[PATCH 2/3] Implement mountee startup.

[Sergiu Ivanov]

* mount.c (mountee_node): New variable.
(mountee_root): Likewise.
(mountee_started): Likewise.
(start_mountee): New function (based on node_set_translator
in nsmux).
(setup_unionmount): New function.
* mount.h (mountee_root): New variable.
(mountee_started): Likewise.
(start_mountee): New function.
(setup_unionmount): New function.
* netfs.c (netfs_validate_stat): Start the mountee at the
first invocation.
---

Hello,

On Sun, Nov 22, 2009 at 09:05:16PM +0100, olafBuddenhagen@gmx.net wrote:
> On Thu, Nov 19, 2009 at 10:28:37AM +0200, Sergiu Ivanov wrote:
> 
> > +  /* Fetch the effective UIDs of the unionfs process.  */
> > +  nuids = geteuids (0, 0);
> > +  if (nuids < 0)
> > +    return EPERM;
> > +  uids = alloca (nuids * sizeof (uid_t));
> > +
> > +  nuids = geteuids (nuids, uids);
> > +  assert (nuids > 0);
> 
> Hrmph, I didn't spot this before: I don't think the assert() is right --
> "nuids" (or "ngids") being exactly 0, is probably a perfectly valid
> case... And even if it is not, the test in the assert should be
> equivalent to the EPERM test above, to avoid confusion.

OK, changed.
 
> > +  /* The mountee will be sitting on this node.  This node is based on
> > +     the netnode of the root node (it is essentially a clone of the
> > +     root node), so that unionfs appears as the underlying translator
> > +     to the mountee.  Note the we cannot set the mountee on the root
> > +     node directly, because in this case the mountee's filesystem will
> > +     obscure the filesystem published by unionfs.  */
> 
> Grammar nitpick: it should be "*would* obscure" :-)
> 
> (It don't think it hampers understanding though, so I can't say that I
> really care... Just a hint for you :-) )

Changed :-) Thank you for the hint :-)

Regards,
scolobb

---
 mount.c |  144 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 mount.h |   17 +++++++
 netfs.c |    7 +++
 3 files changed, 168 insertions(+), 0 deletions(-)

diff --git a/mount.c b/mount.c
index 7bc1fb8..72c720d 100644
--- a/mount.c
+++ b/mount.c
@@ -22,8 +22,152 @@
 
 #define _GNU_SOURCE
 
+#include <hurd/fsys.h>
+#include <fcntl.h>
+
 #include "mount.h"
+#include "lib.h"
 
