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tka: don't look up parent/child information from purged AUMs

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We soft-delete AUMs when they're purged, but when we call `ChildAUMs()`,
we look up soft-deleted AUMs to find the `Children` field.

This patch changes the behaviour of `ChildAUMs()` so it only looks at
not-deleted AUMs. This means we don't need to record child information
on AUMs any more, which is a minor space saving for any newly-recorded
AUMs.

Updates https://github.com/tailscale/tailscale/issues/17566
Updates https://github.com/tailscale/corp/issues/27166

Signed-off-by: Alex Chan <alexc@tailscale.com>
This commit is contained in:
Alex Chan 2025-10-17 10:53:12 +01:00 committed by Alex Chan
parent c3acf25d62
commit 55a43c3736
2 changed files with 109 additions and 61 deletions
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107
tka/tailchonk.go
View File

@ -11,6 +11,7 @@ import (
"fmt"
"os"
"path/filepath"
"slices"
"sync"
"time"
@ -206,10 +207,14 @@ func ChonkDir(dir string) (*FS, error) {
// CBOR was chosen because we are already using it and it serializes
// much smaller than JSON for AUMs. The 'keyasint' thing isn't essential
// but again it saves a bunch of bytes.
//
// We have removed the following fields from fsHashInfo, but they may be
// present in data stored in existing deployments. Do not reuse these values,
// to avoid getting unexpected values from legacy data:
// - cbor:1, Children
type fsHashInfo struct {
Children []AUMHash `cbor:"1,keyasint"`
AUM *AUM `cbor:"2,keyasint"`
CreatedUnix int64 `cbor:"3,keyasint,omitempty"`
AUM *AUM `cbor:"2,keyasint"`
CreatedUnix int64 `cbor:"3,keyasint,omitempty"`
// PurgedUnix is set when the AUM is deleted. The value is
// the unix epoch at the time it was deleted.
@ -285,32 +290,15 @@ func (c *FS) ChildAUMs(prevAUMHash AUMHash) ([]AUM, error) {
c.mu.RLock()
defer c.mu.RUnlock()
info, err := c.get(prevAUMHash)
if err != nil {
if os.IsNotExist(err) {
// not knowing about this hash is not an error
return nil, nil
}
return nil, err
}
// NOTE(tom): We don't check PurgedUnix here because 'purged'
// only applies to that specific AUM (i.e. info.AUM) and not to
// any information about children stored against that hash.
var out []AUM
out := make([]AUM, len(info.Children))
for i, h := range info.Children {
c, err := c.get(h)
if err != nil {
// We expect any AUM recorded as a child on its parent to exist.
return nil, fmt.Errorf("reading child %d of %x: %v", i, h, err)
err := c.scanHashes(func(info *fsHashInfo) {
if info.AUM != nil && bytes.Equal(info.AUM.PrevAUMHash, prevAUMHash[:]) {
out = append(out, *info.AUM)
}
if c.AUM == nil || c.PurgedUnix > 0 {
return nil, fmt.Errorf("child %d of %x: AUM not stored", i, h)
}
out[i] = *c.AUM
}
})
return out, nil
return out, err
}
func (c *FS) get(h AUMHash) (*fsHashInfo, error) {
@ -346,13 +334,45 @@ func (c *FS) Heads() ([]AUM, error) {
c.mu.RLock()
defer c.mu.RUnlock()
out := make([]AUM, 0, 6) // 6 is arbitrary.
err := c.scanHashes(func(info *fsHashInfo) {
if len(info.Children) == 0 && info.AUM != nil && info.PurgedUnix == 0 {
out = append(out, *info.AUM)
// Scan the complete list of AUMs, and build a list of all parent hashes.
// This tells us which AUMs have children.
var parentHashes []AUMHash
allAUMs, err := c.AllAUMs()
if err != nil {
return nil, err
}
for _, h := range allAUMs {
aum, err := c.AUM(h)
if err != nil {
return nil, err
}
})
return out, err
parent, hasParent := aum.Parent()
if !hasParent {
continue
}
if !slices.Contains(parentHashes, parent) {
parentHashes = append(parentHashes, parent)
}
}
// Now scan a second time, and only include AUMs which weren't marked as
// the parent of any other AUM.
out := make([]AUM, 0, 6) // 6 is arbitrary.
for _, h := range allAUMs {
if slices.Contains(parentHashes, h) {
continue
}
aum, err := c.AUM(h)
if err != nil {
return nil, err
}
out = append(out, aum)
}
return out, nil
}
// AllAUMs returns all AUMs stored in the chonk.
@ -362,7 +382,7 @@ func (c *FS) AllAUMs() ([]AUMHash, error) {
out := make([]AUMHash, 0, 6) // 6 is arbitrary.
err := c.scanHashes(func(info *fsHashInfo) {
if info.AUM != nil && info.PurgedUnix == 0 {
if info.AUM != nil {
out = append(out, info.AUM.Hash())
}
})
@ -391,6 +411,9 @@ func (c *FS) scanHashes(eachHashInfo func(*fsHashInfo)) error {
if err != nil {
return fmt.Errorf("reading %x: %v", h, err)
}
if info.PurgedUnix > 0 {
continue
}
eachHashInfo(info)
}
@ -445,24 +468,6 @@ func (c *FS) CommitVerifiedAUMs(updates []AUM) error {
for i, aum := range updates {
h := aum.Hash()
// We keep track of children against their parent so that
// ChildAUMs() do not need to scan all AUMs.
parent, hasParent := aum.Parent()
if hasParent {
err := c.commit(parent, func(info *fsHashInfo) {
// Only add it if its not already there.
for i := range info.Children {
if info.Children[i] == h {
return
}
}
info.Children = append(info.Children, h)
})
if err != nil {
return fmt.Errorf("committing update[%d] to parent %x: %v", i, parent, err)
}
}
err := c.commit(h, func(info *fsHashInfo) {
info.PurgedUnix = 0 // just in-case it was set for some reason
info.AUM = &aum

