[PATCH] Cygwin: allow opening an AF_LOCAL/AF_UNIX socket with O_PATH

[Ken Brown <kbrown at cornell dot edu>]

If that flag is not set, or if an attempt is made to open a different
type of socket, the errno is now EOPNOTSUPP instead of ENXIO.  This is
consistent with POSIX, starting with the 2016 edition.  Earlier
editions were silent on this issue.
---
 winsup/cygwin/fhandler.h               |  2 ++
 winsup/cygwin/fhandler_socket.cc       |  2 +-
 winsup/cygwin/fhandler_socket_local.cc | 16 ++++++++++++++++
 winsup/cygwin/fhandler_socket_unix.cc  | 16 ++++++++++++++++
 winsup/cygwin/release/3.1.3            |  7 +++++++
 winsup/doc/new-features.xml            |  6 ++++++
 6 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index c0d56b4da..71b549d38 100644
--- a/winsup/cygwin/fhandler.h
+++ b/winsup/cygwin/fhandler.h
@@ -822,6 +822,7 @@ class fhandler_socket_local: public fhandler_socket_wsock
   int getsockopt (int level, int optname, const void *optval,
 		  __socklen_t *optlen);
 
+  int open (int flags, mode_t mode = 0);
   int __reg2 fstat (struct stat *buf);
   int __reg2 fstatvfs (struct statvfs *buf);
   int __reg1 fchmod (mode_t newmode);
@@ -1103,6 +1104,7 @@ class fhandler_socket_unix : public fhandler_socket
   virtual int ioctl (unsigned int cmd, void *);
   virtual int fcntl (int cmd, intptr_t);
 
+  int open (int flags, mode_t mode = 0);
   int __reg2 fstat (struct stat *buf);
   int __reg2 fstatvfs (struct statvfs *buf);
   int __reg1 fchmod (mode_t newmode);
diff --git a/winsup/cygwin/fhandler_socket.cc b/winsup/cygwin/fhandler_socket.cc
index 9f33d8087..227004b43 100644
--- a/winsup/cygwin/fhandler_socket.cc
+++ b/winsup/cygwin/fhandler_socket.cc
@@ -269,7 +269,7 @@ fhandler_socket::fcntl (int cmd, intptr_t arg)
 int
 fhandler_socket::open (int flags, mode_t mode)
 {
-  set_errno (ENXIO);
+  set_errno (EOPNOTSUPP);
   return 0;
 }
 
diff --git a/winsup/cygwin/fhandler_socket_local.cc b/winsup/cygwin/fhandler_socket_local.cc
index f88ced22d..dbca74702 100644
--- a/winsup/cygwin/fhandler_socket_local.cc
+++ b/winsup/cygwin/fhandler_socket_local.cc
@@ -634,6 +634,22 @@ fhandler_socket_local::dup (fhandler_base *child, int flags)
   return fhandler_socket_wsock::dup (child, flags);
 }
 
+int
+fhandler_socket_local::open (int flags, mode_t mode)
+{
+  /* 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
 fhandler_socket_local::fstat (struct stat *buf)
 {
diff --git a/winsup/cygwin/fhandler_socket_unix.cc b/winsup/cygwin/fhandler_socket_unix.cc
index eea7e76b3..b3d4da49a 100644
--- a/winsup/cygwin/fhandler_socket_unix.cc
+++ b/winsup/cygwin/fhandler_socket_unix.cc
@@ -2296,6 +2296,22 @@ fhandler_socket_unix::fcntl (int cmd, intptr_t arg)
   return ret;
 }
 
+int
+fhandler_socket_unix::open (int flags, mode_t mode)
+{
+  /* 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
 fhandler_socket_unix::fstat (struct stat *buf)
 {
diff --git a/winsup/cygwin/release/3.1.3 b/winsup/cygwin/release/3.1.3
index 489741136..af9e0f38e 100644
--- a/winsup/cygwin/release/3.1.3
+++ b/winsup/cygwin/release/3.1.3
@@ -1,3 +1,10 @@
+What's new:
+-----------
+
+- AF_LOCAL/AF_UNIX sockets can now be opened with the O_PATH flag.  If
+  that flag is not set, or if an attempt is made to open a different
+  type of socket, the errno is now EOPNOTSUPP instead of ENXIO.
+
 Bug Fixes
 ---------
 
diff --git a/winsup/doc/new-features.xml b/winsup/doc/new-features.xml
index 65bdc17ab..bf481bd04 100644
--- a/winsup/doc/new-features.xml
+++ b/winsup/doc/new-features.xml
@@ -54,6 +54,12 @@ 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>
+AF_LOCAL/AF_UNIX sockets can now be opened with the O_PATH flag.  If
+that flag is not set, or if an attempt is made to open a different
+type of socket, the errno is now EOPNOTSUPP instead of ENXIO.
+</para></listitem>
+
 </itemizedlist>
 
 </sect2>
-- 
2.21.0