Implement Sys_ReLaunch() for Linux, refactor it

It now works on Linux so executing it doesn't freeze the game
like described in
https://github.com/RobertBeckebans/RBDOOM-3-BFG/issues/33

Furthermore, this function doesn't have any parameters anymore
(on any platform) because the only thing supplied was the original
program arguments +"+set com_skipIntroVideos 1" anyway - this is now
done in Sys_ReLaunch() (also on Windows).
Having the program arguments as one string is bad on Linux/POSIX
because there it's expected that the program arguments are one
C-string per argument.

neo/d3xp/menus/MenuScreen_Shell_Stereoscopics.cpp

@@ -219,12 +219,10 @@ void idMenuScreen_Shell_Stereoscopics::HideScreen( const mainMenuTransition_t tr
 				common->Dialog().ClearDialog( msg );
 				if( restart )
 				{
-					idStr cmdLine = Sys_GetCmdLine();
+					// DG: Sys_ReLaunch() doesn't need any options anymore
-					if( cmdLine.Find( "com_skipIntroVideos" ) < 0 )
+					//     (the old way would have been unnecessarily painful on POSIX systems)
-					{
+					Sys_ReLaunch();
-						cmdLine.Append( " +set com_skipIntroVideos 1" );
+					// DG end
-					}
-					Sys_ReLaunch( ( void* )cmdLine.c_str(), cmdLine.Length() );
 				}
 				return idSWFScriptVar();
 			}

neo/d3xp/menus/MenuScreen_Shell_SystemOptions.cpp

@@ -232,12 +232,10 @@ void idMenuScreen_Shell_SystemOptions::HideScreen( const mainMenuTransition_t tr
 				common->Dialog().ClearDialog( msg );
 				if( restart )
 				{
-					idStr cmdLine = Sys_GetCmdLine();
+					// DG: Sys_ReLaunch() doesn't need any options anymore
-					if( cmdLine.Find( "com_skipIntroVideos" ) < 0 )
+					//     (the old way would have been unnecessarily painful on POSIX systems)
-					{
+					Sys_ReLaunch();
-						cmdLine.Append( " +set com_skipIntroVideos 1" );
+					// DG end
-					}
-					Sys_ReLaunch( ( void* )cmdLine.c_str(), cmdLine.Length() );
 				}
 				return idSWFScriptVar();
 			}

neo/sys/linux/linux_main.cpp

@@ -38,6 +38,13 @@ If you have questions concerning this license or the applicable additional terms
 #include <sys/types.h>
 #include <fcntl.h>
 
+// DG: needed for Sys_ReLaunch()
+#include <dirent.h>
+
+static const char** cmdargv = NULL;
+static int cmdargc = 0;
+// DG end
+
 #ifdef ID_MCHECK
 #include <mcheck.h>
 #endif
@@ -46,7 +53,6 @@ static idStr	basepath;
 static idStr	savepath;
 
 
-
 /*
  ==============
  Sys_DefaultSavePath
@@ -645,6 +651,7 @@ Sys_GetCmdLine
 */
 const char* Sys_GetCmdLine()
 {
+	// DG: don't use this, use cmdargv and cmdargc instead!
 	return "TODO Sys_GetCmdLine";
 }
 
