fuse: support large folios for writethrough writes

Add support for folios larger than one page size for writethrough
writes.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: joannekoong

fs/fuse/file.c

@@ -1146,7 +1146,8 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 		size_t tmp;
 		struct folio *folio;
 		pgoff_t index = pos >> PAGE_SHIFT;
-		unsigned bytes = min(PAGE_SIZE - offset, num);
+		unsigned int bytes;
+		unsigned int folio_offset;
 
  again:
 		folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
@@ -1159,7 +1160,10 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 		if (mapping_writably_mapped(mapping))
 			flush_dcache_folio(folio);
 
-		tmp = copy_folio_from_iter_atomic(folio, offset, bytes, ii);
+		folio_offset = ((index - folio->index) << PAGE_SHIFT) + offset;
+		bytes = min(folio_size(folio) - folio_offset, num);
+
+		tmp = copy_folio_from_iter_atomic(folio, folio_offset, bytes, ii);
 		flush_dcache_folio(folio);
 
 		if (!tmp) {
@@ -1179,18 +1183,19 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 		}
 
 		ap->folios[ap->num_folios] = folio;
+		ap->descs[ap->num_folios].offset = folio_offset;
 		ap->descs[ap->num_folios].length = tmp;
 		ap->num_folios++;
 
 		count += tmp;
 		pos += tmp;
 		num -= tmp;
 		offset += tmp;
-		if (offset == PAGE_SIZE)
+		if (offset == folio_size(folio))
 			offset = 0;
 
-		/* If we copied full page, mark it uptodate */
-		if (tmp == PAGE_SIZE)
+		/* If we copied full folio, mark it uptodate */
+		if (tmp == folio_size(folio))
 			folio_mark_uptodate(folio);
 
 		if (folio_test_uptodate(folio)) {