Re: [nfsv4] follow-up of xattr discussion

>>    Such caching is write through in that modification to xattrs is
>>    always done by means of requests to the server and should not be
>>    only done locally. Due to the relative infrequency of xattr
>>    updates, it is suggested that all changes be propagated
>>    synchronously. The client MUST NOT maintain a cache of modified
>>    xattrs.
>>
>> What's the rationale for that MUST NOT?

> Same as the one for all other attributes (except size, time_modify,
change): see https://tools.ietf.org/html/rfc5661#section-10.6

The text in question reads as follows:

Other than those three attributes, the client MUST NOT maintain a
cache of modified attributes. Instead, attribute changes are
immediately sent to the server.

When those two sentences are read together, it seems to me that the
intention is/was to forbid writeback caching of attributes. With just the
first of them present, it might lead someone to suppose that a writethrough
cache of modified attributes is to be forbidden as well. I don't think that
is the intention.

On Fri, Jul 31, 2015 at 11:22 AM, Manoj Naik <mnaik@us.ibm.com> wrote:

>
> "nfsv4" <nfsv4-bounces@ietf.org> wrote on 07/23/2015 11:45:47 AM:
>
> > From: "J. Bruce Fields" <bfields@fieldses.org>
> > To: David Noveck <davenoveck@gmail.com>
> > Cc: Christoph Hellwig <hch@lst.de>, "nfsv4@ietf.org" <nfsv4@ietf.org>
> > Date: 07/23/2015 11:46 AM
> > Subject: Re: [nfsv4] follow-up of xattr discussion
> > Sent by: "nfsv4" <nfsv4-bounces@ietf.org>
> >
> > On Thu, Jul 23, 2015 at 01:15:22PM -0400, David Noveck wrote:
> > > which sound to me like such uses for not allowed.  I'll be reviewing
> > > this document in a bit and will propose some toughening up of the
> > > language.
> >
> > One of the practical difference is the caching.  A lot of the
> > filesystem-specific attributes look incompatible with client caching.
> >
> > Looking at the "caching" section: it does say clients may cache reads,
> > and that the change attribute can be depended on to validate that cache,
> > but:
> >
> >    https://tools.ietf.org/html/draft-naik-nfsv4-xattrs-02#section-6.2.2
> >
> >    Such caching is write through in that modification to xattrs is
> >    always done by means of requests to the server and should not be
> >    only done locally. Due to the relative infrequency of xattr
> >    updates, it is suggested that all changes be propagated
> >    synchronously. The client MUST NOT maintain a cache of modified
> >    xattrs.
> >
> > What's the rationale for that MUST NOT?
>
> Same as the one for all other attributes (except size, time_modify,
> change): see https://tools.ietf.org/html/rfc5661#section-10.6
>
> Manoj.
>
> >
> > --b.
> >
> > _______________________________________________
> > nfsv4 mailing list
> > nfsv4@ietf.org
> > https://www.ietf.org/mailman/listinfo/nfsv4
> >
>
>