Re: [PATCH 08/12] xfs: remove xfs_ifork_ops

[Brian Foster <bfoster@redhat.com>]

On Sat, May 16, 2020 at 10:48:02AM -0700, Darrick J. Wong wrote:
> On Sat, May 09, 2020 at 07:13:44AM -0400, Brian Foster wrote:
> > On Sat, May 09, 2020 at 10:17:15AM +0200, Christoph Hellwig wrote:
> > > On Fri, May 08, 2020 at 11:05:43AM -0400, Brian Foster wrote:
> > > > On Fri, May 08, 2020 at 08:34:19AM +0200, Christoph Hellwig wrote:
> > > > > xfs_ifork_ops add up to two indirect calls per inode read and flush,
> > > > > despite just having a single instance in the kernel.  In xfsprogs
> > > > > phase6 in xfs_repair overrides the verify_dir method to deal with inodes
> > > > > that do not have a valid parent, but that can be fixed pretty easily
> > > > > by ensuring they always have a valid looking parent.
> > > > > 
> > > > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > > > ---
> > > > 
> > > > Code looks fine, but I assume we'll want a repair fix completed and
> > > > merged before wiping this out:
> > > 
> > > With the xfsprogs merge delays I'm not sure merged will work, but I'll
> > > happily take your patch and get it in shape for submission.
> > > 
> > 
> > The critical bit is that repair is fixed before this lands in xfsprogs,
> > otherwise we just reintroduce the regression the callback mechanism was
> > designed to fix. The repair change is not huge, but it's not necessarily
> > trivial so it's probably worth making sure the repair change is at least
> > reviewed before putting this into the kernel pipeline.
> > 
> > BTW, I played with this a bit more yesterday and made some tweaks that I
> > think make it a little cleaner. Namely instead of processing the parent
> > bits in phases 3 and 4 and setting the parent in the internal structures
> > in phase 4, to do everything in phase 3 and skip the repeat checks in
> > phase 4. This has the side effect of eliminating some duplicate error
> > messages where repair complains about the original bogus value in phase
> > 3, sets it to zero, and then complains about the zero value again in
> > phase 4. This still needs some auditing to assess whether we're losing
> > any extra verification by setting the parent in phase 3, however. It
> > also might be worth looking at giving the other dir formats the same
> > treatment. Squashed diff of my local tree below...
> > 
> > Brian
> > 
> > diff --git a/repair/dino_chunks.c b/repair/dino_chunks.c
> > index 6685a4d2..96ed6a5b 100644
> > --- a/repair/dino_chunks.c
> > +++ b/repair/dino_chunks.c
> > @@ -859,14 +859,7 @@ next_readbuf:
> >  		 */
> >  		if (isa_dir)  {
> >  			set_inode_isadir(ino_rec, irec_offset);
> > -			/*
> > -			 * we always set the parent but
> > -			 * we may as well wait until
> > -			 * phase 4 (no inode discovery)
> > -			 * because the parent info will
> > -			 * be solid then.
> > -			 */
> > -			if (!ino_discovery)  {
> > +			if (ino_discovery)  {
> >  				ASSERT(parent != 0);
> >  				set_inode_parent(ino_rec, irec_offset, parent);
> >  				ASSERT(parent ==
> > diff --git a/repair/dir2.c b/repair/dir2.c
> > index cbbce601..9c789b4a 100644
> > --- a/repair/dir2.c
> > +++ b/repair/dir2.c
> > @@ -165,7 +165,6 @@ process_sf_dir2(
> >  	int			tmp_elen;
> >  	int			tmp_len;
> >  	xfs_dir2_sf_entry_t	*tmp_sfep;
> > -	xfs_ino_t		zero = 0;
> >  
> >  	sfp = (struct xfs_dir2_sf_hdr *)XFS_DFORK_DPTR(dip);
> >  	max_size = XFS_DFORK_DSIZE(dip, mp);
> > @@ -480,6 +479,9 @@ _("corrected entry offsets in directory %" PRIu64 "\n"),
> >  	 * check parent (..) entry
> >  	 */
> >  	*parent = libxfs_dir2_sf_get_parent_ino(sfp);
> > +	if (!ino_discovery)
> > +		return 0;
> > +
> >  
> >  	/*
> >  	 * if parent entry is bogus, null it out.  we'll fix it later .
> > @@ -494,7 +496,7 @@ _("bogus .. inode number (%" PRIu64 ") in directory inode %" PRIu64 ", "),
> >  		if (!no_modify)  {
> >  			do_warn(_("clearing inode number\n"));
> >  
> > -			libxfs_dir2_sf_put_parent_ino(sfp, zero);
> > +			libxfs_dir2_sf_put_parent_ino(sfp, mp->m_sb.sb_rootino);
> >  			*dino_dirty = 1;
> >  			*repair = 1;
> >  		} else  {
> > @@ -529,7 +531,7 @@ _("bad .. entry in directory inode %" PRIu64 ", points to self, "),
