Enable epoll on Python manylinux1

The Python packages built for Linux and uploaded to PyPI are required to
target a standardized platform specification dubbed `manylinux1`, which
tries to cover a vast array of Linux distributions, thereby emulating a
legacy lowest-common-denominator distribution, with an old `glibc` that
does not support `epoll_create1`, but provides the `epoll_create`
interface.  While there are race condition risks associated with
utilizing the latter interface and setting the `O_CLOEXEC` flag
immediately on the file descriptor returned by `epoll_create`, the
payoff is well worth the risks for our Python users, who currently end
up falling back on `poll` polling engine when downloading our Linux
binary packages.

src/core/lib/iomgr/ev_epoll1_linux.cc

@@ -26,6 +26,7 @@
 
 #include <assert.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <limits.h>
 #include <poll.h>
 #include <pthread.h>
@@ -84,11 +85,32 @@ typedef struct epoll_set {
 /* The global singleton epoll set */
 static epoll_set g_epoll_set;
 
+static int epoll_create_and_set_flag() {
+#ifdef GRPC_LINUX_EPOLL_CREATE1
+  int fd = epoll_create1(EPOLL_CLOEXEC);
+  if (fd >= 0) {
+    return fd;
+  }
+  gpr_log(GPR_ERROR, "epoll_create1 unavailable");
+  return -1;
+#else
+  int fd = epoll_create(MAX_EPOLL_EVENTS);
+  if (fd < 0) {
+    gpr_log(GPR_ERROR, "epoll_create unavailable");
+    return -1;
+  }
+  if (fcntl(fd, F_SETFD, FD_CLOEXEC) == 0) {
+    return fd;
+  }
+  gpr_log(GPR_ERROR, "fcntl following epoll_create failed");
+  return -1;
+#endif
+}
+
 /* Must be called *only* once */
 static bool epoll_set_init() {
-  g_epoll_set.epfd = epoll_create1(EPOLL_CLOEXEC);
+  g_epoll_set.epfd = epoll_create_and_set_flag();
   if (g_epoll_set.epfd < 0) {
-    gpr_log(GPR_ERROR, "epoll unavailable");
     return false;
   }
 

src/core/lib/iomgr/port.h

@@ -67,8 +67,11 @@
 #define GRPC_POSIX_WAKEUP_FD 1
 #define GRPC_TIMER_USE_GENERIC 1
 #ifdef __GLIBC_PREREQ
-#if __GLIBC_PREREQ(2, 9)
+#if __GLIBC_PREREQ(2, 4)
 #define GRPC_LINUX_EPOLL 1
+#endif
+#if __GLIBC_PREREQ(2, 9)
+#define GRPC_LINUX_EPOLL_CREATE1 1
 #define GRPC_LINUX_EVENTFD 1
 #endif
 #if __GLIBC_PREREQ(2, 10)