dbus: hold node-message-bus, and never restart the bus live (hq ADR 0215)

A live restart of the system bus during an upgrade hung every login on a workstation until a reboot. The module owns the bus's packages, declares the bus running with no restart or reload trigger, publishes only curated events (health, services, denials; never traffic) and serves tools to look at both buses.
2026-10-05 11:50:52 +02:00
parent 4224ac7252
commit 7b5e1d3362
19 changed files with 3106 additions and 0 deletions
@@ -0,0 +1,103 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// busctlName is one line of `busctl list --json`.
+type busctlName struct {
+	Name       string  `json:"name"`
+	PID        *uint32 `json:"pid"`
+	Process    *string `json:"process"`
+	User       *string `json:"user"`
+	Connection string  `json:"connection"`
+	Unit       *string `json:"unit"`
+}
+
+// Name is one well-known name on a bus, with what holds it.
+type Name struct {
+	Name       string `json:"name"`
+	PID        uint32 `json:"pid,omitempty"`
+	Process    string `json:"process,omitempty"`
+	User       string `json:"user,omitempty"`
+	Unit       string `json:"unit,omitempty"`
+	Connection string `json:"connection,omitempty"`
+}
+
+// Names is dbus_names's answer.
+type Names struct {
+	Bus                   string   `json:"bus"`
+	Running               []Name   `json:"running"`
+	ActivatableNotRunning []string `json:"activatable_not_running"`
+	Connections           int      `json:"connections"`
+	Cut                   bool     `json:"cut,omitempty"`
+}
+
+// ParseNames reads `busctl list --json=short`: the well-known names running, the activatable names
+// that are not, and how many connections (unique names) the bus has.
+func ParseNames(bus, out string) (Names, error) {
+	var raw []busctlName
+	if err := json.Unmarshal([]byte(strings.TrimSpace(out)), &raw); err != nil {
+		return Names{}, fmt.Errorf("busctl list answered what is not its JSON: %w", err)
+	}
+	n := Names{Bus: bus, Running: []Name{}, ActivatableNotRunning: []string{}}
+	for _, r := range raw {
+		switch {
+		case r.Name == busName: // the bus itself, which busctl attributes to the service manager
+		case strings.HasPrefix(r.Name, ":"):
+			n.Connections++
+		case r.Connection == "(activatable)" || r.PID == nil:
+			n.ActivatableNotRunning = append(n.ActivatableNotRunning, r.Name)
+		default:
+			n.Running = append(n.Running, Name{Name: r.Name, PID: deref(r.PID), Process: derefS(r.Process),
+				User: derefS(r.User), Unit: derefS(r.Unit), Connection: r.Connection})
+		}
+	}
+	sort.Slice(n.Running, func(i, j int) bool { return n.Running[i].Name < n.Running[j].Name })
+	sort.Strings(n.ActivatableNotRunning)
+	if len(n.Running) > AnswerCap {
+		n.Running, n.Cut = n.Running[:AnswerCap], true
+	}
+	if len(n.ActivatableNotRunning) > AnswerCap {
+		n.ActivatableNotRunning, n.Cut = n.ActivatableNotRunning[:AnswerCap], true
+	}
+	return n, nil
+}
+
+// Names lists one bus's names as this account sees them.
+func (m *Machine) Names(ctx context.Context, bus string) (Names, error) {
+	args, err := m.busArgs(bus)
+	if err != nil {
+		return Names{}, err
+	}
+	out, err := m.Run(ctx, "busctl", append(args, "--json=short", "--no-pager", "list")...)
+	if err != nil {
+		return Names{}, err
+	}
+	return ParseNames(orWord(bus, "system"), out)
+}
+
+func deref(p *uint32) uint32 {
+	if p == nil {
+		return 0
+	}
+	return *p
+}
+
+func derefS(p *string) string {
+	if p == nil {
+		return ""
+	}
+	return *p
+}
+
+func orWord(s, word string) string {
+	if strings.TrimSpace(s) == "" {
+		return word
+	}
+	return s
+}