Re: [PATCH v3 02/10] iov_iter: add iterator type for dmabuf maps

[Pavel Begunkov]

On 5/13/26 14:29, David Laight wrote:
> On Wed, 13 May 2026 11:05:57 +0100
> David Laight <david.laight.linux@xxxxxxxxx> wrote:
>
> ...
> > > @@ -575,7 +575,8 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
> > >   {
> > >   	if (unlikely(i->count < size))
> > >   		size = i->count;
> > > -	if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i))) {
> > > +	if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i)) ||
> > > +	    unlikely(iov_iter_is_dmabuf_map(i))) {
> >
> >
> > Doesn't the extra check add more code to all the non-ubuf cases?
> > This could be fixed by either making iter_type a bitmask (with one bit set)

Not going to do that. It was specifically converted from bitmask
before, and the check optimisations like this were voiced back than.

> > or writing an iter_is_one_of(i, ITER_xxx, ITER_yyy) define that uses
> > '(1 << i->iter_type) & ((1 << ITER_xxx) | ...)'
>
> This seems to DTRT:
>
> #define _ITER_IS_ONE_OF(iter, t1, t2, t3, t4, t5, t6, t7, t8, ...) \
>      ((1u << (iter)->iter_type) & ((1u << ITER_##t1) | (1u << ITER_##t2) | \
>          (1u << ITER_##t3) | (1u << ITER_##t4) | (1u << ITER_##t5) | \
>          (1u << ITER_##t6) | (1u << ITER_##t7) | (1u << ITER_##t8)))
> #define ITER_IS_ONE_OF(iter, t, ...) \
>      _ITER_IS_ONE_OF(iter, t, ## __VA_ARGS__, t, t, t, t, t, t, t)

We definitely don't want that, using them directly would've been
much cleaner.

if (get_type_mask(i) & (TYPE1 | TYPE2)) ...

--
Pavel Begunkov