Squashfs: Update page_actor to not use page->index

This commit removes an unnecessary use of page->index,
and moves the other use over to folio->index.

Signed-off-by: Phillip Lougher <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

fs/squashfs/file.c

···
 			goto skip_pages;
 
 		actor = squashfs_page_actor_init_special(msblk, pages, nr_pages,
-							 expected);
+							expected, start);
 		if (!actor)
 			goto skip_pages;
 

fs/squashfs/file_direct.c

···
 	 * Create a "page actor" which will kmap and kunmap the
 	 * page cache pages appropriately within the decompressor
 	 */
-	actor = squashfs_page_actor_init_special(msblk, page, pages, expected);
+	actor = squashfs_page_actor_init_special(msblk, page, pages, expected,
+						start_index << PAGE_SHIFT);
 	if (actor == NULL)
 		goto out;
 

fs/squashfs/page_actor.c

···
 }
 
 /* Implementation of page_actor for decompressing directly into page cache. */
+static loff_t page_next_index(struct squashfs_page_actor *actor)
+{
+	return page_folio(actor->page[actor->next_page])->index;
+}
+
 static void *handle_next_page(struct squashfs_page_actor *actor)
 {
 	int max_pages = (actor->length + PAGE_SIZE - 1) >> PAGE_SHIFT;
···
 		return NULL;
 
 	if ((actor->next_page == actor->pages) ||
-			(actor->next_index != actor->page[actor->next_page]->index)) {
+			(actor->next_index != page_next_index(actor))) {
 		actor->next_index++;
 		actor->returned_pages++;
 		actor->last_page = NULL;
···
 }
 
 struct squashfs_page_actor *squashfs_page_actor_init_special(struct squashfs_sb_info *msblk,
-	struct page **page, int pages, int length)
+	struct page **page, int pages, int length, loff_t start_index)
 {
 	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
 
···
 	actor->pages = pages;
 	actor->next_page = 0;
 	actor->returned_pages = 0;
-	actor->next_index = page[0]->index & ~((1 << (msblk->block_log - PAGE_SHIFT)) - 1);
+	actor->next_index = start_index >> PAGE_SHIFT;
 	actor->pageaddr = NULL;
 	actor->last_page = NULL;
 	actor->alloc_buffer = msblk->decompressor->alloc_buffer;

fs/squashfs/page_actor.h

···
 				int pages, int length);
 extern struct squashfs_page_actor *squashfs_page_actor_init_special(
 				struct squashfs_sb_info *msblk,
-				struct page **page, int pages, int length);
+				struct page **page, int pages, int length,
+				loff_t start_index);
 static inline struct page *squashfs_page_actor_free(struct squashfs_page_actor *actor)
 {
 	struct page *last_page = actor->last_page;