trans: add identity translator

The 'identity' translator is the simplest possible translator.  It
computes the identity function of Hurdish RPC translations.

* trans/Makefile: Add new files.
* trans/chroot.c: New file.
* trans/chroot.h: Likewise.
* trans/identity.c: Likewise.

4 files changed, 875 insertions, 3 deletions

diff --git a/trans/Makefile b/trans/Makefile
index 65b51d12..e4eba0ab 100644
--- a/trans/Makefile
+++ b/trans/Makefile
@@ -21,10 +21,10 @@ makemode := servers
 
 targets = symlink firmlink ifsock magic null fifo new-fifo fwd crash \
 	  password hello hello-mt streamio fakeroot proxy-defpager remap \
-	  mtab
+	  mtab identity
 SRCS = ifsock.c symlink.c magic.c null.c fifo.c new-fifo.c fwd.c \
 	crash.c firmlink.c password.c hello.c hello-mt.c streamio.c \
-	fakeroot.c proxy-defpager.c remap.c mtab.c
+	fakeroot.c proxy-defpager.c remap.c mtab.c chroot.c identity.c
 OBJS = $(SRCS:.c=.o) fsysServer.o ifsockServer.o passwordServer.o \
 	crashServer.o crash_replyUser.o msgServer.o \
 	default_pagerServer.o default_pagerUser.o \
@@ -65,7 +65,8 @@ proxy-defpager: default_pagerServer.o default_pagerUser.o
 streamio: device_replyServer.o
 symlink: fsysServer.o
 
-fakeroot: ../libnetfs/libnetfs.a
+identity: chroot.o
+fakeroot identity: ../libnetfs/libnetfs.a
 fifo new-fifo: ../libpipe/libpipe.a
 crash fifo firmlink hello hello-mt ifsock magic mtab new-fifo null password proxy-defpager remap streamio: ../libtrivfs/libtrivfs.a
 $(targets): ../libfshelp/libfshelp.a \
diff --git a/trans/chroot.c b/trans/chroot.c
new file mode 100644
index 00000000..0055d6c9
--- /dev/null
+++ b/trans/chroot.c
@@ -0,0 +1,724 @@
+/* chroot.c -- support for writing chrooting translators
+   Copyright (C) 2002, 2003, 2008, 2013, 2016 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+#include <argz.h>
+#include <argp.h>
+#include <dirent.h>
+#include <error.h>
+#include <hurd/netfs.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <pthread.h>
+#include <hurd/ihash.h>
+#include <hurd/paths.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <version.h>
+
+#include "chroot.h"
+
+#include "libnetfs/fs_S.h"
+#include "libnetfs/io_S.h"
+#include "libnetfs/fsys_S.h"
+#include "libports/notify_S.h"
+#include "libports/interrupt_S.h"
+
+/* Make a new virtual node.  Always consumes the ports.  If
+   successful, NP will be locked.  */
+error_t __attribute__ ((weak))
+chroot_new_node (file_t file, size_t size, struct node **np)
+{
+  error_t err;
+  struct netnode *nn;
+
+  *np = netfs_make_node_alloc (sizeof *nn + size);
+  if (*np == NULL)
+    {
+      mach_port_deallocate (mach_task_self (), file);
+      return ENOMEM;
+    }
+  nn = netfs_node_netnode (*np);
+  nn->file = file;
+  return 0;
+}
+
+/* Node NP has no more references; free all its associated storage. */
+void
+netfs_node_norefs (struct node *np)
+{
+  pthread_mutex_unlock (&np->lock);
+
+  chroot_node_norefs (np);
+  mach_port_deallocate (mach_task_self (), netfs_node_netnode (np)->file);
+  free (np);
+}
+
+/* This is the cleanup function we install in netfs_protid_class.  If
+   the associated nodes reference count would also drop to zero, and
+   the node has no faked attributes, we destroy it as well.  */
+static void
+chroot_netfs_release_protid (void *cookie)
+{
+  netfs_release_protid (cookie);
+
+  int cports = ports_count_class (netfs_control_class);
+  int nports = ports_count_class (netfs_protid_class);
+  ports_enable_class (netfs_control_class);
+  ports_enable_class (netfs_protid_class);
+  if (cports == 0 && nports == 0)
+    {
+      /* The last client is gone.  Our job is done.  */
+      error_t err = netfs_shutdown (0);
+      if (! err)
+        exit (EXIT_SUCCESS);
+
+      /* If netfs_shutdown returns EBUSY, we lost a race against
