Re: [PATCH 2/2] iomap: remove the atomic write length check in iomap_dio_bio_iter_one()

[John Garry]

On 11/9/26 18:34, Tal Zussman wrote:
> On 11/8/26 12:06 PM, John Garry wrote:
> > On 11/8/26 04:24, Tal Zussman wrote:
> > > bio_iov_iter_get_pages() and bio_iov_iter_bounce_write() now fail a
> > > REQ_ATOMIC bio that doesn't cover the whole iterator, so the bio here
> > > always covers iomap_length() and the check can't trigger. Remove the
> > > check.
> > >
> > > Suggested-by: John Garry <john.garry@xxxxxxxxx>
> > > Link: https://lore.kernel.org/all/82978d5c-3e08-48e9-bf0a-7913e1cd0507@xxxxxxxxx/
> > > Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>
> >
> > Reviewed-by: John Garry <john.garry@xxxxxxxxx>
>
> Thanks!
>
> > This looks ok. But I am just thinking that a CoW-based atomic write does
> > not have the single bio restriction, so we don't need to fail the atomic
> > in this case. However, we should have consistent rules for iovec's
> > whether it's a block device or regular file for ext4 or xfs, so this
> > makes sense.
> >
> > thanks
> >
> > BTW, you could be a real hero and add an xfstests case for this also.
>
> What specifically would you want to see tested? I can do an atomic write with
> a partially unmapped buffer, with and without stable writes, and check that it
> fails and that nothing is written.

Just something similar to the blktests case which you added.

BTW, have you tested this partially-unmapped case for CoW-based atomics 
on xfs? You can just do that by setting atomic_wr=0

Thanks,
John

> > > ---
> > >    fs/iomap/direct-io.c | 14 --------------
> > >    1 file changed, 14 deletions(-)
> > >
> > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > > index ad041ac3252a..aca7cbaea4af 100644
> > > --- a/fs/iomap/direct-io.c
> > > +++ b/fs/iomap/direct-io.c
> > > @@ -370,15 +370,6 @@ static ssize_t iomap_dio_bio_iter_one(struct iomap_iter *iter,
> > >    		goto out_put_bio;
> > >    	ret = bio->bi_iter.bi_size;
> > >    
> > > -	/*
> > > -	 * An atomic write bio must cover the complete length.  If it doesn't,
> > > -	 * error out.
> > > -	 */
> > > -	if ((op & REQ_ATOMIC) && WARN_ON_ONCE(ret != iomap_length(iter))) {
> > > -		ret = -EINVAL;
> > > -		goto out_bio_release_pages;
> > > -	}
> > > -
> > >    	if (dio->flags & IOMAP_DIO_WRITE)
> > >    		task_io_account_write(ret);
> > >    	else if ((dio->flags & IOMAP_DIO_USER_BACKED) &&
> > > @@ -393,11 +384,6 @@ static ssize_t iomap_dio_bio_iter_one(struct iomap_iter *iter,
> > >    	iomap_dio_submit_bio(iter, dio, bio, pos);
> > >    	return ret;
> > >    
> > > -out_bio_release_pages:
> > > -	if (dio->flags & IOMAP_DIO_BOUNCE)
> > > -		bio_free_folios(bio);
> > > -	else
> > > -		bio_release_pages(bio, false);
> > >    out_put_bio:
> > >    	bio_put(bio);
> > >    	return ret;