rework SystemExec - use vfork wrapper (and lots of related stuff)

gtk2_ardour/ardour_ui.cc

@@ -52,7 +52,6 @@
 #include "pbd/openuri.h"
 #include "pbd/file_utils.h"
 #include "pbd/localtime_r.h"
-#include "pbd/system_exec.h"
 
 #include "gtkmm2ext/application.h"
 #include "gtkmm2ext/bindings.h"
@@ -81,6 +80,7 @@
 #include "ardour/session_state_utils.h"
 #include "ardour/session_utils.h"
 #include "ardour/slave.h"
+#include "ardour/system_exec.h"
 
 #ifdef WINDOWS_VST_SUPPORT
 #include <fst.h>
@@ -3517,7 +3517,7 @@ ARDOUR_UI::start_video_server (Gtk::Window* float_window, bool popup_msg)
 			delete video_server_process;
 		}
 
-		video_server_process = new SystemExec(icsd_exec, argp);
+		video_server_process = new ARDOUR::SystemExec(icsd_exec, argp);
 		if (video_server_process->start()) {
 			warning << _("Cannot launch the video-server") << endmsg;
 			continue;

gtk2_ardour/ardour_ui.h

@@ -38,7 +38,6 @@
 
 #include "pbd/xml++.h"
 #include "pbd/controllable.h"
-#include "pbd/system_exec.h"
 #include <gtkmm/box.h>
 #include <gtkmm/frame.h>
 #include <gtkmm/label.h>
@@ -64,6 +63,7 @@
 #include "ardour/utils.h"
 #include "ardour/plugin.h"
 #include "ardour/session_handle.h"
+#include "ardour/system_exec.h"
 
 #include "video_timeline.h"
 
@@ -626,7 +626,7 @@ class ARDOUR_UI : public Gtkmm2ext::UI, public ARDOUR::SessionHandlePtr
 
 	static UIConfiguration *ui_config;
 
-	PBD::SystemExec *video_server_process;
+	ARDOUR::SystemExec *video_server_process;
 
 	void handle_locations_change (ARDOUR::Location*);
 

gtk2_ardour/transcode_ffmpeg.cc

@@ -109,7 +109,7 @@ TranscodeFfmpeg::probe ()
 	argp[4] = strdup("-show_streams");
 	argp[5] = strdup(infile.c_str());
 	argp[6] = 0;
-	ffcmd = new SystemExec(ffprobe_exe, argp);
+	ffcmd = new ARDOUR::SystemExec(ffprobe_exe, argp);
 	ffcmd->ReadStdout.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffprobeparse, this, _1 ,_2));
 	ffcmd->Terminated.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffexit, this));
 	if (ffcmd->start(1)) {
@@ -382,7 +382,7 @@ TranscodeFfmpeg::encode (std::string outfile, std::string inf_a, std::string inf
 	}
 #endif
 
-	ffcmd = new SystemExec(ffmpeg_exe, argp);
+	ffcmd = new ARDOUR::SystemExec(ffmpeg_exe, argp);
 	ffcmd->ReadStdout.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffmpegparse_v, this, _1 ,_2));
 	ffcmd->Terminated.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffexit, this));
 	if (ffcmd->start(2)) {
@@ -430,7 +430,7 @@ TranscodeFfmpeg::extract_audio (std::string outfile, ARDOUR::framecnt_t /*sample
 	}
 #endif
 
-	ffcmd = new SystemExec(ffmpeg_exe, argp);
+	ffcmd = new ARDOUR::SystemExec(ffmpeg_exe, argp);
 	ffcmd->ReadStdout.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffmpegparse_a, this, _1 ,_2));
 	ffcmd->Terminated.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffexit, this));
 	if (ffcmd->start(2)) {
@@ -490,7 +490,7 @@ TranscodeFfmpeg::transcode (std::string outfile, const int outw, const int outh,
 	printf("\n");
 	}
 #endif
-	ffcmd = new SystemExec(ffmpeg_exe, argp);
+	ffcmd = new ARDOUR::SystemExec(ffmpeg_exe, argp);
 	ffcmd->ReadStdout.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffmpegparse_v, this, _1 ,_2));
 	ffcmd->Terminated.connect_same_thread (*this, boost::bind (&TranscodeFfmpeg::ffexit, this));
 	if (ffcmd->start(2)) {

gtk2_ardour/transcode_ffmpeg.h

@@ -21,7 +21,7 @@
 #define __ardour_transcode_ffmpeg_h__
 
 #include <string>
-#include "pbd/system_exec.h"
+#include "ardour/system_exec.h"
 #include "ardour/types.h"
 
