X test_wcfs_watch_setup and test_wcfs_watch_setup_ahead work again

wcfs/wcfs.go

@@ -615,6 +615,9 @@ type BigFile struct {
 //	//go:generate ./gen-δtail I64 int64 zδtail_i64.go
 //	δtail *ΔTailI64 // [](rev↑, []#blk)
 
+	// blocks that were ever read-accessed (head/ only)	XXX locking by bfdir.δFmu ?
+	accessed SetI64
+
 	// inflight loadings of ZBigFile from ZODB.
 	// successful load results are kept here until blkdata is put into OS pagecache.
 	//
@@ -1349,7 +1352,7 @@ retry:
 //
 // (see "7.2) for all registered client@at watchers ...")
 
-const _traceIso = true
+const _traceIso = false
 func traceIso(format string, argv ...interface{}) {
 	if !_traceIso {
 		return
@@ -1479,6 +1482,7 @@ func (f *BigFile) readPinWatchers(ctx context.Context, blk int64, treepath []btr
 	δFtail := bfdir.δFtail
 	bfdir.δFmu.Lock()		// XXX locking correct? XXX -> better push down?
 	δFtail.Track(f, blk, treepath, zblk)	// XXX pass in zblk.rev here?
+	f.accessed.Add(blk)
 	bfdir.δFmu.Unlock()
 
 	// make sure that file[blk] on clients side stays as of @w.at state.
@@ -1680,6 +1684,14 @@ func (wlink *WatchLink) setupWatch(ctx context.Context, foid zodb.Oid, at zodb.T
 			if already {
 				continue
 			}
+			// blk might be in δFtail because it is adjacent in
+			// ZBigFile.blktab to another blk that was explicitly
+			// tracked. However wcfs tests expect that only blocks
+			// that were previously explicitly accessed are
+			// included into watch setup pins.
+			if !f.accessed.Has(blk) {
+				continue
+			}
 
 			toPin[blk], _ = δFtail.LastBlkRev(ctx, f, blk, at)  // XXX err
 		}
@@ -2170,6 +2182,7 @@ func (head *Head) bigopen(ctx context.Context, oid zodb.Oid) (_ *BigFile, err er
 		// FIXME: scan zfile.blktab - so that we can detect all btree changes
 		// see  "XXX building δFtail lazily ..." in notes.txt
 
+		f.accessed = make(SetI64)
 		f.watchTab = make(map[*Watch]struct{})
 	}
 

wcfs/wcfs_test.py

@@ -1019,7 +1019,7 @@ def _blkRevAt(t, zf, blk, at): # -> rev
     return rev
 
 
-# _pinnedAt returns which blocks needs to be pinned for zf@at compared to zf@head
+# _pinnedAt returns which blocks need to be pinned for zf@at compared to zf@head
 # according to wcfs isolation protocol.
 #
 # Criteria for when blk must be pinned as of @at view:
@@ -1141,7 +1141,6 @@ def test_wcfs_basic():
 
 
 # verify how wcfs processes ZODB invalidations when hole becomes a block with data.
-# TODO merge into test_wcfs_basic & watch tests after δbtree is done
 @func
 def test_wcfs_basic_hole2zblk():
     t = tDB(); zf = t.zfile