From c6c770c33eb0f23e7e8e04976c711653cdf1a41d Mon Sep 17 00:00:00 2001
From: Jeremie Koenig <jk@jk.fr.eu.org>
Date: Thu, 19 Aug 2010 07:48:30 +0000
Subject: Implement lookup for . and ..

* procfs.c (procfs_lookup): Keep track of the parent directory,
  implement the lookup of the dot-directories.  (procfs_cleanup):
  Release the reference to the parent node, if applicable.
* procfs.h: Add a comment about the parent reference.
* netfs.c (netfs_attempt_lookup): Lock the looked up node after
  the directory has been unlocked, in case they are the same.
---
 netfs.c  |  3 ++-
 procfs.c | 26 ++++++++++++++++++++++++--
 procfs.h |  5 ++++-
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/netfs.c b/netfs.c
index 58665085..6b105f91 100644
--- a/netfs.c
+++ b/netfs.c
@@ -151,10 +151,11 @@ error_t netfs_attempt_lookup (struct iouser *user, struct node *dir,
   error_t err;
 
   err = procfs_lookup (dir, name, np);
+  mutex_unlock (&dir->lock);
+
   if (! err)
     mutex_lock (&(*np)->lock);
 
-  mutex_unlock (&dir->lock);
   return err;
 }
 
diff --git a/procfs.c b/procfs.c
index 573bb72f..c5f19497 100644
--- a/procfs.c
+++ b/procfs.c
@@ -14,6 +14,9 @@ struct netnode
   /* (cached) contents of the node */
   void *contents;
   size_t contents_len;
+
+  /* parent directory, if applicable */
+  struct node *parent;
 };
 
 void
@@ -97,8 +100,24 @@ error_t procfs_lookup (struct node *np, const char *name, struct node **npp)
 {
   error_t err = ENOENT;
 
-  if (np->nn->ops->lookup)
-    err = np->nn->ops->lookup (np->nn->hook, name, npp);
+  if (err && ! strcmp (name, "."))
+    {
+      netfs_nref(*npp = np);
+      err = 0;
+    }
+
+  if (err && np->nn->parent && ! strcmp (name, ".."))
+    {
+      netfs_nref(*npp = np->nn->parent);
+      err = 0;
+    }
+
+  if (err && np->nn->ops->lookup)
+    {
+      err = np->nn->ops->lookup (np->nn->hook, name, npp);
+      if (! err)
+	netfs_nref ((*npp)->nn->parent = np);
+    }
 
   return err;
 }
@@ -111,5 +130,8 @@ void procfs_cleanup (struct node *np)
   if (np->nn->ops->cleanup)
     np->nn->ops->cleanup (np->nn->hook);
 
+  if (np->nn->parent)
+    netfs_nrele (np->nn->parent);
+
   free (np->nn);
 }
diff --git a/procfs.h b/procfs.h
index b44db6e3..42eed0e2 100644
--- a/procfs.h
+++ b/procfs.h
@@ -22,7 +22,10 @@ struct procfs_node_ops
 
   /* Lookup NAME in this directory, and store the result in *np.  The
      returned node should be created by lookup() using procfs_make_node() 
-     or a derived function.  */
+     or a derived function.  Note that the parent will be kept alive as
+     long as the child exists, so you can safely reference the parent's
+     data from the child.  You may want to consider locking if there's
+     any mutation going on, though.  */
   error_t (*lookup) (void *hook, const char *name, struct node **np);
 
   /* Destroy this node.  */
-- 
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