xfs: support btrees with overlapping intervals for keys

On a filesystem with both reflink and reverse mapping enabled, it's
possible to have multiple rmap records referring to the same blocks on
disk.  When overlapping intervals are possible, querying a classic
btree to find all records intersecting a given interval is inefficient
because we cannot use the left side of the search interval to filter
out non-matching records the same way that we can use the existing
btree key to filter out records coming after the right side of the
search interval.  This will become important once we want to use the
rmap btree to rebuild BMBTs, or implement the (future) fsmap ioctl.

(For the non-overlapping case, we can perform such queries trivially
by starting at the left side of the interval and walking the tree
until we pass the right side.)

Therefore, extend the btree code to come closer to supporting
intervals as a first-class record attribute.  This involves widening
the btree node's key space to store both the lowest key reachable via
the node pointer (as the btree does now) and the highest key reachable
via the same pointer and teaching the btree modifying functions to
keep the highest-key records up to date.

This behavior can be turned on via a new btree ops flag so that btrees
that cannot store overlapping intervals don't pay the overhead costs
in terms of extra code and disk format changes.

When we're deleting a record in a btree that supports overlapped
interval records and the deletion results in two btree blocks being
joined, we defer updating the high/low keys until after all possible
joining (at higher levels in the tree) have finished.  At this point,
the btree pointers at all levels have been updated to remove the empty
blocks and we can update the low and high keys.

When we're doing this, we must be careful to update the keys of all
node pointers up to the root instead of stopping at the first set of
keys that don't need updating.  This is because it's possible for a
single deletion to cause joining of multiple levels of tree, and so
we need to update everything going back to the root.

The diff_two_keys functions return < 0, 0, or > 0 if key1 is less than,
equal to, or greater than key2, respectively.  This is consistent
with the rest of the kernel and the C library.

In btree_updkeys(), we need to evaluate the force_all parameter before
running the key diff to avoid reading uninitialized memory when we're
forcing a key update.  This happens when we've allocated an empty slot
at level N + 1 to point to a new block at level N and we're in the
process of filling out the new keys.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_btree.c

@@ -51,7 +51,6 @@ static const __uint32_t xfs_magics[2][XFS_BTNUM_MAX] = {
 #define xfs_btree_magic(cur) \
 	xfs_magics[!!((cur)->bc_flags & XFS_BTREE_CRC_BLOCKS)][cur->bc_btnum]
 
-
 STATIC int				/* error (0 or EFSCORRUPTED) */
 xfs_btree_check_lblock(
 	struct xfs_btree_cur	*cur,	/* btree cursor */
@@ -428,6 +427,50 @@ xfs_btree_dup_cursor(
  * into a btree block (xfs_btree_*_offset) or return a pointer to the given
  * record, key or pointer (xfs_btree_*_addr).  Note that all addressing
  * inside the btree block is done using indices starting at one, not zero!
+ *
+ * If XFS_BTREE_OVERLAPPING is set, then this btree supports keys containing
+ * overlapping intervals.  In such a tree, records are still sorted lowest to
+ * highest and indexed by the smallest key value that refers to the record.
+ * However, nodes are different: each pointer has two associated keys -- one
+ * indexing the lowest key available in the block(s) below (the same behavior
+ * as the key in a regular btree) and another indexing the highest key
+ * available in the block(s) below.  Because records are /not/ sorted by the
+ * highest key, all leaf block updates require us to compute the highest key
+ * that matches any record in the leaf and to recursively update the high keys
+ * in the nodes going further up in the tree, if necessary.  Nodes look like
+ * this:
+ *
+ *		+--------+-----+-----+-----+-----+-----+-------+-------+-----+
+ * Non-Leaf:	| header | lo1 | hi1 | lo2 | hi2 | ... | ptr 1 | ptr 2 | ... |
+ *		+--------+-----+-----+-----+-----+-----+-------+-------+-----+
+ *
+ * To perform an interval query on an overlapped tree, perform the usual
+ * depth-first search and use the low and high keys to decide if we can skip
+ * that particular node.  If a leaf node is reached, return the records that
+ * intersect the interval.  Note that an interval query may return numerous
+ * entries.  For a non-overlapped tree, simply search for the record associated
+ * with the lowest key and iterate forward until a non-matching record is
+ * found.  Section 14.3 ("Interval Trees") of _Introduction to Algorithms_ by
+ * Cormen, Leiserson, Rivest, and Stein (2nd or 3rd ed. only) discuss this in
+ * more detail.
+ *
+ * Why do we care about overlapping intervals?  Let's say you have a bunch of
+ * reverse mapping records on a reflink filesystem:
+ *
+ * 1: +- file A startblock B offset C length D -----------+
+ * 2:      +- file E startblock F offset G length H --------------+
+ * 3:      +- file I startblock F offset J length K --+
+ * 4:                                                        +- file L... --+
+ *
+ * Now say we want to map block (B+D) into file A at offset (C+D).  Ideally,
+ * we'd simply increment the length of record 1.  But how do we find the record
+ * that ends at (B+D-1) (i.e. record 1)?  A LE lookup of (B+D-1) would return
+ * record 3 because the keys are ordered first by startblock.  An interval
+ * query would return records 1 and 2 because they both overlap (B+D-1), and
+ * from that we can pick out record 1 as the appropriate left neighbor.
+ *
+ * In the non-overlapped case you can do a LE lookup and decrement the cursor
+ * because a record's interval must end before the next record.
  */
 
