Re: [PATCH 4/9] xfs_repair: rebuild free space btrees with bulk loader

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

On Thu, May 14, 2020 at 11:12:05AM -0400, Brian Foster wrote:
> On Sat, May 09, 2020 at 09:32:08AM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Use the btree bulk loading functions to rebuild the free space btrees
> > and drop the open-coded implementation.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> >  libxfs/libxfs_api_defs.h |    3 
> >  repair/phase5.c          |  858 +++++++++++++---------------------------------
> >  2 files changed, 247 insertions(+), 614 deletions(-)
> > 
> > 
> ...
> > diff --git a/repair/phase5.c b/repair/phase5.c
> > index 7eb24519..94e4610c 100644
> > --- a/repair/phase5.c
> > +++ b/repair/phase5.c
> ...
> > @@ -465,7 +476,7 @@ _("error - not enough free space in filesystem\n"));
> >  
> >  /* Feed one of the new btree blocks to the bulk loader. */
> >  static int
> > -rebuild_alloc_block(
> > +rebuild_claim_block(
> >  	struct xfs_btree_cur	*cur,
> >  	union xfs_btree_ptr	*ptr,
> >  	void			*priv)
> 
> Hmm.. seems like a decent amount of churn here. The above function is
> renamed and finish_rebuild() looks like it's gutted/replaced before
> either is ever used. Can we get the core bits settled into the previous
> patch(es) so they aren't changing when used to implement the tree
> reconstructions?

I bet I committed all this churn to the wrong patch back when you and I
were reviewing the similar patches for online repair.  Sorry I totally
missed this, will fix for the next resend.

(TBH I /really/ hate how diff tries to make the actual bnobt/cntbt
rebuilder changes "comparable".  They're not, and it just makes
reading this a nightmare.  Have kinda wondered if the new code should
just go somewhere else so that phase5.c can shrink a bit...)

--D

> Brian
> 
> > @@ -505,313 +516,32 @@ finish_cursor(bt_status_t *curs)
> >  	free(curs->btree_blocks);
> >  }
> >  
> > +/*
> > + * Scoop up leftovers from a rebuild cursor for later freeing, then free the
> > + * rebuild context.
> > + */
> >  static void
> >  finish_rebuild(
> >  	struct xfs_mount	*mp,
> > -	struct bt_rebuild	*btr)
> > +	struct bt_rebuild	*btr,
> > +	struct xfs_slab		*lost_fsb)
> >  {
> >  	struct xrep_newbt_resv	*resv, *n;
> >  
> >  	for_each_xrep_newbt_reservation(&btr->newbt, resv, n) {
> > -		xfs_agnumber_t	agno;
> > -		xfs_agblock_t	bno;
> > -		xfs_extlen_t	len;
> > -
> > -		if (resv->used >= resv->len)
> > -			continue;
> > -
> > -		/* XXX: Shouldn't this go on the AGFL? */
> > -		/* Put back everything we didn't use. */
> > -		bno = XFS_FSB_TO_AGBNO(mp, resv->fsbno + resv->used);
> > -		agno = XFS_FSB_TO_AGNO(mp, resv->fsbno + resv->used);
> > -		len = resv->len - resv->used;
> > -
> > -		add_bno_extent(agno, bno, len);
> > -		add_bcnt_extent(agno, bno, len);
> > -	}
> > -
> > -	xrep_newbt_destroy(&btr->newbt, 0);
> > -}
> > -
> > -/*
> > - * We need to leave some free records in the tree for the corner case of
> > - * setting up the AGFL. This may require allocation of blocks, and as
> > - * such can require insertion of new records into the tree (e.g. moving
> > - * a record in the by-count tree when a long extent is shortened). If we
> > - * pack the records into the leaves with no slack space, this requires a
> > - * leaf split to occur and a block to be allocated from the free list.
> > - * If we don't have any blocks on the free list (because we are setting
> > - * it up!), then we fail, and the filesystem will fail with the same
> > - * failure at runtime. Hence leave a couple of records slack space in
> > - * each block to allow immediate modification of the tree without
> > - * requiring splits to be done.
> > - *
> > - * XXX(hch): any reason we don't just look at mp->m_alloc_mxr?
> > - */
> > -#define XR_ALLOC_BLOCK_MAXRECS(mp, level) \
> > -	(libxfs_allocbt_maxrecs((mp), (mp)->m_sb.sb_blocksize, (level) == 0) - 2)
> > -
> > -/*
> > - * this calculates a freespace cursor for an ag.
> > - * btree_curs is an in/out.  returns the number of
> > - * blocks that will show up in the AGFL.
