test(9p): run the conformance special-files cases over the wire (#16)

Author: pi0x

.agents/conformance-matrix.md

@@ -6,18 +6,18 @@ One conformance suite (`test/conformance.ts`), written against the driver interf
 
 Generated 2026-07-31 with `pnpm matrix`.
 
-| Column       | What it runs                                                                                                                                                | Result                                                                                                                      |
-| ------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------- |
-| **loopback** | `test/drivers.test.ts` — the driver behind `createLoopback`, no transport                                                                                   | 251 passed, 29 skipped (4 targets: memory; node-fs; unstorage; node:fs/promises (raw))                                      |
-| **FUSE**     | `test/fuse/conformance-mount.test.ts` — a real kernel mount, `node:fs` as the client                                                                        | 130 passed, 10 skipped (2 targets: memory driver, through a FUSE mount; node-fs driver, through a FUSE mount)               |
-| **9P**       | `test/9p/conformance.test.ts` — 9P2000.L through the codecs, the JS client from `test/9p/client.ts`                                                         | 192 passed, 18 skipped (3 targets: memory driver, over 9P; memory driver with no handles, over 9P; node-fs oracle, over 9P) |
-| **NFSv3**    | `test/nfs/v3/conformance.test.ts` — NFSv3 over a TCP socket, the JS client from `test/nfs/v3/client.ts`                                                     | 124 passed, 16 skipped (2 targets: memory driver, over NFS; node-fs driver, over NFS)                                       |
-| **NFSv4.1**  | `test/nfs/v4/conformance.test.ts` — NFSv4.1 over a TCP socket, the JS client from `test/nfs/v4/client.ts` and the driver over it in `test/nfs/v4/driver.ts` | 124 passed, 16 skipped (2 targets: memory driver, over NFSv4.1; node-fs driver, over NFSv4.1)                               |
-| **S3**       | `test/s3/conformance.test.ts` — an S3 gateway in process, the JS client from `test/s3/client.ts`                                                            | 48 passed, 22 skipped (1 target: memory driver, over S3)                                                                    |
+| Column       | What it runs                                                                                                                                                | Result                                                                                                                     |
+| ------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------- |
+| **loopback** | `test/drivers.test.ts` — the driver behind `createLoopback`, no transport                                                                                   | 251 passed, 29 skipped (4 targets: memory; node-fs; unstorage; node:fs/promises (raw))                                     |
+| **FUSE**     | `test/fuse/conformance-mount.test.ts` — a real kernel mount, `node:fs` as the client                                                                        | 130 passed, 10 skipped (2 targets: memory driver, through a FUSE mount; node-fs driver, through a FUSE mount)              |
+| **9P**       | `test/9p/conformance.test.ts` — 9P2000.L through the codecs, the JS client from `test/9p/client.ts`                                                         | 202 passed, 8 skipped (3 targets: memory driver, over 9P; memory driver with no handles, over 9P; node-fs oracle, over 9P) |
+| **NFSv3**    | `test/nfs/v3/conformance.test.ts` — NFSv3 over a TCP socket, the JS client from `test/nfs/v3/client.ts`                                                     | 124 passed, 16 skipped (2 targets: memory driver, over NFS; node-fs driver, over NFS)                                      |
+| **NFSv4.1**  | `test/nfs/v4/conformance.test.ts` — NFSv4.1 over a TCP socket, the JS client from `test/nfs/v4/client.ts` and the driver over it in `test/nfs/v4/driver.ts` | 124 passed, 16 skipped (2 targets: memory driver, over NFSv4.1; node-fs driver, over NFSv4.1)                              |
+| **S3**       | `test/s3/conformance.test.ts` — an S3 gateway in process, the JS client from `test/s3/client.ts`                                                            | 48 passed, 22 skipped (1 target: memory driver, over S3)                                                                   |
 
 ## Capability loss
 
-Derived from the run, not declared here: a requirement counts as unmet in a column when no case that names it passed there. `root` is an environment fact rather than a transport one — it gates the one case that hands a file away, which only root may do — so it is reported in its own column, and _recorded_ there rather than derived: a column can skip that case for want of `symlinks` long before privilege is reached, so the absence of a pass is not evidence about the run's uid. Every column is run with root when root is reachable, including the five that do not need it. A `mountx.*` requirement is left out of this table entirely: the suite calls an extension by name through `fs.mountx`, which only the loopback column has, so a skip everywhere else is a fact about how the case is written and not about what the transport carries (all four sessions do carry `mknod` — see the per-case rows below, and the FUSE column's own `mkfifo`/`mknod`/`bind` case over a real mount).
+Derived from the run, not declared here: a requirement counts as unmet in a column when no case that names it passed there. `root` is an environment fact rather than a transport one — it gates the one case that hands a file away, which only root may do — so it is reported in its own column, and _recorded_ there rather than derived: a column can skip that case for want of `symlinks` long before privilege is reached, so the absence of a pass is not evidence about the run's uid. Every column is run with root when root is reachable, including the five that do not need it. A `mountx.*` requirement is left out of this table entirely: the suite calls an extension by name through `fs.mountx`, so a skip is a fact about whether that column's client offers the name, not about what the transport carries. Two columns do offer it — the loopback one directly, and the 9P one because `Tmknod` carries the whole `mode` and `p9Driver` can hand it over unchanged. The rest skip for reasons of their own: FUSE drives a real mount with `node:fs` as the client, and `node:fs` cannot `mknod(2)`; NFSv3 and NFSv4.1 carry the file type in `ftype3`/`nfs_ftype4` rather than in the mode, so a client there could not offer the whole extension without deciding part of it itself; S3 has no way to name a FIFO at all. All four sessions do carry `mknod` — see the per-case rows below, and the FUSE column's own `mkfifo`/`mknod`/`bind` case over a real mount.
 
