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nixos/switch-to-configuration: Document and test handling of socket-activated services #161838

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nixos/switch-to-configuration: Document and test handling of socket-activated services #161838

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nixos/switch-to-configuration: Document and test socket-activated ser…
dasJ Feb 25, 2022
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nixos/switchTest: Make checks more precise
dasJ Feb 25, 2022
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15 changes: 8 additions & 7 deletions nixos/doc/manual/development/unit-handling.section.md
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Expand Up @@ -41,17 +41,18 @@ checks:
`RefuseManualStop` in the `[Unit]` section, and `X-OnlyManualStart` in the
`[Unit]` section.

- The rest of the behavior is decided whether the unit has `X-StopIfChanged`
in the `[Service]` section set (exposed via
- Further behavior depends on the unit having `X-StopIfChanged` in the
`[Service]` section set to `true` (exposed via
[systemd.services.\<name\>.stopIfChanged](#opt-systemd.services)). This is
set to `true` by default and must be explicitly turned off if not wanted.
If the flag is enabled, the unit is **stop**ped and then **start**ed. If
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not, the unit is **restart**ed. The goal of the flag is to make sure that
the new unit never runs in the old environment which is still in place
before the activation script is run.
before the activation script is run. This behavior is different when the
service is socket-activated, as outlined in the following steps.

- The last thing that is taken into account is whether the unit is a service
and socket-activated. Due to a bug, this is currently only done when
`X-StopIfChanged` is set. If the unit is socket-activated, the socket is
stopped and started, and the service is stopped and to be started by socket
activation.
and socket-activated. If `X-StopIfChanged` is **not** set, the service
is **restart**ed with the others. If it is set, both the service and the
socket are **stop**ped and the socket is **start**ed, leaving socket
activation to start the service when it's needed.
22 changes: 14 additions & 8 deletions nixos/doc/manual/from_md/development/unit-handling.section.xml
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Expand Up @@ -88,9 +88,10 @@
</listitem>
<listitem>
<para>
The rest of the behavior is decided whether the unit has
Further behavior depends on the unit having
<literal>X-StopIfChanged</literal> in the
<literal>[Service]</literal> section set (exposed via
<literal>[Service]</literal> section set to
<literal>true</literal> (exposed via
<link linkend="opt-systemd.services">systemd.services.&lt;name&gt;.stopIfChanged</link>).
This is set to <literal>true</literal> by default and must
be explicitly turned off if not wanted. If the flag is
Expand All @@ -100,17 +101,22 @@
is <emphasis role="strong">restart</emphasis>ed. The goal of
the flag is to make sure that the new unit never runs in the
old environment which is still in place before the
activation script is run.
activation script is run. This behavior is different when
the service is socket-activated, as outlined in the
following steps.
</para>
</listitem>
<listitem>
<para>
The last thing that is taken into account is whether the
unit is a service and socket-activated. Due to a bug, this
is currently only done when
<literal>X-StopIfChanged</literal> is set. If the unit is
socket-activated, the socket is stopped and started, and the
service is stopped and to be started by socket activation.
unit is a service and socket-activated. If
<literal>X-StopIfChanged</literal> is
<emphasis role="strong">not</emphasis> set, the service is
<emphasis role="strong">restart</emphasis>ed with the
others. If it is set, both the service and the socket are
<emphasis role="strong">stop</emphasis>ped and the socket is
<emphasis role="strong">start</emphasis>ed, leaving socket
activation to start the service when it’s needed.
</para>
</listitem>
</itemizedlist>
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9 changes: 6 additions & 3 deletions nixos/modules/system/activation/switch-to-configuration.pl
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Expand Up @@ -307,6 +307,7 @@ sub handleModifiedUnit {
# seem to get applied on daemon-reload.
} elsif ($unit =~ /\.mount$/) {
# Reload the changed mount unit to force a remount.
# FIXME: only reload when Options= changed, restart otherwise
$unitsToReload->{$unit} = 1;
recordUnit($reloadListFile, $unit);
} elsif ($unit =~ /\.socket$/) {
Expand Down Expand Up @@ -339,21 +340,23 @@ sub handleModifiedUnit {
# If this unit is socket-activated, then stop the
# socket unit(s) as well, and restart the
# socket(s) instead of the service.
my $socketActivated = 0;
my $socket_activated = 0;
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why is this snake case when all the other variables are camel case?

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https://metacpan.org/pod/Perl::Critic::Policy::NamingConventions::Capitalization

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makes sense, but what is unitsToReload?

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There is currently a mix between camel case (not yet refactored) and snake case (already refactored)

if ($unit =~ /\.service$/) {
my @sockets = split(/ /, join(" ", @{$unitInfo{Service}{Sockets} // []}));
if (scalar @sockets == 0) {
@sockets = ("$baseName.socket");
}
foreach my $socket (@sockets) {
if (defined $activePrev->{$socket}) {
# We can now be sure this is a socket-activate unit

$unitsToStop->{$socket} = 1;
# Only restart sockets that actually
# exist in new configuration:
if (-e "$out/etc/systemd/system/$socket") {
$unitsToStart->{$socket} = 1;
recordUnit($startListFile, $socket);
$socketActivated = 1;
$socket_activated = 1;
}
# Remove from units to reload so we don't restart and reload
if ($unitsToReload->{$unit}) {
Expand All @@ -368,7 +371,7 @@ sub handleModifiedUnit {
# that this unit needs to be started below.
# We write this to a file to ensure that the
# service gets restarted if we're interrupted.
if (!$socketActivated) {
if (!$socket_activated) {
$unitsToStart->{$unit} = 1;
recordUnit($startListFile, $unit);
}
Expand Down
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