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Date:   Fri, 27 Oct 2023 11:44:05 -0400
From:   Chuck Lever <chuck.lever@oracle.com>
To:     NeilBrown <neilb@suse.de>
Cc:     Jeff Layton <jlayton@kernel.org>, linux-nfs@vger.kernel.org,
        Olga Kornievskaia <kolga@netapp.com>,
        Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>
Subject: Re: [PATCH 0/6] support admin-revocation of v4 state
Message-ID: <ZTvaxWodP4rKFkrm@tissot.1015granger.net>
References: <20231027015613.26247-1-neilb@suse.de>
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On Fri, Oct 27, 2023 at 12:45:28PM +1100, NeilBrown wrote:
> This is a revised version of a patch set I sent over a year ago.
> It now supports v4.0 and has had more testing.
> 
> There are cirsumstances where an admin might need to unmount a
> filesystem that is NFS-exported and in active use, but does not want to
> stop the NFS server completely.  These are certainly unusual
> circumstance and doing this might negatively impact any clients acting
> on the filesystem, but the admin should be able to do this.
> 
> Currently this is quite possible for for NFSv3.  Unexporting the
> filesystem will ensure no new opens happen, and writing the path name to
> /proc/fs/nfsd/unlock_filesystem will ensure anly NLM locks held in the
> filesystem are released so that NFSD no longer prevents the filesystem
> from being unlocked.
> 
> It is not currently possible for NFSv4.  Writing to unlock_filesystem
> does not affect NFSv4, which is arguably a bug.  This series fixes the bug.

I agree that this is a good thing to do.

However, I'd like to migrate the "unlock_filesystem" functionality
to the nfsd netlink protocol first rather than adding this support
to /proc/fs/nfsd/. I don't believe that would be a difficult pre-
requisite to get through.

Does that seem sensible?


> For NFSv4.1 and later code is straight forward.  We add new state types
> for admin-revoked state (open, lock, deleg) and change the type of any
> state on a filesystem - inavlidating any access and closing files as we
> go.  While there are any revoked states we report this to the client in
> the response to SEQUENCE requests, and it will check and free any states
> that need to be freed.
> 
> For NFSv4.0 it isn't quite so easy as there is no mechanism for the
> client to explicitly acknowledged admin-revoked states.  The approach
> this patchset takes is to discard NFSv4.0 admin-revoked states one
> lease-time after they were revoked, or immediately for a state that the
> client tryies to use and gets an "ADMIN_REVOKED" error for.  If the
> filestystem has been unmounted (as expected), the client will see STATE
> errors before it has a chance to see ADMIN_REVOKED errors, so most often
> the timeout will be how states are discarded.
> 
> NeilBrown
> 
>  [PATCH 1/6] nfsd: prepare for supporting admin-revocation of state
>  [PATCH 2/6] nfsd: allow admin-revoked state to appear in
>  [PATCH 3/6] nfsd: allow admin-revoked NFSv4.0 state to be freed.
>  [PATCH 4/6] nfsd: allow lock state ids to be revoked and then freed
>  [PATCH 5/6] nfsd: allow open state ids to be revoked and then freed
>  [PATCH 6/6] nfsd: allow delegation state ids to be revoked and then
> 

-- 
Chuck Lever