diff --git a/ChangeLog b/ChangeLog
index 8b752efd64..b1da834f8e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,25 @@
+2018-01-10  Samuel Thibault  <samuel.thibault@ens-lyon.org>
+
+	* hurd/hurd/fd.h: Include <fcntl.h>
+	(__hurd_at_flags): New function.
+	* hurd/lookup-at.c (__file_name_lookup_at): Replace flag computation
+	with call to __hurd_at_flags.
+	* include/unistd.h (__faccessat, __faccessat_noerrno): Add declaration.
+	* sysdeps/mach/hurd/access.c (access_common): Move implementation to
+	__faccessat
+	(hurd_fail_seterrno, hurd_fail_noerrno): Move to sysdeps/mach/hurd/faccessat.c.
+	(__access_noerrno): Use __faccessat_common instead of access_common.
+	(__access): Likewise.
+	* sysdeps/mach/hurd/euidaccess.c (__euidaccess): Replace implementation
+	with a call to __faccessat.
+	* sysdeps/mach/hurd/faccessat.c (faccessat): Rename into...
+	(__faccessat_common): ... this. Move implementation of __access into it when
+	AT_FLAGS does not contain AT_EACCESS. Make it call __hurd_at_flags, add
+	reauthenticate_cwdir_at helper to implement AT mechanism.
+	(__faccessat_noerrno): New function, just calls __faccessat_common.
+	(__faccessat): New function, just calls __faccessat_common.
+	(faccessat): Define weak alias.
+
 2018-01-10  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #22691]
diff --git a/hurd/hurd/fd.h b/hurd/hurd/fd.h
index 7fd2297779..809a73f5dd 100644
--- a/hurd/hurd/fd.h
+++ b/hurd/hurd/fd.h
@@ -26,6 +26,7 @@
 #include <hurd/hurd_types.h>
 #include <hurd/port.h>
 #include <sys/socket.h>
+#include <fcntl.h>
 
 
 /* Structure representing a file descriptor.  */
@@ -254,6 +255,26 @@ extern int _hurd_select (int nfds, struct pollfd *pollfds,
 			 const struct timespec *timeout,
 			 const sigset_t *sigmask);
 
+/* Apply AT_FLAGS on FLAGS, in preparation for calling
+   __hurd_file_name_lookup.  */
+
+_HURD_FD_H_EXTERN_INLINE error_t
+__hurd_at_flags (int *at_flags, int *flags)
+{
+  if ((*at_flags & AT_SYMLINK_FOLLOW) && (*at_flags & AT_SYMLINK_NOFOLLOW))
+    return EINVAL;
+
+  *flags |= (*at_flags & AT_SYMLINK_NOFOLLOW) ? O_NOLINK : 0;
+  *at_flags &= ~AT_SYMLINK_NOFOLLOW;
+  if (*at_flags & AT_SYMLINK_FOLLOW)
+    *flags &= ~O_NOLINK;
+  *at_flags &= ~AT_SYMLINK_FOLLOW;
+  if (*at_flags != 0)
+    return EINVAL;
+
+  return 0;
+}
+
 /* Variant of file_name_lookup used in *at function implementations.
    AT_FLAGS may only contain AT_SYMLINK_FOLLOW or AT_SYMLINK_NOFOLLOW,
    which will remove and add O_NOLINK from FLAGS respectively.
diff --git a/hurd/lookup-at.c b/hurd/lookup-at.c
index abf9047e57..deddc2264c 100644
--- a/hurd/lookup-at.c
+++ b/hurd/lookup-at.c
@@ -29,16 +29,9 @@ __file_name_lookup_at (int fd, int at_flags,
   error_t err;
   file_t result;
 
