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SubjectRe: (reiserfs) Re: reiserfs and knfsd and NFSv4 and volatile file handles
Alexander Viro wrote:
>
> On Wed, 15 Mar 2000, Hans Reiser wrote:
>
> > Not sure I understand your question, but I'll take a stab at it. Currently the
> > first directory a file is created in stays its packing locality parent for the
> > life of the file. The packing locality parent is the first key component. So,
> > currently, if you know the parent directory id the file was created in you know
> > the first component of the key, and the last component of the key is the offset
> > which you can also know. This leaves the middle of the key unknown.
>
> Ouch. What happens if you
> mkdir foo
> create foo/bar
> rename foo/bar baz/bar
> rmdir foo

packing locality is foo.

> and ditto for
> mkdir foo
> create foo/bar
> open foo/bar
> unlink foo/bar
> rmdir foo
> - where does your packing locality <whatever> go?

packing locality is foo

>
> > The immutability of keys is true merely because we don't yet have a repacker to
> > do re-optimize once a day, and it will change, but for now it is true. The
> > first version of our repacker probably won't change keys, but clearly it should
> > eventually have that functionality.
>
> And how do you expect NFS to handle that?

I don't. NFS v4 guys should listen to Neil.

>
> > The notion that keys/objectids should be immutable over the life of the object
> > is a notion I once believed in but have since conceded was wrong of me.
>
> Unfortunately, NFS can't survive without that. POSIX also requires
> constant inumbers, BTW.

It is bad design to require it. Currently we provide it, but it is bad design.
It appears to be something fundamental that you cannot change access patterns,
and have a fixed id, and avoid adding a random I/O to a usage pattern that could
otherwise be optimized for by a clever repacker that could optimize that I/O
away by packing the object with other objects it is accessed with. I was forced
to concede this many years ago by clever persons working for me. I wanted
immutable objectids, they clean things up so nicely in the architecture.
Mutable ids require what is effectively two way linking. I lost the argument.

Thanks for being helpful to us despite a rocky start to our relationship.

I believe your other questions were answered in other emails, not all by me.
Correct me if I err in this.

Hans
--
You can get ReiserFS at http://devlinux.org/namesys, and customizations and
industrial grade support at reiser@idiom.com.

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