[PATCH 4/4] ubifs: Convert do_writepage() to take a folio

[Matthew Wilcox]

On Tue, Jun 06, 2023 at 08:13:55AM +0200, Richard Weinberger wrote:
> Matthew,
> 
> ----- Ursprüngliche Mail -----
> > Von: "Matthew Wilcox" <willy at infradead.org>
> > len is folio_size(), which is not 0.
> > 
> >        len = offset_in_folio(folio, i_size);
> 
> offset_in_folio(folio, i_size) can give 0.

Oh!  There is a bug, because it shouldn't get here!

        /* Is the folio fully inside i_size? */
        if (folio_pos(folio) + len < i_size) {

should be:

        /* Is the folio fully inside i_size? */
        if (folio_pos(folio) + len <= i_size) {

right?  Consider a file with i_size 4096.  its single-page folio will
have a pos of 0 and a length of 4096.  so it should be written back by
the first call to do_writepage(), not the case where the folio straddles
i_size.