 /*
@@ -478,6 +521,18 @@ xfs_btree_key_offset(
 		(n - 1) * cur->bc_ops->key_len;
 }
 
+/*
+ * Calculate offset of the n-th high key in a btree block.
+ */
+STATIC size_t
+xfs_btree_high_key_offset(
+	struct xfs_btree_cur	*cur,
+	int			n)
+{
+	return xfs_btree_block_len(cur) +
+		(n - 1) * cur->bc_ops->key_len + (cur->bc_ops->key_len / 2);
+}
+
 /*
  * Calculate offset of the n-th block pointer in a btree block.
  */
@@ -518,6 +573,19 @@ xfs_btree_key_addr(
 		((char *)block + xfs_btree_key_offset(cur, n));
 }
 
+/*
+ * Return a pointer to the n-th high key in the btree block.
+ */
+STATIC union xfs_btree_key *
+xfs_btree_high_key_addr(
+	struct xfs_btree_cur	*cur,
+	int			n,
+	struct xfs_btree_block	*block)
+{
+	return (union xfs_btree_key *)
+		((char *)block + xfs_btree_high_key_offset(cur, n));
+}
+
 /*
  * Return a pointer to the n-th block pointer in the btree block.
  */
@@ -1902,6 +1970,73 @@ xfs_btree_get_node_keys(
 	memcpy(key, xfs_btree_key_addr(cur, 1, block), cur->bc_ops->key_len);
 }
 
