lost dotdot caching pessimizes nfs especially

[Bruce Evans]

On Sun, 15 Oct 2006, Mohan Srinivasan wrote:

> of applications. Since the other NFS clients (that matter) Solaris and Linux support it,
> I would argue that not supporting cto consistency is not really an option.

I agree.

> We can however provide a mount option "nocto"  (like those clients do) that overrides
> the default for specific cases (read only mounts, single client mounts etc).

PR 78673 has a patch to break consistency unconditionally for r/o
mounts.  I use this, but it doesn't help for my most active file system
(/usr/obj) since that needs to be r/w.  It is obviously wrong to do
this unconditonally on the client.  It is the server's read-onlyness
that matters.  I don't know how to track the server's read-onlyness
short of asking it on every open() or Access.

Bruce