From 66b2005cbb322bc1d783b90a574b0e14df906bcb Mon Sep 17 00:00:00 2001
From: Yash Tibrewal <yashkt@google.com>
Date: Tue, 27 Nov 2018 12:56:56 -0800
Subject: Enable errqueue support for linux kernel versions 4.0.0 and above

---
 src/core/lib/iomgr/ev_posix.cc          | 10 ++++-----
 src/core/lib/iomgr/internal_errqueue.cc | 39 ++++++++++++++++++++++++++++++---
 src/core/lib/iomgr/internal_errqueue.h  |  8 ++++++-
 src/core/lib/iomgr/iomgr.cc             |  2 ++
 src/core/lib/iomgr/port.h               |  3 +--
 5 files changed, 51 insertions(+), 11 deletions(-)

diff --git a/src/core/lib/iomgr/ev_posix.cc b/src/core/lib/iomgr/ev_posix.cc
index 8a7dc7b004..ef23589480 100644
--- a/src/core/lib/iomgr/ev_posix.cc
+++ b/src/core/lib/iomgr/ev_posix.cc
@@ -36,6 +36,7 @@
 #include "src/core/lib/iomgr/ev_epoll1_linux.h"
 #include "src/core/lib/iomgr/ev_epollex_linux.h"
 #include "src/core/lib/iomgr/ev_poll_posix.h"
+#include "src/core/lib/iomgr/internal_errqueue.h"
 
 grpc_core::TraceFlag grpc_polling_trace(false,
                                         "polling"); /* Disabled by default */
@@ -236,12 +237,11 @@ void grpc_event_engine_shutdown(void) {
 }
 
 bool grpc_event_engine_can_track_errors(void) {
-/* Only track errors if platform supports errqueue. */
-#ifdef GRPC_LINUX_ERRQUEUE
-  return g_event_engine->can_track_err;
-#else
+  /* Only track errors if platform supports errqueue. */
+  if (grpc_core::kernel_supports_errqueue()) {
+    return g_event_engine->can_track_err;
+  }
   return false;
-#endif /* GRPC_LINUX_ERRQUEUE */
 }
 
 grpc_fd* grpc_fd_create(int fd, const char* name, bool track_err) {
diff --git a/src/core/lib/iomgr/internal_errqueue.cc b/src/core/lib/iomgr/internal_errqueue.cc
index 99c22e9055..982d709f09 100644
--- a/src/core/lib/iomgr/internal_errqueue.cc
+++ b/src/core/lib/iomgr/internal_errqueue.cc
@@ -20,17 +20,50 @@
 
 #include "src/core/lib/iomgr/port.h"
 
+#include <grpc/impl/codegen/log.h>
 #include "src/core/lib/iomgr/internal_errqueue.h"
 
 #ifdef GRPC_POSIX_SOCKET_TCP
 
-bool kernel_supports_errqueue() {
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/utsname.h>
+
+namespace grpc_core {
+static bool errqueue_supported = false;
+
+bool kernel_supports_errqueue() { return errqueue_supported; }
+
+void grpc_errqueue_init() {
+/* Both-compile time and run-time linux kernel versions should be atleast 4.0.0
+ */
 #ifdef LINUX_VERSION_CODE
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 0, 0)
-  return true;
+  struct utsname buffer;
+  if (uname(&buffer) != 0) {
+    gpr_log(GPR_ERROR, "uname: %s", strerror(errno));
+    return;
+  }
+  char* release = buffer.release;
+  if (release == nullptr) {
+    return;
+  }
+
+  if (strtol(release, nullptr, 10) >= 4) {
+    errqueue_supported = true;
+  } else {
+    gpr_log(GPR_DEBUG, "ERRQUEUE support not enabled");
+  }
 #endif /* LINUX_VERSION_CODE <= KERNEL_VERSION(4, 0, 0) */
 #endif /* LINUX_VERSION_CODE */
-  return false;
 }
+} /* namespace grpc_core */
+
+#else
+
+namespace grpc_core {
+void grpc_errqueue_init() {}
+} /* namespace grpc_core */
 
 #endif /* GRPC_POSIX_SOCKET_TCP */
diff --git a/src/core/lib/iomgr/internal_errqueue.h b/src/core/lib/iomgr/internal_errqueue.h
index 9d122808f9..f8644c2536 100644
--- a/src/core/lib/iomgr/internal_errqueue.h
+++ b/src/core/lib/iomgr/internal_errqueue.h
@@ -76,8 +76,14 @@ constexpr uint32_t kTimestampingRecordingOptions =
  * Currently allowing only linux kernels above 4.0.0
  */
 bool kernel_supports_errqueue();
-}  // namespace grpc_core
+
+} /* namespace grpc_core */
 
 #endif /* GRPC_POSIX_SOCKET_TCP */
 
+namespace grpc_core {
+/* Initializes errqueue support */
+void grpc_errqueue_init();
+} /* namespace grpc_core */
+
 #endif /* GRPC_CORE_LIB_IOMGR_INTERNAL_ERRQUEUE_H */
diff --git a/src/core/lib/iomgr/iomgr.cc b/src/core/lib/iomgr/iomgr.cc
index 30b68db4df..fd09a6863b 100644
--- a/src/core/lib/iomgr/iomgr.cc
+++ b/src/core/lib/iomgr/iomgr.cc
@@ -36,6 +36,7 @@
 #include "src/core/lib/iomgr/buffer_list.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 #include "src/core/lib/iomgr/executor.h"
+#include "src/core/lib/iomgr/internal_errqueue.h"
 #include "src/core/lib/iomgr/iomgr_internal.h"
 #include "src/core/lib/iomgr/network_status_tracker.h"
 #include "src/core/lib/iomgr/timer.h"
@@ -58,6 +59,7 @@ void grpc_iomgr_init() {
   g_root_object.name = (char*)"root";
   grpc_network_status_init();
   grpc_iomgr_platform_init();
+  grpc_core::grpc_errqueue_init();
 }
 
 void grpc_iomgr_start() { grpc_timer_manager_init(); }
diff --git a/src/core/lib/iomgr/port.h b/src/core/lib/iomgr/port.h
index bf56a7298d..c8046b21dc 100644
--- a/src/core/lib/iomgr/port.h
+++ b/src/core/lib/iomgr/port.h
@@ -62,8 +62,7 @@
 #define GRPC_HAVE_UNIX_SOCKET 1
 #ifdef LINUX_VERSION_CODE
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 0, 0)
-/* TODO(yashykt): Re-enable once Fathom changes are commited.
-#define GRPC_LINUX_ERRQUEUE 1 */
+#define GRPC_LINUX_ERRQUEUE 1
 #endif /* LINUX_VERSION_CODE >= KERNEL_VERSION(4, 0, 0) */
 #endif /* LINUX_VERSION_CODE */
 #define GRPC_LINUX_MULTIPOLL_WITH_EPOLL 1
-- 
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