Added build dir, and gitignore

.gitignore

@@ -0,0 +1 @@
+build/

Makefile

@@ -0,0 +1,24 @@
+SHELL		:= /bin/bash
+CC			:= cc
+MKDIR		:= mkdir
+CFLAGS		:= -Wall -Werror -Os
+BUILD_DIR	:= build
+TARGET		:= $(BUILD_DIR)/fa2json
+SRCS		:= fs-watcher.c json-writer.c
+
+.PHONY: all test dev clean
+
+all: $(TARGET)
+
+$(TARGET): $(SRCS)
+	$(MKDIR) -p $(BUILD_DIR)
+	$(CC) $(CFLAGS) -o $@ $^
+
+test: $(TARGET)
+	node test/test.mjs
+
+dev: $(TARGET)
+	node test/dev.mjs $(ARGS)
+
+clean:
+	rm -rf $(BUILD_DIR)

fs-watcher.c

@@ -58,7 +58,7 @@ static void handle_events(int fafd, int mount_fd) {
 				clock_gettime(CLOCK_MONOTONIC, &mono);
 				clock_gettime(CLOCK_REALTIME, &wall);
 
-				fprintf(stdout, "{\"ts\": [%i, %i, %i, %i]", wall.tv_sec, wall.tv_nsec, mono.tv_sec, mono.tv_nsec);
+				fprintf(stdout, "{\"ts\": [%li, %li, %li, %li]", wall.tv_sec, wall.tv_nsec, mono.tv_sec, mono.tv_nsec);
 
 				char *ptr = (char *)(metadata + 1);
 				char *end = (char *)metadata + metadata->event_len;
@@ -98,7 +98,7 @@ static void handle_events(int fafd, int mount_fd) {
 				}
 
 				if (entry_index++) { fprintf(stdout, ", "); }
-				fprintf(stdout, ", \"mask\": %i}\n", metadata->mask);
+				fprintf(stdout, ", \"mask\": %lli}\n", metadata->mask);
 
 				metadata = FAN_EVENT_NEXT(metadata, size);
 

test/Manual experiment.md

@@ -0,0 +1,82 @@
+## Manual experiment
+
+> [!NOTE]
+> This manual experiment shows how we can do the testing (teardown not included). Note that we don't need the `losetup`-stuff, we know where everything is.
+
+### Compile
+```sh
+gcc fs-watcher.c json-writer.c -o fa2json
+```
+### Create image file
+```sh
+mktemp /tmp/fa2json-test-XXXXXX.img
+```
+
+```text
+/tmp/fa2json-test-UrwpOb.img
+```
+
+```sh
+truncate -s 10M /tmp/fa2json-test-UrwpOb.img
+```
+
+```sh
+mkfs.ext4 /tmp/fa2json-test-UrwpOb.img
+```
+
+```text
+mke2fs 1.47.3 (8-Jul-2025)
+Discarding device blocks: done
+Creating filesystem with 10240 1k blocks and 2560 inodes
+Filesystem UUID: 035c508e-dec0-4a21-a4d1-1efb6fa72415
+Superblock backups stored on blocks:
+        8193
+
+Allocating group tables: done
+Writing inode tables: done
+Creating journal (1024 blocks): done
+Writing superblocks and filesystem accounting information: done
+```
+
+
+### Create mount point
+
+```sh
+mktemp -d /tmp/fa2json-mnt-XXXXXX
+```
+
+```text
+/tmp/fa2json-mnt-ts2Dik
+```
+
+### Mount loop device
+```sh
+sudo mount /tmp/fa2json-test-UrwpOb.img /tmp/fa2json-mnt-ts2Dik/
+```
+
+> [!NOTE]
+> In a different terminal I now ran - but we could do this after `chown` or possibly `chown` + `sync`?
+> ```sh
+> fa2json /tmp/fa2json-mnt-ts2Dik
+> ```
+
+### Let current user own file system
+```sh
+sudo chown $(id -u) /tmp/fa2json-mnt-ts2Dik/
+```
+
+#### `fa2json` output
+```json
+{"ts": [1772658052, 704412412, 386988, 865842867], "name": "/tmp/fa2json-mnt-ts2Dik/.", "mask": 1073741828}
+```
+
+### Touch marker
+```sh
+touch /tmp/fa2json-mnt-ts2Dik/MARKER
+```
+
+#### `fa2json` output
+```json
+{"ts": [1772658064, 151070715, 387000, 312501190], "name": "/tmp/fa2json-mnt-ts2Dik/MARKER", "mask": 256}
+{"ts": [1772658064, 151099105, 387000, 312529600], "name": "/tmp/fa2json-mnt-ts2Dik/MARKER", "mask": 12}
+```

