forked from lix-project/lix
43 lines
1.3 KiB
Plaintext
43 lines
1.3 KiB
Plaintext
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#! /usr/bin/perl -w
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use strict;
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my $hash = $ARGV[0];
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$hash || die "no package hash specified";
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my $prefix = $ENV{"NIX"} || "/nix"; # !!! use prefix
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my $linkdir = "$prefix/var/nix/links";
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# Build the specified package, and all its dependencies.
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my $pkgdir = `nix getpkg $hash`;
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if ($?) { die "`nix getpkg' failed"; }
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chomp $pkgdir;
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my $id = `nix info $hash | cut -c 34-`;
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if ($?) { die "`nix info' failed"; }
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chomp $id;
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# Figure out a generation number.
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my $nr = 0;
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while (-e "$linkdir/$id-$nr") { $nr++; }
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my $link = "$linkdir/$id-$nr";
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print "$pkgdir\n";
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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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# 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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my $current = "$linkdir/current";
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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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