felhom-agent/internal/localapi/guestbind.go

package localapi

import (
	"context"
	"fmt"
	"log/slog"
	"strconv"
	"sync"

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

// Guest data-drive passthrough (slice 10 P2, Model A). An enrolled external user-data drive is
// mounted on the HOST at /mnt/<name>; this binds its felhom-data NAMESPACE into the guest so the
// in-guest controller + apps can use it. Confinement is the inner (host→guest) bind: only
// <drive>/felhom-data crosses into the guest — the customer's other data on the drive never does.
//
// Model A: the felhom-data dir is bound AT the guest's /mnt/<name> (so the guest's /mnt/<name> IS the
// felhom-data namespace; `findmnt` shows /dev/sdXN[/felhom-data], which the controller's mount strip
// already handles). The bind is RW (NOT ro=1 like the bootstrap mount). The namespace is chowned to
// the unprivileged-LXC base so the guest reads it as root-owned (per-app subdirs are chowned to the
// app's mapped UID at deploy — NOT here). Spike-proven on 9201 (see usb-passthrough-spike memory).

// guestMappedRoot is the unprivileged-LXC idmap base — guest root (UID 0) == host UID 100000. chowning
// the namespace to this makes the guest see it as root:root, writable by the in-guest controller.
const guestMappedRoot = "100000:100000"

// felhomDataNS is the Felhom-managed namespace directory created on every external data drive. Only
// this subtree is exposed to the guest (matches the controller's appbackup.FelhomDataDir).
const felhomDataNS = "felhom-data"

// GuestBinder attaches a host data-drive's felhom-data namespace into a guest as an RW bind mount via
// `pct set` (a root@pam op — same fenced Runner the provision back-half uses for its bind). It does
// NOT make HTTP calls; the slot selection + idempotency live in the handler (which has the guest
// config). Satisfies localapi.GuestAttacher.
type GuestBinder struct {
	runner proxmox.Runner
	logger *slog.Logger
	// mountMu serializes AttachDrive/DetachDrive so a concurrent reconnect (controller-triggered) and the
	// agent's periodic reconcile can't both pass the isHostMountpoint check and double-bind the same
	// stable path (a TOCTOU race — observed live as 2 stacked binds).
	mountMu sync.Mutex
}

// NewGuestBinder builds a binder over the given root-CLI runner.
func NewGuestBinder(r proxmox.Runner, logger *slog.Logger) *GuestBinder {
	if logger == nil {
		logger = slog.Default()
	}
	return &GuestBinder{runner: r, logger: logger}
}

// AttachBind creates + chowns <where>/felhom-data on the host and binds it into the guest at <where>
// (Model A). mountKey is the chosen guest slot ("mp3"). Idempotency + slot choice are the caller's
// (it reads the guest config); this performs the host-root steps only.
func (b *GuestBinder) AttachBind(ctx context.Context, vmid int, mountKey, where string) error {
	src := where + "/" + felhomDataNS // host source = the felhom-data namespace on the drive
	// 1. Ensure the namespace dir exists (idempotent; created fresh + uniformly owned, so the drive's
	//    pre-existing mixed-ownership customer data is never touched).
	if err := b.run(ctx, "mkdir", "-p", src); err != nil {
		return fmt.Errorf("guest-attach: create namespace %s: %w", src, err)
	}
	// 2. chown the namespace ROOT to the guest base (NOT -R: per-app subdirs are chowned at deploy).
	if err := b.run(ctx, "chown", guestMappedRoot, src); err != nil {
		return fmt.Errorf("guest-attach: chown namespace %s: %w", src, err)
	}
	// 3. Bind it into the guest at `where`, RW. Bind form (host path), NEVER storage:size (that volume
	//    form would create a fresh empty disk and lose the existing data).
	spec := fmt.Sprintf("%s,mp=%s", src, where)
	if err := b.run(ctx, "pct", "set", strconv.Itoa(vmid), "-"+mountKey, spec); err != nil {
		return fmt.Errorf("guest-attach: pct set %s: %w", spec, err)
	}
	b.logger.Info("guest-attach: data drive bound into guest",
		"vmid", vmid, "slot", mountKey, "source", src, "guest_path", where)
	return nil
}

// DetachBind removes a mountpoint bind from the guest config (`pct set <vmid> --delete <mpN>`). This is
// the decommission/eject counterpart to AttachBind and the C1 FIX: a drive whose bind is removed here
// leaves NO dead `mpN` whose now-missing source would brick the guest on its next reboot (the B3
// critical bug, where decommission unmounted the drive but never deleted the bind). It runs on a RUNNING
// guest — a plain config edit, NOT a start — so it takes no start lock and cannot deadlock (unlike a
// pre-start `--delete`, which is why the boot-time net uses placeholders instead). The live in-guest
// mount lingers until the next reboot; the caller unmounts the host source separately.
func (b *GuestBinder) DetachBind(ctx context.Context, vmid int, mountKey string) error {
	if err := b.run(ctx, "pct", "set", strconv.Itoa(vmid), "--delete", mountKey); err != nil {
		return fmt.Errorf("guest-detach: pct set %d --delete %s: %w", vmid, mountKey, err)
	}
	b.logger.Info("guest-detach: mountpoint bind removed from guest config", "vmid", vmid, "slot", mountKey)
	return nil
}

// RebootGuest reboots the guest (graceful shutdown + start) so persisted-but-inactive mountpoint
// binds activate (slice 10 P2: the host-side live inject is blocked on an unprivileged guest, so a
// drive enrolled into a RUNNING guest activates only at the next boot — this is the user-triggered
// "Újraindítás most" path). `pct reboot` blocks until the guest is back, so callers run it detached.
func (b *GuestBinder) RebootGuest(ctx context.Context, vmid int) error {
	b.logger.Warn("guest-reboot: rebooting guest to activate pending mountpoint binds", "vmid", vmid)
	if err := b.run(ctx, "pct", "reboot", strconv.Itoa(vmid)); err != nil {
		return fmt.Errorf("guest-reboot: pct reboot %d: %w", vmid, err)
	}
	b.logger.Info("guest-reboot: guest back up", "vmid", vmid)
	return nil
}

func (b *GuestBinder) run(ctx context.Context, name string, args ...string) error {
	_, stderr, err := b.runner.Run(ctx, name, args...)
	if err != nil {
		return fmt.Errorf("%s: %w: %s", name, err, string(stderr))
	}
	return nil
}