libxl: event tests: Introduce `fdderegrace' test

This exercises the potential race between fd deregistration and
poll().  (Because we have control of the individual steps, we can do
the whole test in a single thread and ensure that the pessimal order
is always reached.)

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

.gitignore

@@ -289,6 +289,7 @@ tools/libxl/testidl.c
 tools/libxl/*.pyc
 tools/libxl/libxl-save-helper
 tools/libxl/test_timedereg
+tools/libxl/test_fdderegrace
 tools/libxl/xen-init-dom0
 tools/blktap2/control/tap-ctl
 tools/firmware/etherboot/eb-roms.h

tools/libxl/Makefile

@@ -107,7 +107,7 @@ LIBXL_OBJS += libxl_genid.o
 LIBXL_OBJS += _libxl_types.o libxl_flask.o _libxl_types_internal.o
 
 LIBXL_TESTS += timedereg
-LIBXL_TESTS_PROGS = $(LIBXL_TESTS)
+LIBXL_TESTS_PROGS = $(LIBXL_TESTS) fdderegrace
 LIBXL_TESTS_INSIDE = $(LIBXL_TESTS) fdevent
 
 # Each entry FOO in LIBXL_TESTS has two main .c files:

tools/libxl/test_fdderegrace.c

@@ -0,0 +1,56 @@
+#include "test_common.h"
+#include "libxl_test_fdevent.h"
+
+int main(int argc, char **argv) {
+    int rc, i;
+    libxl_asyncop_how how;
+    libxl_event *event;
+
+    test_common_setup(XTL_DEBUG);
+
+    how.callback = NULL;
+    how.u.for_event = 1;
+
+    int fd = open("/dev/null", O_RDONLY);
+    assert(fd > 0);
+
+    rc = libxl_test_fdevent(ctx, fd, POLLIN, &how);
+    assert(!rc);
+
+    test_common_beforepoll();
+
+    rc = libxl_ao_abort(ctx, &how);
+    assert(!rc);
+
+    rc = libxl_event_check(ctx, &event, LIBXL_EVENTMASK_ALL, 0,0);
+    assert(!rc);
+    assert(event);
+    assert(event->for_user = how.u.for_event);
+    assert(event->type == LIBXL_EVENT_TYPE_OPERATION_COMPLETE);
+    assert(event->u.operation_complete.rc == ERROR_ABORTED);
+
+    close(fd);
+
+    test_common_dopoll();
+
+    for (i=0; i<poll_nfds; i++) {
+        if (poll_fds[i].fd == fd && (poll_fds[i].revents & POLLNVAL)) {
+            fprintf(stderr, "POLLNVAL on fd=%d in slot i=%d as expected\n",
+                    fd, i);
+            goto found;
+        }
+    }
+    abort();
+ found:;
+
+    int fd2 = open("/dev/null", O_RDONLY);
+    assert(fd2 == fd);
+
+    how.u.for_event++;
+    rc = libxl_test_fdevent(ctx, fd, POLLIN, &how);
+    assert(!rc);
+
+    test_common_afterpoll();
+
+    fprintf(stderr, "complete\n");
+}