+         fsys_goaway.  Hence we ignore this error.  */
+      if (err != EBUSY)
+        error (1, err, "netfs_shutdown");
+    }
+}
+
+error_t __attribute__ ((weak))
+chroot_init (void)
+{
+  /* Install our own clean routine.  */
+  netfs_protid_class->clean_routine = chroot_netfs_release_protid;
+  return 0;
+}
+
+/* This is called by netfs_S_fsys_getroot.  */
+error_t __attribute__ ((weak))
+netfs_check_open_permissions (struct iouser *user, struct node *np,
+			      int flags, int newnode)
+{
+  return 0;	/* XXX */
+}
+
+error_t __attribute__ ((weak))
+netfs_S_dir_lookup (struct protid *diruser,
+		    char *filename,
+		    int flags,
+		    mode_t mode,
+		    retry_type *do_retry,
+		    char *retry_name,
+		    mach_port_t *retry_port,
+		    mach_msg_type_name_t *retry_port_type)
+{
+  struct node *dnp, *np;
+  error_t err;
+  struct protid *newpi;
+  struct iouser *user;
+  file_t file;
+  file_t dir;
+
+  if (!diruser)
+    return EOPNOTSUPP;
+
+  dnp = diruser->po->np;
+
+  //error (0, 0, "dir_lookup (#uids: %d, %s, flags %x, ...)", diruser->user->uids->num, filename, flags);
+
+  dir = netfs_node_netnode (dnp)->file;
+  err = dir_lookup (dir, filename, flags, mode, do_retry, retry_name, &file);
+  if (err)
+    return err;
+
+  switch (*do_retry)
+    {
+    case FS_RETRY_NORMAL:
+      break;
+
+    case FS_RETRY_REAUTH:
+      /* Fallthrough.  */
+
+    case FS_RETRY_MAGICAL:
+      *retry_port = file;
+      *retry_port_type = MACH_MSG_TYPE_MOVE_SEND;
+      return 0;
+
+    default:
+      /* Invalid response to our dir_lookup request.  */
+      if (MACH_PORT_VALID (file))
+	mach_port_deallocate (mach_task_self (), file);
+      *retry_port = MACH_PORT_NULL;
+      *retry_port_type = MACH_MSG_TYPE_COPY_SEND;
+      return EOPNOTSUPP;
+    }
+
+  /* We have a new port to an underlying node.
+     Find or make our corresponding virtual node.  */
+
+  np = 0;
+
+  err = chroot_new_node (file, 0, &np);
+  if (!err)
+    err = netfs_validate_stat (np, diruser->user);
+  if (err)
+    goto lose;
+
+  assert (*do_retry == FS_RETRY_NORMAL);
+  flags &= ~(O_CREAT|O_EXCL|O_NOLINK|O_NOTRANS|O_NONBLOCK);
+
+  err = iohelp_dup_iouser (&user, diruser->user);
+  if (!err)
+    {
+      newpi = netfs_make_protid (netfs_make_peropen (np, flags, diruser->po),
+				 user);
+      if (! newpi)
+	{
+	  iohelp_free_iouser (user);
+	  err = errno;
+	}
+      else
+	{
+	  *retry_port = ports_get_right (newpi);
+	  *retry_port_type = MACH_MSG_TYPE_MAKE_SEND;
+	  ports_port_deref (newpi);
+	}
+    }
+
+ lose:
+  if (dir != netfs_node_netnode (dnp)->file)
+    mach_port_deallocate (mach_task_self (), dir);
+  if (np != NULL)
+    netfs_nput (np);
+  return err;
+}
+
+/* The user may define this function.  Attempt to set the passive
+   translator record for FILE to ARGZ (of length ARGZLEN) for user
+   CRED. */
+error_t __attribute__ ((weak))
+netfs_set_translator (struct iouser *cred, struct node *np,
+		      char *argz, size_t argzlen)
+{
+  return file_set_translator (netfs_node_netnode (np)->file,
+			      FS_TRANS_EXCL|FS_TRANS_SET,
+			      0, 0,
+			      argz, argzlen,
+			      MACH_PORT_NULL, MACH_MSG_TYPE_COPY_SEND);
+}
+
+/* These callbacks are used only by the standard netfs_S_dir_lookup,
+   which we do not use.  But the shared library requires us to define them.  */
+error_t __attribute__ ((weak))
+netfs_attempt_lookup (struct iouser *user, struct node *dir,
+		      char *name, struct node **np)
+{
+  assert (! "should not be here");
+  return EIEIO;
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_create_file (struct iouser *user, struct node *dir,
+			   char *name, mode_t mode, struct node **np)
+{
+  assert (! "should not be here");
+  return EIEIO;
+}
+
+/* Make sure that NP->nn_stat is filled with the most current information.