 /* The command line for starting the mountee.  */
 char * mountee_argz;
 size_t mountee_argz_len;
+
+/* The node the mountee is sitting on.  */
+node_t * mountee_node;
+
+mach_port_t mountee_root;
+
+int mountee_started = 0;
+
+/* Starts the mountee (given by `argz` and `argz_len`), attaches it to
+   the node `np` and opens a port `port` to the mountee.  */
+error_t
+start_mountee (node_t * np, char * argz, size_t argz_len, mach_port_t * port)
+{
+  error_t err;
+  mach_port_t underlying_port;
+
+  mach_port_t mountee_control;
+
+  /* Identity information about the unionfs process (for
+     fsys_getroot).  */
+  uid_t * uids;
+  size_t nuids;
+
+  gid_t * gids;
+  size_t ngids;
+
+  /* The retry information returned by fsys_getroot.  */
+  string_t retry_name;
+  mach_port_t retry_port;
+
+  /* Fetch the effective UIDs of the unionfs process.  */
+  nuids = geteuids (0, 0);
+  if (nuids < 0)
+    return EPERM;
+  uids = alloca (nuids * sizeof (uid_t));
+
+  nuids = geteuids (nuids, uids);
+  if (nuids < 0)
+    return EPERM;
+
+  /* Fetch the effective GIDs of the unionfs process.  */
+  ngids = getgroups (0, 0);
+  if (ngids < 0)
+    return EPERM;
+  gids = alloca (ngids * sizeof (gid_t));
+
+  ngids = getgroups (ngids, gids);
+  if (ngids < 0)
+    return EPERM;
+
+  /* Opens the port on which to set the mountee.  */
+  error_t open_port (int flags, mach_port_t * underlying,
+                    mach_msg_type_name_t * underlying_type, task_t task,
+                    void *cookie)
+  {
+    err = 0;
+
+    /* The protid which will contain the port to the node on which the
+       mountee will be sitting.  */
+    struct protid * newpi;
+
+    struct iouser * unionfs_user;
+
+    /* Initialize `unionfs_user` with the effective UIDs and GIDs of
+       the unionfs process.  */
+    err = iohelp_create_complex_iouser (&unionfs_user, uids, nuids, gids, 
ngids);
+    if (err)
+      return err;
+
+    /* Create a port to node on which the mountee should sit (np).  */
+    newpi = netfs_make_protid
+      (netfs_make_peropen (np, flags, NULL), unionfs_user);
+    if (!newpi)
+      {
+       iohelp_free_iouser (unionfs_user);
+       return errno;
+      }
+
+    *underlying = underlying_port = ports_get_send_right (newpi);
+    *underlying_type = MACH_MSG_TYPE_COPY_SEND;
+
+    ports_port_deref (newpi);
+
+    return err;
+  }                            /*open_port */
+
+  /* Start the translator.  The value 60000 for the timeout is the one
+     found in settrans.  */
+  err = fshelp_start_translator (open_port, NULL, argz, argz, argz_len,
+                                60000, &mountee_control);
+  if (err)
+    return err;
+
+  /* Attach the mountee to the port opened in the previous call.  */
+  err = file_set_translator (underlying_port, 0, FS_TRANS_SET, 0, argz,
+                            argz_len, mountee_control, 
MACH_MSG_TYPE_COPY_SEND);
+  port_dealloc (underlying_port);
+  if (err)
+    return err;
+
+  /* Obtain the port to the root of the newly-set translator.
+
+     Note that the O_READ flag does not actually limit access to the
+     mountee's filesystem considerably.  Whenever a client looks up a
+     node which is not a directory, unionfs will give off a port to
+     the node itself, withouth proxying it.  Proxying happens only for
+     directory nodes.  */
+  err = fsys_getroot (mountee_control, MACH_PORT_NULL, MACH_MSG_TYPE_COPY_SEND,
+                     uids, nuids, gids, ngids, O_READ, &retry_port,
+                     retry_name, port);
+  return err;
+}                              /* start_mountee */
+
+/* Sets up a proxy node and sets the translator on it.  */
+error_t
+setup_unionmount (void)
+{
+  error_t err = 0;
+
+  /* The mountee will be sitting on this node.  This node is based on
+     the netnode of the root node (it is essentially a clone of the
+     root node), so that unionfs appears as the underlying translator
+     to the mountee.  Note the we cannot set the mountee on the root
+     node directly, because in this case the mountee's filesystem
+     would obscure the filesystem published by unionfs.  */
+  mountee_node = netfs_make_node (netfs_root_node->nn);
+  if (!mountee_node)
+    return ENOMEM;
+
+  /* Set the mountee on the new node.  */
+  err = start_mountee (mountee_node, mountee_argz, mountee_argz_len,
+                      &mountee_root);
+  if (err)
+    return err;
+
+  mountee_started = 1;
+
+  return 0;
+}                              /* setup_unionmount */
+
diff --git a/mount.h b/mount.h
index a7dd933..fd265f0 100644
--- a/mount.h
+++ b/mount.h
@@ -23,10 +23,27 @@
 #ifndef INCLUDED_MOUNT_H
 #define INCLUDED_MOUNT_H
 
+#include <error.h>
 #include <unistd.h>
+#include <hurd/hurd_types.h>
+
+#include "node.h"
 
 /* The command line for starting the mountee.  */
 extern char * mountee_argz;
 extern size_t mountee_argz_len;
 
+extern mach_port_t mountee_root;
+
+extern int mountee_started;
+
+/* Starts the mountee (given by `argz` and `argz_len`), attaches it to
+   the node `np` and opens a port `port` to the mountee.  */
+error_t
+start_mountee (node_t * np, char * argz, size_t argz_len, mach_port_t * port);
+
+/* Sets up a proxy node and sets the translator on it.  */
+error_t
+setup_unionmount (void);
+
 #endif /* not INCLUDED_MOUNT_H */
diff --git a/netfs.c b/netfs.c
index 3c23261..b9ea585 100644
--- a/netfs.c
+++ b/netfs.c
@@ -195,6 +195,13 @@ netfs_validate_stat (struct node *np, struct iouser *cred)
     }
   else 
     {
+      if (!mountee_started)
+       {
+         err = setup_unionmount ();
+         if (err)
+           error (EXIT_FAILURE, err, "failed to set up the mountee");
+       }
+
       _get_node_size (np, &np->nn_stat.st_size); 
     }
 
-- 
1.6.5.3