63
tka/tailchonk_test.go
View File

@ -15,6 +15,7 @@ import (
"github.com/google/go-cmp/cmp"
"github.com/google/go-cmp/cmp/cmpopts"
"golang.org/x/crypto/blake2s"
"tailscale.com/util/must"
)
// randHash derives a fake blake2s hash from the test name
@ -144,9 +145,6 @@ func TestTailchonkFS_Commit(t *testing.T) {
if _, err := os.Stat(filepath.Join(dir, base)); err != nil {
t.Errorf("stat of AUM file failed: %v", err)
}
if _, err := os.Stat(filepath.Join(chonk.base, "M7", "M7LL2NDB4NKCZIUPVS6RDM2GUOIMW6EEAFVBWMVCPUANQJPHT3SQ")); err != nil {
t.Errorf("stat of AUM parent failed: %v", err)
}
info, err := chonk.get(aum.Hash())
if err != nil {
@ -199,6 +197,14 @@ func TestTailchonkFS_PurgeAUMs(t *testing.T) {
}
}
func hashesLess(x, y AUMHash) bool {
return bytes.Compare(x[:], y[:]) < 0
}
func aumHashesLess(x, y AUM) bool {
return hashesLess(x.Hash(), y.Hash())
}
func TestTailchonkFS_AllAUMs(t *testing.T) {
chonk := &FS{base: t.TempDir()}
genesis := AUM{MessageKind: AUMRemoveKey, KeyID: []byte{1, 2}}
@ -220,14 +226,54 @@ func TestTailchonkFS_AllAUMs(t *testing.T) {
if err != nil {
t.Fatal(err)
}
hashesLess := func(a, b AUMHash) bool {
return bytes.Compare(a[:], b[:]) < 0
}
if diff := cmp.Diff([]AUMHash{genesis.Hash(), intermediate.Hash(), leaf.Hash()}, hashes, cmpopts.SortSlices(hashesLess)); diff != "" {
t.Fatalf("AllAUMs() output differs (-want, +got):\n%s", diff)
}
}
func TestTailchonkFS_ChildAUMsOfPurgedAUM(t *testing.T) {
chonk := &FS{base: t.TempDir()}
parent := AUM{MessageKind: AUMRemoveKey, KeyID: []byte{0, 0}}
parentHash := parent.Hash()
child1 := AUM{MessageKind: AUMAddKey, KeyID: []byte{1, 1}, PrevAUMHash: parentHash[:]}
child2 := AUM{MessageKind: AUMAddKey, KeyID: []byte{2, 2}, PrevAUMHash: parentHash[:]}
child3 := AUM{MessageKind: AUMAddKey, KeyID: []byte{3, 3}, PrevAUMHash: parentHash[:]}
child2Hash := child2.Hash()
grandchild2A := AUM{MessageKind: AUMAddKey, KeyID: []byte{2, 2, 2, 2}, PrevAUMHash: child2Hash[:]}
grandchild2B := AUM{MessageKind: AUMAddKey, KeyID: []byte{2, 2, 2, 2, 2}, PrevAUMHash: child2Hash[:]}
commitSet := []AUM{parent, child1, child2, child3, grandchild2A, grandchild2B}
if err := chonk.CommitVerifiedAUMs(commitSet); err != nil {
t.Fatalf("CommitVerifiedAUMs failed: %v", err)
}
// Check the set of hashes is correct
childHashes := must.Get(chonk.ChildAUMs(parentHash))
if diff := cmp.Diff([]AUM{child1, child2, child3}, childHashes, cmpopts.SortSlices(aumHashesLess)); diff != "" {
t.Fatalf("ChildAUMs() output differs (-want, +got):\n%s", diff)
}
// Purge the parent AUM, and check the set of child AUMs is unchanged
chonk.PurgeAUMs([]AUMHash{parent.Hash()})
childHashes = must.Get(chonk.ChildAUMs(parentHash))
if diff := cmp.Diff([]AUM{child1, child2, child3}, childHashes, cmpopts.SortSlices(aumHashesLess)); diff != "" {
t.Fatalf("ChildAUMs() output differs (-want, +got):\n%s", diff)
}
// Now purge one of the child AUMs, and check it no longer appears as a child of the parent
chonk.PurgeAUMs([]AUMHash{child3.Hash()})
childHashes = must.Get(chonk.ChildAUMs(parentHash))
if diff := cmp.Diff([]AUM{child1, child2}, childHashes, cmpopts.SortSlices(aumHashesLess)); diff != "" {
t.Fatalf("ChildAUMs() output differs (-want, +got):\n%s", diff)
}
}
func TestMarkActiveChain(t *testing.T) {
type aumTemplate struct {
AUM AUM
@ -585,10 +631,7 @@ func (c *compactingChonkFake) CommitTime(hash AUMHash) (time.Time, error) {
}
func (c *compactingChonkFake) PurgeAUMs(hashes []AUMHash) error {
lessHashes := func(a, b AUMHash) bool {
return bytes.Compare(a[:], b[:]) < 0
}
if diff := cmp.Diff(c.wantDelete, hashes, cmpopts.SortSlices(lessHashes)); diff != "" {
if diff := cmp.Diff(c.wantDelete, hashes, cmpopts.SortSlices(hashesLess)); diff != "" {
c.t.Errorf("deletion set differs (-want, +got):\n%s", diff)
}
return nil