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

On Mon, 18 May 2026 10:24:35 +0100
Pavel Begunkov <[email protected]> wrote:

> On 5/13/26 14:29, David Laight wrote:
> > On Wed, 13 May 2026 11:05:57 +0100
> > David Laight <[email protected]> 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?
...
> >> 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)) ...

You need to shift all the TYPEn as well.
The above condition would become:
	if (likely(ITER_IS_ONE_OF(i, UBUF, XARRAY, DMABUF_MAP))) {
which reads reasonable well.
Without the token pasting it becomes:
	if (likely(ITER_IS_ONE_OF(i, ITER_UBUF, ITER_XARRAY, ITER_DMABUF_MAP))) {
and the line starts getting long.
Although that version probably needs a check that the mask is constant.

-- David


>