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nixos/switch-to-configuration: Implement reload support

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This is accomplished by comparing the hashes that the unit files
contain. By filtering for a special key `X-Reload-Triggers` in the
`[Unit]` section, we can differentiate between reloads and restarts.

Since activation scripts can request reloads of units as well, more
checking of this behaviour is implemented. If a unit is to be restarted,
it's never reloaded as well which would make no sense.

Also removes a useless subroutine and perl dependencies that are
nowadays handled by the propagated build inputs feature of
`perl.withPackages`.
This commit is contained in:
Janne Heß 2022-01-29 22:56:52 +01:00
parent 78db7b6529
commit b9bb1de341
No known key found for this signature in database
GPG key ID: 69165158F05265DF
2 changed files with 140 additions and 23 deletions
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161
nixos/modules/system/activation/switch-to-configuration.pl
View file

@ -2,10 +2,11 @@
use strict;
use warnings;
use Array::Compare;
use Config::IniFiles;
use File::Path qw(make_path);
use File::Basename;
use File::Slurp;
use File::Slurp qw(read_file write_file edit_file);
use Net::DBus;
use Sys::Syslog qw(:standard :macros);
use Cwd 'abs_path';
@ -20,12 +21,19 @@ my $restartListFile = "/run/nixos/restart-list";
my $reloadListFile = "/run/nixos/reload-list";
# Parse restart/reload requests by the activation script.
# Activation scripts may write newline-separated units to this
# Activation scripts may write newline-separated units to the restart
# file and switch-to-configuration will handle them. While
# `stopIfChanged = true` is ignored, switch-to-configuration will
# handle `restartIfChanged = false` and `reloadIfChanged = true`.
# This is the same as specifying a restart trigger in the NixOS module.
#
# The reload file asks the script to reload a unit. This is the same as
# specifying a reload trigger in the NixOS module and can be ignored if
# the unit is restarted in this activation.
my $restartByActivationFile = "/run/nixos/activation-restart-list";
my $reloadByActivationFile = "/run/nixos/activation-reload-list";
my $dryRestartByActivationFile = "/run/nixos/dry-activation-restart-list";
my $dryReloadByActivationFile = "/run/nixos/dry-activation-reload-list";
make_path("/run/nixos", { mode => oct(755) });
@ -196,12 +204,88 @@ sub recordUnit {
write_file($fn, { append => 1 }, "$unit\n") if $action ne "dry-activate";
}
# As a fingerprint for determining whether a unit has changed, we use
# its absolute path. If it has an override file, we append *its*
# absolute path as well.
sub fingerprintUnit {
my ($s) = @_;
return abs_path($s) . (-f "${s}.d/overrides.conf" ? " " . abs_path "${s}.d/overrides.conf" : "");
# The opposite of recordUnit, removes a unit name from a file
sub unrecord_unit {
my ($fn, $unit) = @_;
edit_file { s/^$unit\n//msx } $fn if $action ne "dry-activate";
}
# Compare the contents of two unit files and return whether the unit
# needs to be restarted or reloaded. If the units differ, the service
# is restarted unless the only difference is `X-Reload-Triggers` in the
# `Unit` section. If this is the only modification, the unit is reloaded
# instead of restarted.
# Returns:
# - 0 if the units are equal
# - 1 if the units are different and a restart action is required
# - 2 if the units are different and a reload action is required
sub compare_units {
my ($old_unit, $new_unit) = @_;
my $comp = Array::Compare->new;
my $ret = 0;
# Comparison hash for the sections
my %section_cmp = map { $_ => 1 } keys %{$new_unit};
# Iterate over the sections
foreach my $section_name (keys %{$old_unit}) {
# Missing section in the new unit?
if (not exists $section_cmp{$section_name}) {
if ($section_name eq 'Unit' and %{$old_unit->{'Unit'}} == 1 and defined(%{$old_unit->{'Unit'}}{'X-Reload-Triggers'})) {
# If a new [Unit] section was removed that only contained X-Reload-Triggers,
# do nothing.
next;
} else {
return 1;
}
}
delete $section_cmp{$section_name};
# Comparison hash for the section contents
my %ini_cmp = map { $_ => 1 } keys %{$new_unit->{$section_name}};
# Iterate over the keys of the section
foreach my $ini_key (keys %{$old_unit->{$section_name}}) {
delete $ini_cmp{$ini_key};
my @old_value = @{$old_unit->{$section_name}{$ini_key}};
# If the key is missing in the new unit, they are different...
if (not $new_unit->{$section_name}{$ini_key}) {
# ... unless the key that is now missing was the reload trigger
if ($section_name eq 'Unit' and $ini_key eq 'X-Reload-Triggers') {
next;
}
return 1;
}
my @new_value = @{$new_unit->{$section_name}{$ini_key}};
# If the contents are different, the units are different
if (not $comp->compare(\@old_value, \@new_value)) {
# Check if only the reload triggers changed
if ($section_name eq 'Unit' and $ini_key eq 'X-Reload-Triggers') {
$ret = 2;
} else {
return 1;
}
}
}
