felhom-agent/internal/localapi/stalelock.go

package localapi

import (
	"context"
	"strconv"

	"gitea.dooplex.hu/admin/felhom-agent/internal/proxmox"
)

// Stale-lock recovery (TESTRUN finding F2-b). A host reboot DURING a vzdump backup leaves the guest
// with a backup lock (`lock: snapshot-delete` after an interrupted snapshot-mode backup, or `lock:
// backup`) and possibly a dangling `vzdump` snapshot. With `onboot: 1`, pve-guests then FAILS to start
// the locked CT ("CT is locked (snapshot-delete)") — the customer box stays DOWN until a human runs
// `pct unlock`. This makes the agent self-heal it at startup.
//
// The load-bearing invariant (B.0): at AGENT STARTUP the agent's own backup loop has not run yet, so a
// backup lock present then is STALE BY DEFINITION — UNLESS a vzdump is genuinely in-flight (an external
// backup, or one that outlived a bare `systemctl restart felhom-agent`). The recovery therefore clears a
// lock ONLY after confirming no vzdump task is running for that guest. If that confirmation can't be
// made, it FAILS SAFE (leaves the lock) — a wrongly-cleared live backup would corrupt state.
//
// Scope is deliberately narrow: only the two vzdump-related locks are ever touched. migrate/disk/create/
// rollback/mounted/snapshot locks are left alone (they belong to a different operation, mid-flight or
// needing different handling). The recovery is idempotent and never touches a guest without a stale lock.

// staleBackupLocks are the lock values an interrupted vzdump can leave. ONLY these are cleared.
var staleBackupLocks = map[string]bool{
	"backup":          true, // interrupted suspend/stop-mode backup
	"snapshot-delete": true, // interrupted snapshot-mode backup's cleanup (the F2-b repro)
}

// vzdumpSnapshotName is the snapshot a vzdump snapshot-mode backup creates then deletes; an interrupted
// one leaves it dangling under exactly this name.
const vzdumpSnapshotName = "vzdump"

// StaleLockController is the seam the recovery composes over. Reads go through the Proxmox API; the
// unlock is the one op with no API equivalent (`pct unlock`, the fenced root-CLI runner). Satisfied in
// production by *staleLockController (over *proxmox.Client + a proxmox.Runner).
type StaleLockController interface {
	// Guests lists the node's guests (vmid + running status).
	Guests(ctx context.Context) ([]proxmox.Guest, error)
	// Lock returns the guest's current lock ("" if unlocked) and its onboot flag.
	Lock(ctx context.Context, vmid int) (lock string, onboot bool, err error)
	// BackupRunning reports whether a vzdump task is genuinely in-flight for vmid (the invariant guard).
	BackupRunning(ctx context.Context, vmid int) (bool, error)
	// HasVzdumpSnapshot reports whether a dangling `vzdump` snapshot exists for vmid.
	HasVzdumpSnapshot(ctx context.Context, vmid int) (bool, error)
	// Unlock clears the guest's lock (`pct unlock` — no API equivalent).
	Unlock(ctx context.Context, vmid int) error
	// DeleteVzdumpSnapshot removes the dangling `vzdump` snapshot (API + WaitTask).
	DeleteVzdumpSnapshot(ctx context.Context, vmid int) error
	// Start starts the guest (API + WaitTask).
	Start(ctx context.Context, vmid int) error
}

// RecoverStaleLockedGuests scans every guest at startup and clears a stale vzdump lock (unlock →
// delete the dangling snapshot → start iff onboot). No-op when the controller is not wired.
func (s *Server) RecoverStaleLockedGuests(ctx context.Context) {
	if s.staleLock == nil {
		return
	}
	guests, err := s.staleLock.Guests(ctx)
	if err != nil {
		s.logger.Warn("stale-lock: guest list unavailable — skipping recovery", "err", err)
		return
	}
	for _, g := range guests {
		s.recoverOneStaleLock(ctx, g)
	}
}