> > - */
> > -static int
> > -calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno,
> > -			xfs_agblock_t *extents, bt_status_t *btree_curs)
> > -{
> > -	xfs_extlen_t		blocks_needed;		/* a running count */
> > -	xfs_extlen_t		blocks_allocated_pt;	/* per tree */
> > -	xfs_extlen_t		blocks_allocated_total;	/* for both trees */
> > -	xfs_agblock_t		num_extents;
> > -	int			i;
> > -	int			extents_used;
> > -	int			extra_blocks;
> > -	bt_stat_level_t		*lptr;
> > -	bt_stat_level_t		*p_lptr;
> > -	extent_tree_node_t	*ext_ptr;
> > -	int			level;
> > -
> > -	num_extents = *extents;
> > -	extents_used = 0;
> > -
> > -	ASSERT(num_extents != 0);
> > -
> > -	lptr = &btree_curs->level[0];
> > -	btree_curs->init = 1;
> > +		while (resv->used < resv->len) {
> > +			xfs_fsblock_t	fsb = resv->fsbno + resv->used;
> > +			int		error;
> >  
> > -	/*
> > -	 * figure out how much space we need for the leaf level
> > -	 * of the tree and set up the cursor for the leaf level
> > -	 * (note that the same code is duplicated further down)
> > -	 */
> > -	lptr->num_blocks = howmany(num_extents, XR_ALLOC_BLOCK_MAXRECS(mp, 0));
> > -	lptr->num_recs_pb = num_extents / lptr->num_blocks;
> > -	lptr->modulo = num_extents % lptr->num_blocks;
> > -	lptr->num_recs_tot = num_extents;
> > -	level = 1;
> > -
> > -#ifdef XR_BLD_FREE_TRACE
> > -	fprintf(stderr, "%s 0 %d %d %d %d\n", __func__,
> > -			lptr->num_blocks,
> > -			lptr->num_recs_pb,
> > -			lptr->modulo,
> > -			lptr->num_recs_tot);
> > -#endif
> > -	/*
> > -	 * if we need more levels, set them up.  # of records
> > -	 * per level is the # of blocks in the level below it
> > -	 */
> > -	if (lptr->num_blocks > 1)  {
> > -		for (; btree_curs->level[level - 1].num_blocks > 1
> > -				&& level < XFS_BTREE_MAXLEVELS;
> > -				level++)  {
> > -			lptr = &btree_curs->level[level];
> > -			p_lptr = &btree_curs->level[level - 1];
> > -			lptr->num_blocks = howmany(p_lptr->num_blocks,
> > -					XR_ALLOC_BLOCK_MAXRECS(mp, level));
> > -			lptr->modulo = p_lptr->num_blocks
> > -					% lptr->num_blocks;
> > -			lptr->num_recs_pb = p_lptr->num_blocks
> > -					/ lptr->num_blocks;
> > -			lptr->num_recs_tot = p_lptr->num_blocks;
> > -#ifdef XR_BLD_FREE_TRACE
> > -			fprintf(stderr, "%s %d %d %d %d %d\n", __func__,
> > -					level,
> > -					lptr->num_blocks,
> > -					lptr->num_recs_pb,
> > -					lptr->modulo,
> > -					lptr->num_recs_tot);
> > -#endif
> > -		}
> > -	}
> > -
> > -	ASSERT(lptr->num_blocks == 1);
> > -	btree_curs->num_levels = level;
> > -
> > -	/*
> > -	 * ok, now we have a hypothetical cursor that
> > -	 * will work for both the bno and bcnt trees.
> > -	 * now figure out if using up blocks to set up the
> > -	 * trees will perturb the shape of the freespace tree.
> > -	 * if so, we've over-allocated.  the freespace trees
> > -	 * as they will be *after* accounting for the free space
> > -	 * we've used up will need fewer blocks to to represent
> > -	 * than we've allocated.  We can use the AGFL to hold
> > -	 * xfs_agfl_size (sector/struct xfs_agfl) blocks but that's it.
> > -	 * Thus we limit things to xfs_agfl_size/2 for each of the 2 btrees.
> > -	 * if the number of extra blocks is more than that,
> > -	 * we'll have to be called again.
> > -	 */
> > -	for (blocks_needed = 0, i = 0; i < level; i++)  {
> > -		blocks_needed += btree_curs->level[i].num_blocks;
> > -	}
> > -
> > -	/*
> > -	 * record the # of blocks we've allocated
> > -	 */
> > -	blocks_allocated_pt = blocks_needed;
> > -	blocks_needed *= 2;
> > -	blocks_allocated_total = blocks_needed;
> > -
> > -	/*
> > -	 * figure out how many free extents will be used up by
> > -	 * our space allocation
> > -	 */
> > -	if ((ext_ptr = findfirst_bcnt_extent(agno)) == NULL)
> > -		do_error(_("can't rebuild fs trees -- not enough free space "
> > -			   "on ag %u\n"), agno);
> > -
> > -	while (ext_ptr != NULL && blocks_needed > 0)  {
> > -		if (ext_ptr->ex_blockcount <= blocks_needed)  {
> > -			blocks_needed -= ext_ptr->ex_blockcount;
> > -			extents_used++;
> > -		} else  {
> > -			blocks_needed = 0;
> > -		}
> > -
> > -		ext_ptr = findnext_bcnt_extent(agno, ext_ptr);
> > -
> > -#ifdef XR_BLD_FREE_TRACE
> > -		if (ext_ptr != NULL)  {
> > -			fprintf(stderr, "got next extent [%u %u]\n",
> > -				ext_ptr->ex_startblock, ext_ptr->ex_blockcount);
> > -		} else  {
> > -			fprintf(stderr, "out of extents\n");
> > -		}
> > -#endif
> > -	}
> > -	if (blocks_needed > 0)
> > -		do_error(_("ag %u - not enough free space to build freespace "
> > -			   "btrees\n"), agno);
> > -
> > -	ASSERT(num_extents >= extents_used);
> > -
> > -	num_extents -= extents_used;
> > -
> > -	/*
> > -	 * see if the number of leaf blocks will change as a result
> > -	 * of the number of extents changing
> > -	 */
> > -	if (howmany(num_extents, XR_ALLOC_BLOCK_MAXRECS(mp, 0))
> > -			!= btree_curs->level[0].num_blocks)  {
> > -		/*
> > -		 * yes -- recalculate the cursor.  If the number of
> > -		 * excess (overallocated) blocks is < xfs_agfl_size/2, we're ok.
> > -		 * we can put those into the AGFL.  we don't try
> > -		 * and get things to converge exactly (reach a
> > -		 * state with zero excess blocks) because there
> > -		 * exist pathological cases which will never
> > -		 * converge.  first, check for the zero-case.
> > -		 */
> > -		if (num_extents == 0)  {
> > -			/*
> > -			 * ok, we've used up all the free blocks
> > -			 * trying to lay out the leaf level. go
> > -			 * to a one block (empty) btree and put the
> > -			 * already allocated blocks into the AGFL
> > -			 */
> > -			if (btree_curs->level[0].num_blocks != 1)  {
> > -				/*
> > -				 * we really needed more blocks because
> > -				 * the old tree had more than one level.
> > -				 * this is bad.
> > -				 */
> > -				 do_warn(_("not enough free blocks left to "
> > -					   "describe all free blocks in AG "
> > -					   "%u\n"), agno);
> > -			}
> > -#ifdef XR_BLD_FREE_TRACE
> > -			fprintf(stderr,
> > -				"ag %u -- no free extents, alloc'ed %d\n",
> > -				agno, blocks_allocated_pt);
> > -#endif
> > -			lptr->num_blocks = 1;
> > -			lptr->modulo = 0;
> > -			lptr->num_recs_pb = 0;
> > -			lptr->num_recs_tot = 0;
> > -
> > -			btree_curs->num_levels = 1;
> > -
> > -			/*
> > -			 * don't reset the allocation stats, assume
> > -			 * they're all extra blocks
> > -			 * don't forget to return the total block count
> > -			 * not the per-tree block count.  these are the
> > -			 * extras that will go into the AGFL.  subtract
> > -			 * two for the root blocks.
