kern/40313: puffs rename protocol is broken

[pooka%iki.fi@localhost]

>Number:         40313
>Category:       kern
>Synopsis:       puffs rename protocol is broken
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jan 01 16:45:00 +0000 2009
>Originator:     Antti Kantee
>Release:        
>Organization:
bug cookery inc.
>Environment:
>Description:
puffs file servers currently depend on the kernel vnode locking protocol.
However, rename is special in the sense that it doesn't protect the
source directory since it's not possible to hold two locks in a single
thread at the same time without knowing the directory layout
(i.e. without being the file system).

In case of a multithreaded or blocking (via puffs_cc) file server,
operations on the source directory are not automatically serialized.
>How-To-Repeat:
sauce meditation
>Fix:
Clarify and document the locking necessary in userspace.