>> - bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
>> + WARN_ON_ONCE(len > (BIO_MAX_VECS * PAGE_SIZE));
>
> How can that happen here? Max fsb size will be 64kB for the
> foreseeable future, the bio can hold 256 pages so it will have a
> minimum size capability of 1MB.
>
I just added it as a pathological check. This will not trigger
anytime in the near future.
> FWIW, as a general observation, I think this is the wrong place to
> be checking that a filesystem block is larger than can be fit in a
> single bio. There's going to be problems all over the place if we
> can't do fsb sized IO in a single bio. i.e. I think this sort of
> validation should be performed during filesystem mount, not
> sporadically checked with WARN_ON() checks in random places in the
> IO path...
>
I agree that it should be a check at a higher level.
As iomap can be used by any filesystem, the check on FSB limitation
should be a part iomap right? I don't see any explicit document/comment
that states the iomap limitations on FSB, etc.
>>
>> - __bio_add_page(bio, page, len, 0);
>> + while (len) {
>> + unsigned int io_len = min_t(unsigned int, len, PAGE_SIZE);
>> +
>> + __bio_add_page(bio, page, io_len, 0);
>> + len -= io_len;
>> + }
>> iomap_dio_submit_bio(iter, dio, bio, pos);
>
> /me wonders if we should have a set of ZERO_FOLIO()s that contain a
> folio of each possible size. Then we just pull the ZERO_FOLIO of the
> correct size and use __bio_add_folio(). i.e. no need for
> looping over the bio to repeatedly add the ZERO_PAGE, etc, and the
> code is then identical for all cases of page size vs FSB size.
>
I was exactly looking for ZERO_FOLIOs. Instead of having a ZERO_PAGE, can
we reserve a ZERO_HUGE_PAGE so that it can be used directly by
bio_add_folio_nofail()?
