fuse: prepare lookup for nfs export

Use d_splice_alias() instead of d_add() in fuse lookup code, to allow NFS
exporting.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fuse/dir.c

@@ -239,18 +239,20 @@ int fuse_valid_type(int m)
  * Add a directory inode to a dentry, ensuring that no other dentry
  * refers to this inode.  Called with fc->inst_mutex.
  */
-static int fuse_d_add_directory(struct dentry *entry, struct inode *inode)
+static struct dentry *fuse_d_add_directory(struct dentry *entry,
+					   struct inode *inode)
 {
 	struct dentry *alias = d_find_alias(inode);
-	if (alias) {
+	if (alias && !(alias->d_flags & DCACHE_DISCONNECTED)) {
 		/* This tries to shrink the subtree below alias */
 		fuse_invalidate_entry(alias);
 		dput(alias);
 		if (!list_empty(&inode->i_dentry))
-			return -EBUSY;
+			return ERR_PTR(-EBUSY);
+	} else {
+		dput(alias);
 	}
-	d_add(entry, inode);
-	return 0;
+	return d_splice_alias(inode, entry);
 }
 
 static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
@@ -259,6 +261,7 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
 	int err;
 	struct fuse_entry_out outarg;
 	struct inode *inode = NULL;
+	struct dentry *newent;
 	struct fuse_conn *fc = get_fuse_conn(dir);
 	struct fuse_req *req;
 	struct fuse_req *forget_req;
@@ -303,21 +306,22 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
 
 	if (inode && S_ISDIR(inode->i_mode)) {
 		mutex_lock(&fc->inst_mutex);
-		err = fuse_d_add_directory(entry, inode);
+		newent = fuse_d_add_directory(entry, inode);
 		mutex_unlock(&fc->inst_mutex);
-		if (err) {
+		if (IS_ERR(newent)) {
 			iput(inode);
-			return ERR_PTR(err);
+			return newent;
 		}
 	} else
-		d_add(entry, inode);
+		newent = d_splice_alias(inode, entry);
 
+	entry = newent ? newent : entry;
 	entry->d_op = &fuse_dentry_operations;
 	if (!err)
 		fuse_change_entry_timeout(entry, &outarg);
 	else
 		fuse_invalidate_entry_cache(entry);
-	return NULL;
+	return newent;
 }
 
 /*