hyperhive/nix/module-eval/boot-wait.nix

# Which units of a container's guest hold its boot open, and which of those can
# hold it past the host's start limit for the container.
#
# A swarm service container is `Type=notify`: the host's `container@<name>`
# start job lasts until the guest's job queue is empty, and ends in a kill at
# `timeoutStartSec`. A guest unit that is pulled in by the boot targets and
# whose start job blocks therefore counts its start timeout against that limit.
# Pure functions over a guest's `config.systemd` and the host's
# `timeoutStartSec` string; ./swarm-services-switch.nix feeds them each named
# container.
{ lib }:
let
  # A time span as seconds; `null` is infinity, which `TimeoutStartSec` spells
  # `0`, `"infinity"` or leaves to `Type=oneshot`'s default.
  spanSeconds =
    v:
    if builtins.isInt v then
      if v == 0 then null else v
    else if v == "infinity" then
      null
    else
      lib.foldl' (acc: t: acc + tokenSeconds t) 0 (lib.splitString " " (lib.trim v));

  unitSeconds = {
    s = 1;
    sec = 1;
    second = 1;
    seconds = 1;
    m = 60;
    min = 60;
    minute = 60;
    minutes = 60;
    h = 3600;
    hr = 3600;
    hour = 3600;
    hours = 3600;
  };
  tokenSeconds =
    token:
    let
      m = builtins.match "([0-9]+)([a-z]*)" token;
      unit = if m == null then null else lib.elemAt m 1;
    in
    if m == null then
      throw "boot-wait: cannot read '${token}' as a time span"
    else if unit == "" then
      lib.toInt (lib.head m)
    else
      lib.toInt (lib.head m)
      * (unitSeconds.${unit} or (throw "boot-wait: unknown time unit '${unit}' in '${token}'"));

  # Where a boot starts: what `multi-user.target` requires, and the targets
  # the stock units pull in alongside it.
  rootTargets = [
    "sysinit.target"
    "basic.target"
    "multi-user.target"
    "sockets.target"
    "timers.target"
    "paths.target"
    "local-fs.target"
  ];

  kinds = {
    services = "service";
    timers = "timer";
    sockets = "socket";
    paths = "path";
    targets = "target";
  };

  # Every unit the guest configures, as `{ name = "<n>.<type>"; unit; }`.
  unitsOf =
    systemd:
    lib.concatLists (
      lib.mapAttrsToList (
        kind: suffix:
        lib.mapAttrsToList (n: unit: {
          name = "${n}.${suffix}";
          inherit unit;
        }) (systemd.${kind} or { })
      ) kinds
    );

  # The units a boot starts: the closure of `rootTargets` over what a unit
  # `wants`/`requires`/`bindsTo` and over the units naming it in
  # `wantedBy`/`requiredBy`. `after`/`before` alone pull nothing in.
  bootSet =
    systemd:
    let
      units = unitsOf systemd;
      byName = lib.listToAttrs (map (u: lib.nameValuePair u.name u.unit) units);
      pulls = u: (u.wants or [ ]) ++ (u.requires or [ ]) ++ (u.bindsTo or [ ]);
      pulledBy = u: (u.wantedBy or [ ]) ++ (u.requiredBy or [ ]);
      children =
        key:
        (pulls (byName.${key} or { }))
        ++ (map (u: u.name) (lib.filter (u: lib.elem key (pulledBy u.unit)) units));
    in
    map (n: n.key) (
      builtins.genericClosure {
        startSet = map (key: { inherit key; }) rootTargets;
        operator = n: map (key: { inherit key; }) (children n.key);
      }
    );

  # Whether the service's start job blocks on the unit's own work rather than
  # ending at the fork: a oneshot, a notifying or forking daemon, or any unit
  # with a start hook (which runs inside the job).
  holdsJob =
    unit:
    let
      sc = unit.serviceConfig or { };
    in
    lib.elem (sc.Type or "simple") [
      "oneshot"
      "notify"
      "notify-reload"
      "forking"
      "dbus"
    ]
    || sc ? ExecStartPre
    || sc ? ExecStartPost
    || (unit.preStart or "") != ""
    || (unit.postStart or "") != "";

  # The services in `guest`'s boot wait whose start job can last `limit` seconds
  # or more: `{ key; seconds; source; }`, `seconds = null` for infinity. A job
  # that ends at `limit` or later can outlast the container's start, because the
  # guest has already spent time booting.
  #
  # `source` says where the number comes from: `stated` is the unit's own
  # `TimeoutStartSec`; `default` is the manager's `DefaultTimeoutStartSec` (90 s
  # unless the guest sets one), which a unit that states none gets; `unbounded`
  # is a oneshot that states none, which systemd leaves without a timeout.
  overBudget =
    { guest, limit }:
    let
      services = guest.systemd.services or { };
      managerDefault = (guest.systemd.settings.Manager or { }).DefaultTimeoutStartSec or 90;
    in
    lib.concatMap (
      key:
      let
        n = lib.removeSuffix ".service" key;
        unit = services.${n};
        sc = unit.serviceConfig or { };
        budget =
          if sc ? TimeoutStartSec then
            {
              source = "stated";
              seconds = spanSeconds sc.TimeoutStartSec;
            }
          else if (sc.Type or "simple") == "oneshot" then
            {
              source = "unbounded";
              seconds = null;
            }
          else
            {
              source = "default";
              seconds = spanSeconds managerDefault;
            };
      in
      lib.optional
        (
          lib.hasSuffix ".service" key
          && services ? ${n}
          && holdsJob unit
          && (budget.seconds == null || budget.seconds >= limit)
        )
        {
          inherit key;
          inherit (budget) seconds source;
        }
    ) (bootSet guest.systemd);
in
{
  inherit
    spanSeconds
    bootSet
    holdsJob
    overBudget
    ;
}