 
@@ -128,7 +128,7 @@ class TranscodeFfmpeg : public sigc::trackable
 #endif
 	protected:
 		std::string infile;
-		PBD::SystemExec  *ffcmd;
+		ARDOUR::SystemExec  *ffcmd;
 
 		bool probe ();
 

gtk2_ardour/video_monitor.cc

@@ -47,7 +47,7 @@ VideoMonitor::VideoMonitor (PublicEditor *ed, std::string xjadeo_bin_path)
 	starting = 0;
 	osdmode = 10; // 1: frameno, 2: timecode, 8: box
 
-	process = new SystemExec(xjadeo_bin_path, X_("-R"));
+	process = new ARDOUR::SystemExec(xjadeo_bin_path, X_("-R"));
 	process->ReadStdout.connect_same_thread (*this, boost::bind (&VideoMonitor::parse_output, this, _1 ,_2));
 	process->Terminated.connect (*this, invalidator (*this), boost::bind (&VideoMonitor::terminated, this), gui_context());
 	XJKeyEvent.connect (*this, invalidator (*this), boost::bind (&VideoMonitor::forward_keyevent, this, _1), gui_context());

gtk2_ardour/video_monitor.h

@@ -22,11 +22,11 @@
 
 #include <string>
 
-#include "pbd/system_exec.h"
 #include "ardour/ardour.h"
 #include "ardour/types.h"
 #include "ardour/session.h"
 #include "ardour/session_handle.h"
+#include "ardour/system_exec.h"
 
 namespace ARDOUR {
 	class Session;
@@ -83,7 +83,7 @@ class VideoMonitor : public sigc::trackable , public ARDOUR::SessionHandlePtr, p
 
 	protected:
 	PublicEditor *editor;
-	PBD::SystemExec *process;
+	ARDOUR::SystemExec *process;
 	float fps;
 	void parse_output (std::string d, size_t s);
 	void terminated ();

libs/ardour/ardour/system_exec.h

@@ -0,0 +1,50 @@
+/*
+    Copyright (C) 2010 Paul Davis
+    Copyright (C) 2010-2014 Robin Gareus <robin@gareus.org>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+#ifndef _ardour_system_exec_h_
+#define _ardour_system_exec_h_
+
+#include "ardour/libardour_visibility.h"
+#include "pbd/system_exec.h"
+
+namespace ARDOUR {
+
+class LIBARDOUR_API SystemExec
+	: public PBD::SystemExec
+{
+
+public:
+	SystemExec (std::string c, std::string a = "");
+	SystemExec (std::string c, char ** a);
+	~SystemExec ();
+
+	int start (int stderr_mode = 1) {
+		return PBD::SystemExec::start(stderr_mode, _vfork_exec_wrapper);
+	}
+
+private:
+	static char * _vfork_exec_wrapper;
+
+}; /* end class */
+
+}; /* end namespace */
+
+#endif /* _libpbd_system_exec_h_ */
+
+