@@ -653,9 +660,80 @@ const char* Sys_GetCmdLine()
 Sys_ReLaunch
 ========================
 */
-void Sys_ReLaunch( void* data, const unsigned int dataSize )
+void Sys_ReLaunch()
 {
-	idLib::Error( "Could not start process: TODO Sys_ReLaunch() " );
+	// DG: implementing this... basic old fork() exec() (+ setsid()) routine..
+	// NOTE: this function used to have parameters: the commandline arguments, but as one string..
+	//       for Linux/Unix we want one char* per argument so we'll just add the friggin'
+	//       " +set com_skipIntroVideos 1" to the other commandline arguments in this function.
+	
+	int ret = fork();
+	if( ret < 0 )
+		idLib::Error( "Sys_ReLaunch(): Couldn't fork(), reason: %s ", strerror( errno ) );
+		
+	if( ret == 0 )
+	{
+		// child process
+		
+		// get our own session so we don't depend on the (soon to be killed)
+		// parent process anymore - else we'll freeze
+		pid_t sId = setsid();
+		if( sId == ( pid_t ) - 1 )
+		{
+			idLib::Error( "Sys_ReLaunch(): setsid() failed! Reason: %s ", strerror( errno ) );
+		}
+		
+		// close all FDs (except for stdin/out/err) so we don't leak FDs
+		DIR* devfd = opendir( "/dev/fd" );
+		if( devfd != NULL )
+		{
+			struct dirent entry;
+			struct dirent* result;
+			while( readdir_r( devfd, &entry, &result ) == 0 )
+			{
+				const char* filename = result->d_name;
+				char* endptr = NULL;
+				long int fd = strtol( filename, &endptr, 0 );
+				if( endptr != filename && fd > STDERR_FILENO )
+					close( fd );
+			}
+		}
+		else
+		{
+			idLib::Warning( "Sys_ReLaunch(): Couldn't open /dev/fd/ - will leak file descriptors. Reason: %s", strerror( errno ) );
+		}
+		
+		// + 3 because "+set" "com_skipIntroVideos" "1" - and note that while we'll skip
+		// one (the first) cmdargv argument, we need one more pointer for NULL at the end.
+		int argc = cmdargc + 3;
+		const char** argv = ( const char** )calloc( argc, sizeof( char* ) );
+		
+		int i;
+		for( i = 0; i < cmdargc - 1; ++i )
+			argv[i] = cmdargv[i + 1]; // ignore cmdargv[0] == executable name
+			
+		// add +set com_skipIntroVideos 1
+		argv[i++] = "+set";
+		argv[i++] = "com_skipIntroVideos";
+		argv[i++] = "1";
+		// execv expects NULL terminated array
+		argv[i] = NULL;
+		
+		const char* exepath = Sys_EXEPath();
+		
+		errno = 0;
+		execv( exepath, ( char** )argv );
+		// we only get here if execv() fails, else the executable is restarted
+		idLib::Error( "Sys_ReLaunch(): WTF exec() failed! Reason: %s ", strerror( errno ) );
+		
+	}
+	else
+	{
+		// original process
+		// just do a clean shutdown
+		cmdSystem->AppendCommandText( "quit\n" );
+	}
+	// DG end
 }
 
 /*
@@ -665,6 +743,10 @@ main
 */
 int main( int argc, const char** argv )
 {
+	// DG: needed for Sys_ReLaunch()
+	cmdargc = argc;
+	cmdargv = argv;
+	// DG end
 #ifdef ID_MCHECK
 	// must have -lmcheck linkage
 	mcheck( abrt_func );

neo/sys/sys_public.h

@@ -432,7 +432,9 @@ void			Sys_Init();
 void			Sys_Shutdown();
 void			Sys_Error( const char* error, ... );
 const char* 	Sys_GetCmdLine();
-void			Sys_ReLaunch( void* launchData, unsigned int launchDataSize );
+// DG: Sys_ReLaunch() doesn't need any options (and the old way is painful for POSIX systems)
+void			Sys_ReLaunch();
+// DG end
 void			Sys_Launch( const char* path, idCmdArgs& args,  void* launchData, unsigned int launchDataSize );
 void			Sys_SetLanguageFromSystem();
 const char* 	Sys_DefaultLanguage();

neo/sys/win32/win_main.cpp

@@ -290,7 +290,7 @@ const char * Sys_GetCmdLine() {
 Sys_ReLaunch
 ========================
 */
-void Sys_ReLaunch( void * data, const unsigned int dataSize ) {
+void Sys_ReLaunch() {
 	TCHAR				szPathOrig[MAX_PRINT_MSG];
 	STARTUPINFO			si;
 	PROCESS_INFORMATION	pi;
@@ -298,7 +298,17 @@ void Sys_ReLaunch( void * data, const unsigned int dataSize ) {
 	ZeroMemory( &si, sizeof(si) );
 	si.cb = sizeof(si);
 
-	strcpy( szPathOrig, va( "\"%s\" %s", Sys_EXEPath(), (const char *)data ) );
+	// DG: we don't have function arguments in Sys_ReLaunch() anymore, everyone only passed
+	//     the command-line +" +set com_skipIntroVideos 1" anyway and it was painful on POSIX systems
+	//     so let's just add it here.
+	idStr cmdLine = Sys_GetCmdLine();
+	if( cmdLine.Find( "com_skipIntroVideos" ) < 0 )
+	{
+		cmdLine.Append( " +set com_skipIntroVideos 1" );
+	}
+
+	strcpy( szPathOrig, va( "\"%s\" %s", Sys_EXEPath(), cmdLine.c_str() ) );
+	// DG end
 
 	CloseHandle( hProcessMutex );