> > -			 */
> > -			btree_curs->num_tot_blocks = blocks_allocated_pt;
> > -			btree_curs->num_free_blocks = blocks_allocated_pt;
> > -
> > -			*extents = 0;
> > -
> > -			return(blocks_allocated_total - 2);
> > -		}
> > -
> > -		lptr = &btree_curs->level[0];
> > -		lptr->num_blocks = howmany(num_extents,
> > -					XR_ALLOC_BLOCK_MAXRECS(mp, 0));
> > -		lptr->num_recs_pb = num_extents / lptr->num_blocks;
> > -		lptr->modulo = num_extents % lptr->num_blocks;
> > -		lptr->num_recs_tot = num_extents;
> > -		level = 1;
> > -
> > -		/*
> > -		 * if we need more levels, set them up
> > -		 */
> > -		if (lptr->num_blocks > 1)  {
> > -			for (level = 1; btree_curs->level[level-1].num_blocks
> > -					> 1 && level < XFS_BTREE_MAXLEVELS;
> > -					level++)  {
> > -				lptr = &btree_curs->level[level];
> > -				p_lptr = &btree_curs->level[level-1];
> > -				lptr->num_blocks = howmany(p_lptr->num_blocks,
> > -					XR_ALLOC_BLOCK_MAXRECS(mp, level));
> > -				lptr->modulo = p_lptr->num_blocks
> > -						% lptr->num_blocks;
> > -				lptr->num_recs_pb = p_lptr->num_blocks
> > -						/ lptr->num_blocks;
> > -				lptr->num_recs_tot = p_lptr->num_blocks;
> > -			}
> > -		}
> > -		ASSERT(lptr->num_blocks == 1);
> > -		btree_curs->num_levels = level;
> > -
> > -		/*
> > -		 * now figure out the number of excess blocks
> > -		 */
> > -		for (blocks_needed = 0, i = 0; i < level; i++)  {
> > -			blocks_needed += btree_curs->level[i].num_blocks;
> > -		}
> > -		blocks_needed *= 2;
> > -
> > -		ASSERT(blocks_allocated_total >= blocks_needed);
> > -		extra_blocks = blocks_allocated_total - blocks_needed;
> > -	} else  {
> > -		if (extents_used > 0) {
> > -			/*
> > -			 * reset the leaf level geometry to account
> > -			 * for consumed extents.  we can leave the
> > -			 * rest of the cursor alone since the number
> > -			 * of leaf blocks hasn't changed.
> > -			 */
> > -			lptr = &btree_curs->level[0];
> > -
> > -			lptr->num_recs_pb = num_extents / lptr->num_blocks;
> > -			lptr->modulo = num_extents % lptr->num_blocks;
> > -			lptr->num_recs_tot = num_extents;
> > +			error = slab_add(lost_fsb, &fsb);
> > +			if (error)
> > +				do_error(
> > +_("Insufficient memory saving lost blocks.\n"));
> > +			resv->used++;
> >  		}
> > -
> > -		extra_blocks = 0;
> >  	}
> >  
> > -	btree_curs->num_tot_blocks = blocks_allocated_pt;
> > -	btree_curs->num_free_blocks = blocks_allocated_pt;
> > -
> > -	*extents = num_extents;
> > -
> > -	return(extra_blocks);
> > +	xrep_newbt_destroy(&btr->newbt, 0);
> >  }
> >  
> >  /* Map btnum to buffer ops for the types that need it. */
> > @@ -838,268 +568,202 @@ btnum_to_ops(
> >  	}
> >  }
> >  
> > +/*
> > + * Free Space Btrees
> > + *
> > + * We need to leave some free records in the tree for the corner case of
> > + * setting up the AGFL. This may require allocation of blocks, and as
> > + * such can require insertion of new records into the tree (e.g. moving
> > + * a record in the by-count tree when a long extent is shortened). If we
> > + * pack the records into the leaves with no slack space, this requires a
> > + * leaf split to occur and a block to be allocated from the free list.
> > + * If we don't have any blocks on the free list (because we are setting
> > + * it up!), then we fail, and the filesystem will fail with the same
> > + * failure at runtime. Hence leave a couple of records slack space in
> > + * each block to allow immediate modification of the tree without
> > + * requiring splits to be done.
> > + */
> > +
> >  static void
> > -prop_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno,
> > -		bt_status_t *btree_curs, xfs_agblock_t startblock,
> > -		xfs_extlen_t blockcount, int level, xfs_btnum_t btnum)
> > +init_freespace_cursors(
> > +	struct repair_ctx	*sc,
> > +	xfs_agnumber_t		agno,
> > +	unsigned int		free_space,
> > +	unsigned int		*nr_extents,
> > +	int			*extra_blocks,
> > +	struct bt_rebuild	*btr_bno,
> > +	struct bt_rebuild	*btr_cnt)
> >  {
> > -	struct xfs_btree_block	*bt_hdr;
> > -	xfs_alloc_key_t		*bt_key;
> > -	xfs_alloc_ptr_t		*bt_ptr;
> > -	xfs_agblock_t		agbno;
> > -	bt_stat_level_t		*lptr;
> > -	const struct xfs_buf_ops *ops = btnum_to_ops(btnum);
> > +	unsigned int		bno_blocks;
> > +	unsigned int		cnt_blocks;
> >  	int			error;
> >  
> > -	ASSERT(btnum == XFS_BTNUM_BNO || btnum == XFS_BTNUM_CNT);
> > +	init_rebuild(sc, &XFS_RMAP_OINFO_AG, free_space, btr_bno);
> > +	init_rebuild(sc, &XFS_RMAP_OINFO_AG, free_space, btr_cnt);
> >  
> > -	level++;
> > -
> > -	if (level >= btree_curs->num_levels)
> > -		return;
> > -
> > -	lptr = &btree_curs->level[level];
> > -	bt_hdr = XFS_BUF_TO_BLOCK(lptr->buf_p);
> > -
> > -	if (be16_to_cpu(bt_hdr->bb_numrecs) == 0)  {
> > -		/*
> > -		 * only happens once when initializing the
> > -		 * left-hand side of the tree.
