git.delta.rocks / fleet / refs/commits / 14689aa0c750

--- a/Cargo.lock
+++ b/Cargo.lock
@@ -607,7 +607,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "993776b509cfb49c750f11b8f07a46fa23e0a1386ffc01fb1e7d343efc387895"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "cexpr",
  "clang-sys",
  "itertools 0.13.0",
@@ -623,6 +623,12 @@
 
 [[package]]
 name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "bitflags"
 version = "2.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4388bee8683e3d04af747c73422af53102d2bd24d9eadb6cbc100baef4b43f8"
@@ -1275,6 +1281,29 @@
 ]
 
 [[package]]
+name = "ctaphid"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa622743e1747e48d25170854b552b3ddc753125a39a6732e57c5c7a5ff7fe11"
+dependencies = [
+ "ctaphid-types",
+ "hex",
+ "hidapi",
+ "log",
+ "rand_core 0.6.4",
+ "tap",
+]
+
+[[package]]
+name = "ctaphid-types"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4714cdd86d5134532b9decaa6774db0a6851ecd07e96a2f239332ae1f3239350"
+dependencies = [
+ "bitflags 1.3.2",
+]
+
+[[package]]
 name = "ctr"
 version = "0.9.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1623,7 +1652,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1e0e367e4e7da84520dedcac1901e4da967309406d1e51017ae1abfb97adbd38"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "block2",
  "libc",
  "objc2",
@@ -2036,11 +2065,14 @@
  "base64 0.22.1",
  "bytes",
  "camino",
+ "chrono",
  "clap",
+ "ctaphid",
  "fleet-usb",
  "futures",
  "goodlog-subscriber",
  "hex",
+ "hidapi",
  "hostname",
  "http-body-util",
  "hyper",
@@ -2048,6 +2080,7 @@
  "nix",
  "nix-eval",
  "rand 0.10.1",
+ "tempfile",
  "tokio",
  "tracing",
 ]
@@ -2539,6 +2572,18 @@
 ]
 
 [[package]]
+name = "hidapi"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "798154e4b6570af74899d71155fb0072d5b17e6aa12f39c8ef22c60fb8ec99e7"
+dependencies = [
+ "cc",
+ "libc",
+ "pkg-config",
+ "winapi",
+]
+
+[[package]]
 name = "hkdf"
 version = "0.12.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -3431,7 +3476,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f02ab6bace2054fb888a3c16f990117b579d14a3088e472d63c6011fa185c9d3"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "libc",
  "plain",
  "redox_syscall 0.8.1",
@@ -3731,7 +3776,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "df9854ea6ad14e3f4698a7f03b65bce0833dd2d81d594a0e4a984170537146b6"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "libc",
  "log",
  "netlink-packet-core",
@@ -3743,7 +3788,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e2288fcb784eb3defd5fb16f4c4160d5f477de192eac730f43e1d11c24d9a007"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "libc",
  "log",
  "netlink-packet-core",
@@ -3819,7 +3864,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf20d2fde8ff38632c426f1165ed7436270b44f199fc55284c38276f9db47c3d"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "cfg-if",
  "cfg_aliases",
  "libc",
@@ -4063,7 +4108,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2a180dd8642fa45cdb7dd721cd4c11b1cadd4929ce112ebd8b9f5803cc79d536"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "block2",
  "dispatch2",
  "libc",
@@ -4076,7 +4121,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c71e34919aba0d701380d911702455038a8a3587467fe0141d6a71501e7ffe48"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "objc2",
  "objc2-core-foundation",
  "objc2-foundation",
@@ -4096,7 +4141,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e3e0adef53c21f888deb4fa59fc59f7eb17404926ee8a6f59f5df0fd7f9f3272"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "block2",
  "libc",
  "objc2",
@@ -4109,7 +4154,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "709fe137109bd1e8b5a99390f77a7d8b2961dafc1a1c5db8f2e60329ad6d895a"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "objc2",
  "objc2-core-foundation",
 ]
@@ -4130,7 +4175,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7216bd11cbda54ccabcab84d523dc93b858ec75ecfb3a7d89513fa22464da396"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "dispatch2",
  "libc",
  "objc2",
@@ -4840,7 +4885,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4b45fcc2344c680f5025fe57779faef368840d0bd1f42f216291f0dc4ace4744"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "num-traits",
  "rand 0.9.4",
  "rand_chacha 0.9.0",
@@ -5067,7 +5112,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ed2bf2547551a7053d6fdfafda3f938979645c44812fbfcda098faae3f1a362d"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
 ]
 
 [[package]]
@@ -5076,7 +5121,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5b44b894f2a6e36457d665d1e08c3866add6ed5e70050c1b4ba8a8ddedb02ce7"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
 ]
 
 [[package]]
@@ -5389,7 +5434,7 @@
 checksum = "bbf893f64684e58da8a68d56a5e84d1cf0440226274c515770fe267707a7d0b0"
 dependencies = [
  "aes 0.9.1",
- "bitflags",
+ "bitflags 2.13.0",
  "block-padding 0.4.2",
  "byteorder",
  "bytes",
@@ -5553,7 +5598,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fdb5bc1ae2baa591800df16c9ca78619bf65c0488b41b96ccec5d11220d8c154"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "errno",
  "libc",
  "linux-raw-sys 0.4.15",
@@ -5566,7 +5611,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6fe4565b9518b83ef4f91bb47ce29620ca828bd32cb7e408f0062e9930ba190"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "errno",
  "libc",
  "linux-raw-sys 0.12.1",
@@ -5769,7 +5814,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b7f4bc775c73d9a02cde8bf7b2ec4c9d12743edf609006c7facc23998404cd1d"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "core-foundation 0.10.1",
  "core-foundation-sys",
  "libc",
@@ -6025,7 +6070,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7a75cbde1bf934313596a004973e462f9a82caa814dcf1a5f507bdf51597eeb4"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
 ]
 
 [[package]]
@@ -6253,7 +6298,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a13f3d0daba03132c0aa9767f98351b3488edc2c100cda2d2ec2b04f3d8d3c8b"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "core-foundation 0.9.4",
  "system-configuration-sys",
 ]
@@ -6299,6 +6344,12 @@
 checksum = "7b2093cf4c8eb1e67749a6762251bc9cd836b6fc171623bd0a9d324d37af2417"
 
