truenas-truecloud-patch/docs/how-it-works.md

# How it works

> Part of [truenas-truecloud-patch](../README.md).

## What is actually patched

**Nothing in TrueNAS's persistent database or configuration is modified**
(other than the boot-hook entry itself). On every boot, `patch/apply.sh` runs
as a PREINIT script. It mounts a writable
[overlayfs](https://docs.kernel.org/filesystems/overlayfs.html) over the
relevant directories in `/usr/` (upper layer in `/run` tmpfs), then patches
`b2.py` and `restic.py` inside that overlay. The overlay is volatile — it
exists only for the current boot — but the PREINIT script recreates it
automatically on every subsequent boot. Nothing in `/usr/` is written to
directly.

PREINIT scripts are executed *by* middlewared, which by then has already
imported the stock modules — so after patching, `apply.sh` schedules a single
detached middlewared restart (transient systemd unit `truecloud-mw-restart`
running `patch/wait_restart.sh`) that loads the patched modules once boot has
*actually* settled: the script waits for the systemd boot job queue to drain
and for the docker/apps state machine to reach a terminal state before
restarting. Expect one middlewared restart shortly after every boot; the UI
and API are briefly unavailable while it happens, and running services are
not affected.

| Module | What changes | Technique |
|---|---|---|
| **providers** | `B2RcloneRemote` gains `get_restic_config()` — skipped automatically if TrueNAS already provides one on the class. `restic.py` URL builder is fixed: strips the stray leading slash and converts the slash separator to a colon (`b2:bucket:path`), which is the format restic 0.16.x expects. URL wrapper is a no-op if the URL is already correctly formed. | File patch applied inside the overlayfs upper layer |
| **providers** (UI) | The Angular bundle's `filterByProviders` binding is widened from `["STORJ_IX"]` to `["STORJ_IX","S3","B2"]` | In-place text replacement in the compiled JS chunk; original is backed up before patching |
| **nested** (opt-in) | `_truecloud_nested.py` is installed into `plugins/cloud/`, and `plugins/cloud/{snapshot,crud}.py` + `plugins/cloud_backup/sync.py` are patched so `snapshot = true` works on a dataset that has child datasets. See [below](nested-snapshots.md). | New module + file patches inside the overlayfs upper layer |

All changes are **fail-safe**: if a patch cannot be applied (e.g. TrueNAS
restructured the relevant code), middlewared starts normally, the affected module
is simply inactive, and the reason is logged to `apply.log` in your repo root. The
two modules are independent — one failing or going native does not disable the
other.


## How persistence works

Two different things must survive two different events:

| Event | What would be lost | What makes it survive |
|---|---|---|
| **Reboot** | The overlay holding the patched files lives in `/run` (tmpfs) and vanishes | The PREINIT hook re-runs `apply.sh` on every boot and schedules one middlewared restart to load the result |
| **TrueNAS update** | `/usr/` is replaced entirely; custom files in `/etc/` are wiped with the new boot environment | This repo lives on your **data pool**, and the hook registration lives in the **TrueNAS config database** — both survive updates. The first boot after an update is just a normal boot |

### What happens on every boot

1. **middlewared starts** with the stock (unpatched) modules. This is
   unavoidable: PREINIT scripts are executed *by* middlewared
   (`ix-preinit.service` → `midclt call initshutdownscript.execute_init_tasks`),
   so nothing registered there can run before it.
2. **Pools import** (`ix-zfs.service`), making `/mnt/<pool>` — and this
   repository — available.
3. **`apply.sh` runs** (`ix-preinit.service`). Before it patches anything it runs
   the **compatibility preflight** ([`tools/compat.py`](../tools/compat.py)) against
   the middlewared that is *actually installed*, and **any module whose assumptions
   no longer hold is not applied** — see [TrueNAS
   compatibility](../README.md#truenas-compatibility). What survives that check gets applied:
   it mounts the writable overlay (upper layer in `/run`), patches `b2.py` and
   `restic.py` on disk inside it, patches the UI bundle, and writes `apply.log` and
   `hook_status.json`.