+   CRED identifies the user responsible for the operation. NP is locked.  */
+error_t __attribute__ ((weak))
+netfs_validate_stat (struct node *np, struct iouser *cred)
+{
+  struct stat st;
+  error_t err = io_stat (netfs_node_netnode (np)->file, &st);
+  if (err)
+    return err;
+
+  np->nn_stat = st;
+  /* XXX */
+  np->nn_translated = S_ISLNK (st.st_mode) ? S_IFLNK : 0;
+
+  return 0;
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_chown (struct iouser *cred, struct node *np,
+		     uid_t uid, uid_t gid)
+{
+  if (! cred)
+    return EOPNOTSUPP;
+  return file_chown (netfs_node_netnode (np)->file, uid, gid);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_chauthor (struct iouser *cred, struct node *np, uid_t author)
+{
+  if (! cred)
+    return EOPNOTSUPP;
+  return file_chauthor (netfs_node_netnode (np)->file, author);
+}
+
+/* This should attempt a chmod call for the user specified by CRED on
+   locked node NODE, to change the mode to MODE.  Unlike the normal Unix
+   and Hurd meaning of chmod, this function is also used to attempt to
+   change files into other types.  If such a transition is attempted which
+   is impossible, then return EOPNOTSUPP.  */
+error_t __attribute__ ((weak))
+netfs_attempt_chmod (struct iouser *cred, struct node *np, mode_t mode)
+{
+  if (! cred)
+    return EOPNOTSUPP;
+  return file_chmod (netfs_node_netnode (np)->file, mode);
+}
+
+/* The user must define this function.  Attempt to turn locked node NP
+   (user CRED) into a symlink with target NAME.  */
+error_t __attribute__ ((weak))
+netfs_attempt_mksymlink (struct iouser *cred, struct node *np, char *name)
+{
+  int namelen = strlen (name) + 1;
+  char trans[sizeof _HURD_SYMLINK + namelen];
+  memcpy (trans, _HURD_SYMLINK, sizeof _HURD_SYMLINK);
+  memcpy (&trans[sizeof _HURD_SYMLINK], name, namelen);
+  return file_set_translator (netfs_node_netnode (np)->file,
+			      FS_TRANS_EXCL|FS_TRANS_SET,
+			      FS_TRANS_EXCL|FS_TRANS_SET, 0,
+			      trans, sizeof trans,
+			      MACH_PORT_NULL, MACH_MSG_TYPE_COPY_SEND);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_mkdev (struct iouser *cred, struct node *np,
+		     mode_t type, dev_t indexes)
+{
+  char *trans = 0;
+  int translen = asprintf (&trans, "%s%c%d%c%d",
+			   S_ISCHR (type) ? _HURD_CHRDEV : _HURD_BLKDEV,
+			   '\0', major (indexes), '\0', minor (indexes));
+  if (trans == 0)
+    return ENOMEM;
+  else
+    {
+      error_t err = file_set_translator (netfs_node_netnode (np)->file,
+					 FS_TRANS_EXCL|FS_TRANS_SET,
+					 FS_TRANS_EXCL|FS_TRANS_SET, 0,
+					 trans, translen + 1,
+					 MACH_PORT_NULL,
+					 MACH_MSG_TYPE_COPY_SEND);
+      free (trans);
+      return err;
+    }
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_chflags (struct iouser *cred, struct node *np, int flags)
+{
+  return file_chflags (netfs_node_netnode (np)->file, flags);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_utimes (struct iouser *cred, struct node *np,
+		      struct timespec *atime, struct timespec *mtime)
+{
+  union tv
+  {
+    struct timeval tv;
+    time_value_t tvt;
+  };
+  union tv a, m;
+  if (atime)
+    {
+      TIMESPEC_TO_TIMEVAL (&a.tv, atime);
+    }
+  else
+    a.tv.tv_sec = a.tv.tv_usec = -1;
+  if (mtime)
+    {
+      TIMESPEC_TO_TIMEVAL (&m.tv, mtime);
+    }
+  else
+    m.tv.tv_sec = m.tv.tv_usec = -1;
+
+  return file_utimes (netfs_node_netnode (np)->file, a.tvt, m.tvt);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_set_size (struct iouser *cred, struct node *np, off_t size)
+{
+  return file_set_size (netfs_node_netnode (np)->file, size);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_statfs (struct iouser *cred, struct node *np, struct statfs *st)
+{
+  return file_statfs (netfs_node_netnode (np)->file, st);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_sync (struct iouser *cred, struct node *np, int wait)
+{
+  return file_sync (netfs_node_netnode (np)->file, wait, 0);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_syncfs (struct iouser *cred, int wait)
+{
+  return 0;
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_mkdir (struct iouser *user, struct node *dir,
+		     char *name, mode_t mode)
+{
+  return dir_mkdir (netfs_node_netnode (dir)->file, name, mode | S_IRWXU);
+}
+
+
+/* XXX
+   Removing a node should mark the netnode so that it is GC'd when
+   it has no hard refs.