// recoverOneStaleLock applies the recovery to a single guest. It acts ONLY on a stale backup lock and
// only when no backup is in-flight; every branch is logged so an operator can see what was (or wasn't)
// cleared.
func (s *Server) recoverOneStaleLock(ctx context.Context, g proxmox.Guest) {
	lock, onboot, err := s.staleLock.Lock(ctx, g.VMID)
	if err != nil {
		s.logger.Warn("stale-lock: read guest config failed — skipping", "vmid", g.VMID, "err", err)
		return
	}
	if !staleBackupLocks[lock] {
		return // unlocked, or a non-backup lock we deliberately leave alone (the overwhelming common case)
	}

	// INVARIANT GUARD: a backup lock is only STALE when no vzdump is genuinely running. Confirm before
	// clearing; on any doubt, FAIL SAFE and leave the lock (clearing a live backup's lock corrupts it).
	running, err := s.staleLock.BackupRunning(ctx, g.VMID)
	if err != nil {
		s.logger.Warn("stale-lock: could not confirm no backup is running — NOT clearing (fail-safe)",
			"vmid", g.VMID, "lock", lock, "err", err)
		return
	}
	if running {
		s.logger.Warn("stale-lock: a vzdump backup is genuinely in-flight — leaving the lock (NOT stale)",
			"vmid", g.VMID, "lock", lock)
		return
	}

	s.logger.Warn("stale-lock: clearing a stale backup lock left by an interrupted backup",
		"vmid", g.VMID, "lock", lock, "onboot", onboot, "status", g.Status)
	if err := s.staleLock.Unlock(ctx, g.VMID); err != nil {
		s.logger.Error("stale-lock: pct unlock failed", "vmid", g.VMID, "err", err)
		return
	}

	// Remove the dangling vzdump snapshot, if any (an interrupted snapshot-mode backup leaves it). Done
	// only when one actually exists, so a stop/suspend-mode interruption (no snapshot) doesn't no-op-fail.
	has, err := s.staleLock.HasVzdumpSnapshot(ctx, g.VMID)
	if err != nil {
		s.logger.Warn("stale-lock: snapshot list failed — skipping snapshot cleanup", "vmid", g.VMID, "err", err)
	} else if has {
		if err := s.staleLock.DeleteVzdumpSnapshot(ctx, g.VMID); err != nil {
			s.logger.Error("stale-lock: delete dangling vzdump snapshot failed", "vmid", g.VMID, "err", err)
		} else {
			s.logger.Info("stale-lock: removed dangling vzdump snapshot", "vmid", g.VMID)
		}
	}

	// Start ONLY a guest that is configured to auto-start AND is not already running. A deliberately-
	// stopped guest (onboot:0, e.g. the golden) is unlocked but never started; an already-running guest
	// (a bare agent restart found it up) is left as-is.
	if onboot && g.Status != "running" {
		if err := s.staleLock.Start(ctx, g.VMID); err != nil {
			s.logger.Error("stale-lock: start after unlock failed", "vmid", g.VMID, "err", err)
			return
		}
		s.logger.Warn("stale-lock: started CT after clearing the stale lock (onboot)", "vmid", g.VMID)
	}
}

// staleLockController is the production StaleLockController over the Proxmox API client + the fenced
// root-CLI runner. Reads (guest list, config, snapshots, running tasks), snapshot-delete and start go
// through the API (token-authed, WaitTask-asserted); only `pct unlock` shells out (no API equivalent).
type staleLockController struct {
	px     staleLockAPI
	runner proxmox.Runner
}

