leak outside this loop, so it has
an obvious lifecycle.

I'm kind of optimistic for Dave Howells' iov_iter addition of an
ITER_MAPPING.  That might simplify all of this code.