Re: How to handle non-local renames?

[Al Viro <viro@ftp.linux.org.uk>]

On Thu, Sep 28, 2006 at 12:53:01PM +0200, Miklos Szeredi wrote:
> > > > Simpler: if alias and our dentry share the parent, it's locked and
> > > > we can rename without s_vfs_rename_mutex.  If they do not, walk the
> > > > tree under alias, unhash all non-directories and kill all directories.
> > > 
> > > What do you mean by "killing directories"?  Unhashing the inode?
> > > 
> > > Are these OK, without holding i_mutex on alias and descendents?
> > 
> > Only dcache locking is needed for unhashing dentries (which is what
> > we do to non-directories).  For directories, we should silently
> > unhash inodes and make sure that all future operations on those inodes
> > would fail.  Up to filesystem how you do that.  Additionally, make
> > sure that revalidation fails on those suckers.
> 
> OK, what about operations currently in progress on those directories
> and files?  Is there no way these can cause trouble?

We need variants of d_move() and d_rehash() that do not take dcache_lock,
so that such fs would use them under dcache_lock, then check if parent
is dead and do the same kind of unhashing/killing if it is.  I.e.
pretend that we'd won the race and killer lookup came later.