jschoubben
e33191161d
nfs-share and smb-share share an intent, not a contract; one seat would be a union with every field optional. What the exemplar exposes is that a seat declared inside one module cannot be implemented by another without depending on it.
92 lines
4.9 KiB
Markdown
92 lines
4.9 KiB
Markdown
---
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status: open
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opened: 2026-09-30
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located-in:
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- mesh-catalog (no module shares a path over the network)
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- hq 02-DECISIONS (a file-share seat, per ADR 0126, is a module's own to define)
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fixed-by:
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amended-design:
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---
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# 169 — A machine shares its files, and the mesh does not know
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## What was observed
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ace serves the operator's media library to the home network with two host services no module
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declares and HAL never managed either:
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```
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/etc/exports: /storage/media 192.168.1.0/24(rw,sync,root_squash,…) nfs-server active, :2049
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/etc/samba/smb.conf: [media] path = /storage/media/ valid users = media smb active, :139/:445
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```
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Two LAN clients were connected at survey (2026-09-30). The library itself is operator data
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(ADR 0051: ~40 TB on ZFS, the mesh owns nothing about it — [issue 153](../153-an-adopted-machines-data-cannot-be-placed-where-it-is/00-report.md)
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is about modules reaching it in place).
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Under the mesh as it stands, this arrangement has no expression and one failure mode:
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- **Nothing declares the listens.** At `converge ace` the filter is the sum of what modules listen
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on (ADR 0045); 2049 and 445 are nobody's, so the shares close — silently, for the two clients
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that mount them.
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- **Nothing owns the configuration.** `/etc/exports` and `smb.conf` are hand-written files on one
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machine; a second machine sharing a directory would be written by hand again.
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- **Nothing can consume it.** A module on another node that wanted the library (a player, an
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indexer, a backup) has no `requires` to state and no binding to read; it would mount by a
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hand-typed host and path.
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- The clients are LAN devices, so this also meets [issue 154](../154-a-machines-own-network-is-not-a-reach/00-report.md)
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(no reach for the machine's own network).
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## The proposal (the operator's, 2026-09-30, settled after two rounds)
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**Two module-defined seats, one per protocol, because NFS and SMB share an intent and not a
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contract.** A seat in the mesh's sense is a contract — what it accepts, emits and serves, and the
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tools its holder must answer (ADR 0126, 0132) — and lined up, the two share almost none of it:
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| | `nfs-share` | `smb-share` |
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|---|---|---|
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| serves | export path(s); the client ranges allowed (`sec=sys` authorises by address) | share name(s), path |
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| pair credential | none | a user and password per consumer |
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| consumer's mount | `at:/path` | `//at/share` with credentials |
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| holder's tools | export / unexport a path for a range | add / remove a share, create a user |
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One `file-share` seat would be the union with every field optional — a consumer could bind it and
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still not know how to mount what it got (the emptiness ADR 0129 warns against). "Export a path to
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the network" is a category, and the mesh needs no seat category: a consumer requires the one it
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can mount. If "give me the library, however" is ever needed, it is a provision an umbrella module
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serves, not a seat.
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Both are node-scoped, one holder per node (ADR 0110), so ace holds both. `nfs` and `samba` are the
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first implementations; a second (Ganesha for `nfs-share`, ksmbd for `smb-share`) is what proves
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0126's promise that "replacing the implementation changes nothing for any caller".
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The holder module:
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- declares the exported paths as `accesses` (ADR 0051: it owns nothing about them — never creates,
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chowns or removes), and *which* paths as the assignment's settings (ADR 0046/0112);
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- writes the share configuration (`/etc/exports`, `smb.conf`) as mesh-managed files and drives the
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units, like `dnsmasq`/`sshd` do for theirs;
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- declares its endpoints (`nfs` 2049/tcp; `smb` 445/tcp, …) so the reach — internal, or the LAN
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once 154 has an answer — is the assignment's, and converge keeps them open;
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- **provides** the seat's provision, so a consumer on another node `requires nfs-share` (or
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`smb-share`) and reads `${bound:nfs-share:at}` and the path from its binding instead of a
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hand-typed mount.
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## The design gap this exposes
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**A seat definition has no home outside the module that first declared it.** Today a seat is
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declared inside a manifest (`showcase` declares `the-showcase`, `ca-trust` its own). If `nfs`
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declared `nfs-share`, Ganesha could hold it only by depending on nfs's manifest — the coupling
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0126 removed for callers, reintroduced for implementations. The protocol needs a neutral place in
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the catalogue beside the modules (a seat definition registered like a manifest), with a module
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saying which seats it implements. This is the first role with an obvious second implementation,
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which is what makes it the exemplar for that mechanism.
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## Open questions for the decision
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- Whether an NFS export over the overlay is an `internal` reach of the same endpoint or a second
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export line — NFS authorises by client address, so the mesh range and the LAN range are two
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entries in one file.
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- How a consumer's binding expresses a *path* to mount (today bindings carry `at`, `port`, `as` and
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whatever the provider `serves`), and whether one share can serve several paths.
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