Re: 2.6.19-rc2-mm2 : empty files on vfat file system

[Nick Piggin <npiggin@suse.de>]

On Sun, Oct 22, 2006 at 05:38:38AM +0900, OGAWA Hirofumi wrote:
> Andrew Morton <akpm@osdl.org> writes:
> 
> > On Sat, 21 Oct 2006 19:38:49 +0200
> > Damien Wyart <damien.wyart@free.fr> wrote:
> >
> >> > --- a/fs/fat/inode.c~fs-prepare_write-fixes
> >> > +++ a/fs/fat/inode.c
> >> > @@ -150,7 +150,11 @@ static int fat_commit_write(struct file 
> >> >  			    unsigned from, unsigned to)
> >> >  {
> >> >  	struct inode *inode = page->mapping->host;
> >> > -	int err = generic_commit_write(file, page, from, to);
> >> > +	int err;
> >> > +	if (to - from > 0)
> >> > +		return 0;
> >> > +
> >
> > That should have been
> >
> > 	if (to - from == 0)
> > 		return 0;
> 
> As I said in this thread, generic_cont_expand() uses "to == from".
> Should we fix generic_cont_expand() instead? I don't know the
> background of this patch.

OK I have to write an RFC for various fs developers, so I'll be sure
to include you.

We want to be able to pass in a short (possibly zero) commit_write
length if the page data can not be fully copied.

generic_cont_expand seems to be using that as a shorthand for
"update the i_size but don't mark anything uptdoate"? If so, I think
it would be nice to fix it. Why does it even need to go through the
prepare/commit? Why not make __generic_cont_expand a standalone
function, and call that from cont_prepare_write?