> > -		 */
> > -		prop_freespace_cursor(mp, agno, btree_curs, startblock,
> > -				blockcount, level, btnum);
> > -	}
> > +	btr_bno->cur = libxfs_allocbt_stage_cursor(sc->mp,
> > +			&btr_bno->newbt.afake, agno, XFS_BTNUM_BNO);
> > +	btr_cnt->cur = libxfs_allocbt_stage_cursor(sc->mp,
> > +			&btr_cnt->newbt.afake, agno, XFS_BTNUM_CNT);
> >  
> > -	if (be16_to_cpu(bt_hdr->bb_numrecs) ==
> > -				lptr->num_recs_pb + (lptr->modulo > 0))  {
> > -		/*
> > -		 * write out current prev block, grab us a new block,
> > -		 * and set the rightsib pointer of current block
> > -		 */
> > -#ifdef XR_BLD_FREE_TRACE
> > -		fprintf(stderr, " %d ", lptr->prev_agbno);
> > -#endif
> > -		if (lptr->prev_agbno != NULLAGBLOCK) {
> > -			ASSERT(lptr->prev_buf_p != NULL);
> > -			libxfs_buf_mark_dirty(lptr->prev_buf_p);
> > -			libxfs_buf_relse(lptr->prev_buf_p);
> > -		}
> > -		lptr->prev_agbno = lptr->agbno;;
> > -		lptr->prev_buf_p = lptr->buf_p;
> > -		agbno = get_next_blockaddr(agno, level, btree_curs);
> > +	/*
> > +	 * Now we need to allocate blocks for the free space btrees using the
> > +	 * free space records we're about to put in them.  Every record we use
> > +	 * can change the shape of the free space trees, so we recompute the
> > +	 * btree shape until we stop needing /more/ blocks.  If we have any
> > +	 * left over we'll stash them in the AGFL when we're done.
> > +	 */
> > +	do {
> > +		unsigned int	num_freeblocks;
> >  
> > -		bt_hdr->bb_u.s.bb_rightsib = cpu_to_be32(agbno);
> > +		bno_blocks = btr_bno->bload.nr_blocks;
> > +		cnt_blocks = btr_cnt->bload.nr_blocks;
> >  
> > -		error = -libxfs_buf_get(mp->m_dev,
> > -				XFS_AGB_TO_DADDR(mp, agno, agbno),
> > -				XFS_FSB_TO_BB(mp, 1), &lptr->buf_p);
> > +		/* Compute how many bnobt blocks we'll need. */
> > +		error = -libxfs_btree_bload_compute_geometry(btr_bno->cur,
> > +				&btr_bno->bload, *nr_extents);
> >  		if (error)
> >  			do_error(
> > -	_("Cannot grab free space btree buffer, err=%d"),
> > -					error);
> > -		lptr->agbno = agbno;
> > +_("Unable to compute free space by block btree geometry, error %d.\n"), -error);
> >  
> > -		if (lptr->modulo)
> > -			lptr->modulo--;
> > -
> > -		/*
> > -		 * initialize block header
> > -		 */
> > -		lptr->buf_p->b_ops = ops;
> > -		bt_hdr = XFS_BUF_TO_BLOCK(lptr->buf_p);
> > -		memset(bt_hdr, 0, mp->m_sb.sb_blocksize);
> > -		libxfs_btree_init_block(mp, lptr->buf_p, btnum, level,
> > -					0, agno);
> > +		/* Compute how many cntbt blocks we'll need. */
> > +		error = -libxfs_btree_bload_compute_geometry(btr_bno->cur,
> > +				&btr_cnt->bload, *nr_extents);
> > +		if (error)
> > +			do_error(
> > +_("Unable to compute free space by length btree geometry, error %d.\n"), -error);
> >  
> > -		bt_hdr->bb_u.s.bb_leftsib = cpu_to_be32(lptr->prev_agbno);
> > +		/* We don't need any more blocks, so we're done. */
> > +		if (bno_blocks >= btr_bno->bload.nr_blocks &&
> > +		    cnt_blocks >= btr_cnt->bload.nr_blocks)
> > +			break;
> >  
> > -		/*
> > -		 * propagate extent record for first extent in new block up
> > -		 */
> > -		prop_freespace_cursor(mp, agno, btree_curs, startblock,
> > -				blockcount, level, btnum);
> > -	}
> > -	/*
> > -	 * add extent info to current block
> > -	 */
> > -	be16_add_cpu(&bt_hdr->bb_numrecs, 1);
> > +		/* Allocate however many more blocks we need this time. */
> > +		if (bno_blocks < btr_bno->bload.nr_blocks)
> > +			setup_rebuild(sc->mp, agno, btr_bno,
> > +					btr_bno->bload.nr_blocks - bno_blocks);
> > +		if (cnt_blocks < btr_cnt->bload.nr_blocks)
> > +			setup_rebuild(sc->mp, agno, btr_cnt,
> > +					btr_cnt->bload.nr_blocks - cnt_blocks);
> >  
> > -	bt_key = XFS_ALLOC_KEY_ADDR(mp, bt_hdr,
> > -				be16_to_cpu(bt_hdr->bb_numrecs));
> > -	bt_ptr = XFS_ALLOC_PTR_ADDR(mp, bt_hdr,
> > -				be16_to_cpu(bt_hdr->bb_numrecs),
> > -				mp->m_alloc_mxr[1]);
> > +		/* Ok, now how many free space records do we have? */
> > +		*nr_extents = count_bno_extents_blocks(agno, &num_freeblocks);
> > +	} while (1);
> >  
> > -	bt_key->ar_startblock = cpu_to_be32(startblock);
> > -	bt_key->ar_blockcount = cpu_to_be32(blockcount);
> > -	*bt_ptr = cpu_to_be32(btree_curs->level[level-1].agbno);
> > +	*extra_blocks = (bno_blocks - btr_bno->bload.nr_blocks) +
> > +			(cnt_blocks - btr_cnt->bload.nr_blocks);
> >  }
> >  
> > -/*
> > - * rebuilds a freespace tree given a cursor and type
> > - * of tree to build (bno or bcnt).  returns the number of free blocks
> > - * represented by the tree.
