xfs: create a predicate to verify per-AG extents

Create a predicate function to verify that a given agbno/blockcount pair
fit entirely within a single allocation group and don't suffer
mathematical overflows. Refactor the existng open-coded logic; we're
going to add more calls to this function in the next patch.

Signed-off-by: Darrick J. Wong <[e-mail]>
Reviewed-by: Dave Chinner <[e-mail]>

fs/xfs/libxfs/xfs_ag.h

···
 	return true;
 }
 
+static inline bool
+xfs_verify_agbext(
+	struct xfs_perag	*pag,
+	xfs_agblock_t		agbno,
+	xfs_agblock_t		len)
+{
+	if (agbno + len <= agbno)
+		return false;
+
+	if (!xfs_verify_agbno(pag, agbno))
+		return false;
+
+	return xfs_verify_agbno(pag, agbno + len - 1);
+}
+
 /*
  * Verify that an AG inode number pointer neither points outside the AG
  * nor points at static metadata.

fs/xfs/libxfs/xfs_alloc.c

···
 		goto out_bad_rec;
 
 	/* check for valid extent range, including overflow */
-	if (!xfs_verify_agbno(pag, *bno))
-		goto out_bad_rec;
-	if (*bno > *bno + *len)
-		goto out_bad_rec;
-	if (!xfs_verify_agbno(pag, *bno + *len - 1))
+	if (!xfs_verify_agbext(pag, *bno, *len))
 		goto out_bad_rec;
 
 	return 0;

fs/xfs/libxfs/xfs_refcount.c

···
 	}
 
 	/* check for valid extent range, including overflow */
-	if (!xfs_verify_agbno(pag, realstart))
-		goto out_bad_rec;
-	if (realstart > realstart + irec->rc_blockcount)
-		goto out_bad_rec;
-	if (!xfs_verify_agbno(pag, realstart + irec->rc_blockcount - 1))
+	if (!xfs_verify_agbext(pag, realstart, irec->rc_blockcount))
 		goto out_bad_rec;
 
 	if (irec->rc_refcount == 0 || irec->rc_refcount > MAXREFCOUNT)

fs/xfs/libxfs/xfs_rmap.c

···
 			goto out_bad_rec;
 	} else {
 		/* check for valid extent range, including overflow */
-		if (!xfs_verify_agbno(pag, irec->rm_startblock))
-			goto out_bad_rec;
-		if (irec->rm_startblock >
-				irec->rm_startblock + irec->rm_blockcount)
-			goto out_bad_rec;
-		if (!xfs_verify_agbno(pag,
-				irec->rm_startblock + irec->rm_blockcount - 1))
+		if (!xfs_verify_agbext(pag, irec->rm_startblock,
+					    irec->rm_blockcount))
 			goto out_bad_rec;
 	}
 

fs/xfs/scrub/alloc.c

···
 	bno = be32_to_cpu(rec->alloc.ar_startblock);
 	len = be32_to_cpu(rec->alloc.ar_blockcount);
 
-	if (bno + len <= bno ||
-	    !xfs_verify_agbno(pag, bno) ||
-	    !xfs_verify_agbno(pag, bno + len - 1))
+	if (!xfs_verify_agbext(pag, bno, len))
 		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
 
 	xchk_allocbt_xref(bs->sc, bno, len);

fs/xfs/scrub/ialloc.c

···
 	xfs_agblock_t			bno;
 
 	bno = XFS_AGINO_TO_AGBNO(mp, agino);
-	if (bno + len <= bno ||
-	    !xfs_verify_agbno(pag, bno) ||
-	    !xfs_verify_agbno(pag, bno + len - 1))
+
+	if (!xfs_verify_agbext(pag, bno, len))
 		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
 
 	xchk_iallocbt_chunk_xref(bs->sc, irec, agino, bno, len);

fs/xfs/scrub/refcount.c

···
 
 	/* Check the extent. */
 	bno &= ~XFS_REFC_COW_START;
-	if (bno + len <= bno ||
-	    !xfs_verify_agbno(pag, bno) ||
-	    !xfs_verify_agbno(pag, bno + len - 1))
+
+	if (!xfs_verify_agbext(pag, bno, len))
 		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
 
 	if (refcount == 0)