make await() fail gracefully when callee has no alive children already

2 files changed, 15 insertions, 10 deletions

diff --git a/src/init/main.c b/src/init/main.c
index 558fb77..8e78b87 100644
--- a/src/init/main.c
+++ b/src/init/main.c
@@ -80,16 +80,17 @@ void fs_test(void) {
 void test_await(void) {
 	char buf[16];
 	int len;
+
 	// the child immediately dies
 	if (!_syscall_fork())
 		_syscall_exit(argify("i'm dead"));
+	if (!_syscall_fork())
+		_syscall_exit(argify("i'm also dead"));
 
-	len = _syscall_await(buf, 16);
-	if (len < 0) {
-		log("await: negative len\n");
-	} else {
+	while ((len = _syscall_await(buf, 16)) >= 0) {
 		log("await returned: ");
 		_syscall_write(tty_fd, buf, len, 0);
 		log("\n");
 	}
+	log("await: negative len\n");
 }
diff --git a/src/kernel/syscalls.c b/src/kernel/syscalls.c
index 0ca7867..ac21cdb 100644
--- a/src/kernel/syscalls.c
+++ b/src/kernel/syscalls.c
@@ -39,22 +39,26 @@ _Noreturn void _syscall_exit(const char __user *msg, size_t len) {
 }
 
 int _syscall_await(char __user *buf, int len) {
+	bool has_children = false;
 	process_current->state = PS_WAITS4CHILDDEATH;
 	process_current->death_msg.buf = buf;
 	process_current->death_msg.len = len;
 
 	// find any already dead children
 	for (struct process *iter = process_current->child;
-			iter; iter = iter->sibling)
-	{
+			iter; iter = iter->sibling) {
 		if (iter->state == PS_DEAD)
 			await_finish(iter, process_current); // doesn't return
+		if (iter->state != PS_DEADER)
+			has_children = true;
 	}
 
-	// no dead children yet
-	// TODO check if the process even has children
-	
-	process_switch_any();
+	if (has_children)
+		process_switch_any(); // wait until a child dies
+	else {
+		process_current->state = PS_RUNNING;
+		return -1; // error
+	}
 }
 
 int _syscall_fork(void) {