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switch-to-configuration-ng: parameterise unit handling over UnitScope

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Introduce a UnitScope enum that abstracts the differences between
/etc/systemd/system and /etc/systemd/user (unit directory, persisted
action-list location) and thread it through handle_modified_unit() and
collect_unit_changes(). The system path is unchanged: all callers pass
UnitScope::System and the resulting unit directory and list-file paths
are identical to the previous constants.

Preparation to reuse the diff logic for user units.
This commit is contained in:
r-vdp
2026-04-21 15:42:26 +02:00
parent 5e4c815e26
commit 5e22ad20da
1 changed files with 96 additions and 25 deletions
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pkgs/by-name/sw/switch-to-configuration-ng/src/main.rs
+96 -25
View File
@@ -142,6 +142,49 @@ impl From<&Action> for &'static str {
}
}
/// Scope of systemd unit management. System units live in /etc/systemd/system and
/// are managed via the system bus; user units live in /etc/systemd/user and are
/// managed via each logged-in user's session bus.
#[derive(Debug, Clone, Copy, PartialEq)]
enum UnitScope {
System,
}
impl UnitScope {
/// Path relative to a toplevel (or to /) where this scope's NixOS-managed
/// unit files live.
fn etc_dir(&self) -> &'static str {
match self {
UnitScope::System => "etc/systemd/system",
}
}
/// Absolute path to the currently-active unit directory for this scope.
fn current_dir(&self) -> &'static Path {
Path::new(match self {
UnitScope::System => "/etc/systemd/system",
})
}
/// Directory where unit action lists are persisted for
/// resume-after-interrupt.
fn list_dir(&self) -> PathBuf {
match self {
UnitScope::System => PathBuf::from("/run/nixos"),
}
}
fn start_list_file(&self) -> PathBuf {
self.list_dir().join("start-list")
}
fn restart_list_file(&self) -> PathBuf {
self.list_dir().join("restart-list")
}
fn reload_list_file(&self) -> PathBuf {
self.list_dir().join("reload-list")
}
}
// Allow for this switch-to-configuration to remain consistent with the perl implementation.
// Perl's "die" uses errno to set the exit code: https://perldoc.perl.org/perlvar#%24%21
fn die() -> ! {
@@ -572,6 +615,7 @@ fn compare_units(current_unit: &UnitInfo, new_unit: &UnitInfo) -> UnitComparison
// figures out of what units are to be stopped, restarted, reloaded, started, and skipped.
fn handle_modified_unit(
toplevel: &Path,
scope: UnitScope,
unit: &str,
base_name: &str,
new_unit_file: &Path,
@@ -584,6 +628,9 @@ fn handle_modified_unit(
units_to_restart: &mut HashMap<String, ()>,
units_to_skip: &mut HashMap<String, ()>,
) -> Result<()> {
let start_list = scope.start_list_file();
let restart_list = scope.restart_list_file();
let reload_list = scope.reload_list_file();
let use_restart_as_stop_and_start = new_unit_info.is_none();
if matches!(
@@ -604,10 +651,10 @@ fn handle_modified_unit(
// crashing it.
if unit == "-.mount" || unit == "nix.mount" {
units_to_reload.insert(unit.to_string(), ());
record_unit(RELOAD_LIST_FILE, unit);
record_unit(&reload_list, unit);
} else {
units_to_restart.insert(unit.to_string(), ());
record_unit(RESTART_LIST_FILE, unit);
record_unit(&restart_list, unit);
}
} else if unit.ends_with(".socket") {
// FIXME: do something?
@@ -631,7 +678,7 @@ fn handle_modified_unit(
})
{
units_to_reload.insert(unit.to_string(), ());
record_unit(RELOAD_LIST_FILE, unit);
record_unit(&reload_list, unit);
} else if !parse_systemd_bool(new_unit_info, "Service", "X-RestartIfChanged", true)
|| parse_systemd_bool(new_unit_info, "Unit", "RefuseManualStop", false)
|| parse_systemd_bool(new_unit_info, "Unit", "X-OnlyManualStart", false)
@@ -645,11 +692,11 @@ fn handle_modified_unit(
{
// This unit should be restarted instead of stopped and started.
units_to_restart.insert(unit.to_string(), ());
record_unit(RESTART_LIST_FILE, unit);
record_unit(&restart_list, unit);
// Remove from units to reload so we don't restart and reload
if units_to_reload.contains_key(unit) {
units_to_reload.remove(unit);
unrecord_unit(RELOAD_LIST_FILE, unit);
unrecord_unit(&reload_list, unit);
}
} else {
// If this unit is socket-activated, then stop the socket unit(s) as well, and
@@ -686,13 +733,13 @@ fn handle_modified_unit(
}
// Only restart sockets that actually exist in new configuration:
if toplevel.join("etc/systemd/system").join(socket).exists() {
if toplevel.join(scope.etc_dir()).join(socket).exists() {
if use_restart_as_stop_and_start {
units_to_restart.insert(socket.to_string(), ());
record_unit(RESTART_LIST_FILE, socket);
record_unit(&restart_list, socket);
} else {
units_to_start.insert(socket.to_string(), ());
record_unit(START_LIST_FILE, socket);
record_unit(&start_list, socket);
}
socket_activated = true;
@@ -701,7 +748,7 @@ fn handle_modified_unit(
// Remove from units to reload so we don't restart and reload
if units_to_reload.contains_key(unit) {
units_to_reload.remove(unit);
unrecord_unit(RELOAD_LIST_FILE, unit);
unrecord_unit(&reload_list, unit);
}
}
}
@@ -719,10 +766,10 @@ fn handle_modified_unit(
if !socket_activated {
if use_restart_as_stop_and_start {
units_to_restart.insert(unit.to_string(), ());
record_unit(RESTART_LIST_FILE, unit);
record_unit(&restart_list, unit);
} else {
units_to_start.insert(unit.to_string(), ());
record_unit(START_LIST_FILE, unit);
record_unit(&start_list, unit);
}
}
@@ -734,7 +781,7 @@ fn handle_modified_unit(
// Remove from units to reload so we don't restart and reload
if units_to_reload.contains_key(unit) {
units_to_reload.remove(unit);
unrecord_unit(RELOAD_LIST_FILE, unit);
unrecord_unit(&reload_list, unit);
}
}
}
@@ -938,14 +985,24 @@ fn remove_file_if_exists(p: impl AsRef<Path>) -> std::io::Result<()> {
}
}
/// Iterate over currently active units, compare each unit's file in
/// /etc/systemd/system against the one in the new toplevel, and populate the
/// Iterate over currently active units in the given scope, compare the unit
/// file in `old_unit_dir` against the one in `new_unit_dir`, and populate the
/// action maps accordingly.