test/PLAN.md

@@ -0,0 +1,123 @@
+# fa2json Test Plan
+
+## Overview
+
+A Node.js test runner (`test/test.mjs`) that exercises `fa2json` against a
+temporary ext4 filesystem on a loop device. The test produces a single
+pass/fail result and cleans up after itself unconditionally.
+
+Requires root (`fanotify` FID reporting and `mount` both need `CAP_SYS_ADMIN`).
+
+---
+
+## Files
+
+| File | Purpose |
+|---|---|
+| `test/test.mjs` | Test runner |
+| `Makefile` | `make test` target calls `sudo node test/test.mjs` |
+
+---
+
+## Setup
+
+1. Create a temporary image file (`mktemp /tmp/fa2json-test-XXXXXX.img`)
+2. `truncate -s 10M` the image (sparse file, no need for `dd`)
+3. `mkfs.ext4` the image
+4. Create a temporary mount directory (`mktemp -d /tmp/fa2json-mnt-XXXXXX`)
+5. `sudo mount <img> <mntdir>` (no `losetup` needed — `mount` accepts image files directly)
+6. `sudo chown $(id -u) <mntdir>` to hand ownership to the current user
+7. `sync` to flush before fa2json starts listening
+8. `sudo` spawn `fa2json <mountpoint>` as a child process (needs `CAP_SYS_ADMIN`)
+9. Attach a `readline` interface to its stdout; parse each line as JSON and
+   push into an event buffer
+
+Steps 6 and 7 ensure the `chown` event never enters the fa2json stream, and
+all subsequent FS operations run unprivileged.
+
+---
+
+## Teardown
+
+Runs unconditionally in a `finally` block:
+
+1. Kill the `fa2json` child process
+2. `sudo umount <mountpoint>`
+3. `rm` the image file
+4. `rmdir` the mount directory
+
+---
+
+## Event Collection and the Marker Pattern
+
+`fa2json` runs continuously for the entire test. To associate events with
+specific operations, a marker file is used as a synchronisation barrier:
+
+1. Perform a filesystem operation
+2. Immediately `touch <mountpoint>/.marker_N` (where N is a counter)
+3. Wait until the event stream contains a CREATE event for `.marker_N`
+4. Collect all events since the previous marker — this batch belongs to the
+   current operation
+5. Assert on the batch, then advance the counter
+
+If a marker event never arrives the test hangs, which indicates a failure at
+the fa2json level itself.
+
+---
+
+## Path Handling
+
+`fa2json` emits full paths including the mount prefix
+(e.g. `/tmp/fa2json-mnt-XXXXX/dir_a/file.txt`). The runner strips this prefix
+so assertions work against a virtual root:
+
+```
+/tmp/fa2json-mnt-XXXXX/dir_a/file.txt  →  /dir_a/file.txt
+```
+
+---
+
+## Fanotify Mask Constants
+
+Relevant flags (bitwise, check with `mask & FLAG`):
+
+| Constant | Value | Meaning |
+|---|---|---|
+| `FAN_ATTRIB` | `0x4` | Metadata/attribute change |
+| `FAN_CLOSE_WRITE` | `0x8` | File closed after writing |
+| `FAN_CREATE` | `0x100` | File or directory created |
+| `FAN_DELETE` | `0x200` | File or directory deleted |
+| `FAN_RENAME` | `0x10000000` | Rename (has `old` and `new` fields) |
+| `FAN_ONDIR` | `0x40000000` | Event subject is a directory |
+
+---
+
+## Operations and Expected Events
+
+Each row is one `doOp()` call. Events are matched by presence (not exact list)
+— extra events from ext4 internals are ignored.
+
+| Operation | Expected event(s) |
+|---|---|
+| `mkdir /dir_a` | CREATE \| ONDIR, name `/dir_a` |
+| `touch /file_a.txt` | CREATE, name `/file_a.txt` |
+| `echo "content" >> /file_a.txt` | CLOSE_WRITE, name `/file_a.txt` |
+| `mkdir /dir_b` | CREATE \| ONDIR, name `/dir_b` |
+| `touch /dir_b/nested.txt` | CREATE, name `/dir_b/nested.txt` |
+| `mv /file_a.txt /file_b.txt` | RENAME, old `/file_a.txt`, new `/file_b.txt` |
+| `mv /dir_b /dir_a/dir_b_moved` | RENAME \| ONDIR, old `/dir_b`, new `/dir_a/dir_b_moved` |
+| `chmod 600 /file_b.txt` | ATTRIB, name `/file_b.txt` |
+| `touch -m /file_b.txt` | ATTRIB, name `/file_b.txt` |
+| `chmod 755 /dir_a` | ATTRIB \| ONDIR, name `/dir_a` |
+| `rm /file_b.txt` | DELETE, name `/file_b.txt` |
+| `rm /dir_a/dir_b_moved/nested.txt` | DELETE, name `/dir_a/dir_b_moved/nested.txt` |
+| `rmdir /dir_a/dir_b_moved` | DELETE \| ONDIR, name `/dir_a/dir_b_moved` |
+| `rmdir /dir_a` | DELETE \| ONDIR, name `/dir_a` |
+
+---
+
+## Pass / Fail
+
+- All assertions pass → print summary, `process.exit(0)`
+- Any assertion throws → print the failing operation, the expected event, and
+  the actual batch received, then `process.exit(1)`

