.

wcfs/internal/xbtree/δbtail.go

@@ -1007,7 +1007,7 @@ func (δBtail *ΔBtail) GetAt(root zodb.Oid, key Key, at zodb.Tid) (value Value,
 // Only tracked keys are guaranteed to be present.
 //
 // Note: contrary to regular go slicing, low is exclusive while high is inclusive.
-func (δBtail *ΔBtail) SliceByRootRev(root zodb.Oid, lo, hi zodb.Tid) (/*readonly*/vδT []ΔTree) {
+func (δBtail *ΔBtail) SliceByRootRev(root zodb.Oid, lo, hi zodb.Tid) (/*readonly*/vδT []ΔTree, err error) {
 	xtail.AssertSlice(δBtail, lo, hi)
 
 	if traceΔBtail {
@@ -1018,22 +1018,22 @@ func (δBtail *ΔBtail) SliceByRootRev(root zodb.Oid, lo, hi zodb.Tid) (/*readon
 	}
 
 	// retrieve vδT snapshot that is rebuilt to take all previous Track requests into account
-	vδT, err := δBtail.vδTSnapForTracked(root)
+	vδT, err = δBtail.vδTSnapForTracked(root)
 	if err != nil {
-		panic(err) // XXX
+		return nil, err
 	}
 	debugfΔBtail("  vδT: %v\n", vδT)
 
 	l := len(vδT)
 	if l == 0 {
-		return nil
+		return nil, nil
 	}
 
 	// find max j : [j].rev ≤ hi		linear scan -> TODO binary search
 	j := l - 1
 	for ; j >= 0 && vδT[j].Rev > hi; j-- {}
 	if j < 0 {
-		return nil // ø
+		return nil, nil // ø
 	}
 
 	// find max i : [i].rev > lo		linear scan -> TODO binary search
@@ -1045,7 +1045,7 @@ func (δBtail *ΔBtail) SliceByRootRev(root zodb.Oid, lo, hi zodb.Tid) (/*readon
 	// modified via RCU: i.e. _ΔTtail.rebuild clones vδT before modifying it.
 	// This way the data we return to caller will stay unchanged even if
 	// rebuild is running simultaneously.
-	return vδT[i:j+1]
+	return vδT[i:j+1], nil
 }
 
 

wcfs/internal/xbtree/δbtail_test.go

@@ -1246,11 +1246,11 @@ func TestΔBtailSliceByRootRev(t_ *testing.T) {
 		t.Errorf("%s:\nhave: %s\nwant: %s", subj, have, want)
 	}
 
-	s00 := δbtail.SliceByRootRev(t.Root(), t0.At, t0.At)
-	s01 := δbtail.SliceByRootRev(t.Root(), t0.At, t1.At)
-	s02 := δbtail.SliceByRootRev(t.Root(), t0.At, t2.At)
-	s12 := δbtail.SliceByRootRev(t.Root(), t1.At, t2.At)
-	s22 := δbtail.SliceByRootRev(t.Root(), t2.At, t2.At)
+	s00, err := δbtail.SliceByRootRev(t.Root(), t0.At, t0.At);  X(err)
+	s01, err := δbtail.SliceByRootRev(t.Root(), t0.At, t1.At);  X(err)
+	s02, err := δbtail.SliceByRootRev(t.Root(), t0.At, t2.At);  X(err)
+	s12, err := δbtail.SliceByRootRev(t.Root(), t1.At, t2.At);  X(err)
+	s22, err := δbtail.SliceByRootRev(t.Root(), t2.At, t2.At);  X(err)
 
 	vδT := δttail.vδT
 	assertvδT("t2.vδT",  vδT,        ΔT{t1.At, δ{2:{f,g}}},   ΔT{t2.At, δ{2:{g,h}}})
@@ -1286,11 +1286,11 @@ func TestΔBtailSliceByRootRev(t_ *testing.T) {
 	trackKeys(δbtail, t2, _1)
 	err = δbtail._rebuildAll();  X(err)
 
-	s00_ := δbtail.SliceByRootRev(t.Root(), t0.At, t0.At)
-	s01_ := δbtail.SliceByRootRev(t.Root(), t0.At, t1.At)
-	s02_ := δbtail.SliceByRootRev(t.Root(), t0.At, t2.At)
-	s12_ := δbtail.SliceByRootRev(t.Root(), t1.At, t2.At)
-	s22_ := δbtail.SliceByRootRev(t.Root(), t2.At, t2.At)
+	s00_, err := δbtail.SliceByRootRev(t.Root(), t0.At, t0.At);  X(err)
+	s01_, err := δbtail.SliceByRootRev(t.Root(), t0.At, t1.At);  X(err)
+	s02_, err := δbtail.SliceByRootRev(t.Root(), t0.At, t2.At);  X(err)
+	s12_, err := δbtail.SliceByRootRev(t.Root(), t1.At, t2.At);  X(err)
+	s22_, err := δbtail.SliceByRootRev(t.Root(), t2.At, t2.At);  X(err)
 
 	vδT = δttail.vδT
 	assertvδT("t12.vδT",   vδT,     ΔT{t1.At, δ{1:{a,b},2:{f,g}}},  ΔT{t2.At, δ{1:{b,c},2:{g,h}}})