libs/ardour/system_exec.cc

@@ -0,0 +1,60 @@
+/*
+    Copyright (C) 2010 Paul Davis
+    Copyright (C) 2010-2014 Robin Gareus <robin@gareus.org>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#include <glibmm/miscutils.h>
+#include "pbd/pathscanner.h"
+#include "pbd/file_utils.h"
+#include "pbd/error.h"
+
+#include "ardour/filesystem_paths.h"
+#include "ardour/system_exec.h"
+
+using namespace ARDOUR;
+
+char * SystemExec::_vfork_exec_wrapper = NULL;
+
+static char *vfork_exec_wrapper_path() {
+	std::string vfork_exec_wrapper;
+	if (!PBD::find_file_in_search_path (
+				PBD::Searchpath(Glib::build_filename(ARDOUR::ardour_dll_directory(), "vfork")),
+				"ardour-exec-wrapper", vfork_exec_wrapper)) {
+		PBD::warning << "vfork exec wrapper not found..'" << endmsg;
+		return NULL;
+	}
+	return strdup(vfork_exec_wrapper.c_str());
+}
+
+SystemExec::SystemExec (std::string c, char ** a)
+	: PBD::SystemExec(c, a)
+{
+	if (!_vfork_exec_wrapper) {
+		_vfork_exec_wrapper = vfork_exec_wrapper_path();
+	}
+}
+
+SystemExec::SystemExec (std::string c, std::string a)
+	: PBD::SystemExec(c, a)
+{
+	if (!_vfork_exec_wrapper) {
+		_vfork_exec_wrapper = vfork_exec_wrapper_path();
+	}
+}
+
+SystemExec::~SystemExec() { }

libs/ardour/vst_info_file.cc

@@ -40,12 +40,18 @@
 #include <glib/gstdio.h>
 #include <glibmm.h>
 
-#include "pbd/error.h"
 
-#ifndef VST_SCANNER_APP
-#include "pbd/system_exec.h"
+#ifdef VST_SCANNER_APP
+#define errormsg cerr
+#define warningmsg cerr
+#define endmsg endl
+#else
 #include "ardour/plugin_manager.h" // scanner_bin_path
 #include "ardour/rc_configuration.h"
+#include "ardour/system_exec.h"
+#include "pbd/error.h"
+#define errormsg PBD::error
+#define warningmsg PBD::warning
 #endif
 
 #include "ardour/filesystem_paths.h"
@@ -324,7 +330,7 @@ vstfx_write_info_file (FILE* fp, vector<VSTInfo *> *infos)
 	} else if (infos->size() == 1) {
 		vstfx_write_info_block(fp, infos->front());
 	} else {
-		PBD::error << "Zero plugins in VST." << endmsg; // XXX here? rather make this impossible before if it ain't already.
+		errormsg << "Zero plugins in VST." << endmsg; // XXX here? rather make this impossible before if it ain't already.
 	}
 }
 
@@ -508,7 +514,7 @@ vstfx_get_info_from_file(const char* dllpath, vector<VSTInfo*> *infos)
 		rv = vstfx_load_info_file(infofile, infos);
 		fclose (infofile);
 		if (!rv) {
-			PBD::warning << "Cannot get VST information form " << dllpath << ": info file load failed." << endmsg;
+			warningmsg << "Cannot get VST information form " << dllpath << ": info file load failed." << endmsg;
 		}
 	}
 	return rv;
@@ -774,7 +780,7 @@ vstfx_instantiate_and_get_info_lx (
 	VSTHandle* h;
 	VSTState* vstfx;
 	if (!(h = vstfx_load(dllpath))) {
-		PBD::warning << "Cannot get LinuxVST information from " << dllpath << ": load failed." << endmsg;
+		warningmsg << "Cannot get LinuxVST information from " << dllpath << ": load failed." << endmsg;
 		return false;
 	}
 
@@ -782,7 +788,7 @@ vstfx_instantiate_and_get_info_lx (
 
 	if (!(vstfx = vstfx_instantiate(h, simple_master_callback, 0))) {
 		vstfx_unload(h);
-		PBD::warning << "Cannot get LinuxVST information from " << dllpath << ": instantiation failed." << endmsg;
+		warningmsg << "Cannot get LinuxVST information from " << dllpath << ": instantiation failed." << endmsg;
 		return false;
 	}
 
@@ -803,7 +809,7 @@ vstfx_instantiate_and_get_info_fst (
 	VSTHandle* h;
 	VSTState* vstfx;
 	if(!(h = fst_load(dllpath))) {
-		PBD::warning << "Cannot get Windows VST information from " << dllpath << ": load failed." << endmsg;
+		warningmsg << "Cannot get Windows VST information from " << dllpath << ": load failed." << endmsg;
 		return false;
 	}
 