-  if ((at_flags & AT_SYMLINK_FOLLOW) && (at_flags & AT_SYMLINK_NOFOLLOW))
-    return (__hurd_fail (EINVAL), MACH_PORT_NULL);
-
-  flags |= (at_flags & AT_SYMLINK_NOFOLLOW) ? O_NOLINK : 0;
-  at_flags &= ~AT_SYMLINK_NOFOLLOW;
-  if (at_flags & AT_SYMLINK_FOLLOW)
-    flags &= ~O_NOLINK;
-  at_flags &= ~AT_SYMLINK_FOLLOW;
-  if (at_flags != 0)
-    return (__hurd_fail (EINVAL), MACH_PORT_NULL);
+  err = __hurd_at_flags (&at_flags, &flags);
+  if (err)
+    return (__hurd_fail (err), MACH_PORT_NULL);
 
   if (fd == AT_FDCWD || file_name[0] == '/')
     return __file_name_lookup (file_name, flags, mode);
diff --git a/include/unistd.h b/include/unistd.h
index f884fdae99..0f91b8babc 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -25,6 +25,9 @@ libc_hidden_proto (readlinkat)
 /* Now define the internal interfaces.  */
 extern int __access (const char *__name, int __type) attribute_hidden;
 extern int __euidaccess (const char *__name, int __type);
+extern int __faccessat (int __fd, const char *__file, int __type, int __flag);
+extern int __faccessat_noerrno (int __fd, const char *__file, int __type,
+			        int __flag);
 extern __off64_t __lseek64 (int __fd, __off64_t __offset, int __whence)
      attribute_hidden;
 extern __off_t __lseek (int __fd, __off_t __offset, int __whence);
diff --git a/sysdeps/mach/hurd/access.c b/sysdeps/mach/hurd/access.c
index 9195bd61ff..31fd5bea56 100644
--- a/sysdeps/mach/hurd/access.c
+++ b/sysdeps/mach/hurd/access.c
@@ -15,145 +15,10 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <errno.h>
 #include <unistd.h>
-#include <hurd.h>
-#include <hurd/port.h>
-#include <hurd/id.h>
-#include <hurd/lookup.h>
 #include <fcntl.h>
 
