Re: [PATCH 1/2] iomap: Add iomap_iter API

[Christoph Hellwig <hch@infradead.org>]

> +loff_t iomap_iter(struct iomap_iter *iter, loff_t written)
> +{
> +	const struct iomap_ops *ops = iter->ops;
> +	struct iomap *iomap = &iter->iomap;
> +	struct iomap *srcmap = &iter->srcmap;

I think it makes sense to only have members in the iter structure
that this function modifies.  That is, just pass inode, ops and flags
as explicit parameters.

OTOH the len argument / return value seems like something that would
seems useful in the iter structure.  That would require renaming the
current len to something like total_len..

> +/* Magic value for first call to iterator */
> +#define IOMAP_FIRST_CALL	LLONG_MIN

Can we find a way to make a a zero initialized field the indicatator
of the first call?  That way we don't need any knowledge of magic
values in the callers.  And also don't need any special initializer
value, but just leave it to the caller to initialize .pos and
.total_len, and be done with it.