///
/// Units whose FragmentPath does not live under /etc/systemd/system are
/// skipped; this avoids touching generator output in /run/systemd/generator*.
/// Units whose FragmentPath does not live under the scope's NixOS-managed
/// directory (`scope.current_dir()`) are skipped; this avoids touching
/// generated units and, for the user scope, units that are shadowed by files
/// in the user's home directory (e.g. those managed by home-manager).
///
/// `old_unit_dir` and `new_unit_dir` are taken explicitly rather than derived
/// from the scope because by the time the user-scope child runs, /etc has
/// already been switched to the new configuration, so the caller must supply
/// a captured reference to the pre-switch unit directory.
fn collect_unit_changes(
toplevel: &Path,
scope: UnitScope,
old_unit_dir: &Path,
new_unit_dir: &Path,
current_active_units: &HashMap<String, UnitState>,
units_to_stop: &mut HashMap<String, ()>,
units_to_start: &mut HashMap<String, ()>,
@@ -954,20 +1011,28 @@ fn collect_unit_changes(
units_to_skip: &mut HashMap<String, ()>,
units_to_filter: &mut HashMap<String, ()>,
) -> Result<()> {
let fragment_prefix = scope
.current_dir()
.to_str()
.expect("scope dir is valid UTF-8");
let start_list = scope.start_list_file();
let reload_list = scope.reload_list_file();
for (unit, unit_state) in current_active_units {
// Don't touch units not explicitly written by NixOS (e.g. units created by generators in
// /run/systemd/generator*)
// Don't touch units that are not loaded from the NixOS-managed
// directory. For system scope this skips generator output; for user
// scope it additionally skips units shadowed by ~/.config/systemd/user.
if !unit_state
.proxy
.get("org.freedesktop.systemd1.Unit", "FragmentPath")
.map(|fragment_path: String| fragment_path.starts_with("/etc/systemd/system"))
.map(|fragment_path: String| fragment_path.starts_with(fragment_prefix))
.unwrap_or_default()
{
continue;
}
let current_unit_file = Path::new("/etc/systemd/system").join(unit);
let new_unit_file = toplevel.join("etc/systemd/system").join(unit);
let current_unit_file = old_unit_dir.join(unit);
let new_unit_file = new_unit_dir.join(unit);
let mut base_unit = unit.clone();
let mut current_base_unit_file = current_unit_file.clone();
@@ -984,8 +1049,8 @@ fn collect_unit_changes(
{
if !current_unit_file.exists() && !new_unit_file.exists() {
base_unit = format!("{template_name}@.{template_instance}");
current_base_unit_file = Path::new("/etc/systemd/system").join(&base_unit);
new_base_unit_file = toplevel.join("etc/systemd/system").join(&base_unit);
current_base_unit_file = old_unit_dir.join(&base_unit);
new_base_unit_file = new_unit_dir.join(&base_unit);
}
}
@@ -1031,7 +1096,7 @@ fn collect_unit_changes(
false,
)) {
units_to_start.insert(unit.to_string(), ());
record_unit(START_LIST_FILE, unit);
record_unit(&start_list, unit);
// Don't spam the user with target units that always get started.
if std::env::var("STC_DISPLAY_ALL_UNITS").as_deref() != Ok("1") {
units_to_filter.insert(unit.to_string(), ());
@@ -1061,6 +1126,7 @@ fn collect_unit_changes(
UnitComparison::UnequalNeedsRestart => {
handle_modified_unit(
toplevel,
scope,
unit,
base_name,
&new_unit_file,
@@ -1076,7 +1142,7 @@ fn collect_unit_changes(
}
UnitComparison::UnequalNeedsReload if !units_to_restart.contains_key(unit) => {
units_to_reload.insert(unit.clone(), ());
record_unit(RELOAD_LIST_FILE, unit);
record_unit(&reload_list, unit);
}
_ => {}
}
@@ -1337,6 +1403,9 @@ won't take effect until you reboot the system.
collect_unit_changes(
&toplevel,
UnitScope::System,
UnitScope::System.current_dir(),
&toplevel.join(UnitScope::System.etc_dir()),
&current_active_units,
&mut units_to_stop,
&mut units_to_start,
@@ -1514,6 +1583,7 @@ won't take effect until you reboot the system.
handle_modified_unit(
&toplevel,
UnitScope::System,
unit,
base_name,
&new_unit_file,
@@ -1685,6 +1755,7 @@ won't take effect until you reboot the system.
handle_modified_unit(
&toplevel,
UnitScope::System,
unit,
base_name,
&new_unit_file,