iomap: Convert to_iomap_page to take a folio

The big comment about only using a head page can go away now that
it takes a folio argument.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>

fs/iomap/buffered-io.c

@@ -22,8 +22,8 @@
 #include "../internal.h"
 
 /*
- * Structure allocated for each page or THP when block size < page size
- * to track sub-page uptodate status and I/O completions.
+ * Structure allocated for each folio when block size < folio size
+ * to track sub-folio uptodate status and I/O completions.
  */
 struct iomap_page {
 	atomic_t		read_bytes_pending;
@@ -32,17 +32,10 @@ struct iomap_page {
 	unsigned long		uptodate[];
 };
 
-static inline struct iomap_page *to_iomap_page(struct page *page)
+static inline struct iomap_page *to_iomap_page(struct folio *folio)
 {
-	/*
-	 * 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);
+	if (folio_test_private(folio))
+		return folio_get_private(folio);
 	return NULL;
 }
 
@@ -51,7 +44,8 @@ static struct bio_set iomap_ioend_bioset;
 static struct iomap_page *
 iomap_page_create(struct inode *inode, struct page *page)
 {
-	struct iomap_page *iop = to_iomap_page(page);
+	struct folio *folio = page_folio(page);
+	struct iomap_page *iop = to_iomap_page(folio);
 	unsigned int nr_blocks = i_blocks_per_page(inode, page);
 
 	if (iop || nr_blocks <= 1)
@@ -144,7 +138,8 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
 static void
 iomap_iop_set_range_uptodate(struct page *page, unsigned off, unsigned len)
 {
-	struct iomap_page *iop = to_iomap_page(page);
+	struct folio *folio = page_folio(page);
+	struct iomap_page *iop = to_iomap_page(folio);
 	struct inode *inode = page->mapping->host;
 	unsigned first = off >> inode->i_blkbits;
 	unsigned last = (off + len - 1) >> inode->i_blkbits;
@@ -173,7 +168,8 @@ static void
 iomap_read_page_end_io(struct bio_vec *bvec, int error)
 {
 	struct page *page = bvec->bv_page;
-	struct iomap_page *iop = to_iomap_page(page);
+	struct folio *folio = page_folio(page);
+	struct iomap_page *iop = to_iomap_page(folio);
 
 	if (unlikely(error)) {
 		ClearPageUptodate(page);
@@ -438,7 +434,8 @@ int
 iomap_is_partially_uptodate(struct page *page, unsigned long from,
 		unsigned long count)
 {
-	struct iomap_page *iop = to_iomap_page(page);
+	struct folio *folio = page_folio(page);
+	struct iomap_page *iop = to_iomap_page(folio);
 	struct inode *inode = page->mapping->host;
 	unsigned len, first, last;
 	unsigned i;
@@ -1012,7 +1009,8 @@ static void
 iomap_finish_page_writeback(struct inode *inode, struct page *page,
 		int error, unsigned int len)
 {
-	struct iomap_page *iop = to_iomap_page(page);
+	struct folio *folio = page_folio(page);
+	struct iomap_page *iop = to_iomap_page(folio);
 
 	if (error) {
 		SetPageError(page);