use closefrom() where available

e.g. on Linux via libbsd - or on BSDs where the symbol exists

CMakeLists.txt

@@ -5,6 +5,17 @@ project(somake C CXX)
 
 include(CheckFunctionExists)
 check_function_exists(wcsdup HAVE_WCSDUP)
+
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+  find_package(PkgConfig)
+  pkg_search_module(BSD libbsd)
+  if (BSD_LIBRARIES)
+    set(HAVE_CLOSEFROM 1)
+  endif()
+else()
+  check_function_exists(closefrom HAVE_CLOSEFROM)
+endif()
+
 configure_file(config.h.in config.h)
 
 add_library(mksh STATIC
@@ -37,10 +48,11 @@ set_property(TARGET ${PROJECT_NAME} mksh vroot PROPERTY INCLUDE_DIRECTORIES
   ${CMAKE_CURRENT_SOURCE_DIR}/include
   ${CMAKE_CURRENT_SOURCE_DIR}
   ${CMAKE_CURRENT_BINARY_DIR}
+  ${BSD_INCLUDE_DIRS}
 )
 
 target_link_libraries(${PROJECT_NAME}
-  mksh vroot pthread
+  mksh vroot pthread ${BSD_LIBRARIES}
 )
 
 # default install prefix is /usr/local

config.h.in

@@ -3,5 +3,6 @@
 #define SOMAKE_CONFIG_H
 
 #cmakedefine HAVE_WCSDUP 1
+#cmakedefine HAVE_CLOSEFROM 1
 
 #endif

lib/mksh/dosys.cc

@@ -51,9 +51,15 @@
 #include <sys/wait.h>		/* wait() */
 #include <ulimit.h>		/* ulimit() */
 #include <unistd.h>		/* close(), dup2() */
+// closefrom only available on Solaris/BSD
 #include <stdlib.h>		/* closefrom() */
+#ifdef __linux
+  #include <bsd/unistd.h>
+#endif
 #include <libintl.h>
 
+#include <config.h>
+
 /*
  * typedefs & structs
  */
@@ -93,12 +99,10 @@ redirect_io(char *stdout_file, char *stderr_file)
 {
 	int	i;
 
-#ifdef __sun
+#ifdef HAVE_CLOSEFROM
 	(void) closefrom(3);
 #else
-        // XXX not available on Linux
+  #warning "Compiling without closefrom ... consider linking libbsd ..."
-        // if necessary, could provide a compatibility function that
-        // iterates over /proc/$(getpid())/fd ...
 #endif
 	if ((i = my_open(stdout_file,
 	         O_WRONLY | O_CREAT | O_TRUNC | O_DSYNC,