+ */
+
+error_t __attribute__ ((weak))
+netfs_attempt_unlink (struct iouser *user, struct node *dir, char *name)
+{
+  return dir_unlink (netfs_node_netnode (dir)->file, name);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_rename (struct iouser *user, struct node *fromdir,
+		      char *fromname, struct node *todir,
+		      char *toname, int excl)
+{
+  return dir_rename (netfs_node_netnode (fromdir)->file, fromname,
+		     netfs_node_netnode (todir)->file, toname, excl);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_rmdir (struct iouser *user,
+		     struct node *dir, char *name)
+{
+  return dir_rmdir (netfs_node_netnode (dir)->file, name);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_link (struct iouser *user, struct node *dir,
+		    struct node *file, char *name, int excl)
+{
+  return dir_link (netfs_node_netnode (dir)->file,
+                   netfs_node_netnode (file)->file, name, excl);
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_mkfile (struct iouser *user, struct node *dir,
+		      mode_t mode, struct node **np)
+{
+  file_t newfile;
+  error_t err = dir_mkfile (netfs_node_netnode (dir)->file, O_RDWR|O_EXEC,
+			    mode, &newfile);
+  pthread_mutex_unlock (&dir->lock);
+  if (err)
+    return err;
+
+  err = chroot_new_node (newfile, 0, np);
+  if (err)
+    return err;
+
+  pthread_mutex_unlock (&(*np)->lock);
+  return err;
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_readlink (struct iouser *user, struct node *np, char *buf)
+{
+  char transbuf[sizeof _HURD_SYMLINK + np->nn_stat.st_size + 1];
+  char *trans = transbuf;
+  size_t translen = sizeof transbuf;
+  error_t err = file_get_translator (netfs_node_netnode (np)->file,
+				     &trans, &translen);
+  if (err == 0)
+    {
+      if (translen < sizeof _HURD_SYMLINK
+	  || memcmp (trans, _HURD_SYMLINK, sizeof _HURD_SYMLINK) != 0)
+	err = EINVAL;
+      else
+	{
+	  assert (translen <= sizeof _HURD_SYMLINK + np->nn_stat.st_size + 1);
+	  memcpy (buf, &trans[sizeof _HURD_SYMLINK],
+		  translen - sizeof _HURD_SYMLINK);
+	}
+      if (trans != transbuf)
+	munmap (trans, translen);
+    }
+  return err;
+}
+
+error_t __attribute__ ((weak))
+netfs_get_dirents (struct iouser *cred, struct node *dir,
+		   int entry, int nentries, char **data,
+		   mach_msg_type_number_t *datacnt,
+		   vm_size_t bufsize, int *amt)
+{
+  error_t err;
+  err = dir_readdir (netfs_node_netnode (dir)->file, data, datacnt,
+                     entry, nentries, bufsize, amt);
+  return err;
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_read (struct iouser *cred, struct node *np,
+		    off_t offset, size_t *len, void *data)
+{
+  char *buf = data;
+  error_t err = io_read (netfs_node_netnode (np)->file,
+			 &buf, len, offset, *len);
+  if (err == 0 && buf != data)
+    {
+      memcpy (data, buf, *len);
+      munmap (buf, *len);
+    }
+  return err;
+}
+
+error_t __attribute__ ((weak))
+netfs_attempt_write (struct iouser *cred, struct node *np,
+		     off_t offset, size_t *len, void *data)
+{
+  return io_write (netfs_node_netnode (np)->file, data, *len, offset, len);
+}
+
+error_t __attribute__ ((weak))
+netfs_report_access (struct iouser *cred, struct node *np, int *types)
+{
+  return file_check_access (netfs_node_netnode (np)->file, types);
+}
+
+error_t __attribute__ ((weak))