+/* Find the high key storage area from a regular key. */
+STATIC union xfs_btree_key *
+xfs_btree_high_key_from_key(
+	struct xfs_btree_cur	*cur,
+	union xfs_btree_key	*key)
+{
+	ASSERT(cur->bc_flags & XFS_BTREE_OVERLAPPING);
+	return (union xfs_btree_key *)((char *)key +
+			(cur->bc_ops->key_len / 2));
+}
+
+/* Determine the low and high keys of a leaf block (overlapped) */
+void
+xfs_btree_get_leaf_keys_overlapped(
+	struct xfs_btree_cur	*cur,
+	struct xfs_btree_block	*block,
+	union xfs_btree_key	*key)
+{
+	int			n;
+	union xfs_btree_rec	*rec;
+	union xfs_btree_key	max_hkey;
+	union xfs_btree_key	hkey;
+	union xfs_btree_key	*high;
+
+	ASSERT(cur->bc_flags & XFS_BTREE_OVERLAPPING);
+	rec = xfs_btree_rec_addr(cur, 1, block);
+	cur->bc_ops->init_key_from_rec(key, rec);
+
+	cur->bc_ops->init_high_key_from_rec(&max_hkey, rec);
+	for (n = 2; n <= xfs_btree_get_numrecs(block); n++) {
+		rec = xfs_btree_rec_addr(cur, n, block);
+		cur->bc_ops->init_high_key_from_rec(&hkey, rec);
+		if (cur->bc_ops->diff_two_keys(cur, &hkey, &max_hkey) > 0)
+			max_hkey = hkey;
+	}
+
+	high = xfs_btree_high_key_from_key(cur, key);
+	memcpy(high, &max_hkey, cur->bc_ops->key_len / 2);
+}
+
+/* Determine the low and high keys of a node block (overlapped) */
+void
+xfs_btree_get_node_keys_overlapped(
+	struct xfs_btree_cur	*cur,
+	struct xfs_btree_block	*block,
+	union xfs_btree_key	*key)
+{
+	int			n;
+	union xfs_btree_key	*hkey;
+	union xfs_btree_key	*max_hkey;
+	union xfs_btree_key	*high;
+
+	ASSERT(cur->bc_flags & XFS_BTREE_OVERLAPPING);
+	memcpy(key, xfs_btree_key_addr(cur, 1, block),
+			cur->bc_ops->key_len / 2);
+
+	max_hkey = xfs_btree_high_key_addr(cur, 1, block);
+	for (n = 2; n <= xfs_btree_get_numrecs(block); n++) {
+		hkey = xfs_btree_high_key_addr(cur, n, block);
+		if (cur->bc_ops->diff_two_keys(cur, hkey, max_hkey) > 0)
+			max_hkey = hkey;
+	}
+
+	high = xfs_btree_high_key_from_key(cur, key);
+	memcpy(high, max_hkey, cur->bc_ops->key_len / 2);
+}
+
 /* Derive the keys for any btree block. */
 STATIC void
 xfs_btree_get_keys(
@@ -1918,14 +2053,107 @@ xfs_btree_get_keys(
 /*
  * Decide if we need to update the parent keys of a btree block.  For
  * a standard btree this is only necessary if we're updating the first
- * record/key.
+ * record/key.  For an overlapping btree, we must always update the
+ * keys because the highest key can be in any of the records or keys
+ * in the block.
  */
 static inline bool
 xfs_btree_needs_key_update(
 	struct xfs_btree_cur	*cur,
 	int			ptr)
 {
-	return ptr == 1;
+	return (cur->bc_flags & XFS_BTREE_OVERLAPPING) || ptr == 1;
+}
+
+/*
+ * Update the low and high parent keys of the given level, progressing
+ * towards the root.  If force_all is false, stop if the keys for a given
+ * level do not need updating.
+ */
+STATIC int
+__xfs_btree_updkeys(
+	struct xfs_btree_cur	*cur,
+	int			level,
+	struct xfs_btree_block	*block,
+	struct xfs_buf		*bp0,
+	bool			force_all)
+{
+	union xfs_btree_bigkey	key;	/* keys from current level */
+	union xfs_btree_key	*lkey;	/* keys from the next level up */
+	union xfs_btree_key	*hkey;
+	union xfs_btree_key	*nlkey;	/* keys from the next level up */
+	union xfs_btree_key	*nhkey;
+	struct xfs_buf		*bp;
+	int			ptr;
+
+	ASSERT(cur->bc_flags & XFS_BTREE_OVERLAPPING);
+
+	/* Exit if there aren't any parent levels to update. */
+	if (level + 1 >= cur->bc_nlevels)
+		return 0;
+
+	trace_xfs_btree_updkeys(cur, level, bp0);
+
+	lkey = (union xfs_btree_key *)&key;
+	hkey = xfs_btree_high_key_from_key(cur, lkey);
+	xfs_btree_get_keys(cur, block, lkey);
+	for (level++; level < cur->bc_nlevels; level++) {
+#ifdef DEBUG
+		int		error;
+#endif
+		block = xfs_btree_get_block(cur, level, &bp);
+		trace_xfs_btree_updkeys(cur, level, bp);
+#ifdef DEBUG
+		error = xfs_btree_check_block(cur, block, level, bp);
+		if (error) {
+			XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
+			return error;
+		}
+#endif
+		ptr = cur->bc_ptrs[level];
+		nlkey = xfs_btree_key_addr(cur, ptr, block);
+		nhkey = xfs_btree_high_key_addr(cur, ptr, block);
+		if (!force_all &&
+		    !(cur->bc_ops->diff_two_keys(cur, nlkey, lkey) != 0 ||
+		      cur->bc_ops->diff_two_keys(cur, nhkey, hkey) != 0))
+			break;
+		xfs_btree_copy_keys(cur, nlkey, lkey, 1);
+		xfs_btree_log_keys(cur, bp, ptr, ptr);
+		if (level + 1 >= cur->bc_nlevels)
+			break;
+		cur->bc_ops->get_node_keys(cur, block, lkey);
+	}
+
+	return 0;
+}
+
+/*
+ * Update all the keys from some level in cursor back to the root, stopping
+ * when we find a key pair that don't need updating.
+ */
+int
+xfs_btree_update_keys_overlapped(
+	struct xfs_btree_cur	*cur,
+	int			level)
+{
+	struct xfs_buf		*bp;
+	struct xfs_btree_block	*block;
+
+	block = xfs_btree_get_block(cur, level, &bp);
+	return __xfs_btree_updkeys(cur, level, block, bp, false);
+}
+
+/* Update all the keys from some level in cursor back to the root. */
+STATIC int
+xfs_btree_updkeys_force(
+	struct xfs_btree_cur	*cur,
+	int			level)
+{
+	struct xfs_buf		*bp;
+	struct xfs_btree_block	*block;
+
+	block = xfs_btree_get_block(cur, level, &bp);
+	return __xfs_btree_updkeys(cur, level, block, bp, true);
 }
 
