Remove the logfile and logSize columns from the database

It's pointless to store these, since Nix knows where the logs are.
Also handle (in fact require) Nix's new log storage scheme.  Also some
cleanups in the build page.

src/lib/Hydra/Helper/AddBuilds.pm

@@ -17,7 +17,7 @@ use File::Temp;
 our @ISA = qw(Exporter);
 our @EXPORT = qw(
     fetchInput evalJobs checkBuild inputsToArgs captureStdoutStderr
-    getReleaseName getBuildLog addBuildProducts restartBuild scmPath
+    getReleaseName addBuildProducts restartBuild scmPath
     getPrevJobsetEval
 );
 
@@ -27,16 +27,6 @@ sub scmPath {
 }
 
 
-sub getBuildLog {
-    my ($drvPath) = @_;
-    my $logPath = ($ENV{NIX_LOG_DIR} || "/nix/var/log/nix"). "/drvs/" . basename $drvPath;
-    return $logPath if -e $logPath;
-    $logPath = "$logPath.bz2";
-    return $logPath if -e $logPath;
-    return undef;
-}
-
-
 sub getStorePathHash {
     my ($storePath) = @_;
     my $hash = `nix-store --query --hash $storePath`
@@ -930,7 +920,6 @@ sub checkBuild {
                 , buildstatus => -f "$outPath/nix-support/failed" ? 6 : 0
                 , starttime => $time
                 , stoptime => $time
-                , logfile => getBuildLog($drvPath)
                 , errormsg => ""
                 , releasename => getReleaseName($outPath)
                 );

src/lib/Hydra/Helper/Nix.pm

@@ -14,7 +14,7 @@ our @EXPORT = qw(
     getPrimaryBuildsForView
     getPrimaryBuildTotal
     getViewResult getLatestSuccessfulViewResult
-    jobsetOverview removeAsciiEscapes logContents);
+    jobsetOverview removeAsciiEscapes getDrvLogPath logContents);
 
 
 sub getHydraHome {
@@ -238,19 +238,39 @@ sub getLatestSuccessfulViewResult {
     return undef;
 }
 
+
+# Return the path of the build log of the given derivation, or undef
+# if the log is gone.
+sub getDrvLogPath {
+    my ($drvPath) = @_;
+    my $base = basename $drvPath;
+    my $fn =
+        ($ENV{NIX_LOG_DIR} || "/nix/var/log/nix") . "/drvs/"
+        . substr($base, 0, 2) . "/"
+        . substr($base, 2);
+    return $fn if -f $fn;
+    $fn .= ".bz2";
+    return $fn if -f $fn;
+    return undef;
+}
+
+
 sub logContents {
-    my ($path, $tail) = @_;
+    my ($drvPath, $tail) = @_;
+    my $logPath = getDrvLogPath($drvPath);
+    die unless defined $logPath;
     my $cmd;
-    if ($path =~ /.bz2$/) {
-        $cmd = "cat $path | bzip2 -d";
-        $cmd = $cmd . " | tail -$tail" if defined $tail;
+    if ($logPath =~ /.bz2$/) {
+        $cmd = "bzip2 -d < $logPath";
+        $cmd = $cmd . " | tail -n $tail" if defined $tail;
     }
     else {
-        $cmd = defined $tail ? "tail -$tail $path" : "cat $path";
+        $cmd = defined $tail ? "tail -$tail $logPath" : "cat $logPath";
     }
-    return `$cmd` if -e $path;
+    return `$cmd`;
 }
 
+
 sub removeAsciiEscapes {
     my ($logtext) = @_;
     $logtext =~ s/\e\[[0-9]*[A-Za-z]//g;