 **What this direction of derivation cannot check.** A column declares its own capabilities (`THROUGH_FUSE`, `THROUGH_9P`/`THROUGH_9P_REOPENED`, `THROUGH_NFS`, `THROUGH_NFS4`, `THROUGH_S3`), and declaring one `false` skips every case that needs it — which is exactly what a real loss looks like from here. So a capability the transport _does_ carry, wrongly declared lost, is reported as a loss with nothing to contradict it; the evidence only ever runs the other way, from a passing case to a capability that must be present. Every entry below is therefore a claim the transport's own test file makes and the run did not refute, and the comment at each declaration is where the reasoning for it lives.
 
@@ -131,13 +131,13 @@ Derived from the run, not declared here: a requirement counts as unmet in a colu
 
 ### special files
 
-| Case                                                                       | Needs          | loopback                                                                       | FUSE               | 9P                 | NFSv3              | NFSv4.1            | S3                 |
-| -------------------------------------------------------------------------- | -------------- | ------------------------------------------------------------------------------ | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ |
-| creates a FIFO and a socket that stat and readdir both name                | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
-| carries the device number of a character and a block device                | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
-| creates a regular file from a mode naming one, or naming no type           | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
-| is an ordinary name once it exists: rename, unlink, stat again             | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
-| refuses an existing name, a missing directory and a type with its own call | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
+| Case                                                                       | Needs          | loopback                                                                       | FUSE               | 9P                                                                                                           | NFSv3              | NFSv4.1            | S3                 |
+| -------------------------------------------------------------------------- | -------------- | ------------------------------------------------------------------------------ | ------------------ | ------------------------------------------------------------------------------------------------------------ | ------------------ | ------------------ | ------------------ |
+| creates a FIFO and a socket that stat and readdir both name                | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | pass (memory driver, over 9P), pass (memory driver with no handles, over 9P), skip (node-fs oracle, over 9P) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
+| carries the device number of a character and a block device                | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | pass (memory driver, over 9P), pass (memory driver with no handles, over 9P), skip (node-fs oracle, over 9P) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
+| creates a regular file from a mode naming one, or naming no type           | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | pass (memory driver, over 9P), pass (memory driver with no handles, over 9P), skip (node-fs oracle, over 9P) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
+| is an ordinary name once it exists: rename, unlink, stat again             | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | pass (memory driver, over 9P), pass (memory driver with no handles, over 9P), skip (node-fs oracle, over 9P) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
+| refuses an existing name, a missing directory and a type with its own call | `mountx.mknod` | pass (memory), skip (node-fs), skip (unstorage), skip (node:fs/promises (raw)) | skip: mountx.mknod | pass (memory driver, over 9P), pass (memory driver with no handles, over 9P), skip (node-fs oracle, over 9P) | skip: mountx.mknod | skip: mountx.mknod | skip: mountx.mknod |
 
 ### metadata
 

.agents/testing.md

@@ -52,9 +52,16 @@ through its Tier-1 JS client, and FUSE contributes a real-mount column.
   passed a case naming it, not every one — the drivers sharing a column need not have
   the same capabilities now that `unstorage` runs beside `memory`. A `mountx.*`
   requirement is dropped from the "capabilities lost" table (not from the per-case
-  rows): the suite reaches an extension by name through `fs.mountx`, which only the
-  loopback column has, so a skip in a transport column is about how the case is
-  written and not about what the wire carries — all four sessions carry `mknod`.
+  rows): the suite reaches an extension by name through `fs.mountx`, and whether a
+  column's client offers that name is a fact about the client. Two do — the loopback
+  column directly, and the 9P one because `Tmknod` carries the whole `mode` and
+  `p9Driver.mountx.mknod` hands it over unchanged, so the special-files cases run
+  there against the memory targets. The rest skip for their own reasons: FUSE's
+  client is `node:fs`, which cannot `mknod(2)` (its column covers special files by
+  its own case and by pjdfstest instead); NFSv3 and NFSv4.1 put the file type in
+  `ftype3`/`nfs_ftype4` rather than in the mode, so a client there cannot offer the
+  whole extension without deciding part of it itself; S3 cannot name a FIFO. All
+  four sessions carry `mknod` either way.
 
