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

[Nick Piggin <npiggin@suse.de>]

On Sat, Oct 21, 2006 at 01:24:31PM -0700, Andrew Morton wrote:
> On Sat, 21 Oct 2006 13:19:32 -0700
> Andrew Morton <akpm@osdl.org> wrote:
> 
> > 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;
> 
> otoh, it's still wrong that we're not updating i_size.  We happen to know
> that the caller will retry without dropping i_mutex, but it's a bit
> incestuous.

It can possibly fail for example if the source buffer gets unmapped.
However in the length == 0 case, that signals a failure to write anything
so we needn't update i_size, I think?