Cygwin: implement getfacl(1) for socket files

Do this by defining the acl_get method for the fhandler_socket_local
and fhandler_socket_unix classes.  Also define acl_set for these
classes.

Partially addresses: https://cygwin.com/pipermail/cygwin/2022-July/251768.html

winsup/cygwin/fhandler.h

@@ -861,6 +861,8 @@ class fhandler_socket_local: public fhandler_socket_wsock
   int fchmod (mode_t newmode);
   int fchown (uid_t newuid, gid_t newgid);
   int facl (int, int, struct acl *);
+  struct __acl_t *acl_get (uint32_t);
+  int acl_set (struct __acl_t *, uint32_t);
   int link (const char *);
 
   /* from here on: CLONING */
@@ -1143,6 +1145,8 @@ class fhandler_socket_unix : public fhandler_socket
   int fchmod (mode_t newmode);
   int fchown (uid_t newuid, gid_t newgid);
   int facl (int, int, struct acl *);
+  struct __acl_t *acl_get (uint32_t);
+  int acl_set (struct __acl_t *, uint32_t);
   int link (const char *);
 
   /* select.cc */

winsup/cygwin/release/3.4.0

@@ -25,3 +25,5 @@ What changed:
 Bug Fixes
 ---------
 
+- Don't error out if getfacl(1) is called on a socket file.
+  Partially addresses: https://cygwin.com/pipermail/cygwin/2022-July/251768.html

winsup/cygwin/sec_posixacl.cc

@@ -633,6 +633,44 @@ fhandler_disk_file::acl_get (acl_type_t type)
   return acl;
 }
 
+acl_t
+fhandler_socket_local::acl_get (acl_type_t type)
+{
+  if (!dev ().isfs ())
+    /* acl_get_fd on a socket. */
+    return fhandler_base::acl_get (type);
+
+  /* acl_get_fd on a socket opened with O_PATH or acl_get_file on a
+     socket file. */
+  if (get_flags () & O_PATH)
+    {
+      set_errno (EBADF);
+      return NULL;
+    }
+  fhandler_disk_file fh (pc);
+  return fh.acl_get (type);
+}
+
+#ifdef __WITH_AF_UNIX
+acl_t
+fhandler_socket_unix::acl_get (acl_type_t type)
+{
+  if (!dev ().isfs ())
+    /* acl_get_fd on a socket. */
+    return fhandler_base::acl_get (type);
+
+  /* acl_get_fd on a socket opened with O_PATH or acl_get_file on a
+     socket file. */
+  if (get_flags () & O_PATH)
+    {
+      set_errno (EBADF);
+      return NULL;
+    }
+  fhandler_disk_file fh (pc);
+  return fh.acl_get (type);
+}
+#endif
+
 extern "C" acl_t
 acl_get_fd (int fd)
 {
@@ -765,6 +803,44 @@ fhandler_disk_file::acl_set (acl_t acl, acl_type_t type)
   return ret;
 }
 
+int
+fhandler_socket_local::acl_set (acl_t acl, acl_type_t type)
+{
+  if (!dev ().isfs ())
+    /* acl_set_fd on a socket. */
+    return fhandler_base::acl_set (acl, type);
+
+  /* acl_set_fd on a socket opened with O_PATH or acl_set_file on a
+     socket file. */
+  if (get_flags () & O_PATH)
+    {
+      set_errno (EBADF);
+      return -1;
+    }
+  fhandler_disk_file fh (pc);
+  return fh.acl_set (acl, type);
+}
+
+#ifdef __WITH_AF_UNIX
+int
+fhandler_socket_unix::acl_set (acl_t acl, acl_type_t type)
+{
+  if (!dev ().isfs ())
+    /* acl_set_fd on a socket. */
+    return fhandler_base::acl_set (acl, type);
+
+  /* acl_set_fd on a socket opened with O_PATH or acl_set_file on a
+     socket file. */
+  if (get_flags () & O_PATH)
+    {
+      set_errno (EBADF);
+      return -1;
+    }
+  fhandler_disk_file fh (pc);
+  return fh.acl_set (acl, type);
+}
+#endif
+
 extern "C" int
 acl_set_fd (int fd, acl_t acl)
 {