Don't assume that stdout is always writable in PollTest.Nfds.

stdout can be (and, in automated testing, often is) a host pipe or
similar resource shared between multiple parallel tests, such that it
can become transiently full during testing.

PiperOrigin-RevId: 231413569
Change-Id: Id14991b5f71e53c894695899e65e1be4dd228cc6

2 files changed, 7 insertions, 3 deletions

diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 8cf83b311..e70742875 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -1246,6 +1246,7 @@ cc_binary(
     linkstatic = 1,
     deps = [
         ":base_poll_test",
+        "//test/util:eventfd_util",
         "//test/util:file_descriptor",
         "//test/util:logging",
         "//test/util:test_main",
diff --git a/test/syscalls/linux/poll.cc b/test/syscalls/linux/poll.cc
index 897fd0bec..7a6a39444 100644
--- a/test/syscalls/linux/poll.cc
+++ b/test/syscalls/linux/poll.cc
@@ -23,6 +23,7 @@
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
 #include "test/syscalls/linux/base_poll_test.h"
+#include "test/util/eventfd_util.h"
 #include "test/util/file_descriptor.h"
 #include "test/util/logging.h"
 #include "test/util/test_util.h"
@@ -256,12 +257,14 @@ TEST_F(PollTest, Nfds) {
   TEST_PCHECK(getrlimit(RLIMIT_NOFILE, &rlim) == 0);
   rlim_t max_fds = rlim.rlim_cur;
 
+  // Create an eventfd. Since its value is initially zero, it is writable.
+  FileDescriptor efd = ASSERT_NO_ERRNO_AND_VALUE(NewEventFD());
+
   // Create the biggest possible pollfd array such that each element is valid.
-  //
-  // Each entry in the 'fds' array refers to stdout (fd=1) and polls for
+  // Each entry in the 'fds' array refers to the eventfd and polls for
   // "writable" events (events=POLLOUT). This essentially guarantees that the
   // poll() is a no-op and allows negative testing of the 'nfds' parameter.
-  std::vector<struct pollfd> fds(max_fds, {.fd = 1, .events = POLLOUT});
+  std::vector<struct pollfd> fds(max_fds, {.fd = efd.get(), .events = POLLOUT});
 
   // Verify that 'nfds' up to RLIMIT_NOFILE are allowed.
   EXPECT_THAT(RetryEINTR(poll)(fds.data(), 1, 1), SyscallSucceedsWithValue(1));