Re: [PATCH v2 09/23] iomap: allow filesystem to implement read path verification

Andrey Albershteyn
2023-04-05T11:02:15Z

Hi Christoph,

On Tue, Apr 04, 2023 at 08:37:02AM -0700, Christoph Hellwig wrote:
> > if (iomap_block_needs_zeroing(iter, pos)) {
> > folio_zero_range(folio, poff, plen);
> > + if (iomap->flags & IOMAP_F_READ_VERITY) {
>
> Wju do we need the new flag vs just testing that folio_ops and
> folio_ops->verify_folio is non-NULL?

Yes, it can be just test, haven't noticed that it's used only here,
initially I used it in several places.

>
> > - ctx->bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs),
> > - REQ_OP_READ, gfp);
> > + ctx->bio = bio_alloc_bioset(iomap->bdev, bio_max_segs(nr_vecs),
> > + REQ_OP_READ, GFP_NOFS, &iomap_read_ioend_bioset);
>
> All other callers don't really need the larger bioset, so I'd avoid
> the unconditional allocation here, but more on that later.

Ok, make sense.

>
> > + ioend = container_of(ctx->bio, struct iomap_read_ioend,
> > + read_inline_bio);
> > + ioend->io_inode = iter->inode;
> > + if (ctx->ops && ctx->ops->prepare_ioend)
> > + ctx->ops->prepare_ioend(ioend);
> > +
>
> So what we're doing in writeback and direct I/O, is to:
>
> a) have a submit_bio hook
> b) allow the file system to then hook the bi_end_io caller
> c) (only in direct O/O for now) allow the file system to provide
> a bio_set to allocate from

I see.

>
> I wonder if that also makes sense and keep all the deferral in the
> file system. We'll need that for the btrfs iomap conversion anyway,
> and it seems more flexible. The ioend processing would then move into
> XFS.
>

Not sure what you mean here.

> > @@ -156,6 +160,11 @@ struct iomap_folio_ops {
> > * locked by the iomap code.
> > */
> > bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap);
> > +
> > + /*
> > + * Verify folio when successfully read
> > + */
> > + bool (*verify_folio)(struct folio *folio, loff_t pos, unsigned int len);
>
> Why isn't this in iomap_readpage_ops?
>

Yes, it can be. But it appears to me to be more relevant to
_folio_ops, any particular reason to move it there? Don't mind
moving it to iomap_readpage_ops.

--
- Andrey