61 lines
1.8 KiB
Perl
Executable file
61 lines
1.8 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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if (scalar @ARGV > 0 && $ARGV[0] eq "--keep") {
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shift @ARGV;
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$keep = 1;
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}
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my $hash = $ARGV[0];
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$hash || die "no package hash specified";
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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 $pkgdir = `nix -qph $hash`;
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if ($?) { die "`nix -qph' failed"; }
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chomp $pkgdir;
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# Figure out a generation number.
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my $nr = 0;
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while (-e "$linkdir/$nr") { $nr++; }
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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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# Also store the hash of $pkgdir. This is useful for garbage
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# collection and the like.
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my $hashfile = "$linkdir/$nr.hash";
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open HASH, "> $hashfile" or die "cannot create $hashfile";
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print HASH "$hash\n";
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close HASH;
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my $current = "$linkdir/current";
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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_current";
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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 || print "cannot delete $oldlink\n";
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unlink("$oldlink.hash") == 1 || print "cannot delete $oldlink.hash\n";
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}
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