 [[package]]
+name = "tap"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "55937e1799185b12863d447f42597ed69d9928686b8d88a1df17376a097d8369"
+
+[[package]]
 name = "tempfile"
 version = "3.27.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -6682,7 +6733,7 @@
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4cfcf7e2740e6fc6d4d688b4ef00650406bb94adf4731e43c096c3a19fe40840"
 dependencies = [
- "bitflags",
+ "bitflags 2.13.0",
  "bytes",
  "futures-util",
  "http",
@@ -7036,7 +7087,7 @@
 checksum = "a5924018406ce0063cd67f8e008104968b74b563ee1b85dde3ed1f7cb87d3dbd"
 dependencies = [
  "arrayvec",
- "bitflags",
+ "bitflags 2.13.0",
  "cursor-icon",
  "log",
  "memchr",

--- a/Cargo.toml
+++ b/Cargo.toml
@@ -41,12 +41,14 @@
 chrono = { version = "0.4.41", features = ["serde"] }
 clap = { version = "4.5", features = ["derive", "env", "unicode", "wrap_help"] }
 clap_complete = "4.5"
+ctaphid = "0.3.1"
 console-subscriber = "0.5.0"
 cxx = "1.0.168"
 cxx-build = "1.0.168"
 ed25519-dalek = "3.0.0-rc.0"
 futures = "0.3.31"
 hex = "0.4.3"
+hidapi = { version = "1.2.6", default-features = false, features = ["linux-static-hidraw"] }
 hmac = "0.13.0"
 hostname = "0.4.1"
 http-body-util = "0.1"

--- a/cmds/fleet/src/cmds/usbd.rs
+++ b/cmds/fleet/src/cmds/usbd.rs
@@ -2,6 +2,7 @@
 	collections::HashSet,
 	fs::File,
 	io::{self, Write as _},
+	os::unix::fs::OpenOptionsExt as _,
 	sync::Arc,
 };
 
@@ -12,15 +13,16 @@
 use clap::Parser;
 use fleet_base::{fleetdata::SecretOwner, host::Config};
 use fleet_usb::{
-	MANIFEST_DONE_NAME, MANIFEST_NAME, MANIFEST_VERSION,
+	DATA_DIR, GC_DIR, MANIFEST_VERSION,
 	manifest::{Manifest, PathEntry, encrypt_manifest},
+	manifest_done_name, manifest_name,
 	names::{self, NAMING_SECRET_SIZE, NamingSecret},
 	stream::EncryptWriter,
 };
-use nix_eval::{Store, eval_store};
+use nix_eval::{Store, eval_store, nix_go, nix_go_json};
 use rand::Rng as _;
 use tokio::task::spawn_blocking;
-use tracing::{info, warn};
+use tracing::{debug, info};
 use zbus::zvariant::{self, OwnedObjectPath};
 
 use super::build_systems::build_task;
@@ -54,8 +56,9 @@
 	/// Write into this directory instead of discovering and mounting the stick via udisks
 	#[clap(long)]
 	mount_point: Option<Utf8PathBuf>,
-	/// Nix secret signing key; its public counterpart must be in trusted-public-keys on the host
-	#[clap(long)]
+	/// Nix secret signing key, overrides hosts.<name>.usbd.signingKeyFiles;
+	/// the public counterpart must be in trusted-public-keys on the host
+	#[clap(long, verbatim_doc_comment)]
 	sign_key: Option<Utf8PathBuf>,
 	#[clap(long, default_value = "toplevel-fleet")]
 	build_attr: String,
@@ -66,16 +69,29 @@
 		let host = config.host(&self.hostname)?;
 		let hostname = host.name.clone();
 		let recipient = config.recipient(&SecretOwner::host(&hostname)).await?;
-		let secret = naming_secret(config, &hostname)?;
+		let secret = naming_secret(config)?;
 
 		let built = build_task(config.clone(), hostname.clone(), &self.build_attr).await?;
 
-		if let Some(key) = self.sign_key.clone() {
+		let mut sign_keys: Vec<Utf8PathBuf> = self.sign_key.clone().into_iter().collect();
+		if sign_keys.is_empty()
+			&& let Some(host_config) = &host.host_config
+		{
+			let usbd = nix_go!(host_config.usbd);
+			let files: Vec<String> = nix_go_json!(usbd.signingKeyFiles);
+			for file in files {
+				let path = Utf8PathBuf::try_from(config.directory.join(&file))
+					.context("fleet directory should be utf8")?;
+				sign_keys.push(path);
+			}
+		}
+		let mut sign_key_names = Vec::new();
+		for key in sign_keys {
+			info!("signing with {key}");
+			sign_key_names.push(sign_key_name(&key)?);
 			let store = eval_store();
 			let path = built.clone();
 			spawn_blocking(move || store.sign_closure(&path, &key)).await??;
-		} else {
-			warn!(target: TARGET, "closure is not signed (no --sign-key), the host will refuse it unless paths are signed by other means");
 		}
 
 		let (stick, dir) = match &self.mount_point {
@@ -88,20 +104,25 @@
 		};
 		info!(target: TARGET, "writing update to {dir}");
 
-		let store = eval_store();
+		// Reopened to avoid nix Store::pathInfoCache: infos cached during the build
+		// would otherwise hide the signatures added by sign_closure above.
+		let store = Arc::new(spawn_blocking(|| Store::open("auto")).await??);
 		let manifest = {
 			let secret = secret.clone();
 			let hostname = hostname.clone();
 			let built = built.clone();
 			let dir = dir.clone();
-			spawn_blocking(move || write_closure(&store, &secret, &dir, &hostname, &built))
-				.await??
+			spawn_blocking(move || {
+				write_closure(&store, &secret, &dir, &hostname, &built, &sign_key_names)
+			})
+			.await??
 		};
 
 		let encrypted = encrypt_manifest(&manifest, std::iter::once(&*recipient))?;
 		{
 			let dir = dir.clone();
-			spawn_blocking(move || write_manifest(&dir, &encrypted)).await??;
+			let host_id = names::host_id(&secret, &hostname);
+			spawn_blocking(move || write_manifest(&dir, &host_id, &encrypted)).await??;
 		}
 
