Re: which ioctls matter across filesystems

Trond Myklebust
2005-04-29T21:16:33Z

fr den 29.04.2005 Klokka 16:47 (-0400) skreiv Robert Love:
> On Fri, 2005-04-29 at 16:42 -0400, Trond Myklebust wrote:
>
> > The problem is that having the server call back a bunch of clients every
> > time a file changes does not really scale too well. The current
> > dnotify-like proposal therefore specifies that notification is not
> > synchronous (i.e. there may be a delay of several seconds), and that the
> > server may want to group several notifications into a single callback.
>
> Yah, so what I am asking is why not use inotify for the user-side
> component of this system?

> Wouldn't the deferring and coalescing of events occur on the server
> side? So the server-side stuff would be whatever you need--your own
> code using whatever protocol you wanted--but the client-side interface
> would be over inotify.

Sure. We're not talking about inventing new user interfaces here. Just
how best to support the existing ones.

> Even if not, I'd be willing to make changes to inotify to accommodate
> NFS's needs.

I think what the IETF NFS working group rather needs right now is an
advocate that is willing to stand up and demonstrate why protocol
support for inotify-style callbacks would be a more scalable solution
than a solution based on a combination of GETATTR polling and read
delegations (essentially the same thing as CIFS' op-locks) for
directories.

The current research (see
http://www3.ietf.org/proceedings/05mar/slides/nfsv4-4/sld1.htm) which
has uses real-life on-the-wire traffic actually leans more towards the
GETATTR solution. That research was based on a set of anonymous tcpdump
traces taken at Harvard University, though, so it reflects the traffic
in a typical university environment. It may be that other use-cases
exist that favour the inotify callbacks case.
If so, now is the time to step forward and say so...

Cheers,
Trond
--
Trond Myklebust <trond.myklebust@fys.uio.no>