explanatory comment and oredering of cases

1 files changed, 22 insertions, 1 deletions

diff --git a/src/tests/userprog/exec-missing.ck b/src/tests/userprog/exec-missing.ck
index 7f9b0cb..749db01 100644
--- a/src/tests/userprog/exec-missing.ck
+++ b/src/tests/userprog/exec-missing.ck
@@ -1,15 +1,36 @@
 # -*- perl -*-
+
+# In this test a program named "exec-missing" tries to start another
+# program that do not exist. This is discovered in the thread of the
+# new program, in the function load.
+
+# Correct handling can be done in three basic ways:
+
+# 1. We only know about the failure when our "exec" system call
+#    returns -1. The "no-such-file" thread never becomes a process and
+#    do not leave any messages.
+
+# 2. We know about the failure both when "exec" return -1 and when the
+#    "no-such-file" thread fails to become a process. It notify the
+#    failure by printing "load: no-such-file: open failed". But it
+#    does not become a process and will thus not leave a
+#    "no-such-file: exit(-1)" message.
+
+# 3. "exec" return -1 and "no-such-file" become a failed process. It
+#    will thus produce a "no-such-file: exit(-1)" message. This
+#    message may occur some time after "open failed".
+
 use strict;
 use warnings;
 use tests::tests;
 check_expected ([<<'EOF', <<'EOF', <<'EOF', <<'EOF', <<'EOF', <<'EOF']);
 (exec-missing) begin
-load: no-such-file: open failed
 (exec-missing) exec("no-such-file"): -1
 (exec-missing) end
 exec-missing: exit(0)
 EOF
 (exec-missing) begin
+load: no-such-file: open failed
 (exec-missing) exec("no-such-file"): -1
 (exec-missing) end
 exec-missing: exit(0)