 		if let Some(stick) = stick {
@@ -112,36 +133,44 @@
 	}
 }
 
-fn naming_secret(config: &Config, host: &str) -> Result<NamingSecret> {
-	let mut extra = config.data.extra.write().expect("no poisoning");
-	let usbd = extra
-		.entry("usbd".to_owned())
-		.or_insert_with(|| serde_json::json!({}));
-	let usbd = usbd
-		.as_object_mut()
-		.context("fleet.nix extra.usbd should be an object")?;
-	let secrets = usbd
-		.entry("namingSecrets")
-		.or_insert_with(|| serde_json::json!({}));
-	let secrets = secrets
-		.as_object_mut()
-		.context("fleet.nix extra.usbd.namingSecrets should be an object")?;
-	if let Some(value) = secrets.get(host) {
-		let value = value
-			.as_str()
-			.context("naming secret should be a base64 string")?;
-		let bytes = BASE64.decode(value).context("naming secret base64")?;
+fn sign_key_name(key_file: &Utf8Path) -> Result<String> {
+	let key = std::fs::read_to_string(key_file)
+		.with_context(|| format!("reading signing key {key_file}"))?;
+	let (name, _) = key
+		.trim()
+		.split_once(':')
+		.with_context(|| format!("signing key {key_file} should look like name:base64"))?;
+	Ok(name.to_owned())
+}
+
+fn naming_secret(config: &Config) -> Result<NamingSecret> {
+	let config_field = &config.config_field;
+	let file: String = nix_go_json!(config_field.usbd.namingSecretFile);
+	let path = Utf8PathBuf::try_from(config.directory.join(&file))
+		.context("fleet directory should be utf8")?;
+	if path.exists() {
+		let value = std::fs::read_to_string(&path)?;
+		let bytes = BASE64
+			.decode(value.trim())
+			.with_context(|| format!("naming secret base64 in {path}"))?;
 		let bytes: [u8; NAMING_SECRET_SIZE] = bytes
 			.try_into()
-			.map_err(|_| anyhow!("naming secret should be {NAMING_SECRET_SIZE} bytes"))?;
+			.map_err(|_| anyhow!("naming secret in {path} should be {NAMING_SECRET_SIZE} bytes"))?;
 		Ok(NamingSecret(bytes))
 	} else {
 		let mut bytes = [0u8; NAMING_SECRET_SIZE];
 		rand::rng().fill_bytes(&mut bytes);
-		secrets.insert(
-			host.to_owned(),
-			serde_json::Value::String(BASE64.encode(bytes)),
-		);
+		if let Some(parent) = path.parent() {
+			std::fs::create_dir_all(parent)?;
+		}
+		let mut file = std::fs::OpenOptions::new()
+			.write(true)
+			.create_new(true)
+			.mode(0o600)
+			.open(&path)
+			.with_context(|| format!("creating naming secret file {path}"))?;
+		writeln!(file, "{}", BASE64.encode(bytes))?;
+		info!(target: TARGET, "generated new usbd naming secret at {path}");
 		Ok(NamingSecret(bytes))
 	}
 }
@@ -152,38 +181,100 @@
 	dir: &Utf8Path,
 	hostname: &str,
 	toplevel: &Utf8Path,
+	sign_key_names: &[String],
 ) -> Result<Manifest> {
+	let data_dir = dir.join(DATA_DIR);
+	let gc_dir = dir.join(GC_DIR);
+	std::fs::create_dir_all(&data_dir)?;
+	std::fs::create_dir_all(&gc_dir)?;
+
 	let mut closure = store.compute_closure(toplevel)?;
 	closure.sort();
 	info!(target: TARGET, "update closure contains {} paths", closure.len());
 
 	let mut existing = HashSet::new();
-	for entry in dir.read_dir_utf8().context("reading stick")? {
-		existing.insert(entry?.file_name().to_owned());
+	for shard in data_dir.read_dir_utf8().context("reading stick")? {
+		let shard = shard?;
+		if !shard.file_type()?.is_dir() {
+			continue;
+		}
+		for entry in shard.path().read_dir_utf8()? {
+			existing.insert(entry?.file_name().to_owned());
+		}
 	}
 
 	let total = closure.len();
 	let mut entries = Vec::with_capacity(total);
+	let mut reused = 0;
 	for (i, path) in closure.iter().enumerate() {
-		let entry = write_path(store, secret, dir, &mut existing, path)
+		let (entry, written) = write_path(store, secret, &data_dir, &mut existing, path)
 			.with_context(|| format!("writing {path}"))?;
-		info!(target: TARGET, "[{}/{total}] {path}", i + 1);
+		if written {
+			info!(target: TARGET, "[{}/{total}] {path}", i + 1);
+		} else {
+			debug!(target: TARGET, "[{}/{total}] {path} (reused)", i + 1);
+			reused += 1;
+		}
+		for name in sign_key_names {
+			if !entry
+				.sigs
+				.iter()
+				.any(|sig| sig.strip_prefix(name).is_some_and(|r| r.starts_with(':')))
+			{
+				bail!(
+					"{path} has no signature by the configured key {name}, refusing to write an update the host would reject; sigs present: {:?}",
+					entry.sigs
+				);
+			}
+		}
 		entries.push(entry);
 	}
+	info!(target: TARGET, "{} paths written, {reused} reused", total - reused);
 
-	let referenced = entries
-		.iter()
-		.flat_map(|e| e.chunks.iter())
-		.map(String::as_str)
-		.collect::<HashSet<_>>();
-	for name in &existing {
-		let stale_data = names::is_data_name(name) && !referenced.contains(name.as_str());
-		let stale_other = name.starts_with(TMP_PREFIX) || name == MANIFEST_DONE_NAME;
-		if stale_data || stale_other {
-			std::fs::remove_file(dir.join(name))
-				.with_context(|| format!("deleting stale {name}"))?;
+	{
+		let tmp = gc_dir.join(format!("{TMP_PREFIX}gc"));
+		let mut file = File::create(&tmp)?;
+		for entry in &entries {
+			for chunk in &entry.chunks {
+				writeln!(file, "{chunk}")?;
+			}
+		}
+		file.sync_all()?;
+		drop(file);
+		std::fs::rename(&tmp, gc_dir.join(names::host_id(secret, hostname)))?;
+	}
+
+	let mut referenced = HashSet::new();
+	for entry in gc_dir.read_dir_utf8()? {
+		let entry = entry?;
+		if entry.file_name().starts_with(TMP_PREFIX) {
+			std::fs::remove_file(entry.path())?;
+			continue;
+		}
+		let list = std::fs::read_to_string(entry.path())
+			.with_context(|| format!("reading gc list {}", entry.file_name()))?;
+		referenced.extend(list.lines().filter(|l| !l.is_empty()).map(str::to_owned));
+	}
+
+	for shard in data_dir.read_dir_utf8()? {
+		let shard = shard?;
+		if !shard.file_type()?.is_dir() {
+			if shard.file_name().starts_with(TMP_PREFIX) {
+				std::fs::remove_file(shard.path())?;
+			}
+			continue;
 		}
+		for entry in shard.path().read_dir_utf8()? {
+			let entry = entry?;
+			let name = entry.file_name();
+			let stale_data = names::is_data_name(name) && !referenced.contains(name);
+			if stale_data || name.starts_with(TMP_PREFIX) {
+				std::fs::remove_file(entry.path())
+					.with_context(|| format!("deleting stale {name}"))?;
+			}
+		}
 	}
+	let _ = std::fs::remove_file(dir.join(manifest_done_name(&names::host_id(secret, hostname))));
 