+netfs_file_get_storage_info (struct iouser *cred,
+			     struct node *np,
+			     mach_port_t **ports,
+			     mach_msg_type_name_t *ports_type,
+			     mach_msg_type_number_t *num_ports,
+			     int **ints,
+			     mach_msg_type_number_t *num_ints,
+			     off_t **offsets,
+			     mach_msg_type_number_t *num_offsets,
+			     char **data,
+			     mach_msg_type_number_t *data_len)
+{
+  *ports_type = MACH_MSG_TYPE_MOVE_SEND;
+  return file_get_storage_info (netfs_node_netnode (np)->file,
+				ports, num_ports,
+				ints, num_ints,
+				offsets, num_offsets,
+				data, data_len);
+}
+
+error_t __attribute__ ((weak))
+netfs_S_file_exec (struct protid *user,
+                   task_t task,
+                   int flags,
+                   char *argv,
+                   size_t argvlen,
+                   char *envp,
+                   size_t envplen,
+                   mach_port_t *fds,
+                   size_t fdslen,
+                   mach_port_t *portarray,
+                   size_t portarraylen,
+                   int *intarray,
+                   size_t intarraylen,
+                   mach_port_t *deallocnames,
+                   size_t deallocnameslen,
+                   mach_port_t *destroynames,
+                   size_t destroynameslen)
+{
+  error_t err;
+  file_t file;
+
+  if (!user)
+    return EOPNOTSUPP;
+
+  file = netfs_node_netnode (user->po->np)->file;
+  err = mach_port_mod_refs (mach_task_self (),
+                            file, MACH_PORT_RIGHT_SEND, 1);
+
+  if (!err)
+    {
+      /* We cannot use MACH_MSG_TYPE_MOVE_SEND because we might need to
+	 retry an interrupted call that would have consumed the rights.  */
+      err = file_exec (file, task, flags, argv, argvlen,
+		       envp, envplen, fds, MACH_MSG_TYPE_COPY_SEND, fdslen,
+		       portarray, MACH_MSG_TYPE_COPY_SEND, portarraylen,
+		       intarray, intarraylen, deallocnames, deallocnameslen,
+		       destroynames, destroynameslen);
+      mach_port_deallocate (mach_task_self (), file);
+    }
+
+  if (err == 0)
+    {
+      size_t i;
+      mach_port_deallocate (mach_task_self (), task);
+      for (i = 0; i < fdslen; ++i)
+	mach_port_deallocate (mach_task_self (), fds[i]);
+      for (i = 0; i < portarraylen; ++i)
+	mach_port_deallocate (mach_task_self (), portarray[i]);
+    }
+  return err;
+}
+
+error_t __attribute__ ((weak))
+netfs_S_io_map (struct protid *user,
+		mach_port_t *rdobj, mach_msg_type_name_t *rdobjtype,
+		mach_port_t *wrobj, mach_msg_type_name_t *wrobjtype)
+{
+  if (!user)
+    return EOPNOTSUPP;
+  *rdobjtype = *wrobjtype = MACH_MSG_TYPE_MOVE_SEND;
+
+  return io_map (netfs_node_netnode (user->po->np)->file, rdobj, wrobj);
+}
+
+error_t __attribute__ ((weak))
+netfs_S_io_map_cntl (struct protid *user,
+                     mach_port_t *obj,
+                     mach_msg_type_name_t *objtype)
+{
+  if (!user)
+    return EOPNOTSUPP;
+  *objtype = MACH_MSG_TYPE_MOVE_SEND;
+
+  return io_map_cntl (netfs_node_netnode (user->po->np)->file, obj);
+}
+
+error_t __attribute__ ((weak))
+netfs_S_io_identity (struct protid *user,
+		     mach_port_t *id,
+		     mach_msg_type_name_t *idtype,
+		     mach_port_t *fsys,
+		     mach_msg_type_name_t *fsystype,
+		     ino_t *fileno)
+{
+  if (!user)
+    return EOPNOTSUPP;
+
