Re: [patch] fix truncate inode time modification breakage

[Nick Piggin <npiggin@suse.de>]

On Tue, Jun 01, 2010 at 03:48:01PM +0200, Christoph Hellwig wrote:
> On Tue, Jun 01, 2010 at 11:39:23PM +1000, Nick Piggin wrote:
> > It appears that I've broken inode time modifications on tmpfs/ext2.
> > While ftruncate always updates these attributes, truncate must not
> > unless size is changed. I hadn't actually understood that until
> > Christoph told me.
> > 
> > Confusion is increased because other filesystems get this wrong.
> > Those without ->setattr or ->truncate get it wrong by default.
> > Others appear to have problems too.
> > 
> > I haven't gone through many yet, but is there any reason not to
> > just do it in the vfs?
> 
> Doing it in the VFS is fine with me, we still have the the file
> pointer in struct iatta to indicate a ftruncate / open O_TRUNC
> if any filesystem really cares.  But I think you need to audit
> all instances if they care about this.  And while you're at it
> also remove the code handling this and the comments about it in
> XFS.

Yes I was starting to look at that. Just want to see if I'm on the
right track.

 
> > -	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
> > -		loff_t newsize = attr->ia_size;
> > +	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE) &&
> > +						newsize != inode->i_size) {
> 
> Btw, the S_ISREG is superflous - we only ever set ATTR_SIZE for
> regular files from the upper layer code.

OK I'll get rid of it in the same patch.