 ## Per area
 

test/9p/client.ts

@@ -1103,9 +1103,35 @@ export function p9Driver(client: P9Client, root: number): FsDriver {
 
   return {
     // A fid is server-side open state that outlives the name it was opened
-    // from, and `Trenameat` is one server operation.
+    // from, and `Trenameat` is one server operation. `extensions` is inferred
+    // from the keys of `mountx` below, so it is not here.
     capabilities: { handles: true, atomicRename: true },
 
+    mountx: {
+      /**
+       * `Tmknod`, which is the one place this adapter offers a `mountx.*`
+       * member by name.
+       *
+       * It is not the extension crossing the wire — it is the wire operation
+       * that already exists wearing the name the driver interface has for it.
+       * 9P2000.L carries the whole `mode`, type bits included, and
+       * `P9Session.#mknod` hands it to `mountx.mknod` unchanged, so every
+       * answer the case sees is the far side's: the memory driver's own
+       * `EEXIST`, `ENOENT` and `EPERM`-for-a-directory, arriving as `Rlerror`.
+       * Nothing is decided here.
+       *
+       * `dev` comes apart the way `P9Session` puts it back together — one
+       * 8-bit split across the project — which is what makes the round trip
+       * through `major`/`minor` and back out of `Rgetattr`'s single `rdev[8]`
+       * worth testing at all.
+       */
+      async mknod(path, mode, dev) {
+        await withParent(path, "mknod", (fid, name) =>
+          client.mknod(fid, name, { mode, major: dev >>> 8, minor: dev & 0xff }),
+        );
+      },
+    },
+
     async stat(path) {
       return withFid(path, true, async (fid) => statsOf(await client.getattr(fid)));
     },

test/9p/conformance.test.ts

@@ -43,11 +43,22 @@ import { P9Client, p9Driver } from "./client.ts";
  *   closes it — so a file unlinked while open stays readable through the fid
  *   that holds it, with no silly-rename anywhere. This is the capability the
  *   plan's `["fuse", "9p", "nfs"]` preference order is *about*.
- * - **`extensions: []`**, as in both other transports: the `mountx.*` namespace
- *   is a driver-to-session channel with no wire representation. `mountx.mknod`
- *   and `mountx.utimens` are reachable from `Tmknod` and `Tsetattr`, but a
- *   client cannot ask for them by name and the suite's extension cases are not
- *   about what a transport happens to route.
+ * - **`extensions: ["mknod"]`**, which the other transport columns do not
+ *   claim. 9P2000.L has an operation for it and carries the whole `mode`, type
+ *   bits included: `p9Driver`'s `mountx.mknod` is a `Tmknod`,
+ *   `P9Session.#mknod` passes the mode to the driver's extension unchanged, and
+ *   every refusal the cases assert — `EEXIST`, `ENOENT`, `EPERM` for a
+ *   directory — is the far side's answer arriving as `Rlerror`. That is the
+ *   capability *carried*, not declared over: a client offering a by-name handle
+ *   onto a wire operation is what a driver adapter is. `utimens` stays off the
+ *   list: `Tsetattr` carries the nanoseconds, but this client spends them
+ *   through `utimes`/`lutimes` and never asks for the extension by name.
+ *
+ *   What the extension cases buy over `session.test.ts`'s dispatch tests is the
+ *   rest of the surface: `stat` and `readdir` agreeing on the seven type
+ *   predicates off the wire's own encoding, `rdev` surviving the `major`/`minor`
+ *   split and `Rgetattr`'s single `rdev[8]` rejoining it, and a FIFO behaving
+ *   as an ordinary name under `rename` and `unlink` afterwards.
  *
  * Everything else — hardlinks, symlinks, permissions, times, truncate, atomic
  * rename, `statfs` — crosses intact, and each of those is a message of its own
@@ -71,7 +82,7 @@ const THROUGH_9P: ResolvedCapabilities = {
   caseSensitive: true,
   statfs: true,
   readOnly: false,
-  extensions: [],
+  extensions: ["mknod"],
 };
 
 /**
@@ -137,7 +148,15 @@ describe("over a 9P2000.L session", () => {
 
   conformance({
     name: "node-fs oracle, over 9P",
-    capabilities: THROUGH_9P,
+    /*
+     * `THROUGH_9P`, minus the one entry that is the *driver's* to answer rather
+     * than the transport's: the oracle implements no `mountx.mknod`, so
+     * `#mknod` answers `ENOSYS` for every type but a regular file, exactly as
+     * it should. The column carries the extension; this target has none to
+     * carry, and declaring one here is the difference between a capability and
+     * a claim.
+     */
+    capabilities: { ...THROUGH_9P, extensions: [] },
     /*
      * The oracle forwards the host kernel's errors, so the *code* is pinned and
      * the *number* is allowed to be either family's.