 	Ok(Manifest {
 		version: MANIFEST_VERSION,
@@ -199,7 +290,7 @@
 	dir: &Utf8Path,
 	existing: &mut HashSet<String>,
 	path: &Utf8Path,
-) -> Result<PathEntry> {
+) -> Result<(PathEntry, bool)> {
 	let info = store.query_path_info(path)?;
 	let key = names::file_key(secret, &info.nar_hash);
 
@@ -217,6 +308,7 @@
 		}
 	}
 
+	let written = chunks.is_none();
 	let chunks = if let Some(chunks) = chunks {
 		chunks
 	} else {
@@ -234,31 +326,36 @@
 			.map(|i| names::chunk_name(secret, &info.nar_hash, i, count))
 			.collect::<Vec<_>>();
 		for (tmp, name) in tmp_files.iter().zip(&chunks) {
-			std::fs::rename(tmp, dir.join(name))?;
+			let dest = dir.join(names::data_rel_path(name));
+			std::fs::create_dir_all(dest.parent().expect("sharded path has a parent"))?;
+			std::fs::rename(tmp, dest)?;
 		}
 		existing.extend(chunks.iter().cloned());
 		chunks
 	};
 
-	Ok(PathEntry {
-		store_path: path.to_owned(),
-		nar_hash: info.nar_hash,
-		nar_size: info.nar_size,
-		references: info.references,
-		sigs: info.sigs,
-		compression: "zstd".to_owned(),
-		key: BASE64.encode(key),
-		chunks,
-	})
+	Ok((
+		PathEntry {
+			store_path: path.to_owned(),
+			nar_hash: info.nar_hash,
+			nar_size: info.nar_size,
+			references: info.references,
+			sigs: info.sigs,
+			compression: "zstd".to_owned(),
+			key: BASE64.encode(key),
+			chunks,
+		},
+		written,
+	))
 }
 
-fn write_manifest(dir: &Utf8Path, encrypted: &[u8]) -> Result<()> {
+fn write_manifest(dir: &Utf8Path, host_id: &str, encrypted: &[u8]) -> Result<()> {
 	let tmp = dir.join(format!("{TMP_PREFIX}manifest"));
 	let mut file = File::create(&tmp)?;
 	file.write_all(encrypted)?;
 	file.sync_all()?;
 	drop(file);
-	std::fs::rename(&tmp, dir.join(MANIFEST_NAME))?;
+	std::fs::rename(&tmp, dir.join(manifest_name(host_id)))?;
 	nix::unistd::sync();
 	Ok(())
 }

--- a/cmds/usbd/Cargo.toml
+++ b/cmds/usbd/Cargo.toml
@@ -11,10 +11,13 @@
 base64.workspace = true
 bytes.workspace = true
 camino.workspace = true
+chrono.workspace = true
 clap.workspace = true
+ctaphid.workspace = true
 fleet-usb.workspace = true
 futures.workspace = true
 goodlog-subscriber.workspace = true
+hidapi.workspace = true
 hostname.workspace = true
 hex.workspace = true
 http-body-util.workspace = true
@@ -23,5 +26,6 @@
 nix = { workspace = true, features = ["mount"] }
 nix-eval.workspace = true
 rand.workspace = true
+tempfile.workspace = true
 tokio = { workspace = true, features = ["net", "process"] }
 tracing.workspace = true

--- a/cmds/usbd/src/main.rs
+++ b/cmds/usbd/src/main.rs
@@ -5,14 +5,17 @@
 use anyhow::{Context as _, Result, bail};
 use camino::{Utf8Path, Utf8PathBuf};
 use clap::Parser;
-use fleet_usb::{MANIFEST_DONE_NAME, MANIFEST_NAME, manifest::decrypt_manifest};
+use fleet_usb::{
+	DATA_DIR, LOGS_DIR, MANIFEST_DONE_SUFFIX, MANIFEST_PREFIX, manifest::decrypt_manifest, names,
+};
 use goodlog_subscriber::{LogOpts, setup_logging};
 use nix::mount::MsFlags;
 use nix_eval::{
 	Store, gc_register_my_thread, gc_unregister_my_thread, init_libraries, init_tokio_for_nix,
 };
+use rand::RngExt as _;
 use tokio::task::spawn_blocking;
-use tracing::{error, info, warn};
+use tracing::{debug, error, info, warn};
 
 const MOUNT_TARGET: &str = "/run/fleet-usbd/mnt";
 
@@ -39,6 +42,17 @@
 	/// copying, switching, done, noop, failed <error>
 	#[clap(long, verbatim_doc_comment)]
 	hook: Option<Utf8PathBuf>,
+	/// Blink connected Nitrokey 3 devices while the daemon is working:
+	/// blinking stopped and the machine rebooted - update succeeded,
+	/// blinking stopped without a reboot - update failed
+	#[clap(long, verbatim_doc_comment)]
+	nk3_wink: bool,
+	/// After every run, dump the journal onto the stick, encrypted to this armored OpenPGP public key
+	#[clap(long)]
+	log_recipient_file: Option<Utf8PathBuf>,
+	/// journalctl --since window of the log dump
+	#[clap(long, default_value = "-48h")]
+	log_since: String,
 	#[clap(long, default_value = "/nix/var/nix/profiles/system")]
 	profile: String,
 	/// Do not reboot after the update is applied
@@ -92,28 +106,110 @@
 	Ok(())
 }
 
-fn mark_done(dir: &Utf8Path) -> Result<()> {
-	std::fs::rename(dir.join(MANIFEST_NAME), dir.join(MANIFEST_DONE_NAME))
-		.context("marking update as done")?;
+fn mark_done(manifest_path: &Utf8Path) -> Result<()> {
+	std::fs::rename(
+		manifest_path,
+		format!("{manifest_path}{MANIFEST_DONE_SUFFIX}"),
+	)
+	.context("marking update as done")?;
 	nix::unistd::sync();
 	Ok(())
 }
 