 /*
@@ -1942,6 +2170,8 @@ xfs_btree_update_keys(
 	union xfs_btree_key	key;
 	int			ptr;
 
+	ASSERT(!(cur->bc_flags & XFS_BTREE_OVERLAPPING));
+
 	XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);
 	XFS_BTREE_TRACE_ARGIK(cur, level, keyp);
 
@@ -2021,7 +2251,7 @@ xfs_btree_update(
 					    ptr, LASTREC_UPDATE);
 	}
 
-	/* Updating first rec in leaf. Pass new key value up to our parent. */
+	/* Pass new key value up to our parent. */
 	if (xfs_btree_needs_key_update(cur, ptr)) {
 		error = cur->bc_ops->update_keys(cur, 0);
 		if (error)
@@ -2052,12 +2282,14 @@ xfs_btree_lshift(
 	int			lrecs;		/* left record count */
 	struct xfs_buf		*rbp;		/* right buffer pointer */
 	struct xfs_btree_block	*right;		/* right btree block */
+	struct xfs_btree_cur	*tcur;		/* temporary btree cursor */
 	int			rrecs;		/* right record count */
 	union xfs_btree_ptr	lptr;		/* left btree pointer */
 	union xfs_btree_key	*rkp = NULL;	/* right btree key */
 	union xfs_btree_ptr	*rpp = NULL;	/* right address pointer */
 	union xfs_btree_rec	*rrp = NULL;	/* right record pointer */
 	int			error;		/* error return value */
+	int			i;
 
 	XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);
 	XFS_BTREE_TRACE_ARGI(cur, level);
@@ -2196,10 +2428,33 @@ xfs_btree_lshift(
 			xfs_btree_rec_addr(cur, 1, right));
 	}
 
+	/*
+	 * Using a temporary cursor, update the parent key values of the
+	 * block on the left.
+	 */
+	error = xfs_btree_dup_cursor(cur, &tcur);
+	if (error)
+		goto error0;
+	i = xfs_btree_firstrec(tcur, level);
+	XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, i == 1, error0);
+
+	error = xfs_btree_decrement(tcur, level, &i);
+	if (error)
+		goto error1;
+
 	/* Update the parent keys of the right block. */
 	error = cur->bc_ops->update_keys(cur, level);
 	if (error)
-		goto error0;
+		goto error1;
+
+	/* Update the parent high keys of the left block, if needed. */
+	if (tcur->bc_flags & XFS_BTREE_OVERLAPPING) {
+		error = tcur->bc_ops->update_keys(tcur, level);
+		if (error)
+			goto error1;
+	}
+
+	xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
 
 	/* Slide the cursor value left one. */
 	cur->bc_ptrs[level]--;
@@ -2216,6 +2471,11 @@ out0:
 error0:
 	XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
 	return error;
+
+error1:
+	XFS_BTREE_TRACE_CURSOR(tcur, XBT_ERROR);
+	xfs_btree_del_cursor(tcur, XFS_BTREE_ERROR);
+	return error;
 }
 
 /*
@@ -2367,6 +2627,13 @@ xfs_btree_rshift(
 	if (error)
 		goto error1;
 