wcfs/internal/zdata/δftail.go

@@ -645,9 +645,17 @@ type _ZinblkOverlay struct {
 // Only tracked blocks are guaranteed to be present.
 //
 // Note: contrary to regular go slicing, low is exclusive while high is inclusive.
-func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*readonly*/[]*ΔFile {
+func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) (/*readonly*/[]*ΔFile, error) {
 	foid := zfile.POid()
 	//fmt.Printf("\nslice f<%s> (@%s,@%s]\n", foid, lo, hi)
+	vδf, err := δFtail._SliceByFileRev(foid, lo, hi)
+	if err != nil {
+		err = fmt.Errorf("slice f<%s> (@%s,@%s]: %e", foid, lo, hi, err)
+	}
+	return vδf, err
+}
+
+func (δFtail *ΔFtail) _SliceByFileRev(foid zodb.Oid, lo, hi zodb.Tid) (/*readonly*/[]*ΔFile, error) {
 	xtail.AssertSlice(δFtail, lo, hi)
 
 	// query .δBtail.SliceByRootRev(file.blktab, lo, hi) +
@@ -669,7 +677,7 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 
 	vδE, headRoot, err := δFtail.vδEForFile(foid)
 	if err != nil {
-		panic(err) // XXX
+		return nil, err
 	}
 
 	var vδf []*ΔFile
@@ -776,7 +784,10 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 		// vδT for current epoch
 		var vδT []xbtree.ΔTree
 		if root != xbtree.VDEL {
-			vδT = δFtail.δBtail.SliceByRootRev(root, epoch, head) // NOTE @head, not hi
+			vδT, err = δFtail.δBtail.SliceByRootRev(root, epoch, head) // NOTE @head, not hi
+			if err != nil {
+				return nil, err
+			}
 		}
 		it := len(vδT) - 1
 		if it >= 0 {
@@ -887,7 +898,7 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 		vδf[i], vδf[j] = vδf[j], vδf[i]
 	}
 
-	return vδf
+	return vδf, nil
 }
 
 // ZinblkOverlay

wcfs/internal/zdata/δftail_test.go

@@ -551,7 +551,7 @@ func testΔFtail(t_ *testing.T, testq chan ΔFTestEntry) {
 				hi := vδf[k].Rev
 
 				vδf_ok := vδf[j:k+1] // [j,k]
-				vδf_ := δFtail.SliceByFileRev(zfile, lo, hi)
+				vδf_, err := δFtail.SliceByFileRev(zfile, lo, hi);  X(err)
 				if !reflect.DeepEqual(vδf_, vδf_ok) {
 					t.Errorf("slice (@%s,@%s]:\nhave: %v\nwant: %v", t.AtSymb(lo), t.AtSymb(hi), t.vδfstr(vδf_), t.vδfstr(vδf_ok))
 				}
@@ -654,7 +654,7 @@ func TestΔFtailSliceUntrackedUniform(t_ *testing.T) {
 	// (at1, at4]  -> changes to both 0 and 1, because they both are changed in the same bucket @at2
 	lo := t1.At
 	hi := t4.At
-	vδf := δFtail.SliceByFileRev(zfile, lo, hi)
+	vδf, err := δFtail.SliceByFileRev(zfile, lo, hi);  X(err)
 	vδf_ok := []*ΔFile{
 		&ΔFile{Rev: t2.At, Blocks: b(0,1), Size: true},
 		&ΔFile{Rev: t3.At, Blocks: b(0,1), Size: false},
@@ -667,7 +667,7 @@ func TestΔFtailSliceUntrackedUniform(t_ *testing.T) {
 
 	// (at2, at4]  -> changes to only 0, because there is no change to 2 via blktab
 	lo = t2.At
-	vδf = δFtail.SliceByFileRev(zfile, lo, hi)
+	vδf, err = δFtail.SliceByFileRev(zfile, lo, hi);  X(err)
 	vδf_ok = []*ΔFile{
 		&ΔFile{Rev: t3.At, Blocks: b(0),   Size: false},
 	}
@@ -677,7 +677,7 @@ func TestΔFtailSliceUntrackedUniform(t_ *testing.T) {
 
 	// (at3, at4]  -> changes to only 0, ----/----
 	lo = t3.At
-	vδf = δFtail.SliceByFileRev(zfile, lo, hi)
+	vδf, err = δFtail.SliceByFileRev(zfile, lo, hi);  X(err)
 	vδf_ok = []*ΔFile(nil)
 	if !reflect.DeepEqual(vδf, vδf_ok) {
 		t.Errorf("slice (@%s,@%s]:\nhave: %v\nwant: %v", t.AtSymb(lo), t.AtSymb(hi), t.vδfstr(vδf), t.vδfstr(vδf_ok))

wcfs/wcfs.go

@@ -1742,7 +1742,11 @@ func (wlink *WatchLink) setupWatch(ctx context.Context, foid zodb.Oid, at zodb.T
 	toPin := map[int64]zodb.Tid{} // blk -> @rev
 
 	δFtail := bfdir.δFtail
-	for _, δfile := range δFtail.SliceByFileRev(f.zfile, at, headAt) { // XXX locking δFtail
+	vδf, err := δFtail.SliceByFileRev(f.zfile, at, headAt)	// XXX locking δFtail
+	if err != nil {
+		panic(err)	// XXX
+	}
+	for _, δfile := range vδf {
 		if δfile.Epoch {
 			// file epochs are currently forbidden (see watcher), so the only
 			// case when we could see an epoch here is creation of