+fn dump_logs(dir: &Utf8Path, recipient: &Utf8Path, since: &str) -> Result<()> {
+	use std::process::{Command, Stdio};
+	let logs_dir = dir.join(LOGS_DIR);
+	std::fs::create_dir_all(&logs_dir)?;
+	let tmp = logs_dir.join("usbd-tmp-log");
+	let _ = std::fs::remove_file(&tmp);
+
+	let _ = Command::new("journalctl").arg("--sync").status();
+
+	let gpg_home = tempfile::tempdir().context("creating gpg home")?;
+	let mut journalctl = Command::new("journalctl")
+		.args(["-o", "export"])
+		.arg(format!("--since={since}"))
+		.stdout(Stdio::piped())
+		.spawn()
+		.context("spawning journalctl")?;
+	let gpg = Command::new("gpg")
+		.env("GNUPGHOME", gpg_home.path())
+		.args([
+			"--batch",
+			"--no-tty",
+			"--yes",
+			"--trust-model",
+			"always",
+			"--encrypt",
+			"--recipient-file",
+		])
+		.arg(recipient)
+		.arg("--output")
+		.arg(&tmp)
+		.stdin(journalctl.stdout.take().expect("stdout is piped"))
+		.status()
+		.context("running gpg")?;
+	let journalctl = journalctl.wait()?;
+	if !journalctl.success() {
+		bail!("journalctl failed: {journalctl}");
+	}
+	if !gpg.success() {
+		bail!("gpg failed: {gpg}");
+	}
+
+	let file = std::fs::File::open(&tmp)?;
+	file.sync_all()?;
+	drop(file);
+	let name = format!(
+		"{}-{:04x}.export.gpg",
+		chrono::Local::now().format("%Y-%m-%d-%H-%M-%S"),
+		rand::rng().random::<u16>(),
+	);
+	std::fs::rename(&tmp, logs_dir.join(&name))?;
+	info!("journal dumped to {LOGS_DIR}/{name}");
+	Ok(())
+}
+
 async fn apply(opts: &Opts, dir: &Utf8Path, hook: &Hook) -> Result<Outcome> {
-	let manifest_path = dir.join(MANIFEST_NAME);
-	if !manifest_path.exists() {
-		if dir.join(MANIFEST_DONE_NAME).exists() {
-			info!("update on this stick is already applied");
+	let identity = host_identity(&opts.host_key)?;
+
+	let mut manifests = Vec::new();
+	let mut done_files = Vec::new();
+	for entry in dir.read_dir_utf8().context("reading stick")? {
+		let entry = entry?;
+		let name = entry.file_name();
+		if !name.starts_with(MANIFEST_PREFIX) {
+			continue;
+		}
+		if name.ends_with(MANIFEST_DONE_SUFFIX) {
+			done_files.push(entry.path().to_owned());
 		} else {
-			info!("no update manifest on the stick");
+			manifests.push(entry.path().to_owned());
 		}
-		return Ok(Outcome::Nothing);
 	}
 
-	let identity = host_identity(&opts.host_key)?;
-	let data = std::fs::read(&manifest_path).context("reading manifest")?;
-	let manifest = decrypt_manifest(&data, &identity)
-		.context("decrypting manifest, is this stick meant for this machine?")?;
+	let mut found = None;
+	for path in manifests {
+		let data = std::fs::read(&path).with_context(|| format!("reading manifest {path}"))?;
+		match decrypt_manifest(&data, &identity).with_context(|| format!("manifest {path}"))? {
+			Some(manifest) => {
+				found = Some((path, manifest));
+				break;
+			}
+			None => debug!("manifest {path} is for a different host"),
+		}
+	}
+	let Some((manifest_path, manifest)) = found else {
+		for path in done_files {
+			let data = std::fs::read(&path)?;
+			if decrypt_manifest(&data, &identity)?.is_some() {
+				info!("update on this stick is already applied");
+				return Ok(Outcome::Nothing);
+			}
+		}
+		info!("no update for this host on the stick");
+		return Ok(Outcome::Nothing);
+	};
 
 	let host = match &opts.hostname {
 		Some(host) => host.clone(),
@@ -132,15 +228,16 @@
 	let current = std::fs::read_link("/run/current-system").ok();
 	if current.as_deref() == Some(manifest.toplevel.as_std_path()) {
 		info!("system is already up to date");
-		mark_done(dir)?;
+		mark_done(&manifest_path)?;
 		return Ok(Outcome::UpToDate);
 	}
 
+	let data_dir = dir.join(DATA_DIR);
 	let missing = manifest
 		.paths
 		.iter()
 		.flat_map(|e| e.chunks.iter())
-		.filter(|c| !dir.join(c.as_str()).exists())
+		.filter(|c| !data_dir.join(names::data_rel_path(c)).exists())
 		.count();
 	if missing > 0 {
 		bail!("stick is missing {missing} update files, was it synchronized fully?");
@@ -152,13 +249,21 @@
 		manifest.paths.len()
 	);
 	hook.call("copying", None).await;
-	let cache = server::CacheServer::start(dir.to_owned(), &manifest).await?;
+	let cache = server::CacheServer::start(dir, &manifest).await?;
 	{
 		let url = cache.url.clone();
 		let toplevel = manifest.toplevel.clone();
+		let paths = manifest
+			.paths
+			.iter()
+			.map(|e| e.store_path.clone())
+			.collect::<Vec<_>>();
 		spawn_blocking(move || -> Result<()> {
 			let src = Store::open(&url)?;
 			let dst = Store::open("auto")?;
+			for path in &paths {
+				dst.add_temp_root(path)?;
+			}
 			src.copy_to(&dst, &toplevel)
 		})
 		.await?
@@ -186,12 +291,44 @@
 		bail!("{switch} boot failed: {status}");
 	}
 
-	mark_done(dir)?;
+	mark_done(&manifest_path)?;
 	Ok(Outcome::Applied)
 }
 
+fn wink_all() -> Result<()> {
+	let hidapi = hidapi::HidApi::new().context("initializing hidapi")?;
+	for info in hidapi.device_list() {
+		let nk3 = info.vendor_id() == 0x20a0 && info.product_id() == 0x42b2;
+		let fido = info.usage_page() == 0xf1d0;
+		if !nk3 && !fido {
+			continue;
+		}
+		let winked = info
+			.open_device(&hidapi)
+			.map_err(anyhow::Error::from)
+			.and_then(|device| Ok(ctaphid::Device::new(device, info.clone())?))
+			.and_then(|device| Ok(device.wink()?));
+		if let Err(e) = winked {
+			debug!("winking {:?}: {e:#}", info.path());
+		}
+	}
+	Ok(())
+}
+
 async fn run(opts: &Opts) -> Result<()> {
 	let hook = Hook(opts.hook.clone());
+	let winker = opts.nk3_wink.then(|| {
+		tokio::spawn(async {
+			loop {
+				match spawn_blocking(wink_all).await {
+					Ok(Ok(())) => {}
+					Ok(Err(e)) => debug!("nk3 wink: {e:#}"),
+					Err(e) => debug!("nk3 wink task: {e}"),
+				}
+				tokio::time::sleep(std::time::Duration::from_secs(5)).await;
+			}
+		})
+	});
 
 	let mounted = match &opts.device {
 		Some(device) => {
@@ -207,10 +344,28 @@
 
 	let outcome = apply(opts, &dir, &hook).await;
 