-static int
-hurd_fail_seterrno (error_t err)
-{
-  return __hurd_fail (err);
-}
-
-static int
-hurd_fail_noerrno (error_t err)
-{
-  return -1;
-}
-
-static int
-access_common (const char *file, int type, int (*errfunc) (error_t))
-{
-  error_t err;
-  file_t rcrdir, rcwdir, io;
-  int flags, allowed;
-
-  error_t reauthenticate (int which, file_t *result)
-    {
-      /* Get a port to our root directory, authenticated with the real IDs.  */
-      error_t err;
-      mach_port_t ref;
-      ref = __mach_reply_port ();
-      err = HURD_PORT_USE
-	(&_hurd_ports[which],
-	 ({
-	   err = __io_reauthenticate (port, ref, MACH_MSG_TYPE_MAKE_SEND);
-	   if (!err)
-	     err = __auth_user_authenticate (_hurd_id.rid_auth,
-					     ref, MACH_MSG_TYPE_MAKE_SEND,
-					     result);
-	   err;
-	 }));
-      __mach_port_destroy (__mach_task_self (), ref);
-      return err;
-    }
-
-  error_t init_port (int which, error_t (*operate) (mach_port_t))
-    {
-      switch (which)
-	{
-	case INIT_PORT_AUTH:
-	  return (*operate) (_hurd_id.rid_auth);
-	case INIT_PORT_CRDIR:
-	  return (reauthenticate (INIT_PORT_CRDIR, &rcrdir) ?:
-		  (*operate) (rcrdir));
-	case INIT_PORT_CWDIR:
-	  return (reauthenticate (INIT_PORT_CWDIR, &rcwdir) ?:
-		  (*operate) (rcwdir));
-	default:
-	  return _hurd_ports_use (which, operate);
-	}
-    }
-
-  rcrdir = rcwdir = MACH_PORT_NULL;
-
-  HURD_CRITICAL_BEGIN;
-
-  __mutex_lock (&_hurd_id.lock);
-  /* Get _hurd_id up to date.  */
-  if (err = _hurd_check_ids ())
-    goto lose;
-
-  if (_hurd_id.rid_auth == MACH_PORT_NULL)
-    {
-      /* Set up _hurd_id.rid_auth.  This is a special auth server port
-	 which uses the real uid and gid (the first aux uid and gid) as
-	 the only effective uid and gid.  */
-
-      if (_hurd_id.aux.nuids < 1 || _hurd_id.aux.ngids < 1)
-	{
-	  /* We do not have a real UID and GID.  Lose, lose, lose!  */
-	  err = EGRATUITOUS;
-	  goto lose;
-	}
-
-      /* Create a new auth port using our real UID and GID (the first
-	 auxiliary UID and GID) as the only effective IDs.  */
-      if (err = __USEPORT (AUTH,
-			   __auth_makeauth (port,
-					    NULL, MACH_MSG_TYPE_COPY_SEND, 0,
-					    _hurd_id.aux.uids, 1,
-					    _hurd_id.aux.uids,
-					    _hurd_id.aux.nuids,
-					    _hurd_id.aux.gids, 1,
-					    _hurd_id.aux.gids,
-					    _hurd_id.aux.ngids,
-					    &_hurd_id.rid_auth)))
-	goto lose;
-    }
-
-  if (!err)
-    /* Look up the file name using the modified init ports.  */
-    err = __hurd_file_name_lookup (&init_port, &__getdport, 0,
-				   file, 0, 0, &io);
-
-  /* We are done with _hurd_id.rid_auth now.  */
- lose:
-  __mutex_unlock (&_hurd_id.lock);
-
-  HURD_CRITICAL_END;
-
-  if (rcrdir != MACH_PORT_NULL)
-    __mach_port_deallocate (__mach_task_self (), rcrdir);
-  if (rcwdir != MACH_PORT_NULL)
-    __mach_port_deallocate (__mach_task_self (), rcwdir);
-  if (err)
-    return errfunc (err);
-
-  /* Find out what types of access we are allowed to this file.  */
-  err = __file_check_access (io, &allowed);
-  __mach_port_deallocate (__mach_task_self (), io);
-  if (err)
-    return errfunc (err);
-
-  flags = 0;
-  if (type & R_OK)
-    flags |= O_READ;
-  if (type & W_OK)
-    flags |= O_WRITE;
-  if (type & X_OK)
-    flags |= O_EXEC;
-
-  if (flags & ~allowed)
-    /* We are not allowed all the requested types of access.  */
-    return errfunc (EACCES);
-
-  return 0;
-}
-
 /* Test for access to FILE by our real user and group IDs without setting
    errno.  This may be unsafe to run during initialization of tunables
    since access_common calls __hurd_file_name_lookup, which calls
@@ -161,13 +26,13 @@ access_common (const char *file, int type, int (*errfunc) (error_t))
 int
 __access_noerrno (const char *file, int type)
 {
-  return access_common (file, type, hurd_fail_noerrno);
+  return __faccessat_noerrno (AT_FDCWD, file, type, 0);
 }
 
 /* Test for access to FILE by our real user and group IDs.  */
 int
 __access (const char *file, int type)
 {
-  return access_common (file, type, hurd_fail_seterrno);
+  return __faccessat (AT_FDCWD, file, type, 0);
 }
 weak_alias (__access, access)
diff --git a/sysdeps/mach/hurd/euidaccess.c b/sysdeps/mach/hurd/euidaccess.c
index 613872a207..2c7ce1f2b6 100644
--- a/sysdeps/mach/hurd/euidaccess.c
+++ b/sysdeps/mach/hurd/euidaccess.c
@@ -16,42 +16,13 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
-#include <stddef.h>
 #include <unistd.h>
 #include <fcntl.h>
-#include <hurd.h>
 