> > - */
> > -static xfs_extlen_t
> > -build_freespace_tree(xfs_mount_t *mp, xfs_agnumber_t agno,
> > -		bt_status_t *btree_curs, xfs_btnum_t btnum)
> > +static void
> > +get_freesp_data(
> > +	struct xfs_btree_cur		*cur,
> > +	struct extent_tree_node		*bno_rec,
> > +	xfs_agblock_t			*freeblks)
> >  {
> > -	xfs_agnumber_t		i;
> > -	xfs_agblock_t		j;
> > -	struct xfs_btree_block	*bt_hdr;
> > -	xfs_alloc_rec_t		*bt_rec;
> > -	int			level;
> > -	xfs_agblock_t		agbno;
> > -	extent_tree_node_t	*ext_ptr;
> > -	bt_stat_level_t		*lptr;
> > -	xfs_extlen_t		freeblks;
> > -	const struct xfs_buf_ops *ops = btnum_to_ops(btnum);
> > -	int			error;
> > +	struct xfs_alloc_rec_incore	*arec = &cur->bc_rec.a;
> >  
> > -	ASSERT(btnum == XFS_BTNUM_BNO || btnum == XFS_BTNUM_CNT);
> > -
> > -#ifdef XR_BLD_FREE_TRACE
> > -	fprintf(stderr, "in build_freespace_tree, agno = %d\n", agno);
> > -#endif
> > -	level = btree_curs->num_levels;
> > -	freeblks = 0;
> > +	arec->ar_startblock = bno_rec->ex_startblock;
> > +	arec->ar_blockcount = bno_rec->ex_blockcount;
> > +	if (freeblks)
> > +		*freeblks += bno_rec->ex_blockcount;
> > +}
> >  
> > -	ASSERT(level > 0);
> > +/* Grab one bnobt record. */
> > +static int
> > +get_bnobt_record(
> > +	struct xfs_btree_cur		*cur,
> > +	void				*priv)
> > +{
> > +	struct bt_rebuild		*btr = priv;
> >  
> > -	/*
> > -	 * initialize the first block on each btree level
> > -	 */
> > -	for (i = 0; i < level; i++)  {
> > -		lptr = &btree_curs->level[i];
> > +	get_freesp_data(cur, btr->bno_rec, btr->freeblks);
> > +	btr->bno_rec = findnext_bno_extent(btr->bno_rec);
> > +	return 0;
> > +}
> >  
> > -		agbno = get_next_blockaddr(agno, i, btree_curs);
> > -		error = -libxfs_buf_get(mp->m_dev,
> > -				XFS_AGB_TO_DADDR(mp, agno, agbno),
> > -				XFS_FSB_TO_BB(mp, 1), &lptr->buf_p);
> > -		if (error)
> > -			do_error(
> > -	_("Cannot grab free space btree buffer, err=%d"),
> > -					error);
> > +/* Rebuild a free space by block number btree. */
> > +static void
> > +build_bnobt(
> > +	struct repair_ctx	*sc,
> > +	xfs_agnumber_t		agno,
> > +	struct bt_rebuild	*btr_bno,
> > +	xfs_agblock_t		*freeblks)
> > +{
> > +	int			error;
> >  
> > -		if (i == btree_curs->num_levels - 1)
> > -			btree_curs->root = agbno;
> > +	*freeblks = 0;
> > +	btr_bno->bload.get_record = get_bnobt_record;
> > +	btr_bno->bload.claim_block = rebuild_claim_block;
> > +	btr_bno->bno_rec = findfirst_bno_extent(agno);
> > +	btr_bno->freeblks = freeblks;
> >  
> > -		lptr->agbno = agbno;
> > -		lptr->prev_agbno = NULLAGBLOCK;
> > -		lptr->prev_buf_p = NULL;
> > -		/*
> > -		 * initialize block header
> > -		 */
> > -		lptr->buf_p->b_ops = ops;
> > -		bt_hdr = XFS_BUF_TO_BLOCK(lptr->buf_p);
> > -		memset(bt_hdr, 0, mp->m_sb.sb_blocksize);
> > -		libxfs_btree_init_block(mp, lptr->buf_p, btnum, i, 0, agno);
> > -	}
> > -	/*
> > -	 * run along leaf, setting up records.  as we have to switch
> > -	 * blocks, call the prop_freespace_cursor routine to set up the new
> > -	 * pointers for the parent.  that can recurse up to the root
> > -	 * if required.  set the sibling pointers for leaf level here.