+	if let Err(e) = &outcome {
+		error!("update failed: {e:#}");
+	}
+	if let Some(recipient) = &opts.log_recipient_file {
+		let recipient = recipient.clone();
+		let dir = dir.clone();
+		let since = opts.log_since.clone();
+		let dumped = spawn_blocking(move || dump_logs(&dir, &recipient, &since))
+			.await
+			.expect("dump_logs should not panic");
+		if let Err(e) = dumped {
+			warn!("failed to dump logs onto the stick: {e:#}");
+		}
+	}
+
 	nix::unistd::sync();
 	if mounted && let Err(e) = nix::mount::umount(MOUNT_TARGET) {
 		warn!("unmounting the stick: {e}");
 	}
+	if let Some(winker) = winker {
+		winker.abort();
+	}
 
 	match outcome {
 		Ok(Outcome::Applied) => {

--- a/crates/fleet-usb/src/lib.rs
+++ b/crates/fleet-usb/src/lib.rs
@@ -2,6 +2,17 @@
 pub mod names;
 pub mod stream;
 
-pub const MANIFEST_NAME: &str = "usbd-update";
-pub const MANIFEST_DONE_NAME: &str = "usbd-update.done";
+pub const MANIFEST_PREFIX: &str = "usbd-update-";
+pub const MANIFEST_DONE_SUFFIX: &str = ".done";
 pub const MANIFEST_VERSION: u32 = 1;
+pub const DATA_DIR: &str = "update-data";
+pub const GC_DIR: &str = "gc";
+pub const LOGS_DIR: &str = "logs";
+
+pub fn manifest_name(host_id: &str) -> String {
+	format!("{MANIFEST_PREFIX}{host_id}")
+}
+
+pub fn manifest_done_name(host_id: &str) -> String {
+	format!("{MANIFEST_PREFIX}{host_id}{MANIFEST_DONE_SUFFIX}")
+}

--- a/crates/fleet-usb/src/manifest.rs
+++ b/crates/fleet-usb/src/manifest.rs
@@ -44,11 +44,14 @@
 	Ok(out)
 }
 
-pub fn decrypt_manifest(data: &[u8], identity: &dyn Identity) -> Result<Manifest> {
+/// Ok(None) means the manifest is valid but encrypted for a different host.
+pub fn decrypt_manifest(data: &[u8], identity: &dyn Identity) -> Result<Option<Manifest>> {
 	let decryptor = age::Decryptor::new(data).context("age decrypt")?;
-	let mut reader = decryptor
-		.decrypt(std::iter::once(identity))
-		.context("manifest is not encrypted for this identity")?;
+	let mut reader = match decryptor.decrypt(std::iter::once(identity)) {
+		Ok(reader) => reader,
+		Err(age::DecryptError::NoMatchingKeys) => return Ok(None),
+		Err(e) => return Err(e).context("decrypting manifest"),
+	};
 	let mut json = Vec::new();
 	reader.read_to_end(&mut json)?;
 	let manifest: Manifest = serde_json::from_slice(&json).context("manifest json")?;
@@ -58,5 +61,5 @@
 			manifest.version
 		);
 	}
-	Ok(manifest)
+	Ok(Some(manifest))
 }

--- a/crates/fleet-usb/src/names.rs
+++ b/crates/fleet-usb/src/names.rs
@@ -18,14 +18,14 @@
 }
 
 pub fn file_key(secret: &NamingSecret, nar_hash: &str) -> [u8; 32] {
-	derive(secret, &[b"fleet-usb.v1.key\0", nar_hash.as_bytes()])
+	derive(secret, &[b"fleet-usb.v1.key", nar_hash.as_bytes()])
 }
 
 pub fn chunk_name(secret: &NamingSecret, nar_hash: &str, index: u32, count: u32) -> String {
 	let h = derive(
 		secret,
 		&[
-			b"fleet-usb.v1.name\0",
+			b"fleet-usb.v1.name",
 			nar_hash.as_bytes(),
 			&index.to_le_bytes(),
 			&count.to_le_bytes(),
@@ -34,6 +34,15 @@
 	hex::encode(&h[..16])
 }
 
+pub fn host_id(secret: &NamingSecret, host: &str) -> String {
+	let h = derive(secret, &[b"fleet-usb.v1.host", host.as_bytes()]);
+	hex::encode(&h[..16])
+}
+
+pub fn data_rel_path(name: &str) -> String {
+	format!("{}/{name}", &name[..2])
+}
+
 pub fn is_data_name(name: &str) -> bool {
 	name.len() == 32
 		&& name

--- a/crates/nix-eval/src/lib.cc
+++ b/crates/nix-eval/src/lib.cc
@@ -204,6 +204,17 @@
   return out;
 }
 
+rust::String add_temp_root(Store *store, rust::Str path) {
+  try {
+    auto nixStore = store->ptr;
+    auto sp = nixStore->parseStorePath(std::string(path));
+    nixStore->addTempRoot(sp);
+    return rust::String();
+  } catch (const std::exception &e) {
+    return rust::String(e.what());
+  }
+}
+
 CxxBuildResult compute_closure(Store *store, rust::Str path) {
   CxxBuildResult res{rust::String(), {}};
   try {

--- a/crates/nix-eval/src/lib.hh
+++ b/crates/nix-eval/src/lib.hh
@@ -34,6 +34,8 @@
 struct CxxPathInfo;
 CxxPathInfo query_path_info(Store *store, rust::Str path);
 
+rust::String add_temp_root(Store *store, rust::Str path);
+
 CxxBuildResult compute_closure(Store *store, rust::Str path);
 
 rust::String nar_from_path(Store *store, rust::Str path, size_t sink_data,

--- a/crates/nix-eval/src/lib.rs
+++ b/crates/nix-eval/src/lib.rs
@@ -141,6 +141,9 @@
 		unsafe fn query_path_info(store: *mut Store, path: &str) -> CxxPathInfo;
 
 		#[allow(clippy::missing_safety_doc)]
+		unsafe fn add_temp_root(store: *mut Store, path: &str) -> String;
+
+		#[allow(clippy::missing_safety_doc)]
 		unsafe fn compute_closure(store: *mut Store, path: &str) -> CxxBuildResult;
 
 		#[allow(clippy::missing_safety_doc)]
@@ -665,6 +668,16 @@
 		})
 	}
 
+	/// The root is held for the lifetime of this process.
+	#[instrument(skip(self))]
+	pub fn add_temp_root(&self, path: &Utf8Path) -> Result<()> {
+		let msg = unsafe { nix_cxx::add_temp_root(self.as_ptr().cast(), path.as_str()) };
+		if !msg.is_empty() {
+			bail!("failed to add temp root for {path}: {msg}");
+		}
+		Ok(())
+	}
+
 	#[instrument(skip(self))]
 	pub fn compute_closure(&self, path: &Utf8Path) -> Result<Vec<Utf8PathBuf>> {
 		let res = unsafe { nix_cxx::compute_closure(self.as_ptr().cast(), path.as_str()) };

--- a/docs/features/usbd.adoc
+++ b/docs/features/usbd.adoc
@@ -2,24 +2,24 @@
 
 For airgapped deployments/system updates for low-tech users with limited internet access, it is better to have something more manual than pusher.
 
