vboxsf: Convert vboxsf_read_folio() to use a folio

Remove conversion to a page and use folio APIs throughout.  This includes
a removal of setting the error flag as nobody checks the error flag on
vboxsf folios.  This does not include large folio support as we would
have to map each page individually.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240530202110.2653630-15-willy@infradead.orgTested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/vboxsf/file.c

@@ -228,26 +228,19 @@ const struct inode_operations vboxsf_reg_iops = {
 
 static int vboxsf_read_folio(struct file *file, struct folio *folio)
 {
-	struct page *page = &folio->page;
 	struct vboxsf_handle *sf_handle = file->private_data;
-	loff_t off = page_offset(page);
+	loff_t off = folio_pos(folio);
 	u32 nread = PAGE_SIZE;
 	u8 *buf;
 	int err;
 
-	buf = kmap(page);
+	buf = kmap_local_folio(folio, 0);
 
 	err = vboxsf_read(sf_handle->root, sf_handle->handle, off, &nread, buf);
-	if (err == 0) {
-		memset(&buf[nread], 0, PAGE_SIZE - nread);
-		flush_dcache_page(page);
-		SetPageUptodate(page);
-	} else {
-		SetPageError(page);
-	}
+	buf = folio_zero_tail(folio, nread, buf + nread);
 
-	kunmap(page);
-	unlock_page(page);
+	kunmap_local(buf);
+	folio_end_read(folio, err == 0);
 	return err;
 }
 
@@ -295,7 +288,6 @@ static int vboxsf_writepage(struct page *page, struct writeback_control *wbc)
 	kref_put(&sf_handle->refcount, vboxsf_handle_release);
 
 	if (err == 0) {
-		ClearPageError(page);
 		/* mtime changed */
 		sf_i->force_restat = 1;
 	} else {