[AFS]: Add "directory write" support.

Add support for the create, link, symlink, unlink, mkdir, rmdir and
rename VFS operations to the in-kernel AFS filesystem.

Also:

 (1) Fix dentry and inode revalidation.  d_revalidate should only look at
     state of the dentry.  Revalidation of the contents of an inode pointed to
     by a dentry is now separate.

 (2) Fix afs_lookup() to hash negative dentries as well as positive ones.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/afs/file.c

@@ -50,6 +50,7 @@ int afs_open(struct inode *inode, struct file *file)
 {
 	struct afs_vnode *vnode = AFS_FS_I(inode);
 	struct key *key;
+	int ret;
 
 	_enter("{%x:%x},", vnode->fid.vid, vnode->fid.vnode);
 
@@ -59,6 +60,12 @@ int afs_open(struct inode *inode, struct file *file)
 		return PTR_ERR(key);
 	}
 
+	ret = afs_validate(vnode, key);
+	if (ret < 0) {
+		_leave(" = %d [val]", ret);
+		return ret;
+	}
+
 	file->private_data = key;
 	_leave(" = 0");
 	return 0;