[NaCl SDK] nacl_io: Fix select() implementation so it doesn't assume entire fs_sets.

native_client_sdk/src/libraries/nacl_io/kernel_proxy.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "nacl_io/kernel_proxy.h"
 
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
@@ skipping 1011 matching lines @@
 
   // Unknown signum
   errno = EINVAL;
   return -1;
 }
 
 #ifdef PROVIDES_SOCKET_API
 
 int KernelProxy::select(int nfds, fd_set* readfds, fd_set* writefds,
                         fd_set* exceptfds, struct timeval* timeout) {
-  fd_set ignore;
   std::vector<pollfd> pollfds;
 
-  // Simplify logic, by using an IGNORE set for any undefined set
-  FD_ZERO(&ignore);
-  if (NULL == readfds)
-    readfds = &ignore;
-  if (NULL == writefds)
-    writefds = &ignore;
-  if (NULL == exceptfds)
-    exceptfds = &ignore;
-
   for (int fd = 0; fd < nfds; fd++) {
     int events = 0;
-    if (FD_ISSET(fd, readfds))
+    if (readfds && FD_ISSET(fd, readfds)) {
       events |= POLLIN;
+      FD_CLR(fd, readfds);
+    }
 
-    if (FD_ISSET(fd, writefds))
+    if (writefds && FD_ISSET(fd, writefds)) {
       events |= POLLOUT;
+      FD_CLR(fd, writefds);
+    }
 
-    if (FD_ISSET(fd, exceptfds))
+    if (exceptfds && FD_ISSET(fd, exceptfds)) {
       events |= POLLERR | POLLHUP;
+      FD_CLR(fd, exceptfds);
+    }
 
     if (events) {
       pollfd info;
       info.fd = fd;
       info.events = events;
       pollfds.push_back(info);
     }
   }
 
-  FD_ZERO(readfds);
-  FD_ZERO(writefds);
-  FD_ZERO(exceptfds);
-
   // NULL timeout signals wait forever.
   int ms_timeout = -1;
   if (timeout != NULL) {
     int64_t ms = timeout->tv_sec * 1000 + ((timeout->tv_usec + 500) / 1000);
 
     // If the timeout is invalid or too long (larger than signed 32 bit).
     if ((timeout->tv_sec < 0) || (timeout->tv_sec >= (INT_MAX / 1000)) ||
         (timeout->tv_usec < 0) || (timeout->tv_usec >= 1000000) ||
         (ms < 0) || (ms >= INT_MAX)) {
       errno = EINVAL;
@@ skipping 567 matching lines @@
     errno = ENOTSOCK;
     return -1;
   }
 
   return 0;
 }
 
 #endif  // PROVIDES_SOCKET_API
 
 }  // namespace_nacl_io