mm/gup: Add folio_add_pins()

long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,

		      struct folio **folios, unsigned int max_folios,

		      pgoff_t *offset);

int folio_add_pins(struct folio *folio, unsigned int pins);

int get_user_pages_fast(unsigned long start, int nr_pages,

			unsigned int gup_flags, struct page **pages);

	return ret;

}

EXPORT_SYMBOL_GPL(memfd_pin_folios);

/**

 * folio_add_pins() - add pins to an already-pinned folio

 * @folio: the folio to add more pins to

 * @pins: number of pins to add

 *

 * Try to add more pins to an already-pinned folio. The semantics

 * of the pin (e.g., FOLL_WRITE) follow any existing pin and cannot

 * be changed.

 *

 * This function is helpful when having obtained a pin on a large folio

 * using memfd_pin_folios(), but wanting to logically unpin parts

 * (e.g., individual pages) of the folio later, for example, using

 * unpin_user_page_range_dirty_lock().

 *

 * This is not the right interface to initially pin a folio.

 */

int folio_add_pins(struct folio *folio, unsigned int pins)

{

	VM_WARN_ON_ONCE(!folio_maybe_dma_pinned(folio));

	return try_grab_folio(folio, pins, FOLL_PIN);

}

EXPORT_SYMBOL_GPL(folio_add_pins);