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

[David Laight <david.laight.linux@gmail.com>]

On Wed, 13 May 2026 11:05:57 +0100
David Laight <david.laight.linux@gmail.com> 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)
> 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)

int foo(void *);
int f(struct iov_iter *i)
{
    return ITER_IS_ONE_OF(i, UBUF, KVEC) ? foo(i) : 0;
}

See https://godbolt.org/z/sMz93zah1

Pasting ITER_ on the front ensures the values are constants of the right type.
OTOH it makes it harder to search for uses of each type.
You could paste _ITER_ on the front, elsewhere define _ITER_ITER_UVEC
to be ITER_UVEC (etc), and require the caller use the full name.

-- David