+	/* Update the parent high keys of the left block, if needed. */
+	if (cur->bc_flags & XFS_BTREE_OVERLAPPING) {
+		error = cur->bc_ops->update_keys(cur, level);
+		if (error)
+			goto error1;
+	}
+
 	/* Update the parent keys of the right block. */
 	error = cur->bc_ops->update_keys(tcur, level);
 	if (error)
@@ -2548,6 +2815,14 @@ __xfs_btree_split(
 		xfs_btree_set_sibling(cur, rrblock, &rptr, XFS_BB_LEFTSIB);
 		xfs_btree_log_block(cur, rrbp, XFS_BB_LEFTSIB);
 	}
+
+	/* Update the parent high keys of the left block, if needed. */
+	if (cur->bc_flags & XFS_BTREE_OVERLAPPING) {
+		error = cur->bc_ops->update_keys(cur, level);
+		if (error)
+			goto error0;
+	}
+
 	/*
 	 * If the cursor is really in the right block, move it there.
 	 * If it's just pointing past the last entry in left, then we'll
@@ -2988,7 +3263,8 @@ xfs_btree_insrec(
 	struct xfs_buf		*bp;	/* buffer for block */
 	union xfs_btree_ptr	nptr;	/* new block ptr */
 	struct xfs_btree_cur	*ncur;	/* new btree cursor */
-	union xfs_btree_key	nkey;	/* new block key */
+	union xfs_btree_bigkey	nkey;	/* new block key */
+	union xfs_btree_key	*lkey;
 	int			optr;	/* old key/record index */
 	int			ptr;	/* key/record index */
 	int			numrecs;/* number of records */
@@ -2996,11 +3272,13 @@ xfs_btree_insrec(
 #ifdef DEBUG
 	int			i;
 #endif
+	xfs_daddr_t		old_bn;
 
 	XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);
 	XFS_BTREE_TRACE_ARGIPR(cur, level, *ptrp, &rec);
 
 	ncur = NULL;
+	lkey = (union xfs_btree_key *)&nkey;
 
 	/*
 	 * If we have an external root pointer, and we've made it to the
@@ -3029,6 +3307,7 @@ xfs_btree_insrec(
 
 	/* Get pointers to the btree buffer and block. */
 	block = xfs_btree_get_block(cur, level, &bp);
+	old_bn = bp ? bp->b_bn : XFS_BUF_DADDR_NULL;
 	numrecs = xfs_btree_get_numrecs(block);
 
 #ifdef DEBUG
@@ -3055,7 +3334,7 @@ xfs_btree_insrec(
 	xfs_btree_set_ptr_null(cur, &nptr);
 	if (numrecs == cur->bc_ops->get_maxrecs(cur, level)) {
 		error = xfs_btree_make_block_unfull(cur, level, numrecs,
-					&optr, &ptr, &nptr, &ncur, &nkey, stat);
+					&optr, &ptr, &nptr, &ncur, lkey, stat);
 		if (error || *stat == 0)
 			goto error0;
 	}
@@ -3140,8 +3419,17 @@ xfs_btree_insrec(
 	/* Log the new number of records in the btree header. */
 	xfs_btree_log_block(cur, bp, XFS_BB_NUMRECS);
 
-	/* If we inserted at the start of a block, update the parents' keys. */
-	if (xfs_btree_needs_key_update(cur, optr)) {
+	/*
+	 * If we just inserted into a new tree block, we have to
+	 * recalculate nkey here because nkey is out of date.
+	 *
+	 * Otherwise we're just updating an existing block (having shoved
+	 * some records into the new tree block), so use the regular key
+	 * update mechanism.
+	 */
+	if (bp && bp->b_bn != old_bn) {
+		xfs_btree_get_keys(cur, block, lkey);
+	} else if (xfs_btree_needs_key_update(cur, optr)) {
 		error = cur->bc_ops->update_keys(cur, level);
 		if (error)
 			goto error0;
@@ -3162,7 +3450,7 @@ xfs_btree_insrec(
 	 */
 	*ptrp = nptr;
 	if (!xfs_btree_ptr_is_null(cur, &nptr)) {
-		xfs_btree_copy_keys(cur, key, &nkey, 1);
+		xfs_btree_copy_keys(cur, key, lkey, 1);
 		*curp = ncur;
 	}
 
