fuse: refactor fuse_fill_write_pages()

Refactor the logic in fuse_fill_write_pages() for copying out write
data. This will make the future change for supporting large folios for
writes easier. No functional changes.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Bernd Schubert <bschubert@ddn.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: joannekoong

fs/fuse/file.c

@@ -1132,21 +1132,21 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 	struct fuse_args_pages *ap = &ia->ap;
 	struct fuse_conn *fc = get_fuse_conn(mapping->host);
 	unsigned offset = pos & (PAGE_SIZE - 1);
-	unsigned int nr_pages = 0;
 	size_t count = 0;
-	int err;
+	unsigned int num;
+	int err = 0;
+
+	num = min(iov_iter_count(ii), fc->max_write);
+	num = min(num, max_pages << PAGE_SHIFT);
 
 	ap->args.in_pages = true;
 	ap->descs[0].offset = offset;
 
-	do {
+	while (num) {
 		size_t tmp;
 		struct folio *folio;
 		pgoff_t index = pos >> PAGE_SHIFT;
-		size_t bytes = min_t(size_t, PAGE_SIZE - offset,
-				     iov_iter_count(ii));
-
-		bytes = min_t(size_t, bytes, fc->max_write - count);
+		unsigned bytes = min(PAGE_SIZE - offset, num);
 
  again:
 		folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
@@ -1178,14 +1178,13 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 			goto again;
 		}
 
-		err = 0;
 		ap->folios[ap->num_folios] = folio;
 		ap->descs[ap->num_folios].length = tmp;
 		ap->num_folios++;
-		nr_pages++;
 
 		count += tmp;
 		pos += tmp;
+		num -= tmp;
 		offset += tmp;
 		if (offset == PAGE_SIZE)
 			offset = 0;
@@ -1200,10 +1199,9 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 			ia->write.folio_locked = true;
 			break;
 		}
-		if (!fc->big_writes)
+		if (!fc->big_writes || offset != 0)
 			break;
-	} while (iov_iter_count(ii) && count < fc->max_write &&
-		 nr_pages < max_pages && offset == 0);
+	}
 
 	return count > 0 ? count : err;
 }