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use strict;
use File::Find;
use File::Copy;
use File::Path;
use File::Basename;
use File::Slurp;
my $etc = $ARGV[0] or die;
my $static = "/etc/static";
sub atomicSymlink {
my ($source, $target) = @_;
my $tmp = "$target.tmp";
unlink $tmp;
symlink $source, $tmp or return 0;
if (rename $tmp, $target) {
return 1;
} else {
unlink $tmp;
return 0;
}
}
# Atomically update /etc/static to point at the etc files of the
# current configuration.
atomicSymlink $etc, $static or die;
# Returns 1 if the argument points to the files in /etc/static. That
# means either argument is a symlink to a file in /etc/static or a
# directory with all children being static.
sub isStatic {
my $path = shift;
if (-l $path) {
my $target = readlink $path;
return substr($target, 0, length "/etc/static/") eq "/etc/static/";
}
if (-d $path) {
opendir DIR, "$path" or return 0;
my @names = readdir DIR or die;
closedir DIR;
foreach my $name (@names) {
next if $name eq "." || $name eq "..";
unless (isStatic("$path/$name")) {
return 0;
}
}
return 1;
}
return 0;
}
# Remove dangling symlinks that point to /etc/static. These are
# configuration files that existed in a previous configuration but not
# in the current one. For efficiency, don't look under /etc/nixos
# (where all the NixOS sources live).
sub cleanup {
if ($File::Find::name eq "/etc/nixos") {
$File::Find::prune = 1;
return;
}
if (-l $_) {
my $target = readlink $_;
if (substr($target, 0, length $static) eq $static) {
my $x = "/etc/static/" . substr($File::Find::name, length "/etc/");
unless (-l $x) {
print STDERR "removing obsolete symlink ‘$File::Find::name’...\n";
unlink "$_";
}
}
}
}
find(\&cleanup, "/etc");
# Use /etc/.clean to keep track of copied files.
my @oldCopied = read_file("/etc/.clean", chomp => 1, err_mode => 'quiet');
open CLEAN, ">>/etc/.clean";
# For every file in the etc tree, create a corresponding symlink in
# /etc to /etc/static. The indirection through /etc/static is to make
# switching to a new configuration somewhat more atomic.
my %created;
my @copied;
sub link {
my $fn = substr $File::Find::name, length($etc) + 1 or next;
# nixos-enter sets up /etc/resolv.conf as a bind mount, so skip it.
if ($fn eq "resolv.conf" and $ENV{'IN_NIXOS_ENTER'}) {
return;
}
my $target = "/etc/$fn";
File::Path::make_path(dirname $target);
$created{$fn} = 1;
# Rename doesn't work if target is directory.
if (-l $_ && -d $target) {
if (isStatic $target) {
rmtree $target or warn;
} else {
warn "$target directory contains user files. Symlinking may fail.";
}
}
if (-e "$_.mode") {
my $mode = read_file("$_.mode"); chomp $mode;
if ($mode eq "direct-symlink") {
atomicSymlink readlink("$static/$fn"), $target or warn "could not create symlink $target";
} else {
my $uid = read_file("$_.uid"); chomp $uid;
my $gid = read_file("$_.gid"); chomp $gid;
copy "$static/$fn", "$target.tmp" or warn;
$uid = getpwnam $uid unless $uid =~ /^\+/;
$gid = getgrnam $gid unless $gid =~ /^\+/;
chown int($uid), int($gid), "$target.tmp" or warn;
chmod oct($mode), "$target.tmp" or warn;
unless (rename "$target.tmp", $target) {
warn "could not create target $target";
unlink "$target.tmp";
}
}
push @copied, $fn;
print CLEAN "$fn\n";
} elsif (-l "$_") {
atomicSymlink "$static/$fn", $target or warn "could not create symlink $target";
}
}
find(\&link, $etc);
# Delete files that were copied in a previous version but not in the
# current.
foreach my $fn (@oldCopied) {
if (!defined $created{$fn}) {
$fn = "/etc/$fn";
print STDERR "removing obsolete file ‘$fn’...\n";
unlink "$fn";
}
}
# Rewrite /etc/.clean.
close CLEAN;
write_file("/etc/.clean", map { "$_\n" } sort @copied);
# Create /etc/NIXOS tag if not exists.
# When /etc is not on a persistent filesystem, it will be wiped after reboot,
# so we need to check and re-create it during activation.
open TAG, ">>/etc/NIXOS";
close TAG;
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