@@ -812,7 +818,7 @@ vstfx_instantiate_and_get_info_fst (
 	if(!(vstfx = fst_instantiate(h, simple_master_callback, 0))) {
 		fst_unload(&h);
 		vstfx_current_loading_id = 0;
-		PBD::warning << "Cannot get Windows VST information from " << dllpath << ": instantiation failed." << endmsg;
+		warningmsg << "Cannot get Windows VST information from " << dllpath << ": instantiation failed." << endmsg;
 		return false;
 	}
 	vstfx_current_loading_id = 0;
@@ -834,14 +840,14 @@ static char * _errorlog_dll = 0;
 static void parse_scanner_output (std::string msg, size_t /*len*/)
 {
 	if (!_errorlog_fd && !_errorlog_dll) {
-		PBD::error << "VST scanner: " << msg;
+		errormsg << "VST scanner: " << msg;
 		return;
 	}
 
 	if (!_errorlog_fd) {
 		if (!(_errorlog_fd = fopen(vstfx_errorfile_path(_errorlog_dll, 0).c_str(), "w"))) {
 			if (!(_errorlog_fd = fopen(vstfx_errorfile_path(_errorlog_dll, 1).c_str(), "w"))) {
-				PBD::error << "Cannot create plugin error-log for plugin " << _errorlog_dll;
+				errormsg << "Cannot create plugin error-log for plugin " << _errorlog_dll;
 				free(_errorlog_dll);
 				_errorlog_dll = NULL;
 			}
@@ -851,7 +857,7 @@ static void parse_scanner_output (std::string msg, size_t /*len*/)
 	if (_errorlog_fd) {
 		fprintf (_errorlog_fd, "%s\n", msg.c_str());
 	} else {
-		PBD::error << "VST scanner: " << msg;
+		errormsg << "VST scanner: " << msg;
 	}
 }
 
@@ -907,11 +913,11 @@ vstfx_get_info (const char* dllpath, enum ARDOUR::PluginType type, enum VSTScanM
 		argp[2] = 0;
 
 		set_error_log(dllpath);
-		PBD::SystemExec scanner (scanner_bin_path, argp);
+		ARDOUR::SystemExec scanner (scanner_bin_path, argp);
 		PBD::ScopedConnectionList cons;
 		scanner.ReadStdout.connect_same_thread (cons, boost::bind (&parse_scanner_output, _1 ,_2));
 		if (scanner.start (2 /* send stderr&stdout via signal */)) {
-			PBD::error << "Cannot launch VST scanner app '" << scanner_bin_path << "': "<< strerror(errno) << endmsg;
+			errormsg << "Cannot launch VST scanner app '" << scanner_bin_path << "': "<< strerror(errno) << endmsg;
 			close_error_log();
 			return infos;
 		} else {
@@ -977,7 +983,7 @@ vstfx_get_info (const char* dllpath, enum ARDOUR::PluginType type, enum VSTScanM
 	/* crate cache/whitelist */
 	infofile = vstfx_infofile_for_write (dllpath);
 	if (!infofile) {
-		PBD::warning << "Cannot cache VST information for " << dllpath << ": cannot create new FST info file." << endmsg;
+		warningmsg << "Cannot cache VST information for " << dllpath << ": cannot create new FST info file." << endmsg;
 		return infos;
 	} else {
 		vstfx_write_info_file (infofile, infos);
@@ -1005,7 +1011,7 @@ get_personal_vst_blacklist_dir() {
 	/* if the directory doesn't exist, try to create it */
 	if (!Glib::file_test (dir, Glib::FILE_TEST_IS_DIR)) {
 		if (g_mkdir (dir.c_str (), 0700)) {
-			PBD::error << "Cannot create VST blacklist folder '" << dir << "'" << endmsg;
+			errormsg << "Cannot create VST blacklist folder '" << dir << "'" << endmsg;
 			//exit(1);
 		}
 	}
@@ -1018,7 +1024,7 @@ get_personal_vst_info_cache_dir() {
 	/* if the directory doesn't exist, try to create it */
 	if (!Glib::file_test (dir, Glib::FILE_TEST_IS_DIR)) {
 		if (g_mkdir (dir.c_str (), 0700)) {
-			PBD::error << "Cannot create VST info folder '" << dir << "'" << endmsg;
+			errormsg << "Cannot create VST info folder '" << dir << "'" << endmsg;
 			//exit(1);
 		}
 	}

