lguest: use eventfds for device notification

Currently, when a Guest wants to perform I/O it calls LHCALL_NOTIFY with
an address: the main Launcher process returns with this address, and figures
out what device to run.

A far nicer model is to let processes bind an eventfd to an address: if we
find one, we simply signal the eventfd.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Davide Libenzi <davidel@xmailserver.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index d0298dc45d97..508569c9571a 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -198,9 +198,11 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                 /* It's possible the Guest did a NOTIFY hypercall to the
                  * Launcher, in which case we return from the read() now. */
                 if (cpu->pending_notify) {
-                        if (put_user(cpu->pending_notify, user))
-                                return -EFAULT;
-                        return sizeof(cpu->pending_notify);
+                        if (!send_notify_to_eventfd(cpu)) {
+                                if (put_user(cpu->pending_notify, user))
+                                        return -EFAULT;
+                                return sizeof(cpu->pending_notify);
+                        }
                 }
 
                 /* Check for signals */