Fix bugs in poll(), select(), ppoll(), and pselect()

poll() and select() now delegate to ppoll() and pselect() for assurances
that both polyfill implementations are correct and well-tested. Poll now
polyfills XNU and BSD quirks re: the hanndling of POLLNVAL and the other
similar status flags. This change resolves a misunderstanding concerning
how select(exceptfds) is intended to map to POLPRI. We now use E2BIG for
bouncing requests that exceed the 64 handle limit on Windows. With pipes
and consoles on Windows our poll impl will now report POLLHUP correctly.

Issues with Windows path generation have been fixed. For example, it was
problematic on Windows to say: posix_spawn_file_actions_addchdir_np("/")
due to the need to un-UNC paths in some additional places. Calling fstat
on UNC style volume path handles will now work. posix_spawn now supports
simulating the opening of /dev/null and other special paths on Windows.

Cosmopolitan no longer defines epoll(). I think wepoll is a nice project
for using epoll() on Windows socket handles. However we need generalized
file descriptor support to make epoll() for Windows work well enough for
inclusion in a C library. It's also not worth having epoll() if we can't
get it to work on XNU and BSD OSes which provide different abstractions.
Even epoll() on Linux isn't that great of an abstraction since it's full
of footguns. Last time I tried to get it to be useful I had little luck.
Considering how long it took to get poll() and select() to be consistent
across platforms, we really have no business claiming to have epoll too.
While it'd be nice to have fully implemented, the only software that use
epoll() are event i/o libraries used by things like nodejs. Event i/o is
not the best paradigm for handling i/o; threads make so much more sense.

test/libc/calls/select_test.c

@@ -0,0 +1,94 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/sock/select.h"
+#include "libc/calls/calls.h"
+#include "libc/calls/pledge.h"
+#include "libc/calls/struct/sigaction.h"
+#include "libc/calls/struct/sigset.h"
+#include "libc/calls/struct/timeval.h"
+#include "libc/dce.h"
+#include "libc/errno.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sock/sock.h"
+#include "libc/sysv/consts/sig.h"
+#include "libc/testlib/testlib.h"
+#include "libc/time.h"
+
+bool gotsig;
+
+void SetUpOnce(void) {
+  __pledge_mode = PLEDGE_PENALTY_KILL_PROCESS | PLEDGE_STDERR_LOGGING;
+  ASSERT_SYS(0, 0, pledge("stdio", 0));
+}
+
+void SetUp(void) {
+  gotsig = false;
+}
+
+void OnSig(int sig) {
+  gotsig = true;
+}
+
+TEST(select, allZero1) {
+  sigset_t set, old;
+  struct sigaction oldss;
+  struct sigaction sa = {.sa_handler = OnSig};
+  ASSERT_SYS(0, 0, sigaction(SIGQUIT, &sa, &oldss));
+  ASSERT_SYS(0, 0, sigfillset(&set));
+  ASSERT_SYS(0, 0, sigprocmask(SIG_SETMASK, &set, &old));
+  EXPECT_SYS(0, 0, kill(getpid(), SIGQUIT));
+  EXPECT_SYS(EINTR, -1, pselect(0, 0, 0, 0, 0, &old));
+  EXPECT_TRUE(gotsig);
+  EXPECT_SYS(0, 0, sigprocmask(SIG_SETMASK, &old, 0));
+  EXPECT_SYS(0, 0, sigaction(SIGQUIT, &oldss, 0));
+}
+
+TEST(select, pipe_hasInputFromSameProcess) {
+  fd_set rfds;
+  char buf[2];
+  int pipefds[2];
+  struct timeval tv = {.tv_usec = 100 * 1000};
+  EXPECT_SYS(0, 0, pipe(pipefds));
+  FD_ZERO(&rfds);
+  FD_SET(pipefds[0], &rfds);
+  EXPECT_SYS(0, 2, write(pipefds[1], "hi", 2));
+  EXPECT_SYS(0, 1, select(pipefds[0] + 1, &rfds, 0, 0, &tv));
+  EXPECT_TRUE(FD_ISSET(pipefds[0], &rfds));
+  EXPECT_SYS(0, 2, read(pipefds[0], buf, 2));
+  EXPECT_SYS(0, 0, select(pipefds[0] + 1, &rfds, 0, 0, &tv));
+  EXPECT_TRUE(!FD_ISSET(pipefds[0], &rfds));
+  EXPECT_SYS(0, 0, close(pipefds[0]));
+  EXPECT_SYS(0, 0, close(pipefds[1]));
+}
+
+#if 0  // flaky
+TEST(select, testSleep) {
+  int64_t e;
+  long double n;
+  struct timeval t = {0, 2000};
+  n = nowl();
+  EXPECT_SYS(0, 0, select(0, 0, 0, 0, &t));
+  e = (nowl() - n) * 1e6;
+  EXPECT_GT(e, 1000);
+  if (IsLinux()) {
+    EXPECT_EQ(0, t.tv_sec);
+    EXPECT_EQ(0, t.tv_usec);
+  }
+}
+#endif