test/dev.mjs

@@ -0,0 +1,43 @@
+#!/usr/bin/env node
+// Developer mode: set up loop device, stream fa2json output through jq,
+// tear down on exit. Optionally launch a terminal at the mount point.
+//
+// Usage:
+//   sudo node test/dev.mjs
+//   sudo node test/dev.mjs --terminal konsole
+//   sudo node test/dev.mjs --terminal "konsole -e bash"
+
+import { spawn } from 'node:child_process';
+import { createInterface } from 'node:readline';
+import { setup, spawnFa2json } from './lib/setup.mjs';
+
+const terminalArg = (() => {
+	const i = process.argv.indexOf('--terminal');
+	return i !== -1 ? process.argv.slice(i + 1).join(' ') : null;
+})();
+
+const { mnt, teardown } = await setup();
+console.error(`Mount point: ${mnt}`);
+
+// Pipe fa2json stdout through jq for pretty coloured output
+const fa2json = spawnFa2json(mnt);
+const jq = spawn('jq', ['-C', '--unbuffered', '.'], { stdio: ['pipe', 'inherit', 'inherit'] });
+fa2json.stdout.pipe(jq.stdin);
+
+fa2json.on('exit', async () => {
+	jq.stdin.end();
+	await teardown();
+	process.exit(0);
+});
+
+// Launch optional terminal at mount point
+if (terminalArg) {
+	const [cmd, ...args] = terminalArg.split(' ');
+	spawn(cmd, [...args, '--workdir', mnt], { detached: true, stdio: 'ignore' }).unref();
+	console.error(`Launched: ${terminalArg} --workdir ${mnt}`);
+}
+
+// Clean teardown on Ctrl+C
+process.on('SIGINT', async () => {
+	fa2json.kill('SIGTERM');
+});

test/lib/setup.mjs

@@ -0,0 +1,34 @@
+import { execSync, spawn } from 'node:child_process';
+import { mkdtempSync, mkdirSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+const FA2JSON = new URL('../../build/fa2json', import.meta.url).pathname;
+
+export async function setup() {
+	// Create image file and format
+	const img = execSync('mktemp /tmp/fa2json-test-XXXXXX.img').toString().trim();
+	execSync(`truncate -s 10M ${img}`);
+	execSync(`mkfs.ext4 -q ${img}`);
+
+	// Create mount point and mount
+	const mnt = execSync('mktemp -d /tmp/fa2json-mnt-XXXXXX').toString().trim();
+	execSync(`sudo mount ${img} ${mnt}`);
+
+	// Hand ownership to current user, then sync before fa2json starts
+	execSync(`sudo chown ${process.getuid()} ${mnt}`);
+	execSync('sync');
+
+	async function teardown() {
+		try { execSync(`sudo umount ${mnt}`); } catch {}
+		try { execSync(`rm -f ${img}`); } catch {}
+		try { execSync(`rmdir ${mnt}`); } catch {}
+	}
+
+	return { img, mnt, teardown };
+}
+
+export function spawnFa2json(mnt) {
+	const proc = spawn('sudo', [FA2JSON, mnt], { stdio: ['ignore', 'pipe', 'inherit'] });
+	return proc;
+}

