[DirectoryWatcher][linux] Fix build for older kernels

[jkorous]

Summary

Mikael let me know that DirectoryWatcher broke build for older kernels because of IN_EXCL_UNLINK.

We have RHEL 6.10 buildbots with glibc 2.12.2 and kernel 2.6.32 where I see

• Looking for include file sys/inotify.h
• Looking for include file sys/inotify.h - found

but then get

/repo/uabelho/master/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp:335:48:
error: 'IN_EXCL_UNLINK' was not declared in this scope

IN_CREATE | IN_DELETE | IN_DELETE_SELF | IN_EXCL_UNLINK |

IN_MODIFY |

http://man7.org/linux/man-pages/man7/inotify.7.html

IN_EXCL_UNLINK (since Linux 2.6.36)

[gribozavr]

clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp

322

Group it with other includes?

clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp

EventsReceivingThread = std::thread([this]() {
       InitialScan();
       EventReceivingLoop();
     });
   }
 }
 
 } // namespace
 
+#include <linux/version.h>
+
 std::unique_ptr<DirectoryWatcher> clang::DirectoryWatcher::create(
     StringRef Path,
     std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)> Receiver,
     bool WaitForInitialSync) {
   if (Path.empty())
     return nullptr;
 
   const int InotifyFD = inotify_init1(IN_CLOEXEC);
   if (InotifyFD == -1)
     return nullptr;
 
   const int InotifyWD = inotify_add_watch(
       InotifyFD, Path.str().c_str(),
-      IN_CREATE | IN_DELETE | IN_DELETE_SELF | IN_EXCL_UNLINK | IN_MODIFY |
-          IN_MOVED_FROM | IN_MOVE_SELF | IN_MOVED_TO | IN_ONLYDIR | IN_IGNORED);
+      IN_CREATE | IN_DELETE | IN_DELETE_SELF | IN_MODIFY |
+      IN_MOVED_FROM | IN_MOVE_SELF | IN_MOVED_TO | IN_ONLYDIR | IN_IGNORED
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,36)
+      | IN_EXCL_UNLINK
+#endif
+      );
   if (InotifyWD == -1)
     return nullptr;
 
   auto InotifyPollingStopper = SemaphorePipe::create();
 
   if (!InotifyPollingStopper)
     return nullptr;
 
   return llvm::make_unique<DirectoryWatcherLinux>(
       Path, Receiver, WaitForInitialSync, InotifyFD, InotifyWD,
       std::move(*InotifyPollingStopper));
 }
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