@@ -3193,18 +3481,20 @@ xfs_btree_insert(
 	union xfs_btree_ptr	nptr;	/* new block number (split result) */
 	struct xfs_btree_cur	*ncur;	/* new cursor (split result) */
 	struct xfs_btree_cur	*pcur;	/* previous level's cursor */
-	union xfs_btree_key	key;	/* key of block to insert */
+	union xfs_btree_bigkey	bkey;	/* key of block to insert */
+	union xfs_btree_key	*key;
 	union xfs_btree_rec	rec;	/* record to insert */
 
 	level = 0;
 	ncur = NULL;
 	pcur = cur;
+	key = (union xfs_btree_key *)&bkey;
 
 	xfs_btree_set_ptr_null(cur, &nptr);
 
 	/* Make a key out of the record data to be inserted, and save it. */
 	cur->bc_ops->init_rec_from_cur(cur, &rec);
-	cur->bc_ops->init_key_from_rec(&key, &rec);
+	cur->bc_ops->init_key_from_rec(key, &rec);
 
 	/*
 	 * Loop going up the tree, starting at the leaf level.
@@ -3216,7 +3506,7 @@ xfs_btree_insert(
 		 * Insert nrec/nptr into this level of the tree.
 		 * Note if we fail, nptr will be null.
 		 */
-		error = xfs_btree_insrec(pcur, level, &nptr, &rec, &key,
+		error = xfs_btree_insrec(pcur, level, &nptr, &rec, key,
 				&ncur, &i);
 		if (error) {
 			if (pcur != cur)
@@ -3915,6 +4205,16 @@ xfs_btree_delrec(
 	if (level > 0)
 		cur->bc_ptrs[level]--;
 
+	/*
+	 * We combined blocks, so we have to update the parent keys if the
+	 * btree supports overlapped intervals.  However, bc_ptrs[level + 1]
+	 * points to the old block so that the caller knows which record to
+	 * delete.  Therefore, the caller must be savvy enough to call updkeys
+	 * for us if we return stat == 2.  The other exit points from this
+	 * function don't require deletions further up the tree, so they can
+	 * call updkeys directly.
+	 */
+
 	XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
 	/* Return value means the next level up has something to do. */
 	*stat = 2;
@@ -3940,6 +4240,7 @@ xfs_btree_delete(
 	int			error;	/* error return value */
 	int			level;
 	int			i;
+	bool			joined = false;
 
 	XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);
 
@@ -3953,6 +4254,18 @@ xfs_btree_delete(
 		error = xfs_btree_delrec(cur, level, &i);
 		if (error)
 			goto error0;
+		if (i == 2)
+			joined = true;
+	}
+
+	/*
+	 * If we combined blocks as part of deleting the record, delrec won't
+	 * have updated the parent high keys so we have to do that here.
+	 */
+	if (joined && (cur->bc_flags & XFS_BTREE_OVERLAPPING)) {
+		error = xfs_btree_updkeys_force(cur, 0);
+		if (error)
+			goto error0;
 	}
 
 	if (i == 0) {

fs/xfs/libxfs/xfs_btree.h

@@ -44,6 +44,20 @@ union xfs_btree_key {
 	xfs_inobt_key_t		inobt;
 };
 
+/*
+ * In-core key that holds both low and high keys for overlapped btrees.
+ * The two keys are packed next to each other on disk, so do the same
+ * in memory.  Preserve the existing xfs_btree_key as a single key to
+ * avoid the mental model breakage that would happen if we passed a
+ * bigkey into a function that operates on a single key.
+ */
+union xfs_btree_bigkey {
+	struct xfs_bmbt_key		bmbt;
+	xfs_bmdr_key_t			bmbr;	/* bmbt root block */
+	xfs_alloc_key_t			alloc;
+	struct xfs_inobt_key		inobt;
+};
+
 union xfs_btree_rec {
 	xfs_bmbt_rec_t		bmbt;
 	xfs_bmdr_rec_t		bmbr;	/* bmbt root block */
@@ -162,11 +176,21 @@ struct xfs_btree_ops {
 				     union xfs_btree_rec *rec);
 	void	(*init_ptr_from_cur)(struct xfs_btree_cur *cur,
 				     union xfs_btree_ptr *ptr);
+	void	(*init_high_key_from_rec)(union xfs_btree_key *key,
+					  union xfs_btree_rec *rec);
 