test/test.mjs

@@ -0,0 +1,119 @@
+#!/usr/bin/env node
+// Automated test runner. Exit 0 = pass, exit 1 = fail.
+// Requires root (sudo) for mount and fa2json.
+
+import { createInterface } from 'node:readline';
+import { promises as fs } from 'node:fs';
+import { join } from 'node:path';
+import { setup, spawnFa2json } from './lib/setup.mjs';
+
+// Fanotify mask flags
+const FAN_ATTRIB      = 0x4;
+const FAN_CLOSE_WRITE = 0x8;
+const FAN_CREATE      = 0x100;
+const FAN_DELETE      = 0x200;
+const FAN_RENAME      = 0x10000000;
+const FAN_ONDIR       = 0x40000000;
+
+const { mnt, teardown } = await setup();
+const fa2json = spawnFa2json(mnt);
+
+// Event buffer and marker machinery
+const events = [];
+let markerResolve = null;
+let markerName = null;
+let markerCounter = 0;
+
+const rl = createInterface({ input: fa2json.stdout });
+rl.on('line', line => {
+	const event = JSON.parse(line);
+	// Strip mount prefix from all path fields
+	for (const key of ['name', 'old', 'new']) {
+		if (event[key]) event[key] = event[key].slice(mnt.length);
+	}
+	events.push(event);
+	if (markerResolve && event.name === `/.marker_${markerName}` && (event.mask & FAN_CREATE)) {
+		markerResolve();
+		markerResolve = null;
+	}
+});
+
+// Perform a FS operation, drop a marker, collect events up to that marker
+async function doOp(label, fn) {
+	const id = markerCounter++;
+	await fn();
+	await fs.writeFile(join(mnt, `.marker_${id}`), '');
+	await new Promise(resolve => {
+		markerName = id;
+		markerResolve = resolve;
+	});
+	// Collect all events since previous marker (excluding marker events themselves)
+	const batch = events.splice(0).filter(e => !e.name?.startsWith('/.marker_'));
+	return { label, batch };
+}
+
+function assert(label, batch, check) {
+	if (!check(batch)) {
+		console.error(`FAIL: ${label}`);
+		console.error('Batch:', JSON.stringify(batch, null, 2));
+		throw new Error(`Assertion failed: ${label}`);
+	}
+}
+
+function hasEvent(batch, flags, path, field = 'name') {
+	return batch.some(e => (e.mask & flags) === flags && e[field] === path);
+}
+
+try {
+	let op;
+
+	op = await doOp('mkdir /dir_a', () => fs.mkdir(join(mnt, 'dir_a')));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_CREATE | FAN_ONDIR, '/dir_a'));
+
+	op = await doOp('touch /file_a.txt', () => fs.writeFile(join(mnt, 'file_a.txt'), ''));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_CREATE, '/file_a.txt'));
+
+	op = await doOp('write /file_a.txt', () => fs.writeFile(join(mnt, 'file_a.txt'), 'content'));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_CLOSE_WRITE, '/file_a.txt'));
+
+	op = await doOp('mkdir /dir_b', () => fs.mkdir(join(mnt, 'dir_b')));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_CREATE | FAN_ONDIR, '/dir_b'));
+
+	op = await doOp('touch /dir_b/nested.txt', () => fs.writeFile(join(mnt, 'dir_b', 'nested.txt'), ''));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_CREATE, '/dir_b/nested.txt'));
+
+	op = await doOp('mv /file_a.txt /file_b.txt', () => fs.rename(join(mnt, 'file_a.txt'), join(mnt, 'file_b.txt')));
+	assert(op.label, op.batch, b => b.some(e => (e.mask & FAN_RENAME) && e.old === '/file_a.txt' && e.new === '/file_b.txt'));
+
+	op = await doOp('mv /dir_b /dir_a/dir_b_moved', () => fs.rename(join(mnt, 'dir_b'), join(mnt, 'dir_a', 'dir_b_moved')));
+	assert(op.label, op.batch, b => b.some(e => (e.mask & FAN_RENAME) && (e.mask & FAN_ONDIR) && e.old === '/dir_b' && e.new === '/dir_a/dir_b_moved'));
+
+	op = await doOp('chmod 600 /file_b.txt', () => fs.chmod(join(mnt, 'file_b.txt'), 0o600));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_ATTRIB, '/file_b.txt'));
+
+	op = await doOp('touch -m /file_b.txt', () => fs.utimes(join(mnt, 'file_b.txt'), new Date(), new Date()));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_ATTRIB, '/file_b.txt'));
+
+	op = await doOp('chmod 755 /dir_a', () => fs.chmod(join(mnt, 'dir_a'), 0o755));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_ATTRIB | FAN_ONDIR, '/dir_a'));
+
+	op = await doOp('rm /file_b.txt', () => fs.unlink(join(mnt, 'file_b.txt')));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_DELETE, '/file_b.txt'));
+
+	op = await doOp('rm /dir_a/dir_b_moved/nested.txt', () => fs.unlink(join(mnt, 'dir_a', 'dir_b_moved', 'nested.txt')));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_DELETE, '/dir_a/dir_b_moved/nested.txt'));
+
+	op = await doOp('rmdir /dir_a/dir_b_moved', () => fs.rmdir(join(mnt, 'dir_a', 'dir_b_moved')));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_DELETE | FAN_ONDIR, '/dir_a/dir_b_moved'));
+
+	op = await doOp('rmdir /dir_a', () => fs.rmdir(join(mnt, 'dir_a')));
+	assert(op.label, op.batch, b => hasEvent(b, FAN_DELETE | FAN_ONDIR, '/dir_a'));
+
+	console.log('PASS');
+} catch (e) {
+	console.error(e.message);
+	process.exitCode = 1;
+} finally {
+	fa2json.kill();
+	await teardown();
+}