> > -	 */
> > -	if (btnum == XFS_BTNUM_BNO)
> > -		ext_ptr = findfirst_bno_extent(agno);
> > -	else
> > -		ext_ptr = findfirst_bcnt_extent(agno);
> > +	error = -libxfs_trans_alloc_empty(sc->mp, &sc->tp);
> > +	if (error)
> > +		do_error(
> > +_("Insufficient memory to construct bnobt rebuild transaction.\n"));
> >  
> > -#ifdef XR_BLD_FREE_TRACE
> > -	fprintf(stderr, "bft, agno = %d, start = %u, count = %u\n",
> > -		agno, ext_ptr->ex_startblock, ext_ptr->ex_blockcount);
> > -#endif
> > +	/* Add all observed bnobt records. */
> > +	error = -libxfs_btree_bload(btr_bno->cur, &btr_bno->bload, btr_bno);
> > +	if (error)
> > +		do_error(
> > +_("Error %d while creating bnobt btree for AG %u.\n"), error, agno);
> >  
> > -	lptr = &btree_curs->level[0];
> > +	/* Since we're not writing the AGF yet, no need to commit the cursor */
> > +	libxfs_btree_del_cursor(btr_bno->cur, 0);
> > +	error = -libxfs_trans_commit(sc->tp);
> > +	if (error)
> > +		do_error(
> > +_("Error %d while writing bnobt btree for AG %u.\n"), error, agno);
> > +	sc->tp = NULL;
> > +}
> >  
> > -	for (i = 0; i < btree_curs->level[0].num_blocks; i++)  {
> > -		/*
> > -		 * block initialization, lay in block header
> > -		 */
> > -		lptr->buf_p->b_ops = ops;
> > -		bt_hdr = XFS_BUF_TO_BLOCK(lptr->buf_p);
> > -		memset(bt_hdr, 0, mp->m_sb.sb_blocksize);
> > -		libxfs_btree_init_block(mp, lptr->buf_p, btnum, 0, 0, agno);
> > +/* Grab one cntbt record. */
> > +static int
> > +get_cntbt_record(
> > +	struct xfs_btree_cur		*cur,
> > +	void				*priv)
> > +{
> > +	struct bt_rebuild		*btr = priv;
> >  
> > -		bt_hdr->bb_u.s.bb_leftsib = cpu_to_be32(lptr->prev_agbno);
> > -		bt_hdr->bb_numrecs = cpu_to_be16(lptr->num_recs_pb +
> > -							(lptr->modulo > 0));
> > -#ifdef XR_BLD_FREE_TRACE
> > -		fprintf(stderr, "bft, bb_numrecs = %d\n",
> > -				be16_to_cpu(bt_hdr->bb_numrecs));
> > -#endif
> > +	get_freesp_data(cur, btr->bno_rec, btr->freeblks);
> > +	btr->bno_rec = findnext_bcnt_extent(cur->bc_ag.agno, btr->bno_rec);
> > +	return 0;
> > +}
> >  
> > -		if (lptr->modulo > 0)
> > -			lptr->modulo--;
> > +/* Rebuild a freespace by count btree. */
> > +static void
> > +build_cntbt(
> > +	struct repair_ctx	*sc,
> > +	xfs_agnumber_t		agno,
> > +	struct bt_rebuild	*btr_cnt,
> > +	xfs_agblock_t		*freeblks)
> > +{
> > +	int			error;
> >  
> > -		/*
> > -		 * initialize values in the path up to the root if
> > -		 * this is a multi-level btree
> > -		 */
> > -		if (btree_curs->num_levels > 1)
> > -			prop_freespace_cursor(mp, agno, btree_curs,
> > -					ext_ptr->ex_startblock,
> > -					ext_ptr->ex_blockcount,
> > -					0, btnum);
> > -
> > -		bt_rec = (xfs_alloc_rec_t *)
> > -			  ((char *)bt_hdr + XFS_ALLOC_BLOCK_LEN(mp));
> > -		for (j = 0; j < be16_to_cpu(bt_hdr->bb_numrecs); j++) {
> > -			ASSERT(ext_ptr != NULL);
> > -			bt_rec[j].ar_startblock = cpu_to_be32(
> > -							ext_ptr->ex_startblock);
> > -			bt_rec[j].ar_blockcount = cpu_to_be32(
> > -							ext_ptr->ex_blockcount);
> > -			freeblks += ext_ptr->ex_blockcount;
> > -			if (btnum == XFS_BTNUM_BNO)
> > -				ext_ptr = findnext_bno_extent(ext_ptr);
> > -			else
> > -				ext_ptr = findnext_bcnt_extent(agno, ext_ptr);
> > -#if 0
> > -#ifdef XR_BLD_FREE_TRACE
> > -			if (ext_ptr == NULL)
> > -				fprintf(stderr, "null extent pointer, j = %d\n",
> > -					j);
> > -			else
> > -				fprintf(stderr,
> > -				"bft, agno = %d, start = %u, count = %u\n",
> > -					agno, ext_ptr->ex_startblock,
> > -					ext_ptr->ex_blockcount);
> > -#endif
> > -#endif
> > -		}
> > +	*freeblks = 0;
> > +	btr_cnt->bload.get_record = get_cntbt_record;
> > +	btr_cnt->bload.claim_block = rebuild_claim_block;
> > +	btr_cnt->bno_rec = findfirst_bcnt_extent(agno);
> > +	btr_cnt->freeblks = freeblks;
> >  
> > -		if (ext_ptr != NULL)  {
> > -			/*
> > -			 * get next leaf level block
> > -			 */
> > -			if (lptr->prev_buf_p != NULL)  {
> > -#ifdef XR_BLD_FREE_TRACE
> > -				fprintf(stderr, " writing fst agbno %u\n",
> > -					lptr->prev_agbno);
> > -#endif
> > -				ASSERT(lptr->prev_agbno != NULLAGBLOCK);
> > -				libxfs_buf_mark_dirty(lptr->prev_buf_p);
> > -				libxfs_buf_relse(lptr->prev_buf_p);
> > -			}
> > -			lptr->prev_buf_p = lptr->buf_p;
> > -			lptr->prev_agbno = lptr->agbno;
> > -			lptr->agbno = get_next_blockaddr(agno, 0, btree_curs);
> > -			bt_hdr->bb_u.s.bb_rightsib = cpu_to_be32(lptr->agbno);
> > +	error = -libxfs_trans_alloc_empty(sc->mp, &sc->tp);
> > +	if (error)
> > +		do_error(
> > +_("Insufficient memory to construct cntbt rebuild transaction.\n"));
> >  
> > -			error = -libxfs_buf_get(mp->m_dev,
> > -					XFS_AGB_TO_DADDR(mp, agno, lptr->agbno),
> > -					XFS_FSB_TO_BB(mp, 1),
> > -					&lptr->buf_p);
> > -			if (error)
> > -				do_error(
> > -	_("Cannot grab free space btree buffer, err=%d"),
> > -						error);
> > -		}
> > -	}
> > +	/* Add all observed cntbt records. */
> > +	error = -libxfs_btree_bload(btr_cnt->cur, &btr_cnt->bload, btr_cnt);
> > +	if (error)
> > +		do_error(
> > +_("Error %d while creating cntbt btree for AG %u.\n"), error, agno);
> >  
> > -	return(freeblks);
> > +	/* Since we're not writing the AGF yet, no need to commit the cursor */
> > +	libxfs_btree_del_cursor(btr_cnt->cur, 0);
> > +	error = -libxfs_trans_commit(sc->tp);
> > +	if (error)
> > +		do_error(
> > +_("Error %d while writing cntbt btree for AG %u.\n"), error, agno);
> > +	sc->tp = NULL;
> >  }
> >  
> >  /*
> > @@ -2233,6 +1897,27 @@ _("Insufficient memory to construct refcount cursor."));
> >  	free_slab_cursor(&refc_cur);
> >  }
> >  
> > +/* Fill the AGFL with any leftover bnobt rebuilder blocks. */
> > +static void
> > +fill_agfl(
> > +	struct bt_rebuild	*btr,
> > +	__be32			*agfl_bnos,
> > +	int			*i)
> > +{
> > +	struct xrep_newbt_resv	*resv, *n;
> > +	struct xfs_mount	*mp = btr->newbt.sc->mp;
> > +
> > +	for_each_xrep_newbt_reservation(&btr->newbt, resv, n) {
> > +		xfs_agblock_t	bno;
> > +
> > +		bno = XFS_FSB_TO_AGBNO(mp, resv->fsbno + resv->used);
> > +		while (resv->used < resv->len && (*i) < libxfs_agfl_size(mp)) {
> > +			agfl_bnos[(*i)++] = cpu_to_be32(bno++);
> > +			resv->used++;
> > +		}
> > +	}
> > +}
> > +
> >  /*
> >   * build both the agf and the agfl for an agno given both
> >   * btree cursors.