// staleLockAPI is the subset of *proxmox.Client the controller uses (kept narrow for clarity/testing).
type staleLockAPI interface {
	ListLXC(ctx context.Context) ([]proxmox.Guest, error)
	GuestConfig(ctx context.Context, vmid int) (proxmox.GuestConfig, error)
	ListSnapshots(ctx context.Context, vmid int) ([]proxmox.Snapshot, error)
	ListRunningTasks(ctx context.Context) ([]proxmox.TaskStatus, error)
	DeleteSnapshot(ctx context.Context, vmid int, snapname string) (string, error)
	Start(ctx context.Context, vmid int) (string, error)
	WaitTask(ctx context.Context, upid string, opts proxmox.WaitOptions) (proxmox.TaskStatus, error)
}

// NewStaleLockController builds the production controller. Returns nil if px or runner is nil (the
// feature then stays unwired and RecoverStaleLockedGuests is a no-op).
func NewStaleLockController(px staleLockAPI, runner proxmox.Runner) StaleLockController {
	if px == nil || runner == nil {
		return nil
	}
	return &staleLockController{px: px, runner: runner}
}

func (c *staleLockController) Guests(ctx context.Context) ([]proxmox.Guest, error) {
	return c.px.ListLXC(ctx)
}

func (c *staleLockController) Lock(ctx context.Context, vmid int) (string, bool, error) {
	cfg, err := c.px.GuestConfig(ctx, vmid)
	if err != nil {
		return "", false, err
	}
	return cfg.Lock(), cfg.OnBoot(), nil
}

func (c *staleLockController) BackupRunning(ctx context.Context, vmid int) (bool, error) {
	tasks, err := c.px.ListRunningTasks(ctx)
	if err != nil {
		return false, err
	}
	id := strconv.Itoa(vmid)
	for _, t := range tasks {
		// A single-guest vzdump task carries the vmid in its ID field.
		if t.Type == "vzdump" && t.ID == id {
			return true, nil
		}
	}
	return false, nil
}

func (c *staleLockController) HasVzdumpSnapshot(ctx context.Context, vmid int) (bool, error) {
	snaps, err := c.px.ListSnapshots(ctx, vmid)
	if err != nil {
		return false, err
	}
	for _, sn := range snaps {
		if sn.Name == vzdumpSnapshotName {
			return true, nil
		}
	}
	return false, nil
}

func (c *staleLockController) Unlock(ctx context.Context, vmid int) error {
	_, stderr, err := c.runner.Run(ctx, "pct", "unlock", strconv.Itoa(vmid))
	if err != nil {
		return &runnerError{op: "pct unlock", stderr: string(stderr), err: err}
	}
	return nil
}

func (c *staleLockController) DeleteVzdumpSnapshot(ctx context.Context, vmid int) error {
	upid, err := c.px.DeleteSnapshot(ctx, vmid, vzdumpSnapshotName)
	if err != nil {
		return err
	}
	if upid == "" {
		return nil // synchronous completion (no task to wait on)
	}
	_, err = c.px.WaitTask(ctx, upid, proxmox.WaitOptions{})
	return err
}

func (c *staleLockController) Start(ctx context.Context, vmid int) error {
	upid, err := c.px.Start(ctx, vmid)
	if err != nil {
		return err
	}
	if upid == "" {
		return nil
	}
	// AllowWarnings: an unprivileged LXC start emits a "WARNINGS: 1" advisory (the systemd-nesting
	// notice) even when the guest boots fine — same as the restore-test's start step (task.go). Without
	// this the recovery false-logs a start error for a guest that is actually up (seen live on 9999).
	_, err = c.px.WaitTask(ctx, upid, proxmox.WaitOptions{AllowWarnings: true})
	return err
}

// runnerError wraps a fenced-runner failure with its stderr (the runner returns the two separately).
type runnerError struct {
	op     string
	stderr string
	err    error
}

func (e *runnerError) Error() string {
	if e.stderr != "" {
		return e.op + ": " + e.err.Error() + ": " + e.stderr
	}
	return e.op + ": " + e.err.Error()
}

func (e *runnerError) Unwrap() error { return e.err }