> >  		if (!no_modify)  {
> >  			do_warn(_("clearing inode number\n"));
> >  
> > -			libxfs_dir2_sf_put_parent_ino(sfp, zero);
> > +			libxfs_dir2_sf_put_parent_ino(sfp, mp->m_sb.sb_rootino);
> >  			*dino_dirty = 1;
> >  			*repair = 1;
> >  		} else  {
> > diff --git a/repair/phase6.c b/repair/phase6.c
> > index beceea9a..43bcea50 100644
> > --- a/repair/phase6.c
> > +++ b/repair/phase6.c
> > @@ -26,58 +26,6 @@ static struct xfs_name		xfs_name_dot = {(unsigned char *)".",
> >  						1,
> >  						XFS_DIR3_FT_DIR};
> >  
> > -/*
> > - * When we're checking directory inodes, we're allowed to set a directory's
> > - * dotdot entry to zero to signal that the parent needs to be reconnected
> > - * during phase 6.  If we're handling a shortform directory the ifork
> > - * verifiers will fail, so temporarily patch out this canary so that we can
> > - * verify the rest of the fork and move on to fixing the dir.
> > - */
> > -static xfs_failaddr_t
> > -phase6_verify_dir(
> > -	struct xfs_inode		*ip)
> > -{
> > -	struct xfs_mount		*mp = ip->i_mount;
> > -	struct xfs_ifork		*ifp;
> > -	struct xfs_dir2_sf_hdr		*sfp;
> > -	xfs_failaddr_t			fa;
> > -	xfs_ino_t			old_parent;
> > -	bool				parent_bypass = false;
> > -	int				size;
> > -
> > -	ifp = XFS_IFORK_PTR(ip, XFS_DATA_FORK);
> > -	sfp = (struct xfs_dir2_sf_hdr *)ifp->if_u1.if_data;
> > -	size = ifp->if_bytes;
> > -
> > -	/*
> > -	 * If this is a shortform directory, phase4 may have set the parent
> > -	 * inode to zero to indicate that it must be fixed.  Temporarily
> > -	 * set a valid parent so that the directory verifier will pass.
> > -	 */
> > -	if (size > offsetof(struct xfs_dir2_sf_hdr, parent) &&
> > -	    size >= xfs_dir2_sf_hdr_size(sfp->i8count)) {
> > -		old_parent = libxfs_dir2_sf_get_parent_ino(sfp);
> > -		if (old_parent == 0) {
> > -			libxfs_dir2_sf_put_parent_ino(sfp, mp->m_sb.sb_rootino);
> > -			parent_bypass = true;
> > -		}
> > -	}
> > -
> > -	fa = libxfs_default_ifork_ops.verify_dir(ip);
> > -
> > -	/* Put it back. */
> > -	if (parent_bypass)
> > -		libxfs_dir2_sf_put_parent_ino(sfp, old_parent);
> > -
> > -	return fa;
> > -}
> > -
> > -static struct xfs_ifork_ops phase6_ifork_ops = {
> > -	.verify_attr	= xfs_attr_shortform_verify,
> > -	.verify_dir	= phase6_verify_dir,
> > -	.verify_symlink	= xfs_symlink_shortform_verify,
> > -};
> > -
> >  /*
> >   * Data structures used to keep track of directories where the ".."
> >   * entries are updated. These must be rebuilt after the initial pass
> > @@ -1104,7 +1052,7 @@ mv_orphanage(
> >  					(unsigned long long)ino, ++incr);
> >  
> >  	/* Orphans may not have a proper parent, so use custom ops here */
> > -	err = -libxfs_iget(mp, NULL, ino, 0, &ino_p, &phase6_ifork_ops);
> > +	err = -libxfs_iget(mp, NULL, ino, 0, &ino_p, &xfs_default_ifork_ops);
> 
> Hmm.  I'll have to look at this more thoroughly on a non-weekend, but I
> think I like this approach, since it removes the weird quirk that if
> repair fails after writing out a sf directory with parent==0, we'll have
> transformed an fs with bad directory parent pointers to an fs with a
> directory that totally fails the verifier.
> 

I don't _think_ xfs_repair should ever write back the parent == 0
condition it creates. IIUC it's intended to be a transient state and the
directory should eventually be fixed up or junked (or maybe lost+found?)
in phase 6. However there is a similar quirk within xfs_repair itself in
that phase 3 sets the parent from whatever bad value it is to zero, then
phase 4 repeats the same general scan and complains about parent == 0
because that is also invalid. ;P

Brian

> So for the kernel patch, provisionally:
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> 
> --D
> 
> >  	if (err)
> >  		do_error(_("%d - couldn't iget disconnected inode\n"), err);
> >  
> > @@ -2875,7 +2823,7 @@ process_dir_inode(
> >  
> >  	ASSERT(!is_inode_refchecked(irec, ino_offset) || dotdot_update);
> >  
> > -	error = -libxfs_iget(mp, NULL, ino, 0, &ip, &phase6_ifork_ops);
> > +	error = -libxfs_iget(mp, NULL, ino, 0, &ip, &xfs_default_ifork_ops);
> >  	if (error) {
> >  		if (!no_modify)
> >  			do_error(
> > 
>