> > @@ -2243,8 +1928,8 @@ static void
> >  build_agf_agfl(
> >  	struct xfs_mount	*mp,
> >  	xfs_agnumber_t		agno,
> > -	struct bt_status	*bno_bt,
> > -	struct bt_status	*bcnt_bt,
> > +	struct bt_rebuild	*btr_bno,
> > +	struct bt_rebuild	*btr_cnt,
> >  	xfs_extlen_t		freeblks,	/* # free blocks in tree */
> >  	int			lostblocks,	/* # blocks that will be lost */
> >  	struct bt_status	*rmap_bt,
> > @@ -2256,7 +1941,6 @@ build_agf_agfl(
> >  	int			i;
> >  	struct xfs_agfl		*agfl;
> >  	struct xfs_agf		*agf;
> > -	xfs_fsblock_t		fsb;
> >  	__be32			*freelist;
> >  	int			error;
> >  
> > @@ -2288,10 +1972,14 @@ build_agf_agfl(
> >  		agf->agf_length = cpu_to_be32(mp->m_sb.sb_dblocks -
> >  			(xfs_rfsblock_t) mp->m_sb.sb_agblocks * agno);
> >  
> > -	agf->agf_roots[XFS_BTNUM_BNO] = cpu_to_be32(bno_bt->root);
> > -	agf->agf_levels[XFS_BTNUM_BNO] = cpu_to_be32(bno_bt->num_levels);
> > -	agf->agf_roots[XFS_BTNUM_CNT] = cpu_to_be32(bcnt_bt->root);
> > -	agf->agf_levels[XFS_BTNUM_CNT] = cpu_to_be32(bcnt_bt->num_levels);
> > +	agf->agf_roots[XFS_BTNUM_BNO] =
> > +			cpu_to_be32(btr_bno->newbt.afake.af_root);
> > +	agf->agf_levels[XFS_BTNUM_BNO] =
> > +			cpu_to_be32(btr_bno->newbt.afake.af_levels);
> > +	agf->agf_roots[XFS_BTNUM_CNT] =
> > +			cpu_to_be32(btr_cnt->newbt.afake.af_root);
> > +	agf->agf_levels[XFS_BTNUM_CNT] =
> > +			cpu_to_be32(btr_cnt->newbt.afake.af_levels);
> >  	agf->agf_roots[XFS_BTNUM_RMAP] = cpu_to_be32(rmap_bt->root);
> >  	agf->agf_levels[XFS_BTNUM_RMAP] = cpu_to_be32(rmap_bt->num_levels);
> >  	agf->agf_freeblks = cpu_to_be32(freeblks);
> > @@ -2311,9 +1999,8 @@ build_agf_agfl(
> >  		 * Don't count the root blocks as they are already
> >  		 * accounted for.
> >  		 */
> > -		blks = (bno_bt->num_tot_blocks - bno_bt->num_free_blocks) +
> > -			(bcnt_bt->num_tot_blocks - bcnt_bt->num_free_blocks) -
> > -			2;
> > +		blks = btr_bno->newbt.afake.af_blocks +
> > +			btr_cnt->newbt.afake.af_blocks - 2;
> >  		if (xfs_sb_version_hasrmapbt(&mp->m_sb))
> >  			blks += rmap_bt->num_tot_blocks - rmap_bt->num_free_blocks - 1;
> >  		agf->agf_btreeblks = cpu_to_be32(blks);
> > @@ -2357,49 +2044,14 @@ build_agf_agfl(
> >  	}
> >  
> >  	freelist = xfs_buf_to_agfl_bno(agfl_buf);
> > +	i = 0;
> >  
> > -	/*
> > -	 * do we have left-over blocks in the btree cursors that should
> > -	 * be used to fill the AGFL?
