f8035d06f2
NAME'. E.g., on the losser Subversion server, I do `nix-switch --name svn $(fix ...)' to atomically upgrade the server (the SVN server uses the Apache and Subversion installations in /nix/var/nix/links/svn).
87 lines
2.4 KiB
Perl
Executable file
87 lines
2.4 KiB
Perl
Executable file
#! /usr/bin/perl -w
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use strict;
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my $keep = 0;
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my $sourceroot = 0;
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my $name = "current";
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my $srcid;
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my $argnr = 0;
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while ($argnr < scalar @ARGV) {
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my $arg = $ARGV[$argnr++];
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if ($arg eq "--keep") { $keep = 1; }
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elsif ($arg eq "--source-root") { $sourceroot = 1; }
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elsif ($arg eq "--name") { $name = $ARGV[$argnr++]; }
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elsif ($arg =~ /^([0-9a-z]{32})$/) { $srcid = $arg; }
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else { die "unknown argument `$arg'" };
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}
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my $linkdir = "@localstatedir@/nix/links";
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# Build the specified package, and all its dependencies.
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my $nfid = `nix --install $srcid`;
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if ($?) { die "`nix --install' failed"; }
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chomp $nfid;
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die unless $nfid =~ /^([0-9a-z]{32})$/;
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my $pkgdir = `nix --query --list $nfid`;
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if ($?) { die "`nix --query --list' failed"; }
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chomp $pkgdir;
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# Figure out a generation number.
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opendir(DIR, $linkdir);
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my $nr = 0;
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foreach my $n (sort(readdir(DIR))) {
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next if (!($n =~ /^\d+$/));
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$nr = $n + 1 if ($n >= $nr);
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}
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closedir(DIR);
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my $link = "$linkdir/$nr";
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# Create a symlink from $link to $pkgdir.
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symlink($pkgdir, $link) or die "cannot create $link: $!";
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# Store the id of the normal form. This is useful for garbage
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# collection and the like.
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my $idfile = "$linkdir/$nr.id";
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open ID, "> $idfile" or die "cannot create $idfile";
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print ID "$nfid\n";
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close ID;
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# Optionally store the source id.
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if ($sourceroot) {
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$idfile = "$linkdir/$nr-src.id";
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open ID, "> $idfile" or die "cannot create $idfile";
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print ID "$srcid\n";
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close ID;
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}
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my $current = "$linkdir/$name";
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# Read the current generation so that we can delete it (if --keep
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# wasn't specified).
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my $oldlink = readlink($current);
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# Make $link the current generation by pointing $linkdir/current to
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# it. The rename() system call is supposed to be essentially atomic
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# on Unix. That is, if we have links `current -> X' and `new_current
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# -> Y', and we rename new_current to current, a process accessing
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# current will see X or Y, but never a file-not-found or other error
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# condition. This is sufficient to atomically switch the current link
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# tree.
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print "switching $current to $link\n";
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my $tmplink = "$linkdir/.new_$name";
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symlink($link, $tmplink) or die "cannot create $tmplink";
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rename($tmplink, $current) or die "cannot rename $tmplink";
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if (!$keep && defined $oldlink) {
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print "deleting old $oldlink\n";
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unlink($oldlink) == 1 or print "cannot delete $oldlink\n";
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unlink("$oldlink.id") == 1 or print "cannot delete $oldlink.id\n";
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unlink("$oldlink-src.id");
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}
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