   An incompatible module is skipped **for this boot only**. It is not the kill
   switch: install a release that supports your TrueNAS and the patch re-applies
   itself on the next boot, with no manual step. (The kill switch is permanent and
   is set only when TrueNAS has made the patch *unnecessary* — a different
   situation, and the opposite conclusion.)
4. **A deferred restart is scheduled.** The middlewared that is running
   imported the stock modules in step 1 and never re-imports, so the on-disk
   patch alone is not enough. `apply.sh` detects it was invoked by middlewared
   and creates a transient systemd unit (`truecloud-mw-restart`, via
   `systemd-run --no-block`) running `patch/wait_restart.sh` — detached so it
   cannot disrupt the remainder of the boot sequence.
5. **Once boot has settled, middlewared restarts once** and imports the
   patched modules from the overlay. `wait_restart.sh` holds the restart until
   the systemd boot job queue has drained (so in-flight `ix-*` units like
   `ix-reporting` finish first) *and* middlewared's docker/apps startup has
   reached a terminal state — plain unit ordering cannot see either, and
   restarting middlewared while they run kills apps and dashboard reporting
   for the whole boot. S3/B2 backup support is then active until the next
   reboot, when the cycle repeats.

What you will observe: one middlewared restart shortly after every boot (a
brief web UI/API blip; running services are unaffected). Between steps 3
and 5 there is a short window — typically well under a minute — where the UI
already shows S3/B2 (the JS bundle is read from disk per request) but the
backend is still stock. A backup job that fires inside that window fails once
with `NotImplementedError` and succeeds on its next run; see
[Troubleshooting](recovery.md) if it persists beyond boot.

Manual runs of `bash patch/apply.sh` never trigger the restart — that only
happens in boot context. `install.sh` and `recover.sh` perform their own
explicit restarts instead, which is why a manual re-apply must be followed by
`systemctl restart middlewared`.

---


## If TrueNAS adds native support

The patch is **two independent modules**, and each retires on its own — TrueNAS
is likely to ship one of these natively long before the other, and a module
going native must not take the other one down with it.

| Module | What it does | Detected as native when |
|---|---|---|
| **providers** | B2/S3 credentials for TrueCloud Backup (`b2.py`, `restic.py`, UI dropdown) | `B2RcloneRemote` carries a real `get_restic_config()` |
| **nested** | Snapshots on datasets with child datasets (`plugins/cloud/*`) | the *"no further nesting"* validation is gone from `plugins/cloud/crud.py` |

At every boot `apply.sh` checks both:

- **One module goes native** → that module is skipped and logged; the other keeps
  working, and the patch stays installed.
- **Both are done** (native, or nested was never enabled) → the kill switch
  (`disabled` file) is set, overlays are unmounted, and `apply.log` tells you to
  run `uninstall.sh`.

So on a box using only the provider patch, native B2 support retires the whole
thing as before. On a box that also uses nested snapshots, native B2 support
retires *just* that half.

Check the log after any TrueNAS update:
```bash
tail -20 /mnt/tank/truenas-truecloud-patch/apply.log
```

`hook_status.json` reports each module separately (`module.providers`,
`module.nested_snapshots`) with an `active` flag and a reason.

**Scenarios where the auto-detect may not fire** (manual check needed):

| Scenario | What happens | Action |
|---|---|---|
| B2 support added to a **base class** (not `B2RcloneRemote` directly) | `__dict__` check misses it; our method shadows native | Uninstall manually |
| B2 **credential schema changed** (e.g. `provider["account"]` renamed) | `KeyError` on first backup | Uninstall or update the patch |
| **URL builder** fixed but B2 class unchanged | URL wrapper becomes a no-op; no harm, but patch is dead weight | Uninstall at your convenience |

---

## After a TrueNAS update

A TrueNAS update replaces `/usr/` wholesale, wiping the patch. You do **not** need
to reinstall: `patch/apply.sh` runs at every boot and re-applies itself from your
clone. But it targets internal APIs with no stability contract, so an update *can*
break it — and the failure is quiet by design (middlewared starts fine; the patch
just doesn't).

