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

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Date:	Mon, 23 Oct 2006 21:39:44 +0100
From:	mel@...net.ie (Mel Gorman)
To:	Damien Wyart <damien.wyart@...e.fr>
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>, Andrew Morton <akpm@...l.org>
Subject: Re: 2.6.19-rc2-mm2 : empty files on vfat file system

On (21/10/06 19:38), Damien Wyart didst pronounce:
> > > I have noticed something strange (and bad :) since using
> > > 2.6.19-rc2-mm2 (the problem is NOT present on 2.6.19-rc2-mm1 ; do
> > > not know for mainline, I have not been able to test yet, but I think
> > > there have not been recent changes in this area) : writing a file to
> > > a vfat fs (fat 32) writes it, but with size 0 and no content.
> 
> * OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> [2006-10-21 22:24]:
> > diff -puN fs/fat/inode.c~fs-prepare_write-fixes fs/fat/inode.c
> > --- 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;
> > +
> > +	err = generic_commit_write(file, page, from, to);
> >  	if (!err && !(MSDOS_I(inode)->i_attrs & ATTR_ARCH)) {
> >  		inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
> >  		MSDOS_I(inode)->i_attrs |= ATTR_ARCH;
> 
> > This change does't update ->i_size. Could you just delete, and test
> > it? Anyway, this seems wrong even if it's "if ((to - from) == 0)".
> 
> Reverting the change makes the problem go away. But I do not know if
> this is safe wrt the fs-prepare_write-fixes patch.
> 

I don't know about the fix, but the issue is pretty serious for IA64 and the
EFI bootloader. On the IA64 I have access to, the bootloader and related
files are stored on a VFAT file system so when an automated system ran a
simple boot-test, the bootloader was blown away as a result.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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