nixos/modules/system/etc/setup-etc.pl

   1 use strict;
   2 use File::Find;
   3 use File::Copy;
   4 use File::Path;
   5 use File::Basename;
   6 use File::Slurp;
   7
   8 my $etc = $ARGV[0] or die;
   9 my $static = "/etc/static";
  10
  11 sub atomicSymlink {
  12     my ($source, $target) = @_;
  13     my $tmp = "$target.tmp";
  14     unlink $tmp;
  15     symlink $source, $tmp or return 0;
  16     if (rename $tmp, $target) {
  17         return 1;
  18     } else {
  19         unlink $tmp;
  20         return 0;
  21     }
  22 }
  23
  24
  25 # Atomically update /etc/static to point at the etc files of the
  26 # current configuration.
  27 atomicSymlink $etc, $static or die;
  28
  29 # Returns 1 if the argument points to the files in /etc/static.  That
  30 # means either argument is a symlink to a file in /etc/static or a
  31 # directory with all children being static.
  32 sub isStatic {
  33     my $path = shift;
  34
  35     if (-l $path) {
  36         my $target = readlink $path;
  37         return substr($target, 0, length "/etc/static/") eq "/etc/static/";
  38     }
  39
  40     if (-d $path) {
  41         opendir DIR, "$path" or return 0;
  42         my @names = readdir DIR or die;
  43         closedir DIR;
  44
  45         foreach my $name (@names) {
  46             next if $name eq "." || $name eq "..";
  47             unless (isStatic("$path/$name")) {
  48                 return 0;
  49             }
  50         }
  51         return 1;
  52     }
  53
  54     return 0;
  55 }
  56
  57 # Remove dangling symlinks that point to /etc/static.  These are
  58 # configuration files that existed in a previous configuration but not
  59 # in the current one.  For efficiency, don't look under /etc/nixos
  60 # (where all the NixOS sources live).
  61 sub cleanup {
  62     if ($File::Find::name eq "/etc/nixos") {
  63         $File::Find::prune = 1;
  64         return;
  65     }
  66     if (-l $_) {
  67         my $target = readlink $_;
  68         if (substr($target, 0, length $static) eq $static) {
  69             my $x = "/etc/static/" . substr($File::Find::name, length "/etc/");
  70             unless (-l $x) {
  71                 print STDERR "removing obsolete symlink ‘$File::Find::name’...\n";
  72                 unlink "$_";
  73             }
  74         }
  75     }
  76 }
  77
  78 find(\&cleanup, "/etc");
  79
  80
  81 # Use /etc/.clean to keep track of copied files.
  82 my @oldCopied = read_file("/etc/.clean", chomp => 1, err_mode => 'quiet');
  83 open CLEAN, ">>/etc/.clean";
  84
  85
  86 # For every file in the etc tree, create a corresponding symlink in
  87 # /etc to /etc/static.  The indirection through /etc/static is to make
  88 # switching to a new configuration somewhat more atomic.
  89 my %created;
  90 my @copied;
  91
  92 sub link {
  93     my $fn = substr $File::Find::name, length($etc) + 1 or next;
  94
  95     # nixos-enter sets up /etc/resolv.conf as a bind mount, so skip it.
  96     if ($fn eq "resolv.conf" and $ENV{'IN_NIXOS_ENTER'}) {
  97         return;
  98     }
  99
 100     my $target = "/etc/$fn";
 101     File::Path::make_path(dirname $target);
 102     $created{$fn} = 1;
 103
 104     # Rename doesn't work if target is directory.
 105     if (-l $_ && -d $target) {
 106         if (isStatic $target) {
 107             rmtree $target or warn;
 108         } else {
 109             warn "$target directory contains user files. Symlinking may fail.";
 110         }
 111     }
 112
 113     if (-e "$_.mode") {
 114         my $mode = read_file("$_.mode"); chomp $mode;
 115         if ($mode eq "direct-symlink") {
 116             atomicSymlink readlink("$static/$fn"), $target or warn "could not create symlink $target";
 117         } else {
 118             my $uid = read_file("$_.uid"); chomp $uid;
 119             my $gid = read_file("$_.gid"); chomp $gid;
 120             copy "$static/$fn", "$target.tmp" or warn;
 121             $uid = getpwnam $uid unless $uid =~ /^\+/;
 122             $gid = getgrnam $gid unless $gid =~ /^\+/;
 123             chown int($uid), int($gid), "$target.tmp" or warn;
 124             chmod oct($mode), "$target.tmp" or warn;
 125             unless (rename "$target.tmp", $target) {
 126                 warn "could not create target $target";
 127                 unlink "$target.tmp";
 128             }
 129         }
 130         push @copied, $fn;
 131         print CLEAN "$fn\n";
 132     } elsif (-l "$_") {
 133         atomicSymlink "$static/$fn", $target or warn "could not create symlink $target";
 134     }
 135 }
 136
 137 find(\&link, $etc);
 138
 139
 140 # Delete files that were copied in a previous version but not in the
 141 # current.
 142 foreach my $fn (@oldCopied) {
 143     if (!defined $created{$fn}) {
 144         $fn = "/etc/$fn";
 145         print STDERR "removing obsolete file ‘$fn’...\n";
 146         unlink "$fn";
 147     }
 148 }
 149
 150
 151 # Rewrite /etc/.clean.
 152 close CLEAN;
 153 write_file("/etc/.clean", map { "$_\n" } sort @copied);
 154
 155 # Create /etc/NIXOS tag if not exists.
 156 # When /etc is not on a persistent filesystem, it will be wiped after reboot,
 157 # so we need to check and re-create it during activation.
 158 open TAG, ">>/etc/NIXOS";
 159 close TAG;