[kernel] Add object_signal system call

Add a system call to assert signals on a given object, only within the
range of user-settable signals. Also made object_wait return
immediately if any of the given signals are already set.

src/kernel/objects/kobject.h

@@ -60,6 +60,9 @@ public:
 	/// \arg s  The set of signals to check
 	inline bool check_signal(j6_signal_t s) const { return (m_signals & s) == s; }
 
+	/// Get the current object signal state
+	inline j6_signal_t signals() const { return m_signals; }
+
 	/// Increment the handle refcount
 	inline void handle_retain() { ++m_handle_count; }
 

src/kernel/syscalls.inc

@@ -2,6 +2,7 @@ SYSCALL(0x00, system_log,       const char *)
 SYSCALL(0x01, system_noop,      void)
 
 SYSCALL(0x09, object_wait,      j6_handle_t, j6_signal_t, j6_signal_t *)
+SYSCALL(0x0a, object_signal,    j6_handle_t, j6_signal_t)
 
 SYSCALL(0x10, process_koid,     j6_koid_t *)
 SYSCALL(0x11, process_exit,     int64_t)

src/kernel/syscalls/object.cpp

@@ -1,4 +1,5 @@
 #include "j6/errors.h"
+#include "j6/signals.h"
 #include "j6/types.h"
 
 #include "log.h"
@@ -19,6 +20,12 @@ object_wait(j6_handle_t handle, j6_signal_t mask, j6_signal_t *sigs)
 	if (!obj)
 		return j6_err_invalid_arg;
 
+	j6_signal_t current = obj->signals();
+	if ((current & mask) != 0) {
+		*sigs = current;
+		return j6_status_ok;
+	}
+
 	obj->add_blocked_thread(th);
 	th->wait_on_signals(obj, mask);
 	s.schedule();
@@ -30,4 +37,22 @@ object_wait(j6_handle_t handle, j6_signal_t mask, j6_signal_t *sigs)
 	return result;
 }
 
+j6_status_t
+object_signal(j6_handle_t handle, j6_signal_t signals)
+{
+	if ((signals & j6_signal_user_mask) != signals)
+		return j6_err_invalid_arg;
+
+	scheduler &s = scheduler::get();
+	thread *th = thread::from_tcb(s.current());
+	process &p = th->parent();
+
+	kobject *obj = p.lookup_handle(handle);
+	if (!obj)
+		return j6_err_invalid_arg;
+
+	obj->assert_signal(signals);
+	return j6_status_ok;
+}
+
 } // namespace syscalls