Re: [PATCH v1 02/16] iomap: rename cur_folio_in_bio to folio_unlockedOM

[Christoph Hellwig <hch@infradead.org>]

On Wed, Sep 03, 2025 at 01:26:37PM -0700, Darrick J. Wong wrote:
> On Fri, Aug 29, 2025 at 04:56:13PM -0700, Joanne Koong wrote:
> > The purpose of struct iomap_readpage_ctx's cur_folio_in_bio is to track
> > if the folio needs to be unlocked or not. Rename this to folio_unlocked
> > to make the purpose more clear and so that when iomap read/readahead
> > logic is made generic, the name also makes sense for filesystems that
> > don't use bios.
> 
> Hrmmm.  The problem is, "cur_folio_in_bio" captures the meaning that the
> (locked) folio is attached to the bio, so the bio_io_end function has to
> unlock the folio.  The readahead context is basically borrowing the
> folio and cannot unlock the folio itelf.
> 
> The name folio_unlocked doesn't capture the change in ownership, it just
> fixates on the lock state which (imo) is a side effect of the folio lock
> ownership.

Agreed.  Not sure what a good name is in a world where the folio can be
in something else than the bio.  Maybe just replace bio with ctx or
similar? cur_folio_in_ctx?  cur_folio_locked_by_ctx?

> > +	bool			folio_unlocked;
> 
> Maybe this ought to be called cur_folio_borrowed?

I don't think 'borrow' makes much sense here.  It's not like we're
borrowing it, we transfer the lock context to the bio (or whatever else
Joanne is going to use for fuse, I haven't read down to that yet).