iomap: Support arbitrarily many blocks per page

#include "../internal.h"

/*

 * Structure allocated for each page when block size < PAGE_SIZE to track

 * sub-page uptodate status and I/O completions.

 * Structure allocated for each page or THP when block size < page size

 * to track sub-page uptodate status and I/O completions.

 */

struct iomap_page {

	atomic_t		read_count;

	atomic_t		write_count;

	spinlock_t		uptodate_lock;

	DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);

	unsigned long		uptodate[];

};

static inline struct iomap_page *to_iomap_page(struct page *page)

{

	/*

	 * per-block data is stored in the head page.  Callers should

	 * not be dealing with tail pages (and if they are, they can

	 * call thp_head() first.

	 */

	VM_BUG_ON_PGFLAGS(PageTail(page), page);

	if (page_has_private(page))

		return (struct iomap_page *)page_private(page);

	return NULL;

iomap_page_create(struct inode *inode, struct page *page)

{

	struct iomap_page *iop = to_iomap_page(page);

	unsigned int nr_blocks = i_blocks_per_page(inode, page);

	if (iop || i_blocks_per_page(inode, page) <= 1)

	if (iop || nr_blocks <= 1)

		return iop;

	iop = kzalloc(sizeof(*iop), GFP_NOFS | __GFP_NOFAIL);

	iop = kzalloc(struct_size(iop, uptodate, BITS_TO_LONGS(nr_blocks)),

			GFP_NOFS | __GFP_NOFAIL);

	spin_lock_init(&iop->uptodate_lock);

	attach_page_private(page, iop);

	return iop;

iomap_page_release(struct page *page)

{

	struct iomap_page *iop = detach_page_private(page);

	unsigned int nr_blocks = i_blocks_per_page(page->mapping->host, page);

	if (!iop)

		return;

	WARN_ON_ONCE(atomic_read(&iop->read_count));

	WARN_ON_ONCE(atomic_read(&iop->write_count));

	WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=

			PageUptodate(page));

	kfree(iop);

}