fuse: use req->page_descs[] for argpages cases

Previously, anyone who set flag 'argpages' only filled req->pages[] and set
per-request page_offset. This patch re-works all cases where argpages=1 to
fill req->page_descs[] properly.

Having req->page_descs[] filled properly allows to re-work fuse_copy_pages()
to copy page fragments described by req->page_descs[]. This will be useful
for next patches optimizing direct_IO.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index d04bcc5..ed8f8c5 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1317,6 +1317,7 @@
 	req->out.argpages = 1;
 	req->num_pages = 1;
 	req->pages[0] = page;
+	req->page_descs[0].length = PAGE_SIZE;
 	if (fc->do_readdirplus) {
 		attr_version = fuse_get_attr_version(fc);
 		fuse_read_fill(req, file, file->f_pos, PAGE_SIZE,