Re: [PATCH v1 1/3] mm/gup: Introduce pin_user_pages_fd() for pinning shmem/hugetlbfs file pages

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Oct 06, 2023 at 10:03:33AM +0200, David Hildenbrand wrote:
> > + *
> > + * Returns number of pages pinned. This would be equal to the number of
> > + * pages requested.
> > + * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns
> > + * -errno.
> > + */
> > +long pin_user_pages_fd(int fd, pgoff_t start, unsigned long nr_pages,
> > +		       unsigned int gup_flags, struct page **pages)
> > +{
> > +	struct page *page;
> > +	struct file *filep;
> > +	unsigned int flags, i;
> > +	long ret;
> > +
> > +	if (nr_pages <= 0)
> > +		return 0;
> 
> I think we should just forbid that and use a WARN_ON_ONCE() here / return
> -EINVAL. So we'll never end up returning 0.

Why is the check even needed? It looked like it just runs through
normally and returns 0, that is fine..

Jason