 	/* difference between key value and cursor value */
 	__int64_t (*key_diff)(struct xfs_btree_cur *cur,
 			      union xfs_btree_key *key);
 
+	/*
+	 * Difference between key2 and key1 -- positive if key1 > key2,
+	 * negative if key1 < key2, and zero if equal.
+	 */
+	__int64_t (*diff_two_keys)(struct xfs_btree_cur *cur,
+				   union xfs_btree_key *key1,
+				   union xfs_btree_key *key2);
+
 	const struct xfs_buf_ops	*buf_ops;
 
 #if defined(DEBUG) || defined(XFS_WARN)
@@ -249,6 +273,7 @@ typedef struct xfs_btree_cur
 #define XFS_BTREE_ROOT_IN_INODE		(1<<1)	/* root may be variable size */
 #define XFS_BTREE_LASTREC_UPDATE	(1<<2)	/* track last rec externally */
 #define XFS_BTREE_CRC_BLOCKS		(1<<3)	/* uses extended btree blocks */
+#define XFS_BTREE_OVERLAPPING		(1<<4)	/* overlapping intervals */
 
 
 #define	XFS_BTREE_NOERROR	0
@@ -493,5 +518,10 @@ void xfs_btree_get_leaf_keys(struct xfs_btree_cur *cur,
 void xfs_btree_get_node_keys(struct xfs_btree_cur *cur,
 		struct xfs_btree_block *block, union xfs_btree_key *key);
 int xfs_btree_update_keys(struct xfs_btree_cur *cur, int level);
+void xfs_btree_get_leaf_keys_overlapped(struct xfs_btree_cur *cur,
+		struct xfs_btree_block *block, union xfs_btree_key *key);
+void xfs_btree_get_node_keys_overlapped(struct xfs_btree_cur *cur,
+		struct xfs_btree_block *block, union xfs_btree_key *key);
+int xfs_btree_update_keys_overlapped(struct xfs_btree_cur *cur, int level);
 
 #endif	/* __XFS_BTREE_H__ */

fs/xfs/xfs_trace.h

@@ -38,6 +38,7 @@ struct xlog_recover_item;
 struct xfs_buf_log_format;
 struct xfs_inode_log_format;
 struct xfs_bmbt_irec;
+struct xfs_btree_cur;
 
 DECLARE_EVENT_CLASS(xfs_attr_list_class,
 	TP_PROTO(struct xfs_attr_list_context *ctx),
@@ -2185,6 +2186,41 @@ DEFINE_DISCARD_EVENT(xfs_discard_toosmall);
 DEFINE_DISCARD_EVENT(xfs_discard_exclude);
 DEFINE_DISCARD_EVENT(xfs_discard_busy);
 
+/* btree cursor events */
+DECLARE_EVENT_CLASS(xfs_btree_cur_class,
+	TP_PROTO(struct xfs_btree_cur *cur, int level, struct xfs_buf *bp),
+	TP_ARGS(cur, level, bp),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(xfs_btnum_t, btnum)
+		__field(int, level)
+		__field(int, nlevels)
+		__field(int, ptr)
+		__field(xfs_daddr_t, daddr)
+	),
+	TP_fast_assign(
+		__entry->dev = cur->bc_mp->m_super->s_dev;
+		__entry->btnum = cur->bc_btnum;
+		__entry->level = level;
+		__entry->nlevels = cur->bc_nlevels;
+		__entry->ptr = cur->bc_ptrs[level];
+		__entry->daddr = bp ? bp->b_bn : -1;
+	),
+	TP_printk("dev %d:%d btnum %d level %d/%d ptr %d daddr 0x%llx",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->btnum,
+		  __entry->level,
+		  __entry->nlevels,
+		  __entry->ptr,
+		  (unsigned long long)__entry->daddr)
+)
+
+#define DEFINE_BTREE_CUR_EVENT(name) \
+DEFINE_EVENT(xfs_btree_cur_class, name, \
+	TP_PROTO(struct xfs_btree_cur *cur, int level, struct xfs_buf *bp), \
+	TP_ARGS(cur, level, bp))
+DEFINE_BTREE_CUR_EVENT(xfs_btree_updkeys);
+
 #endif /* _TRACE_XFS_H */
 
 #undef TRACE_INCLUDE_PATH