Re: find_fh_dentry returned a DISCONNECTED directory

["J. Bruce Fields" <bfields@fieldses.org>]

On Fri, Feb 14, 2014 at 09:02:30AM -0800, Eric W. Biederman wrote:
> "J. Bruce Fields" <bfields@fieldses.org> writes:
> 
> > On Fri, Feb 14, 2014 at 07:49:35AM -0800, Eric W. Biederman wrote:
> >> 
> >> I believe we want both groups of dentries on the s_anon list so that if
> >> they remain disconnected when the filesystem is unmounted we can
> >> find them and deal with them.
> >
> > Note it's IS_ROOT(), not DCACHE_DISCONNECTED, that determines whether a
> > hashed dentry is on s_anon or not.  (See
> > 7632e465feb182cadc3c9aa1282a057201818a8c for more detailed
> > discussion.)
> 
> Interesting.  It remains the case that d_obtain_alias that sets
> DCACHE_DISCONNECTED is the only way to get on the s_anon list.

You're right, I forgot that.

> >From the rest of the conversation below I think what is needed is
> d_obtain_alias_root.   A function like d_obtain_alias but that does not
> set DCACHE_DISCONNECTED, that places IS_ROOT dentries on the s_anon list
> and that is usually expected to not find an alias.

Sounds good.

> I suspect the code would be much clearer if we were to do a mass
> s/DCACHE_DISCONNECTED/DCACHE_CONNECTING/ to make it clear that the
> flag is not intended to cover the general case of when dentries are
> floating around without parents.

I'm all for it.

bfields@pepper:linux-2.6$ git grep DCACHE_DISCONNECTED|wc -l
24

So it's not so terrible.  All but a few are in dcache.c and expfs.c.

> I am in the final stages of putting together some patches so that
> filesystems don't need to like to the vfs to preserve vfs invariants
> about mountpoints.  In particular I am implemeting automatic detaching
> of mountpionts on unlink and d_invalidate.  Once that is done and
> everyone is dropping directory dentries instead of sticking to the
> silly 2.2 era logic that present resides in d_invalidate some of these
> other dcache uses should become a little less mysterious.

OK.

--b.