-fleet-usbd is a simple update daemon, which watches for a USB stick with the system update to be inserted into the machine, reads the manifest (usbd-update) from it, copies the closure from the USB stick, switches the current system generation, moves the manifest (usbd-update.done) and reboots.
+fleet-usbd is a simple update daemon, which watches for a USB stick with the system update to be inserted into the machine, finds its manifest on it, copies the closure from the USB stick, switches the current system generation, renames the manifest to *.done and reboots.
 
 The stick is discovered by volume label; the label is only a discovery hint, not a trust anchor. Detection is a systemd device unit on /dev/disk/by-label/<label> with the daemon service bound to it (WantedBy=), no udisks dependency.
 
 == Update flow
 
 1. Stick inserted, device unit starts the service, stick is mounted.
-2. Daemon decrypts the manifest, checks the system name matches this host.
+2. Daemon scans usbd-update-* files and tries to decrypt each; the one encrypted to this host's key is its manifest (the daemon has no naming secret, so it cannot derive its manifest name directly). The system name inside is checked as well.
 3. If the manifest's system is already the current generation - noop. Guards against reinsertion when the .done rename previously failed.
 4. Closure is copied from the stick. Hash verification is part of the copy; copying already-present paths is a noop.
 5. New generation is set as the boot default (boot, not switch), so the existing on-boot health-check rollback applies.
-6. Manifest is renamed to usbd-update.done.
+6. Manifest is renamed to *.done.
 7. Reboot.
 
 == Requirements
 
 One file per store path:: it should be possible to rewrite the system update on USB stick in incremental fashion: unchanged store paths keep their exact file name and bytes, only added/removed paths change on the stick.
-Deterministic, non-leaking names and ciphertext:: file names and file contents must be byte-stable across rewrites (otherwise incremental sync degrades to full rewrite), but must not leak store path names/contents. Mix a secret into the derivation: per-file key and file name are derived from (deployment secret, narHash); the deployment secret is an ordinary fleet shared secret owned by the target host. Derivation must use narHash, not the store path: input-addressed paths can be rebuilt nondeterministically, yielding the same store path with different contents, and a same-name-different-bytes file breaks both immutability and size-only synchronization. Note age cannot be used for the path files - its encryption is randomized, so ciphertext would churn on every rewrite.
+Deterministic, non-leaking names and ciphertext:: file names and file contents must be byte-stable across rewrites (otherwise incremental sync degrades to full rewrite), but must not leak store path names/contents. Mix a secret into the derivation: per-file key and file name are derived from (naming secret, narHash); the naming secret is project-wide, writer-side state in the file referenced by the `usbd.namingSecretFile` option (relative to the project directory, generated on first write). Hosts never need it - each manifest carries the keys for its paths - and because it is shared across hosts, a store path used by two hosts maps to the same file name and key, so shared sticks dedup naturally. Derivation must use narHash, not the store path: input-addressed paths can be rebuilt nondeterministically, yielding the same store path with different contents, and a same-name-different-bytes file breaks both immutability and size-only synchronization. Note age cannot be used for the path files - its encryption is randomized, so ciphertext would churn on every rewrite.
 Manifest encrypted to the host ssh key:: the manifest is encrypted the same way fleet already performs secret encryption (age, ssh-ed25519 host key recipient). It carries the system name and the per-path metadata listed in the copying section.
 Manifest should include system name:: update daemon should check if the system update is suitable for it.
 User feedback via callbacks:: how the user learns "update running / done / safe to remove" differs per client (screen, beep, LED). The daemon only exposes callback hooks for overriding; no built-in feedback.
@@ -33,7 +33,7 @@
 2. Daemon binds an ephemeral HTTP listener on 127.0.0.1 serving the binary cache protocol: /nix-cache-info, synthesized <hash>.narinfo (Sig: from build time, URL: nar/<derived-name>, Compression: zstd) and /nar/<derived-name>, which streaming-decrypts the stick file (chunked AEAD) into the .nar.zst; nix does the decompression and NAR hash check itself.
 3. The copy goes through the nix-eval FFI (Store::open on the localhost cache, copy_to into the local store), not a subprocess. A random token path prefix in the cache URL keeps other local processes from pulling decrypted NARs off the listener.
 4. Signatures are verified by nix against trusted-public-keys; the deployer signing key is pinned there by the fleet module.
-5. The copy holds a temporary GC root on the system path so a concurrent GC cannot race it. The listener is shut down after the copy, then the normal flow continues: set boot generation, rename manifest, reboot.
+5. The daemon holds a temporary GC root on every update path for the duration of the copy (temp roots protect not-yet-valid paths individually, so intermediate paths are covered before the toplevel becomes reachable), so a concurrent GC cannot race it. The listener is shut down after the copy, then the normal flow continues: set boot generation, rename manifest, reboot.
 
 Stick writing is the mirror image and also goes through the FFI: query path infos of the system closure, sign, dump each path to NAR, zstd-compress, encrypt with the derived per-file key, write under the derived name, write the age-encrypted manifest last.
 
@@ -41,6 +41,15 @@
 
 FAT32 (mkfs.vfat): universally supported and more robust against unclean ejects than exFAT. The 4 GiB file size limit is handled by splitting large encrypted files into fixed-size chunks; chunk names are derived from (deployment secret, narHash, chunk index) and the manifest lists the chunk sequence per path. This is plain size-splitting, unrelated to dedup chunking. Filesystem is case-insensitive; derived file names should be lowercase.
 