libs/ardour/wscript

@@ -197,6 +197,7 @@ libardour_sources = [
         'speakers.cc',
         'srcfilesource.cc',
         'strip_silence.cc',
+        'system_exec.cc',
         'revision.cc',
         'tape_file_matcher.cc',
         'template_utils.cc',

libs/pbd/pbd/system_exec.h

@@ -107,7 +107,7 @@ class LIBPBD_API SystemExec
 		 * @return If the process is already running or was launched successfully
 		 * the function returns zero (0). A negative number indicates an error.
 		 */
-		int start (int stderr_mode = 1);
+		int start (int stderr_mode, const char *_vfork_exec_wrapper);
 		/** kill running child-process
 		 *
 		 * if a child process exists trt to shut it down by closing its STDIN.

libs/pbd/system_exec.cc

@@ -43,6 +43,8 @@
 #endif
 
 
+#define USE_VFORK
+
 #include "pbd/system_exec.h"
 
 using namespace std;
@@ -51,7 +53,7 @@ using namespace PBD;
 static void * interposer_thread (void *arg);
 static void close_fd (int& fd) { if (fd >= 0) ::close (fd); fd = -1; }
 
-#ifndef PLATFORM_WINDOWS
+#if (!defined PLATFORM_WINDOWS && defined NO_VFORK)
 /*
  * This function was part of libasyncns.
  * LGPL v2.1
@@ -146,7 +148,7 @@ static int close_allv(const int except_fds[]) {
 
 	return 0;
 }
-#endif /* not on windows */
+#endif /* not on windows, nor vfork */
 
 
 SystemExec::SystemExec (std::string c, std::string a)
@@ -324,7 +326,7 @@ SystemExec::is_running ()
 }
 
 int
-SystemExec::start (int stderr_mode)
+SystemExec::start (int stderr_mode, const char * /*vfork_exec_wrapper*/)
 {
 	char* working_dir = 0;
 
@@ -596,7 +598,7 @@ SystemExec::is_running ()
 }
 
 int
-SystemExec::start (int stderr_mode)
+SystemExec::start (int stderr_mode, const char *vfork_exec_wrapper)
 {
 	if (is_running()) {
 		return 0; // mmh what to return here?
@@ -608,7 +610,7 @@ SystemExec::start (int stderr_mode)
 		return -1;
 	}
 
-#ifdef USE_VFORK
+#ifndef NO_VFORK
 	r = ::vfork();
 #else
 	r = ::fork();
@@ -631,11 +633,11 @@ SystemExec::start (int stderr_mode)
 				/* child process returned from execve */
 				pid=0;
 				close_fd(pok[0]);
+				close_fd(pok[1]);
 				close_fd(pin[1]);
 				close_fd(pin[0]);
 				close_fd(pout[1]);
 				close_fd(pout[0]);
-				pin[1] = -1;
 				return -3;
 			} else if ( n==-1 ) {
 				 if ( errno==EAGAIN || errno==EINTR )
@@ -659,7 +661,7 @@ SystemExec::start (int stderr_mode)
 		return 0; /* all systems go - return to main */
 	}
 
-#ifndef USE_VFORK
+#ifdef NO_VFORK
 	/* child process - exec external process */
 	close_fd(pok[0]);
 	::fcntl(pok[1], F_SETFD, FD_CLOEXEC);
@@ -713,12 +715,12 @@ SystemExec::start (int stderr_mode)
 #else
 
