Pad B*-tree files to the alloc block size

This bug was corrupting all volumes over 32 MB (i.e. with a block size
exceeding 512 bytes). Oops!

machfs/btree.py

@@ -103,7 +103,9 @@ def dump_btree(buf):
         this_leaf = ndFLink
 
 
-def make_btree(records, bthKeyLen):
+def make_btree(records, bthKeyLen, blksize):
+    nodemult = blksize // 512
+
     nodelist = [] # append to this as we go
 
     # pointers per index node, range 2-11
@@ -156,7 +158,7 @@ def make_btree(records, bthKeyLen):
     # Add map nodes with 3952-bit bitmap recs to cover every node
     bits_covered = 2048
     mapnodes = []
-    while bits_covered < len(nodelist):
+    while bits_covered < bitmanip.pad_up(len(nodelist), nodemult):
         mapnode = _Node(ndType=2, ndNHeight=1)
         nodelist.append(mapnode)
         mapnodes.append(mapnode)
@@ -188,4 +190,7 @@ def make_btree(records, bthKeyLen):
         bthDepth, bthRoot, bthNRecs, bthFNode, bthLNode,
         bthNodeSize, bthKeyLen, bthNNodes, bthFree)
 
+    slop_nodes = bitmanip.pad_up(len(nodelist), nodemult) - len(nodelist)
+    nodelist.append(512 * slop_nodes)
+
     return b''.join(bytes(node) for node in nodelist)

machfs/main.py

@@ -243,7 +243,7 @@ class Volume(directory.AbstractFolder):
         blkaccum = []
 
         # <<< put the empty extents overflow file in here >>>
-        extoflowfile = btree.make_btree([], bthKeyLen=7)
+        extoflowfile = btree.make_btree([], bthKeyLen=7, blksize=drAlBlkSiz)
         # also need to do some cleverness to ensure that this gets picked up...
         drXTFlSize = len(extoflowfile)
         drXTExtRec_Start = len(blkaccum)
@@ -344,7 +344,7 @@ class Volume(directory.AbstractFolder):
 
         # now it is time to sort these records! fuck that shit...
         catalog.sort(key=_catalog_rec_sort)
-        catalogfile = btree.make_btree(catalog, bthKeyLen=37)
+        catalogfile = btree.make_btree(catalog, bthKeyLen=37, blksize=drAlBlkSiz)
         # also need to do some cleverness to ensure that this gets picked up...
         drCTFlSize = len(catalogfile)
         drCTExtRec_Start = len(blkaccum)