3 files changed, 16 insertions, 2 deletions
diff --git a/winsup/cygwin/forkable.cc b/winsup/cygwin/forkable.cc
index cc28f9f4f..da45643ae 100644
--- a/winsup/cygwin/forkable.cc
+++ b/winsup/cygwin/forkable.cc
@@ -522,6 +522,11 @@ dll::create_forkable ()
 size_t
 dll_list::forkable_ntnamesize (dll_type type, PCWCHAR fullntname, PCWCHAR modname)
 {
+  /* per process, this is the first forkables-method ever called */
+  if (forkables_needs == forkables_unknown &&
+      !cygwin_shared->prefer_forkable_hardlinks)
+      forkables_needs = forkables_impossible; /* short cut */
+
   if (forkables_needs == forkables_impossible)
     return 0;
 
@@ -667,6 +672,7 @@ dll_list::update_forkables_needs ()
 	{
 	  debug_printf ("impossible, not on NTFS %W", fn.Buffer);
 	  forkables_needs = forkables_impossible;
+	  cygwin_shared->prefer_forkable_hardlinks = 0;
 	}
     }
 
@@ -1056,6 +1062,13 @@ dll_list::request_forkables ()
 
   set_forkables_inheritance (true);
 
+  if (forkables_needs == forkables_disabled)
+    {
+      /* we do not support (re-)enabling on the fly */
+      forkables_needs = forkables_impossible;
+      cygwin_shared->prefer_forkable_hardlinks = 0;
+    }
+
   if (forkables_needs <= forkables_needless)
     return;
 
diff --git a/winsup/cygwin/include/cygwin/version.h b/winsup/cygwin/include/cygwin/version.h
index 8926d49ae..f7ed351d3 100644
--- a/winsup/cygwin/include/cygwin/version.h
+++ b/winsup/cygwin/include/cygwin/version.h
@@ -518,7 +518,7 @@ details. */
    regions.  It is incremented when incompatible changes are made to the shared
    memory region *or* to any named shared mutexes, semaphores, etc. */
 
-#define CYGWIN_VERSION_SHARED_DATA 5
+#define CYGWIN_VERSION_SHARED_DATA 6
 
 /* An identifier used in the names used to create shared objects.  The full
    names include the CYGWIN_VERSION_SHARED_DATA version as well as this
diff --git a/winsup/cygwin/shared_info.h b/winsup/cygwin/shared_info.h
index 1a5648b24..8f0954f50 100644
--- a/winsup/cygwin/shared_info.h
+++ b/winsup/cygwin/shared_info.h
@@ -33,7 +33,7 @@ public:
 /* Data accessible to all tasks */
 
 
-#define CURR_SHARED_MAGIC 0x6758de88U
+#define CURR_SHARED_MAGIC 0x3a6025edU
 
 #define USER_VERSION   1
 
@@ -51,6 +51,7 @@ class shared_info
   mtinfo mt;
   loadavginfo loadavg;
   LONG pid_src;
+  char prefer_forkable_hardlinks; /* single byte access always is atomic */
 
   void initialize ();
   void init_obcaseinsensitive ();