On Tue, Mar 20, 2018 at 01:46:20PM +0000, Trond Myklebust wrote:
> On Tue, 2018-03-20 at 13:35 +0000, David Howells wrote:
> > J. Bruce Fields <bfields@xxxxxxxxxx> wrote:
> >
> > > @@ -139,6 +139,9 @@ struct cred {
> > > struct key *thread_keyring; /* keyring private to
> > > this thread */
> > > struct key *request_key_auth; /* assumed
> > > request_key authority */
> > > #endif
> > > +#ifdef CONFIG_FILE_LOCKING
> > > + void *lease_breaker; /* identify NFS client
> > > breaking a delegation */
> > > +#endif
> > > #ifdef CONFIG_SECURITY
> > > void *security; /* subjective LSM
> > > security */
> > > #endif
> >
> > Sorry, but ewww.
> >
> > Two reasons for that comment:
> >
> > (1) The cred struct may get retained long past where you expect if
> > it gets
> > attached to another process or a file descriptor.
> >
> > (2) The ->lease_breaker pointer needs lifetime management in
> > cred.c. It will
> > potentially get copied around and may need cleaning up.
> >
> > Can you stick your breaker identity in a key struct as Jeff
> > suggested?
> >
>
> Bruce,
>
> Do you really need to do more than just identify that this is a knfsd
> thread vs not a knfsd thread? I'm assuming that a knfsd thread will
> usually be in a position to recall delegations before it even initiates
> an operation on the inode in question, won't it?
I think it could. I'm reluctant:
- Once we support write delegations, I think we end up having to
do that before basically every operation on a inode.
- I'd like this to make it easy for someone to extend delegation
support to userspace eventually too. I'm not sure exactly how
we'd identify self-conflicts in that case (struct files?), but
anyway I'd rather this wasn't too nfsd-specific.
That said, I'm still curious:
> IOW: what if you were to modify the lease code to allow knfsd threads
> to return a "please ignore me, and proceed with the operation that
> triggered the lease break" reply, and then handle conflicts between NFS
> clients outside the lease callback code altogether?
So if you're a random bit of code, how would you recommend testing
whether you're running in a knfsd thread?
--b.
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