+  *idtype = *fsystype = MACH_MSG_TYPE_MOVE_SEND;
+
+  return io_identity (netfs_node_netnode (user->po->np)->file,
+                      id, fsys, fileno);
+}
+
+#define NETFS_S_SIMPLE(name)			\
+error_t	 __attribute__ ((weak))			\
+netfs_S_##name (struct protid *user)		\
+{						\
+  if (!user)					\
+    return EOPNOTSUPP;				\
+						\
+  return name (netfs_node_netnode (user->po->np)->file);		\
+}
+
+NETFS_S_SIMPLE (io_get_conch)
+NETFS_S_SIMPLE (io_release_conch)
+NETFS_S_SIMPLE (io_eofnotify)
+NETFS_S_SIMPLE (io_readnotify)
+NETFS_S_SIMPLE (io_readsleep)
+NETFS_S_SIMPLE (io_sigio)
+
+error_t __attribute__ ((weak))
+netfs_S_io_prenotify (struct protid *user,
+                      vm_offset_t start, vm_offset_t stop)
+{
+  if (!user)
+    return EOPNOTSUPP;
+
+  return io_prenotify (netfs_node_netnode (user->po->np)->file, start, stop);
+}
+
+error_t __attribute__ ((weak))
+netfs_S_io_postnotify (struct protid *user,
+                       vm_offset_t start, vm_offset_t stop)
+{
+  if (!user)
+    return EOPNOTSUPP;
+
+  return io_postnotify (netfs_node_netnode (user->po->np)->file, start, stop);
+}
+
+/* This overrides the library's definition.  */
+int __attribute__ ((weak))
+netfs_demuxer (mach_msg_header_t *inp,
+	       mach_msg_header_t *outp)
+{
+  mig_routine_t routine;
+  if ((routine = netfs_io_server_routine (inp)) ||
+      (routine = netfs_fs_server_routine (inp)) ||
+      (routine = ports_notify_server_routine (inp)) ||
+      (routine = netfs_fsys_server_routine (inp)) ||
+      /* XXX we should intercept interrupt_operation and do
+	 the ports_S_interrupt_operation work as well as
+	 sending an interrupt_operation to the underlying file.
+       */
+      (routine = ports_interrupt_server_routine (inp)))
+    {
+      (*routine) (inp, outp);
+      return TRUE;
+    }
+  else
+    {
+      /* We didn't recognize the message ID, so pass the message through
+	 unchanged to the underlying file.  */
+      struct protid *cred;
+      if (MACH_MSGH_BITS_LOCAL (inp->msgh_bits) ==
+	  MACH_MSG_TYPE_PROTECTED_PAYLOAD)
+	cred = ports_lookup_payload (netfs_port_bucket,
+				     inp->msgh_protected_payload,
+				     netfs_protid_class);
+      else
+	cred = ports_lookup_port (netfs_port_bucket,
+				  inp->msgh_local_port,
+				  netfs_protid_class);
+      if (cred == 0)
+	/* This must be an unknown message on our fsys control port.  */
+	return 0;
+      else
+	{
+	  error_t err;
+	  assert (MACH_MSGH_BITS_LOCAL (inp->msgh_bits)
+		  == MACH_MSG_TYPE_MOVE_SEND
+		  || MACH_MSGH_BITS_LOCAL (inp->msgh_bits)
+		  == MACH_MSG_TYPE_PROTECTED_PAYLOAD);
+	  inp->msgh_bits = (inp->msgh_bits & MACH_MSGH_BITS_COMPLEX)
+	    | MACH_MSGH_BITS (MACH_MSG_TYPE_COPY_SEND,
+			      MACH_MSGH_BITS_REMOTE (inp->msgh_bits));
+	  inp->msgh_local_port = inp->msgh_remote_port;	/* reply port */
+	  inp->msgh_remote_port = netfs_node_netnode (cred->po->np)->file;
+	  err = mach_msg (inp, MACH_SEND_MSG, inp->msgh_size, 0,
+			  MACH_PORT_NULL, MACH_MSG_TIMEOUT_NONE,
+			  MACH_PORT_NULL);
+	  if (err)
+	    ((mig_reply_header_t *) outp)->RetCode = err;
+	  else
+	    /* We already sent the message, so the server loop
+	       shouldn't do it again.  */
+	    ((mig_reply_header_t *) outp)->RetCode = MIG_NO_REPLY;
+	  ports_port_deref (cred);
+	  return 1;
+	}
+    }
+}
diff --git a/trans/chroot.h b/trans/chroot.h
