Re: [patch] threading fix, tid-2.5.47-A3

[Ingo Molnar]

and we have VM_DONTCOPY already, which is used by the DRM code. So it
would only be a question of exporting this API to userspace. The attached
patch adds MAP_DONTCOPY. I made it unpriviledged, i doubt it has any
security impact.

	Ingo

--- linux/include/asm-i386/mman.h.orig2	2002-11-18 13:07:16.000000000 +0100
+++ linux/include/asm-i386/mman.h	2002-11-18 13:07:44.000000000 +0100
@@ -20,6 +20,7 @@
 #define MAP_NORESERVE	0x4000		/* don't check for reservations */
 #define MAP_POPULATE	0x8000		/* populate (prefault) pagetables */
 #define MAP_NONBLOCK	0x10000		/* do not block on IO */
+#define MAP_DONTCOPY	0x20000		/* do not block on IO */
 
 #define MS_ASYNC	1		/* sync memory asynchronously */
 #define MS_INVALIDATE	2		/* invalidate the caches */
--- linux/mm/mmap.c.orig2	2002-11-18 13:08:03.000000000 +0100
+++ linux/mm/mmap.c	2002-11-18 13:08:44.000000000 +0100
@@ -450,6 +450,11 @@
 	 */
 	vm_flags = calc_vm_flags(prot,flags) | mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
 
+	/*
+	 * Copy the mapping on fork?
+	 */
+	if (flags & MAP_DONTCOPY)
+		vm_flags |= VM_DONTCOPY;
 	if (flags & MAP_LOCKED) {
 		if (!capable(CAP_IPC_LOCK))
 			return -EPERM;