 	/* XXX this should be done before vfork()
-	 * calling malloc here only increases the time we vfork() blocks
+	 * calling malloc here only increases the time vfork() blocks
 	 */
 	int argn = 0;
 	for (int i=0;argp[i];++i) { argn++; }
 	char **argx = (char **) malloc((argn + 10) * sizeof(char *));
-	argx[0] = strdup("/home/rgareus/src/git/ardourCairoCanvas/tools/exec_wrapper"); // XXX TODO
+	argx[0] = strdup(vfork_exec_wrapper); // XXX
 
 #define FDARG(NUM, FDN) \
 	argx[NUM] = (char*) calloc(6, sizeof(char)); snprintf(argx[NUM], 6, "%d", FDN);

libs/vfork/README

@@ -0,0 +1,44 @@
+vfork-exec-wrapper
+==================
+
+A tiny tool that redirects stdio file-descriptors and executes a program.
+
+Motivation
+----------
+
+Ardour can start external helper applications for various purposes
+(e.g. video-server, video-monitor, plugin-scanner, post-export scripts,...)
+and has the need to bidirectionally communicate with the external app.
+
+On POSIX platforms (OSX, GNU/Linux, BSD,..) launching an external app is a
+combination of fork() and execve(2). The problem with that is that fork(2)
+duplicates the complete page-table (incl. allocated locked memory, and 
+file-descriptors) which -  even if fork(2) is done from a non-realtime
+thread - may cause audio I/O glitches or worse out-of-memory errors if
+the mlock(2) limit is reached.
+
+vfork(2) on the other hand "is a special case of clone(2). It is used to
+create new processes without copying the page tables of the parent process.
+It may be useful in performance-sensitive applications where a child is
+created which then immediately issues an execve(2)." [vfork man page].
+
+The problem with vfork(2) is that file-descriptors are not cloned, which
+makes bi-directional communication impossible without additional work.
+This is exactly what this vfork-exec-wrapper does: It takes a list of
+file-descriptors, re-directs them to stdio and calls execve(2) again.
+
+This code was previously in pbd/system_exec.cc (done after fork(2),
+which become a NOOP with vfork(2)).
+
+Usage
+-----
+
+ardour-exec-wrapper <file-des> <mode> <nice> <command> [args]
+
+ardour-exec-wrapper takes three pairs of file-descriptors, stderr mode,
+nice-level followed by the command to execute and optional arguments.
+
+The first set FDs is used to communicate failure back to the parent process.
+They are closed if execve(2) succeeds. The following two FDs are stdin and
+stdout. The mode specifies handling of stderr: 0: keep stderr, 1: close and
+ignore, 2: merge stderr into stdout.

libs/vfork/exec_wrapper.c

@@ -3,6 +3,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <fcntl.h>
+#include <signal.h>
 
 #ifndef STDIN_FILENO
 #define STDIN_FILENO 0
@@ -82,6 +83,12 @@ int main(int argc, char *argv[]) {
 	}
 	envp[i] = 0;
 
+#ifdef HAVE_SIGSET
+	sigset(SIGPIPE, SIG_DFL);
+#else
+	signal(SIGPIPE, SIG_DFL);
+#endif
+
 	/* all systems go */
 	execve(argv[9], &argv[9], envp);
 

libs/vfork/wscript

@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+from waflib.extras import autowaf as autowaf
+from waflib import TaskGen
+import os
+import sys
+
+# Mandatory variables
+top = '.'
+out = 'build'
+
+def options(opt):
+    autowaf.set_options(opt)
+
+def configure(conf):
+    conf.load('compiler_c')
+    autowaf.configure(conf)
+
+def build(bld):
+    if bld.env['build_target'] == 'mingw':
+        return
+    obj = bld (features = 'c cprogram')
+    obj.source = 'exec_wrapper.c'
+    obj.target = 'ardour-exec-wrapper'
+    obj.install_path = os.path.join(bld.env['LIBDIR'], 'ardour3/vfork')
+    obj.defines = [
+            '_POSIX_SOURCE',
+            '_XOPEN_SOURCE=700',
+    ]

wscript

@@ -74,7 +74,9 @@ children = [
         'mcp',
         'patchfiles',
         'headless',
+        # shared helper binaries (plugin-scanner, exec-wrapper)
         'libs/fst',
+        'libs/vfork',
 ]
 
 i18n_children = [