Re: [PATCH 1/2] iomap: Add a page_prepare callback

[Christoph Hellwig <hch@lst.de>]

On Thu, Apr 25, 2019 at 10:32:52AM +0200, Jan Kara wrote:
> Also just looking at the code I was wondering about the following. E.g. in
> iomap_write_end() we have code like:
> 
>         if (iomap->type == IOMAP_INLINE) {
> 		foo
> 	} else if (iomap->flags & IOMAP_F_BUFFER_HEAD) {
> 		bar
> 	} else {
> 		baz
> 	}
> 
> 	if (iomap->page_done)
> 		iomap->page_done(...);
> 
> And now something very similar is in iomap_write_begin(). So won't it be
> more natural to just mandate ->page_prepare() and ->page_done() callbacks
> and each filesystem would set it to a helper function it needs? Probably we
> could get rid of IOMAP_F_BUFFER_HEAD flag that way...

I don't want pointless indirect calls for the default, non-buffer
head case.  Also inline really is a special case independent of
what the caller could pass in as flags or callbacks.  We could try to
hide the buffer_head stuff in there, but then again I'd rather kill
that off sooner than later.