xfs: track active state of allocation btree cursors

The upcoming allocation algorithm update searches multiple
allocation btree cursors concurrently. As such, it requires an
active state to track when a particular cursor should continue
searching. While active state will be modified based on higher level
logic, we can define base functionality based on the result of
allocation btree lookups.

Define an active flag in the private area of the btree cursor.
Update it based on the result of lookups in the existing allocation
btree helpers. Finally, provide a new helper to query the current
state.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_alloc.c

@@ -146,9 +146,13 @@ xfs_alloc_lookup_eq(
 	xfs_extlen_t		len,	/* length of extent */
 	int			*stat)	/* success/failure */
 {
+	int			error;
+
 	cur->bc_rec.a.ar_startblock = bno;
 	cur->bc_rec.a.ar_blockcount = len;
-	return xfs_btree_lookup(cur, XFS_LOOKUP_EQ, stat);
+	error = xfs_btree_lookup(cur, XFS_LOOKUP_EQ, stat);
+	cur->bc_private.a.priv.abt.active = (*stat == 1);
+	return error;
 }
 
 /*
@@ -162,9 +166,13 @@ xfs_alloc_lookup_ge(
 	xfs_extlen_t		len,	/* length of extent */
 	int			*stat)	/* success/failure */
 {
+	int			error;
+
 	cur->bc_rec.a.ar_startblock = bno;
 	cur->bc_rec.a.ar_blockcount = len;
-	return xfs_btree_lookup(cur, XFS_LOOKUP_GE, stat);
+	error = xfs_btree_lookup(cur, XFS_LOOKUP_GE, stat);
+	cur->bc_private.a.priv.abt.active = (*stat == 1);
+	return error;
 }
 
 /*
@@ -178,9 +186,19 @@ xfs_alloc_lookup_le(
 	xfs_extlen_t		len,	/* length of extent */
 	int			*stat)	/* success/failure */
 {
+	int			error;
 	cur->bc_rec.a.ar_startblock = bno;
 	cur->bc_rec.a.ar_blockcount = len;
-	return xfs_btree_lookup(cur, XFS_LOOKUP_LE, stat);
+	error = xfs_btree_lookup(cur, XFS_LOOKUP_LE, stat);
+	cur->bc_private.a.priv.abt.active = (*stat == 1);
+	return error;
+}
+
+static inline bool
+xfs_alloc_cur_active(
+	struct xfs_btree_cur	*cur)
+{
+	return cur && cur->bc_private.a.priv.abt.active;
 }
 
 /*

fs/xfs/libxfs/xfs_alloc_btree.c

@@ -507,6 +507,7 @@ xfs_allocbt_init_cursor(
 
 	cur->bc_private.a.agbp = agbp;
 	cur->bc_private.a.agno = agno;
+	cur->bc_private.a.priv.abt.active = false;
 
 	if (xfs_sb_version_hascrc(&mp->m_sb))
 		cur->bc_flags |= XFS_BTREE_CRC_BLOCKS;

fs/xfs/libxfs/xfs_btree.h

@@ -183,6 +183,9 @@ union xfs_btree_cur_private {
 		unsigned long	nr_ops;		/* # record updates */
 		int		shape_changes;	/* # of extent splits */
 	} refc;
+	struct {
+		bool		active;		/* allocation cursor state */
+	} abt;
 };
 
 /*