new file mode 100644
index 00000000..057a251f
--- /dev/null
+++ b/trans/chroot.h
@@ -0,0 +1,34 @@
+#ifndef __HURD_CHROOT_H__
+#define __HURD_CHROOT_H__
+
+struct netnode
+{
+  file_t file;			/* port on real file */
+};
+
+struct chroot_node;
+
+error_t chroot_init (void);
+
+/* Make a new virtual node.  Always consumes the ports.  If
+   successful, NP will be locked.  */
+error_t chroot_new_node (file_t file, size_t size, struct node **np);
+
+/* Users must implement this.  */
+void chroot_node_norefs (struct node *np);
+
+/* Return the address of the chroot_node for NODE.  NODE must have been
+   allocated using chroot_new_node.  */
+static inline struct chroot_node *
+chroot_node (struct node *node)
+{
+  return (struct chroot_node *) ((char *) netfs_node_netnode (node)
+				 + sizeof (struct netnode));
+}
+
+// XXX
+pthread_mutex_t idport_ihash_lock;
+struct hurd_ihash idport_ihash;
+
+
+#endif /* __HURD_CHROOT_H__ */
diff --git a/trans/identity.c b/trans/identity.c
new file mode 100644
index 00000000..875fc4f3
--- /dev/null
+++ b/trans/identity.c
@@ -0,0 +1,113 @@
+/* identity -- a translator interposing file RPCs.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+#include <argp.h>
+#include <error.h>
+#include <fcntl.h>
+#include <hurd/netfs.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <version.h>
+
+#include "chroot.h"
+
+const char *argp_program_version = STANDARD_HURD_VERSION (identity);
+
+char *netfs_server_name = "identity";
+char *netfs_server_version = HURD_VERSION;
+int netfs_maxsymlinks = 16;	/* arbitrary */
+
+struct chroot_node
+{
+};
+
+void
+chroot_node_norefs (struct node *np)
+{
+}
+
+
+static struct argp_option options[] =
+{
+  {0}
+};
+
+static char *args_doc = "";
+static char *doc =
+  "The identity translator relays file RPCs without changing them."
+  "\v"
+  "It can be used in conjunction with settrans --chroot to implement "
+  "a hurdish chroot utility.";
+
+static error_t
+parse_opt (int key, char *arg, struct argp_state *state)
+{
+  switch (key)
+    {
+    default:
+      return ARGP_ERR_UNKNOWN;
+    }
+  return 0;
+}
+
+int
+main (int argc, char **argv)
+{
+  error_t err;
+  mach_port_t bootstrap;
+
+  struct argp argp =
+    {
+      .options = options,
+      .parser = parse_opt,
+      .args_doc = args_doc,
+      .doc = doc,
+    };
+
+  /* Parse our command line arguments (all none of them).  */
+  argp_parse (&argp, argc, argv, 0, 0, 0);
+
+  task_get_bootstrap_port (mach_task_self (), &bootstrap);
+  if (! MACH_PORT_VALID (bootstrap))
+    error (1, 0, "Must be started as a translator");
+
+  netfs_init ();
+  chroot_init ();
+
+  /* Get our underlying node (we presume it's a directory) and use
+     that to make the root node of the filesystem.  */
+  err = chroot_new_node (netfs_startup (bootstrap, O_READ),
+                         sizeof (struct chroot_node), &netfs_root_node);
+  if (err)
+    error (5, err, "Cannot create root node");
+
+  err = netfs_validate_stat (netfs_root_node, 0);
+  if (err)
+    error (6, err, "Cannot stat underlying node");
+
+  netfs_root_node->nn_stat.st_mode &= ~(S_IPTRANS | S_IATRANS);
+  netfs_root_node->nn_stat.st_mode |= S_IROOT;
+  pthread_mutex_unlock (&netfs_root_node->lock);
+
+  netfs_server_loop ();		/* Never returns.  */
+
+  /*NOTREACHED*/
+  return 0;
+}