daemon: Run 'guix offload' directly.

* nix/scripts/offload.in: Remove.
* nix/local.mk (nodist_pkglibexec_SCRIPTS) [BUILD_DAEMON_OFFLOAD]:
Remove 'scripts/offload'.
* config-daemon.ac: Don't output 'nix/scripts/offload'.
* build-aux/pre-inst-env.in: Don't set 'NIX_BUILD_HOOK'.
* nix/libstore/build.cc (HookInstance::HookInstance): Run 'guix
offload'.
(DerivationGoal::tryBuildHook): Remove reference to 'NIX_BUILD_HOOK'.
* nix/nix-daemon/guix-daemon.cc (main) [HAVE_DAEMON_OFFLOAD_HOOK]: Don't
set 'NIX_BUILD_HOOK'.
* nix/nix-daemon/nix-daemon.cc (performOp) [!HAVE_DAEMON_OFFLOAD_HOOK]:
Leave 'settings.useBuildHook' unchanged.

build-aux/pre-inst-env.in

@@ -48,10 +48,6 @@ NIX_LIBEXEC_DIR="@abs_top_builddir@/nix/scripts" # for 'authenticate', etc.
 
 export NIX_LIBEXEC_DIR
 
-NIX_BUILD_HOOK="$abs_top_builddir/nix/scripts/offload"
-@BUILD_DAEMON_OFFLOAD_TRUE@export NIX_BUILD_HOOK
-@BUILD_DAEMON_OFFLOAD_FALSE@# No offloading support.
-@BUILD_DAEMON_OFFLOAD_FALSE@unset NIX_BUILD_HOOK
 # The daemon invokes 'guix'; tell it which one to use.
 GUIX="$abs_top_builddir/scripts/guix"
 export GUIX

config-daemon.ac

@@ -150,8 +150,6 @@ if test "x$guix_build_daemon" = "xyes"; then
   GUIX_CHECK_LOCALSTATEDIR
   AC_CONFIG_FILES([nix/scripts/substitute],
     [chmod +x nix/scripts/substitute])
-  AC_CONFIG_FILES([nix/scripts/offload],
-    [chmod +x nix/scripts/offload])
 fi
 
 AM_CONDITIONAL([HAVE_LIBBZ2], [test "x$HAVE_LIBBZ2" = "xyes"])

nix/libstore/build.cc

@@ -614,9 +614,7 @@ HookInstance::HookInstance()
 {
     debug("starting build hook");
 
-    Path buildHook = getEnv("NIX_BUILD_HOOK");
-    if (string(buildHook, 0, 1) != "/") buildHook = settings.nixLibexecDir + "/nix/" + buildHook;
-    buildHook = canonPath(buildHook);
+    const Path &buildHook = settings.guixProgram;
 
     /* Create a pipe to get the output of the child. */
     fromHook.create();
@@ -642,13 +640,14 @@ HookInstance::HookInstance()
         if (dup2(builderOut.writeSide, 4) == -1)
             throw SysError("dupping builder's stdout/stderr");
 
-        execl(buildHook.c_str(), buildHook.c_str(), settings.thisSystem.c_str(),
+        execl(buildHook.c_str(), buildHook.c_str(), "offload",
+	    settings.thisSystem.c_str(),
             (format("%1%") % settings.maxSilentTime).str().c_str(),
             (format("%1%") % settings.printBuildTrace).str().c_str(),
             (format("%1%") % settings.buildTimeout).str().c_str(),
             NULL);
 
-        throw SysError(format("executing `%1%'") % buildHook);
+        throw SysError(format("executing `%1% offload'") % buildHook);
     });
 
     pid.setSeparatePG(true);
@@ -1581,7 +1580,7 @@ void DerivationGoal::buildDone()
 
 HookReply DerivationGoal::tryBuildHook()
 {
-    if (!settings.useBuildHook || getEnv("NIX_BUILD_HOOK") == "") return rpDecline;
+    if (!settings.useBuildHook) return rpDecline;
 
     if (!worker.hook)
         worker.hook = std::shared_ptr<HookInstance>(new HookInstance);

nix/local.mk

@@ -157,13 +157,6 @@ noinst_HEADERS =						\
 nodist_pkglibexec_SCRIPTS =			\
   %D%/scripts/substitute
 
-if BUILD_DAEMON_OFFLOAD
-
-nodist_pkglibexec_SCRIPTS +=			\
-  %D%/scripts/offload
-
-endif BUILD_DAEMON_OFFLOAD
-
 # The '.service' files for systemd.
 systemdservicedir = $(libdir)/systemd/system
 nodist_systemdservice_DATA = etc/guix-daemon.service etc/guix-publish.service

nix/nix-daemon/guix-daemon.cc

@@ -474,15 +474,8 @@ main (int argc, char *argv[])
       settings.set ("substitute-urls", GUIX_SUBSTITUTE_URLS);
 
 #ifdef HAVE_DAEMON_OFFLOAD_HOOK
-      /* Use our build hook for distributed builds by default.  */
+      /* Use 'guix offload' for distributed builds by default.  */
       settings.useBuildHook = true;
-      if (getenv ("NIX_BUILD_HOOK") == NULL)
-	{
-	  std::string build_hook;
-
-	  build_hook = settings.nixLibexecDir + "/offload";
-	  setenv ("NIX_BUILD_HOOK", build_hook.c_str (), 1);
-	}
 #else
       /* We are not installing any build hook, so disable it.  */
       settings.useBuildHook = false;

nix/nix-daemon/nix-daemon.cc

@@ -580,8 +580,14 @@ static void performOp(bool trusted, unsigned int clientVersion,
             settings.set("build-max-silent-time", std::to_string(readInt(from)));
         }
 
-        if (GET_PROTOCOL_MINOR(clientVersion) >= 2)
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 2) {
+#ifdef HAVE_DAEMON_OFFLOAD_HOOK
             settings.useBuildHook = readInt(from) != 0;
+#else
+	    readInt(from);			  // ignore the user's setting
+#endif
+	}
+
         if (GET_PROTOCOL_MINOR(clientVersion) >= 4) {
             settings.buildVerbosity = (Verbosity) readInt(from);
             logType = (LogType) readInt(from);

nix/scripts/offload.in

@@ -1,11 +0,0 @@
-#!@SHELL@
-# A shorthand for "guix offload", for use by the daemon.
-
-if test "x$GUIX_UNINSTALLED" = "x"
-then
-    prefix="@prefix@"
-    exec_prefix="@exec_prefix@"
-    exec "@bindir@/guix" offload "$@"
-else
-    exec guix offload "$@"
-fi