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.

libc/calls/select-nt.c

@@ -16,7 +16,6 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/assert.h"
 #include "libc/calls/internal.h"
 #include "libc/calls/state.internal.h"
 #include "libc/calls/struct/timeval.h"
@@ -31,37 +30,48 @@
 #include "libc/sysv/errfuns.h"
 #ifdef __x86_64__
 
+// <sync libc/sysv/consts.sh>
+#define POLLERR_    0x0001  // implied in events
+#define POLLHUP_    0x0002  // implied in events
+#define POLLNVAL_   0x0004  // implied in events
+#define POLLIN_     0x0300
+#define POLLRDNORM_ 0x0100
+#define POLLRDBAND_ 0x0200
+#define POLLOUT_    0x0010
+#define POLLWRNORM_ 0x0010
+#define POLLWRBAND_ 0x0020  // MSDN undocumented
+#define POLLPRI_    0x0400  // MSDN unsupported
+// </sync libc/sysv/consts.sh>
+
 int sys_select_nt(int nfds, fd_set *readfds, fd_set *writefds,
                   fd_set *exceptfds, struct timeval *timeout,
                   const sigset_t *sigmask) {
-  int i, pfds, events, fdcount;
+  int pfds = 0;
 
   // convert bitsets to pollfd
-  struct pollfd fds[64];
-  for (pfds = i = 0; i < nfds; ++i) {
-    events = 0;
-    if (readfds && FD_ISSET(i, readfds))
-      events |= POLLIN;
-    if (writefds && FD_ISSET(i, writefds))
-      events |= POLLOUT;
-    if (exceptfds && FD_ISSET(i, exceptfds))
-      events |= POLLERR;
+  struct pollfd fds[128];
+  for (int fd = 0; fd < nfds; ++fd) {
+    int events = 0;
+    if (readfds && FD_ISSET(fd, readfds))
+      events |= POLLIN_;
+    if (writefds && FD_ISSET(fd, writefds))
+      events |= POLLOUT_;
+    if (exceptfds && FD_ISSET(fd, exceptfds))
+      events |= POLLPRI_;
     if (events) {
-      if (pfds < ARRAYLEN(fds)) {
-        fds[pfds].fd = i;
-        fds[pfds].events = events;
-        fds[pfds].revents = 0;
-        pfds += 1;
-      } else {
-        return enomem();
-      }
+      if (pfds == ARRAYLEN(fds))
+        return e2big();
+      fds[pfds].fd = fd;
+      fds[pfds].events = events;
+      fds[pfds].revents = 0;
+      ++pfds;
     }
   }
 
   // convert the wait time to a word
   uint32_t millis;
   if (!timeout) {
-    millis = -1;
+    millis = -1u;
   } else {
     int64_t ms = timeval_tomillis(*timeout);
     if (ms < 0 || ms > UINT32_MAX) {
@@ -72,9 +82,8 @@ int sys_select_nt(int nfds, fd_set *readfds, fd_set *writefds,
   }
 
   // call our nt poll implementation
-  fdcount = sys_poll_nt(fds, pfds, &millis, sigmask);
-  unassert(fdcount < 64);
-  if (fdcount < 0)
+  int fdcount = sys_poll_nt(fds, pfds, &millis, sigmask);
+  if (fdcount == -1)
     return -1;
 
   // convert pollfd back to bitsets
@@ -85,20 +94,20 @@ int sys_select_nt(int nfds, fd_set *readfds, fd_set *writefds,
   if (exceptfds)
     FD_ZERO(exceptfds);
   int bits = 0;
-  for (i = 0; i < pfds; ++i) {
-    if (fds[i].revents & POLLIN) {
+  for (int i = 0; i < pfds; ++i) {
+    if (fds[i].revents & (POLLIN_ | POLLHUP_ | POLLERR_ | POLLNVAL_)) {
       if (readfds) {
         FD_SET(fds[i].fd, readfds);
         ++bits;
       }
     }
-    if (fds[i].revents & POLLOUT) {
+    if (fds[i].revents & POLLOUT_) {
       if (writefds) {
         FD_SET(fds[i].fd, writefds);
         ++bits;
       }
     }
-    if (fds[i].revents & (POLLERR | POLLNVAL)) {
+    if (fds[i].revents & POLLPRI_) {
       if (exceptfds) {
         FD_SET(fds[i].fd, exceptfds);
         ++bits;
@@ -107,9 +116,8 @@ int sys_select_nt(int nfds, fd_set *readfds, fd_set *writefds,
   }
 
   // store remaining time back in caller's timeval
-  if (timeout) {
+  if (timeout)
     *timeout = timeval_frommillis(millis);
-  }
 
   return bits;
 }