> > -	 */
> > -	if (bno_bt->num_free_blocks > 0 || bcnt_bt->num_free_blocks > 0)  {
> > -		/*
> > -		 * yes, now grab as many blocks as we can
> > -		 */
> > -		i = 0;
> > -		while (bno_bt->num_free_blocks > 0 && i < libxfs_agfl_size(mp))
> > -		{
> > -			freelist[i] = cpu_to_be32(
> > -					get_next_blockaddr(agno, 0, bno_bt));
> > -			i++;
> > -		}
> > -
> > -		while (bcnt_bt->num_free_blocks > 0 && i < libxfs_agfl_size(mp))
> > -		{
> > -			freelist[i] = cpu_to_be32(
> > -					get_next_blockaddr(agno, 0, bcnt_bt));
> > -			i++;
> > -		}
> > -		/*
> > -		 * now throw the rest of the blocks away and complain
> > -		 */
> > -		while (bno_bt->num_free_blocks > 0) {
> > -			fsb = XFS_AGB_TO_FSB(mp, agno,
> > -					get_next_blockaddr(agno, 0, bno_bt));
> > -			error = slab_add(lost_fsb, &fsb);
> > -			if (error)
> > -				do_error(
> > -_("Insufficient memory saving lost blocks.\n"));
> > -		}
> > -		while (bcnt_bt->num_free_blocks > 0) {
> > -			fsb = XFS_AGB_TO_FSB(mp, agno,
> > -					get_next_blockaddr(agno, 0, bcnt_bt));
> > -			error = slab_add(lost_fsb, &fsb);
> > -			if (error)
> > -				do_error(
> > -_("Insufficient memory saving lost blocks.\n"));
> > -		}
> > +	/* Fill the AGFL with leftover blocks or save them for later. */
> > +	fill_agfl(btr_bno, freelist, &i);
> > +	fill_agfl(btr_cnt, freelist, &i);
> >  
> > +	/* Set the AGF counters for the AGFL. */
> > +	if (i > 0) {
> >  		agf->agf_flfirst = 0;
> >  		agf->agf_fllast = cpu_to_be32(i - 1);
> >  		agf->agf_flcount = cpu_to_be32(i);
> > @@ -2497,8 +2149,8 @@ phase5_func(
> >  	uint64_t		num_free_inos;
> >  	uint64_t		finobt_num_inos;
> >  	uint64_t		finobt_num_free_inos;
> > -	bt_status_t		bno_btree_curs;
> > -	bt_status_t		bcnt_btree_curs;
> > +	struct bt_rebuild	btr_bno;
> > +	struct bt_rebuild	btr_cnt;
> >  	bt_status_t		ino_btree_curs;
> >  	bt_status_t		fino_btree_curs;
> >  	bt_status_t		rmap_btree_curs;
> > @@ -2506,9 +2158,7 @@ phase5_func(
> >  	int			extra_blocks = 0;
> >  	uint			num_freeblocks;
> >  	xfs_extlen_t		freeblks1;
> > -#ifdef DEBUG
> >  	xfs_extlen_t		freeblks2;
> > -#endif
> >  	xfs_agblock_t		num_extents;
> >  
> >  	if (verbose)
> > @@ -2517,7 +2167,7 @@ phase5_func(
> >  	/*
> >  	 * build up incore bno and bcnt extent btrees
> >  	 */
> > -	num_extents = mk_incore_fstree(mp, agno);
> > +	num_extents = mk_incore_fstree(mp, agno, &num_freeblocks);
> >  
> >  #ifdef XR_BLD_FREE_TRACE
> >  	fprintf(stderr, "# of bno extents is %d\n",
> > @@ -2596,8 +2246,8 @@ phase5_func(
> >  	/*
> >  	 * track blocks that we might really lose
> >  	 */
> > -	extra_blocks = calculate_freespace_cursor(mp, agno,
> > -				&num_extents, &bno_btree_curs);
> > +	init_freespace_cursors(&sc, agno, num_freeblocks, &num_extents,
> > +			&extra_blocks, &btr_bno, &btr_cnt);
> >  
> >  	/*
> >  	 * freespace btrees live in the "free space" but
> > @@ -2615,13 +2265,6 @@ phase5_func(
> >  	if (extra_blocks > 0)
> >  		sb_fdblocks_ag[agno] -= extra_blocks;
> >  
> > -	bcnt_btree_curs = bno_btree_curs;
> > -
> > -	bno_btree_curs.owner = XFS_RMAP_OWN_AG;
> > -	bcnt_btree_curs.owner = XFS_RMAP_OWN_AG;
> > -	setup_cursor(mp, agno, &bno_btree_curs);
> > -	setup_cursor(mp, agno, &bcnt_btree_curs);
> > -
> >  #ifdef XR_BLD_FREE_TRACE
> >  	fprintf(stderr, "# of bno extents is %d\n",
> >  			count_bno_extents(agno));
> > @@ -2629,25 +2272,13 @@ phase5_func(
> >  			count_bcnt_extents(agno));
> >  #endif
> >  
> > -	/*
> > -	 * now rebuild the freespace trees
> > -	 */
> > -	freeblks1 = build_freespace_tree(mp, agno,
> > -				&bno_btree_curs, XFS_BTNUM_BNO);
> > +	/* Rebuild the freespace btrees. */
> > +	build_bnobt(&sc, agno, &btr_bno, &freeblks1);
> > +	build_cntbt(&sc, agno, &btr_cnt, &freeblks2);
> > +
> >  #ifdef XR_BLD_FREE_TRACE
> > -	fprintf(stderr, "# of free blocks == %d\n", freeblks1);
> > -#endif
> > -	write_cursor(&bno_btree_curs);
> > -
> > -#ifdef DEBUG
> > -	freeblks2 = build_freespace_tree(mp, agno,
> > -				&bcnt_btree_curs, XFS_BTNUM_CNT);
> > -#else
> > -	(void) build_freespace_tree(mp, agno,
> > -				&bcnt_btree_curs, XFS_BTNUM_CNT);
> > +	fprintf(stderr, "# of free blocks == %d/%d\n", freeblks1, freeblks2);
> >  #endif
> > -	write_cursor(&bcnt_btree_curs);
> > -
> >  	ASSERT(freeblks1 == freeblks2);
> >  
> >  	if (xfs_sb_version_hasrmapbt(&mp->m_sb)) {
> > @@ -2665,9 +2296,9 @@ phase5_func(
> >  	/*
> >  	 * set up agf and agfl
> >  	 */
> > -	build_agf_agfl(mp, agno, &bno_btree_curs,
> > -			&bcnt_btree_curs, freeblks1, extra_blocks,
> > +	build_agf_agfl(mp, agno, &btr_bno, &btr_cnt, freeblks1, extra_blocks,
> >  			&rmap_btree_curs, &refcnt_btree_curs, lost_fsb);
> > +
> >  	/*
> >  	 * build inode allocation tree.
> >  	 */
> > @@ -2691,15 +2322,14 @@ phase5_func(
> >  	/*
> >  	 * tear down cursors
> >  	 */
> > -	finish_cursor(&bno_btree_curs);
> > -	finish_cursor(&ino_btree_curs);
> > +	finish_rebuild(mp, &btr_bno, lost_fsb);
> > +	finish_rebuild(mp, &btr_cnt, lost_fsb);
> >  	if (xfs_sb_version_hasrmapbt(&mp->m_sb))
> >  		finish_cursor(&rmap_btree_curs);
> >  	if (xfs_sb_version_hasreflink(&mp->m_sb))
> >  		finish_cursor(&refcnt_btree_curs);
> >  	if (xfs_sb_version_hasfinobt(&mp->m_sb))
> >  		finish_cursor(&fino_btree_curs);
> > -	finish_cursor(&bcnt_btree_curs);
> >  
> >  	/*
> >  	 * release the incore per-AG bno/bcnt trees so
> > 
>