Detect available memory on OpenBSD.

While there, rename freebsd_sysctl() to sysctl(), since sysctl is available
on number of different platforms.

Author: PiotrSikora

src/vm_memory_monitor.erl

@@ -239,10 +239,13 @@ get_total_memory({unix,darwin}) ->
     PageSize * (Inactive + Active + Free + Wired);
 
 get_total_memory({unix,freebsd}) ->
-    PageSize  = freebsd_sysctl("vm.stats.vm.v_page_size"),
-    PageCount = freebsd_sysctl("vm.stats.vm.v_page_count"),
+    PageSize  = sysctl("vm.stats.vm.v_page_size"),
+    PageCount = sysctl("vm.stats.vm.v_page_count"),
     PageCount * PageSize;
 
+get_total_memory({unix,openbsd}) ->
+    sysctl("hw.usermem");
+
 get_total_memory({win32,_OSname}) ->
     %% Due to the Erlang print format bug, on Windows boxes the memory
     %% size is broken. For example Windows 7 64 bit with 4Gigs of RAM
@@ -342,7 +345,7 @@ parse_line_aix(Line) ->
          false -> list_to_integer(Value)
      end}.
 
-freebsd_sysctl(Def) ->
+sysctl(Def) ->
     list_to_integer(cmd("/sbin/sysctl -n " ++ Def) -- "\n").
 
 %% file:read_file does not work on files in /proc as it seems to get