# A key was introduced that was missing in the old unit
if (%ini_cmp) {
if ($section_name eq 'Unit' and %ini_cmp == 1 and defined($ini_cmp{'X-Reload-Triggers'})) {
# If the newly introduced key was the reload triggers, reload the unit
$ret = 2;
} else {
return 1;
}
};
}
# A section was introduced that was missing in the old unit
if (%section_cmp) {
if (%section_cmp == 1 and defined($section_cmp{'Unit'}) and %{$new_unit->{'Unit'}} == 1 and defined(%{$new_unit->{'Unit'}}{'X-Reload-Triggers'})) {
# If a new [Unit] section was introduced that only contains X-Reload-Triggers,
# reload instead of restarting
$ret = 2;
} else {
return 1;
}
}
return $ret;
}
sub handleModifiedUnit {
@ -224,7 +308,7 @@ sub handleModifiedUnit {
# More details: https://github.com/NixOS/nixpkgs/issues/74899#issuecomment-981142430
} else {
my %unitInfo = $newUnitInfo ? %{$newUnitInfo} : parseUnit($newUnitFile);
if (parseSystemdBool(\%unitInfo, "Service", "X-ReloadIfChanged", 0)) {
if (parseSystemdBool(\%unitInfo, "Service", "X-ReloadIfChanged", 0) and not $unitsToRestart->{$unit} and not $unitsToStop->{$unit}) {
$unitsToReload->{$unit} = 1;
recordUnit($reloadListFile, $unit);
}
@ -238,6 +322,11 @@ sub handleModifiedUnit {
# stopped and started.
$unitsToRestart->{$unit} = 1;
recordUnit($restartListFile, $unit);
# Remove from units to reload so we don't restart and reload
if ($unitsToReload->{$unit}) {
delete $unitsToReload->{$unit};
unrecord_unit($reloadListFile, $unit);
}
} else {
# If this unit is socket-activated, then stop the
# socket unit(s) as well, and restart the
@ -258,6 +347,11 @@ sub handleModifiedUnit {
recordUnit($startListFile, $socket);
$socketActivated = 1;
}
# Remove from units to reload so we don't restart and reload
if ($unitsToReload->{$unit}) {
delete $unitsToReload->{$unit};
unrecord_unit($reloadListFile, $unit);
}
}
}
}
@ -272,6 +366,11 @@ sub handleModifiedUnit {
}
$unitsToStop->{$unit} = 1;
# Remove from units to reload so we don't restart and reload
if ($unitsToReload->{$unit}) {
delete $unitsToReload->{$unit};
unrecord_unit($reloadListFile, $unit);
}
}
}
}
@ -348,8 +447,16 @@ while (my ($unit, $state) = each %{$activePrev}) {
}
}
elsif (fingerprintUnit($prevUnitFile) ne fingerprintUnit($newUnitFile)) {
handleModifiedUnit($unit, $baseName, $newUnitFile, undef, $activePrev, \%unitsToStop, \%unitsToStart, \%unitsToReload, \%unitsToRestart, \%unitsToSkip);
else {
my %old_unit_info = parseUnit($prevUnitFile);
my %new_unit_info = parseUnit($newUnitFile);
my $diff = compare_units(\%old_unit_info, \%new_unit_info);
if ($diff eq 1) {
handleModifiedUnit($unit, $baseName, $newUnitFile, \%new_unit_info, $activePrev, \%unitsToStop, \%unitsToStart, \%unitsToReload, \%unitsToRestart, \%unitsToSkip);
} elsif ($diff eq 2 and not $unitsToRestart{$unit}) {
$unitsToReload{$unit} = 1;
recordUnit($reloadListFile, $unit);
}
}
}
}
@ -365,17 +472,6 @@ sub pathToUnitName {
return $escaped;
}
sub unique {
my %seen;
my @res;
foreach my $name (@_) {
next if $seen{$name};
$seen{$name} = 1;
push @res, $name;
}
return @res;
}
# Compare the previous and new fstab to figure out which filesystems
# need a remount or need to be unmounted. New filesystems are mounted
# automatically by starting local-fs.target. FIXME: might be nicer if
@ -477,6 +573,16 @@ if ($action eq "dry-activate") {
}
unlink($dryRestartByActivationFile);
foreach (split('\n', read_file($dryReloadByActivationFile, err_mode => 'quiet') // "")) {
my $unit = $_;
if (defined($activePrev->{$unit}) and not $unitsToRestart{$unit} and not $unitsToStop{$unit}) {
$unitsToReload{$unit} = 1;
recordUnit($reloadListFile, $unit);
}
}
unlink($dryReloadByActivationFile);
print STDERR "would restart systemd\n" if $restartSystemd;
print STDERR "would reload the following units: ", join(", ", sort(keys %unitsToReload)), "\n"
if scalar(keys %unitsToReload) > 0;
@ -534,6 +640,17 @@ foreach (split('\n', read_file($restartByActivationFile, err_mode => 'quiet') //
# We can remove the file now because it has been propagated to the other restart/reload files
unlink($restartByActivationFile);
foreach (split('\n', read_file($reloadByActivationFile, err_mode => 'quiet') // "")) {
my $unit = $_;
if (defined($activePrev->{$unit}) and not $unitsToRestart{$unit} and not $unitsToStop{$unit}) {
$unitsToReload{$unit} = 1;
recordUnit($reloadListFile, $unit);
}
}
# We can remove the file now because it has been propagated to the other reload file
unlink($reloadByActivationFile);
# Restart systemd if necessary. Note that this is done using the
# current version of systemd, just in case the new one has trouble
# communicating with the running pid 1.

2
nixos/modules/system/activation/top-level.nix
View file

@ -117,7 +117,7 @@ let
configurationName = config.boot.loader.grub.configurationName;
# Needed by switch-to-configuration.
perl = pkgs.perl.withPackages (p: with p; [ FileSlurp NetDBus XMLParser XMLTwig ConfigIniFiles ]);
perl = pkgs.perl.withPackages (p: with p; [ ArrayCompare ConfigIniFiles FileSlurp NetDBus ]);
};
# Handle assertions and warnings