**Check the log after any TrueNAS update:**

```bash
tail -30 /mnt/tank/truenas-truecloud-patch/apply.log
python3 /mnt/tank/truenas-truecloud-patch/patch/create_task.py verify
```

| What you see | What it means |
|---|---|
| `[OK] providers`, `[OK]`/`[SKIP] nested_snapshots` | Fine. Nothing to do. |
| `WARNING: … pattern not found` (UI) | The Angular bundle changed. The UI dropdown reverts to Storj-only, but **backups keep working** — create tasks with `create_task.py` meanwhile, and [open an issue](https://github.com/sudolulo/truenas-truecloud-patch/issues) with your TrueNAS version. |
| `WARNING: truecloud-patch is NOT COMPATIBLE with this TrueNAS version` | This TrueNAS changed middleware underneath the patch, and the named module was **deliberately not applied** — see `incompatible.json` for exactly which assumption broke. TrueNAS is left stock, so nothing is half-patched. Check [TrueNAS compatibility](../README.md#truenas-compatibility), then `bash update.sh` once a release supports your version; it re-applies itself on the next boot. This is **not** the kill switch and needs no manual reset. |
| `[FAIL] providers` | **Your B2/S3 backups will not run.** middlewared is fine, but the credential/URL handling is gone. Open an issue with your version. |
| `[FAIL] nested_snapshots` | The stock guard is back, so tasks with `snapshot = true` on a nested dataset will fail validation. Turn the option off on those tasks until it's fixed. |

"Fail-safe" means *the box stays up* — not that your backups keep running. A
`[FAIL] providers` is a broken backup, so check the log rather than assume.

Then update the patch itself if a newer release fixes it:

```bash
bash /mnt/tank/truenas-truecloud-patch/update.sh
```

---



## TrueNAS 26

TrueNAS 26 changes three things underneath the nested module. **Each one alone is
backup-breaking**, and none of them is visible from the `cloud_backup` files:

| what changed | what it would do |
| --- | --- |
| `cloud_backup` rewritten **async → synchronous** | an `async def` wrapper hands `sync.py` a coroutine where it unpacks a tuple |
| `get_dataset_recursive()` **deleted** from `plugins/cloud/snapshot.py` | `NameError` — the injected block called it out of the host module's namespace |
| `plugins/zfs_/dataset.py` and `zfs_/snapshot.py` **deleted** | `zfs.dataset.query`, `zfs.snapshot.query` and `zfs.snapshot.delete` all vanish. 26 uses `filesystem.statfs` and `zfs.resource.*` |

The first two are fixed: the patch reads which flavour of `cloud_backup` your box
declares and injects the wrapper that matches (one implementation of the real logic,
two thin wrappers), and it carries its own copy of the deleted helper.

The third is **not** fixed, and is why 26 reports BROKEN. Porting it means rewriting
the module's ZFS calls onto 26's new API, and no single API spans 24.10 through 26 —
so it needs a real 26 box to verify against, not a plausible-looking diff. Shipping a
port nobody has run is exactly the failure this project exists to avoid.

It is also the row that would have hurt most. `zfs.snapshot.delete` is what sweeps the
recursive snapshot; without it, **every run would orphan one snapshot per descendant
dataset — 250 on a real pool — forever.** The compatibility check caught it only
because it now asserts the middleware *methods the patch calls*, not just the symbols
it wraps.

`master` (development after 26) reports BROKEN too: iXsystems are still reshaping
these functions there, renaming `middleware` → `context` and `cloud_backup` → `entry`
and adding a required `credentials` parameter. That is a moving target and is
deliberately not chased; the check keeps reporting it until it settles into a beta,
which is when it becomes worth fixing.