Re: [PATCH 02/12] iomap: Introduce iomap_read_folio_ops

[Darrick J. Wong]

On Sat, Oct 05, 2024 at 03:20:06AM +0100, Matthew Wilcox wrote:
> On Fri, Oct 04, 2024 at 04:04:29PM -0400, Goldwyn Rodrigues wrote:
> > iomap_read_folio_ops provide additional functions to allocate or submit
> > the bio. Filesystems such as btrfs have additional operations with bios
> > such as verifying data checksums. Creating a bio submission hook allows
> > the filesystem to process and verify the bio.
> 
> But surely you're going to need something similar for writeback too?
> So why go to all this trouble to add a new kind of ops instead of making
> it part of iomap_ops or iomap_folio_ops?

iomap_folio_ops, and maybe it's time to rename it iomap_pagecache_ops.

I almost wonder if we should have this instead:

struct iomap_pagecache_ops {
	struct iomap_ops ops;

	/* folio management */
	struct folio *(*get_folio)(struct iomap_iter *iter, loff_t pos,
			unsigned len);
	void (*put_folio)(struct inode *inode, loff_t pos, unsigned copied,
			struct folio *folio);

	/* mapping revalidation */
	bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap);

	/* writeback */
	int (*map_blocks)(struct iomap_writepage_ctx *wpc, struct inode *inode,
			  loff_t offset, unsigned len);

	int (*prepare_ioend)(struct iomap_ioend *ioend, int status);
	void (*discard_folio)(struct folio *folio, loff_t pos);
};

and then we change the buffered-io.c functions to take a (const struct
iomap_pagecache_ops*) instead of iomap_ops+iomap_folio_ops, or
iomap_ops+iomap_writeback_ops.

Same embedding suggestion for iomap_dio_ops.

--D