Re: [PATCH 1/4] xfs: introduce fake roots for ag-rooted btrees

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Mar 05, 2020 at 12:20:54PM +1100, Dave Chinner wrote:
> On Tue, Mar 03, 2020 at 07:28:28PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Create an in-core fake root for AG-rooted btree types so that callers
> > can generate a whole new btree using the upcoming btree bulk load
> > function without making the new tree accessible from the rest of the
> > filesystem.  It is up to the individual btree type to provide a function
> > to create a staged cursor (presumably with the appropriate callouts to
> > update the fakeroot) and then commit the staged root back into the
> > filesystem.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> .....
> > @@ -188,6 +188,16 @@ union xfs_btree_cur_private {
> >  	} abt;
> >  };
> >  
> > +/* Private information for a AG-rooted btree. */
> > +struct xfs_btree_priv_ag {			/* needed for BNO, CNT, INO */
> > +	union {
> > +		struct xfs_buf		*agbp;	/* agf/agi buffer pointer */
> > +		struct xbtree_afakeroot	*afake;	/* fake ag header root */
> > +	};
> > +	xfs_agnumber_t			agno;	/* ag number */
> > +	union xfs_btree_cur_private	priv;
> > +};
> > +
> >  /*
> >   * Btree cursor structure.
> >   * This collects all information needed by the btree code in one place.
> > @@ -209,11 +219,7 @@ typedef struct xfs_btree_cur
> >  	xfs_btnum_t	bc_btnum;	/* identifies which btree type */
> >  	int		bc_statoff;	/* offset of btre stats array */
> >  	union {
> > -		struct {			/* needed for BNO, CNT, INO */
> > -			struct xfs_buf	*agbp;	/* agf/agi buffer pointer */
> > -			xfs_agnumber_t	agno;	/* ag number */
> > -			union xfs_btree_cur_private	priv;
> > -		} a;
> > +		struct xfs_btree_priv_ag a;
> >  		struct {			/* needed for BMAP */
> >  			struct xfs_inode *ip;	/* pointer to our inode */
> >  			int		allocated;	/* count of alloced */
> 
> I don't really like the mess this is turning into. I'll write a
> quick cleanup patch set for this union to make it much neater and
> the code much less verbose before we make the code even more
> unreadable. :/

Ok, thank you!

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com