Introduce "hcall" pointer to indicate pending hypercall.

Currently we look at the "trapnum" to see if the Guest wants a
hypercall.  But once the hypercall is done we have to reset trapnum to
a bogus value, otherwise if we exit to userspace and return, we'd run
the same hypercall twice (that was a nasty bug to find!).

This has two main effects:

1) When Jes's patch changes the hypercall args to be a generic "struct
   hcall_args" we simply change the type of "lg->hcall".  It's set by
   arch code, so if it has to copy args or something it can do so, and
   point "hcall" into lg->arch somewhere.

2) Async hypercalls only get run when an actual hypercall is pending.
   This simplfies the code a little and is a more logical semantic.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 06869a2..02556ba 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -198,10 +198,10 @@ int run_guest(struct lguest *lg, unsigned long __user *user)
 {
 	/* We stop running once the Guest is dead. */
 	while (!lg->dead) {
-		/* First we run any hypercalls the Guest wants done: either in
-		 * the hypercall ring in "struct lguest_data", or directly by
-		 * using int 31 (LGUEST_TRAP_ENTRY). */
-		do_hypercalls(lg);
+		/* First we run any hypercalls the Guest wants done. */
+		if (lg->hcall)
+			do_hypercalls(lg);
+
 		/* It's possible the Guest did a SEND_DMA hypercall to the
 		 * Launcher, in which case we return from the read() now. */
 		if (lg->dma_is_pending) {