Fix handling of free descriptors when calling dup2.

native_client_sdk/src/tests/nacl_io_test/kernel_proxy_test.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 <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ skipping 509 matching lines @@
   ASSERT_EQ(4, ki_write(dup_fd, "more", 4));
 
   ASSERT_EQ(0, ki_close(dup2_fd));
   // fd, new_fd -> "/bar"
   // dup_fd -> "/foo"
 
   ASSERT_EQ(dup_fd, ki_dup2(fd, dup_fd));
   // fd, new_fd, dup_fd -> "/bar"
 }
 
+TEST_F(KernelProxyTest, DescriptorAllocationConsistency) {
+  // Check that the descriptor free list returns the expected ones,
+  // as the order is mandated by POSIX.
+
+  // Open a file to a get a descriptor to copy for this test.
+  // The test makes the assumption at all descriptors
+  // open by default are contiguous starting from zero.
+  int fd = ki_open("/foo", O_CREAT | O_RDWR, 0777);
+  ASSERT_GT(fd, -1);
+
+  // The next descriptor allocated should follow the first.
+  int dup_fd = ki_dup(fd);
+  ASSERT_EQ(fd + 1, dup_fd);
+
+  // Allocate a high descriptor number.
+  ASSERT_EQ(100, ki_dup2(fd, 100));
+
+  // The next descriptor allocate should still come 2 places
+  // after the first.
+  int dup_fd2 = ki_dup(fd);
+  ASSERT_EQ(fd + 2, dup_fd2);
+}
+
 TEST_F(KernelProxyTest, Lstat) {
   int fd = ki_open("/foo", O_CREAT | O_RDWR, 0777);
   ASSERT_GT(fd, -1);
   ASSERT_EQ(0, ki_mkdir("/bar", S_IREAD | S_IWRITE));
 
   struct stat buf;
   EXPECT_EQ(0, ki_lstat("/foo", &buf));
   EXPECT_EQ(0, buf.st_size);
   EXPECT_TRUE(S_ISREG(buf.st_mode));
 
@@ skipping 465 matching lines @@
 
   int fd = ki_open("/dummy", O_RDONLY, 0);
   EXPECT_NE(0, fd);
 
   char buf[20];
   EXPECT_EQ(-1, ki_read(fd, &buf[0], 20));
   // The Filesystem should be able to return whatever error it wants and have it
   // propagate through.
   EXPECT_EQ(1234, errno);
 }