lguest: update commentry
Every so often, after code shuffles, I need to go through and unbitrot
the Lguest Journey (see drivers/lguest/README). Since we now use RCU in
a simple form in one place I took the opportunity to expand that explanation.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
index 787ab4b..83511eb 100644
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -59,7 +59,7 @@
case LHCALL_SHUTDOWN: {
char msg[128];
/*
- * Shutdown is such a trivial hypercall that we do it in four
+ * Shutdown is such a trivial hypercall that we do it in five
* lines right here.
*
* If the lgread fails, it will call kill_guest() itself; the
@@ -245,6 +245,10 @@
* device), the Guest will still see the old page. In practice, this never
* happens: why would the Guest read a page which it has never written to? But
* a similar scenario might one day bite us, so it's worth mentioning.
+ *
+ * Note that if we used a shared anonymous mapping in the Launcher instead of
+ * mapping /dev/zero private, we wouldn't worry about cop-on-write. And we
+ * need that to switch the Launcher to processes (away from threads) anyway.
:*/
/*H:100