[PATCH] Cygwin: fhandler_socket::open: support the O_PATH flag

[Ken Brown]

If that flag is not set, fail with EOPNOTSUPP instead of ENXIO.  This
is consistent with POSIX, starting with the 2016 edition.  Earlier
editions were silent on this issue.
---
 winsup/cygwin/fhandler_socket.cc | 13 +++++++++++--
 winsup/cygwin/release/3.1.3      |  5 +++++
 winsup/doc/new-features.xml      |  5 +++++
 3 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 winsup/cygwin/release/3.1.3

diff --git a/winsup/cygwin/fhandler_socket.cc b/winsup/cygwin/fhandler_socket.cc
index 9f33d8087..4a46d5a64 100644
--- a/winsup/cygwin/fhandler_socket.cc
+++ b/winsup/cygwin/fhandler_socket.cc
@@ -269,8 +269,17 @@ fhandler_socket::fcntl (int cmd, intptr_t arg)
 int
 fhandler_socket::open (int flags, mode_t mode)
 {
-  set_errno (ENXIO);
-  return 0;
+  /* We don't support opening sockets unless O_PATH is specified. */
+  if (!(flags & O_PATH))
+    {
+      set_errno (EOPNOTSUPP);
+      return 0;
+    }
+
+  query_open (query_read_attributes);
+  nohandle (true);
+  set_flags (flags);
+  return 1;
 }
 
 int __reg2
diff --git a/winsup/cygwin/release/3.1.3 b/winsup/cygwin/release/3.1.3
new file mode 100644
index 000000000..8755c93df
--- /dev/null
+++ b/winsup/cygwin/release/3.1.3
@@ -0,0 +1,5 @@
+What changed:
+-------------
+
+- Sockets can now be opened with the O_PATH flag.  If that flag is not
+  specified, the errno is now EOPNOTSUPP instead of ENXIO.
diff --git a/winsup/doc/new-features.xml b/winsup/doc/new-features.xml
index 65bdc17ab..c8b48d1ca 100644
--- a/winsup/doc/new-features.xml
+++ b/winsup/doc/new-features.xml
@@ -54,6 +54,11 @@ Allow times(2) to have a NULL argument, as on Linux.
 Improve /proc/cpuinfo output and align more closely with Linux.
 </para></listitem>
 
+<listitem><para>
+Sockets can now be opened with the O_PATH flag.  If that flag is not
+specified, the errno is now EOPNOTSUPP instead of ENXIO.
+</para></listitem>
+
 </itemizedlist>
 
 </sect2>
-- 
2.21.0