 int
 __euidaccess (const char *file, int type)
 {
-  error_t err;
-  file_t port;
-  int allowed, flags;
-
-  port = __file_name_lookup (file, 0, 0);
-  if (port == MACH_PORT_NULL)
-    return -1;
-
-  /* Find out what types of access we are allowed to this file.  */
-  err = __file_check_access (port, &allowed);
-  __mach_port_deallocate (__mach_task_self (), port);
-  if (err)
-    return __hurd_fail (err);
-
-  flags = 0;
-  if (type & R_OK)
-    flags |= O_READ;
-  if (type & W_OK)
-    flags |= O_WRITE;
-  if (type & X_OK)
-    flags |= O_EXEC;
-
-  if (flags & ~allowed)
-    /* We are not allowed all the requested types of access.  */
-    return __hurd_fail (EACCES);
-
-  return 0;
+  return __faccessat (AT_FDCWD, file, type, AT_EACCESS);
 }
 weak_alias (__euidaccess, euidaccess)
 weak_alias (__euidaccess, eaccess)
diff --git a/sysdeps/mach/hurd/faccessat.c b/sysdeps/mach/hurd/faccessat.c
index 260060639f..d9bceaada7 100644
--- a/sysdeps/mach/hurd/faccessat.c
+++ b/sysdeps/mach/hurd/faccessat.c
@@ -23,31 +23,167 @@
 #include <sys/types.h>
 #include <hurd.h>
 #include <hurd/fd.h>
+#include <hurd/port.h>
+#include <hurd/id.h>
+#include <hurd/lookup.h>
 
-int
-faccessat (int fd, const char *file, int type, int flag)
+static int
+hurd_fail_seterrno (error_t err)
+{
+  return __hurd_fail (err);
+}
+
+static int
+hurd_fail_noerrno (error_t err)
+{
+  return -1;
+}
+
+static int
+__faccessat_common (int fd, const char *file, int type, int at_flags,
+                    int (*errfunc) (error_t))
 {
   error_t err;
-  file_t port;
-  int allowed, flags;
+  file_t rcrdir, rcwdir, io;
+  int flags, allowed;
 
-  if ((flag & AT_EACCESS) == 0)
+  if ((at_flags & AT_EACCESS) == AT_EACCESS)
     {
-      if (fd == AT_FDCWD || file[0] == '/')
-	return __access (file, type);
-      __set_errno (ENOTSUP);	/* XXX later */
-      return -1;
+      /* Use effective permissions.  */
+      io = __file_name_lookup_at (fd, at_flags &~ AT_EACCESS, file, 0, 0);
+      if (io == MACH_PORT_NULL)
+	return -1;
     }
+  else
+    {
+      /* We have to use real permissions instead of the
+         usual effective permissions.  */
+
+      int hurd_flags = 0;
+      __hurd_at_flags (&at_flags, &hurd_flags);
+
+      error_t reauthenticate_cwdir_at (file_t *result)
+	{
+	  /* Get a port to the FD directory, authenticated with the real IDs.  */
+	  error_t err;
+	  mach_port_t ref;
+	  ref = __mach_reply_port ();
+	  err = HURD_DPORT_USE
+	    (fd,
+	     ({
+	       err = __io_reauthenticate (port, ref, MACH_MSG_TYPE_MAKE_SEND);
+	       if (!err)
+		 err = __auth_user_authenticate (_hurd_id.rid_auth,
+						 ref, MACH_MSG_TYPE_MAKE_SEND,
+						 result);
+	       err;
+	     }));
+	  __mach_port_destroy (__mach_task_self (), ref);
+	  return err;
+	}
+
+      error_t reauthenticate (int which, file_t *result)
+	{
+	  /* Get a port to our root directory, authenticated with the real IDs.  */
+	  error_t err;
+	  mach_port_t ref;
+	  ref = __mach_reply_port ();
+	  err = HURD_PORT_USE
+	    (&_hurd_ports[which],
+	     ({
+	       err = __io_reauthenticate (port, ref, MACH_MSG_TYPE_MAKE_SEND);
+	       if (!err)
+		 err = __auth_user_authenticate (_hurd_id.rid_auth,
+						 ref, MACH_MSG_TYPE_MAKE_SEND,
+						 result);
+	       err;
+	     }));
+	  __mach_port_destroy (__mach_task_self (), ref);
+	  return err;
+	}
+
+      error_t init_port (int which, error_t (*operate) (mach_port_t))
+	{
+	  switch (which)
+	    {
+	    case INIT_PORT_AUTH:
+	      return (*operate) (_hurd_id.rid_auth);
+	    case INIT_PORT_CRDIR:
+	      return (reauthenticate (INIT_PORT_CRDIR, &rcrdir) ?:
+		      (*operate) (rcrdir));
+	    case INIT_PORT_CWDIR:
+	      if (fd == AT_FDCWD || file[0] == '/')
+		return (reauthenticate (INIT_PORT_CWDIR, &rcwdir) ?:
+			(*operate) (rcwdir));
+	      else
+		return (reauthenticate_cwdir_at (&rcwdir) ?:
+			(*operate) (rcwdir));
+	    default:
+	      return _hurd_ports_use (which, operate);
+	    }
+	}
+
+      rcrdir = rcwdir = MACH_PORT_NULL;
+
+      HURD_CRITICAL_BEGIN;
+
+      __mutex_lock (&_hurd_id.lock);
+      /* Get _hurd_id up to date.  */
+      if (err = _hurd_check_ids ())
+	goto lose;
 