+Layout:
+
+/usbd-update-<derive(hostname)>:: age-encrypted manifest for one host, renamed to *.done after a successful update. One manifest per host, so several hosts can share a stick.
+/update-data/<xx>/<name>:: encrypted path chunks under derived names, sharded into 256 subdirectories by the first two name characters.
+/gc/<derive(hostname)>:: plaintext list of chunk names referenced by that host's update (bare names, the shard prefix is implied). The writer refreshes its own list, then deletes only data files referenced by no list, so several hosts' updates can share one stick without the writers deleting each other's files.
+/logs/<timestamp>-<random>.export.gpg:: journal dump in `journalctl -o export` format, written by the daemon after every run when `logRecipientFile` is set. Encrypted with OpenPGP to the operator key, so it can be decrypted with a smartcard. The random suffix avoids collisions between hosts sharing a stick (the daemon cannot derive its host id, and a plaintext hostname would leak).
+
+FAT32 allows at most 65536 directory entries per directory; a 32-character name costs 4 entries (3 LFN + 1 short), so a flat directory would cap out at ~16000 files. The 256-way shard gives each subdirectory its own budget (~4M files total), and as a side effect keeps the volume root nearly empty, so even a FAT16-formatted stick with its fixed 512-entry root directory works.
+
 == Synchronization
 
 Stick content should be synchronizable from http with a known tool that works on Windows. Flat content-addressed layout plus one manifest file satisfies this: rclone handles it (single portable exe, can be pre-installed on the stick itself with a .bat wrapper running `rclone sync --progress`; rclone has no native GUI and its experimental web GUI downloads assets from github on first run, so it is unusable here). Files are immutable under their derived names, so size-only comparison suffices. Sync should use --delete-before: rclone does not order transfers and by default deletes extraneous files last, which would require the stick to hold the old and new closure simultaneously. A partially synced stick is safe: the copy is hash-verified and the closure must be complete before the switch happens; the daemon should stat all manifest-referenced files upfront to report a partially synced stick cleanly.
@@ -57,6 +66,14 @@
     signPublicKeys = [ "client-1:..." ];
     # Optional user feedback script: receives copying/switching/done/noop/failed
     # hook = ./usbd-hook.sh;
+    # Optional builtin feedback: blink connected Nitrokey 3 devices while working.
+    # Blinking stopped and the machine rebooted - success; stopped without
+    # a reboot - failed, send the stick back (it carries the encrypted logs).
+    # The blink is the standard CTAPHID wink: white, firmware-fixed duration,
+    # no colors - the nk3 admin app exposes nothing else.
+    # nk3Wink = true;
+    # Optional journal back-channel, encrypted to this OpenPGP key
+    # logRecipientFile = ./operator.asc;
   };
 }
 ----
@@ -68,16 +85,33 @@
 [source,shell]
 ----
 mkfs.vfat -n FLEETUSBD /dev/sdX1
-fleet usbd write HOSTNAME --sign-key ./client-1.secret
+fleet usbd write HOSTNAME
 ----
 
-The signing keypair is generated once with `nix key generate-secret --key-name client-1`.
+The signing keypair is generated once with `nix key generate-secret --key-name client-1`; the secret key file is referenced from the fleet configuration (or overridden with `--sign-key`):
+
+[source,nix]
+----
+{
+  hosts.HOSTNAME.usbd.signingKeyFiles = [ "client-1.secret" ];
+}
+----
+
+Paths are resolved relative to the fleet project directory and deliberately are not nix paths, so the secret key is never imported into the store.
+
+Reading a journal dump from the stick:
 
+[source,shell]
+----
+gpg -d logs/2026-07-07-10-10-20-1a2b.export.gpg | systemd-journal-remote -o /tmp/metis.journal -
+journalctl --file /tmp/metis.journal -b
+----
+
 == Not a requirement
 
 Rollback prevention:: not a concern for any of the current clients.
 Update authenticity in the daemon:: handled by nix itself via store signatures during the copy; nothing to do on the usbd level.
 Chunking of large paths:: attic-style sub-path chunking would help large paths that change slightly, but conflicts with ease of synchronization; skipped.
-Status/log back-channel on the stick:: postponed, depends on the client.
+Encrypted journal on the host:: journald has no built-in journal encryption (FSS sealing is tamper-evidence only), which is why logs are exported and encrypted on the way to the stick instead.
 GC of old generations:: not a daemon problem.
-Multi-host sticks:: conflicts with incremental stick rewrite; one stick per host for now.
+Hiding cross-host linkage:: the naming secret is shared project-wide for dedup, so an observer of a shared stick can tell which files two hosts have in common (not what they are). Per-host secrets would hide this at the cost of duplicating shared paths; not a concern for the current clients.

--- a/flake.nix
+++ b/flake.nix
@@ -175,6 +175,7 @@
 
                 pkg-config
                 openssl
+                udev
                 rustPlatform.bindgenHook
                 inputs'.nix.packages.nix-expr-c
                 inputs'.nix.packages.nix-flake-c

--- a/modules/module-list.nix
+++ b/modules/module-list.nix
@@ -6,4 +6,5 @@
   ./nixos.nix
   ./nixpkgs.nix
   ./secrets.nix
+  ./usbd.nix
 ]

--- a/modules/nixos/usbd.nix
+++ b/modules/nixos/usbd.nix
@@ -47,6 +47,24 @@
         failed <error>.
       '';
     };
+    nk3Wink = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Blink connected Nitrokey 3 devices while an update is running.
+        Blinking stopped and the machine rebooted - update succeeded;
+        blinking stopped without a reboot - update failed.
+      '';
+    };
+    logRecipientFile = mkOption {
+      type = types.nullOr types.path;
+      default = null;
+      description = ''
+        Armored OpenPGP public key. When set, the daemon dumps the journal
+        of the last 48 hours onto the stick after every run, encrypted to
+        this key.
+      '';
+    };
     extraArgs = mkOption {
       type = types.listOf types.str;
       default = [ ];
@@ -64,6 +82,10 @@
         deviceUnit
         "local-fs.target"
       ];
+      path = [
+        pkgs.gnupg
+        config.systemd.package
+      ];
       serviceConfig = {
         Type = "oneshot";
         ExecStartPre = "-${pkgs.dosfstools}/bin/fsck.vfat -a ${devicePath}";
@@ -77,6 +99,11 @@
             "--hook"
             cfg.hook
           ]
+          ++ optionals cfg.nk3Wink [ "--nk3-wink" ]
+          ++ optionals (cfg.logRecipientFile != null) [
+            "--log-recipient-file"
+            cfg.logRecipientFile
+          ]
           ++ cfg.extraArgs
         );
       };

--- a/pkgs/fleet-usbd.nix
+++ b/pkgs/fleet-usbd.nix
@@ -6,6 +6,7 @@
   stdenv,
   pkg-config,
   rustPlatform,
+  udev,
 }:
 let
   system = stdenv.hostPlatform.system;
@@ -28,6 +29,7 @@
     inputs.nix.packages.${system}.nix-expr-c
     inputs.nix.packages.${system}.nix-flake-c
     inputs.nix.packages.${system}.nix-fetchers-c
+    udev
   ];
   nativeBuildInputs = [
     pkg-config