-  port = __file_name_lookup_at (fd, flag &~ AT_EACCESS, file, 0, 0);
-  if (port == MACH_PORT_NULL)
-    return -1;
+      if (_hurd_id.rid_auth == MACH_PORT_NULL)
+	{
+	  /* Set up _hurd_id.rid_auth.  This is a special auth server port
+	     which uses the real uid and gid (the first aux uid and gid) as
+	     the only effective uid and gid.  */
+
+	  if (_hurd_id.aux.nuids < 1 || _hurd_id.aux.ngids < 1)
+	    {
+	      /* We do not have a real UID and GID.  Lose, lose, lose!  */
+	      err = EGRATUITOUS;
+	      goto lose;
+	    }
+
+	  /* Create a new auth port using our real UID and GID (the first
+	     auxiliary UID and GID) as the only effective IDs.  */
+	  if (err = __USEPORT (AUTH,
+			       __auth_makeauth (port,
+						NULL, MACH_MSG_TYPE_COPY_SEND, 0,
+						_hurd_id.aux.uids, 1,
+						_hurd_id.aux.uids,
+						_hurd_id.aux.nuids,
+						_hurd_id.aux.gids, 1,
+						_hurd_id.aux.gids,
+						_hurd_id.aux.ngids,
+						&_hurd_id.rid_auth)))
+	    goto lose;
+	}
+
+      if (!err)
+	/* Look up the file name using the modified init ports.  */
+	err = __hurd_file_name_lookup (&init_port, &__getdport, 0,
+				       file, hurd_flags, 0, &io);
+
+      /* We are done with _hurd_id.rid_auth now.  */
+     lose:
+      __mutex_unlock (&_hurd_id.lock);
+
+      HURD_CRITICAL_END;
+
+      if (rcrdir != MACH_PORT_NULL)
+	__mach_port_deallocate (__mach_task_self (), rcrdir);
+      if (rcwdir != MACH_PORT_NULL)
+	__mach_port_deallocate (__mach_task_self (), rcwdir);
+      if (err)
+	return errfunc (err);
+    }
 
   /* Find out what types of access we are allowed to this file.  */
-  err = __file_check_access (port, &allowed);
-  __mach_port_deallocate (__mach_task_self (), port);
+  err = __file_check_access (io, &allowed);
+  __mach_port_deallocate (__mach_task_self (), io);
   if (err)
-    return __hurd_fail (err);
+    return errfunc (err);
 
   flags = 0;
   if (type & R_OK)
@@ -59,7 +195,20 @@ faccessat (int fd, const char *file, int type, int flag)
 
   if (flags & ~allowed)
     /* We are not allowed all the requested types of access.  */
-    return __hurd_fail (EACCES);
+    return errfunc (EACCES);
 
   return 0;
 }
+
+int
+__faccessat_noerrno (int fd, const char *file, int type, int at_flags)
+{
+  return __faccessat_common (fd, file, type, at_flags, hurd_fail_noerrno);
+}
+
+int
+__faccessat (int fd, const char *file, int type, int at_flags)
+{
+  return __faccessat_common (fd, file, type, at_flags, hurd_fail_seterrno);
+}
+weak_alias (__faccessat, faccessat)
