NFSD automatically releases all states when underlying file system is unmounted

[Dai Ngo <dai.ngo@oracle.com>]

Hi,

Currently when the local file system needs to be unmounted for maintenance
the admin needs to make sure all the NFS clients have stopped using any files
on the NFS shares before the umount(8) can succeed.

In an environment where there are thousands of clients this manual process
seems almost impossible or impractical. The only option available now is to
restart the NFS server which would works since the NFS client can recover its
state but it seems like this is a big hammer approach.

Ideally, when the umount command is run there is a callback from the VFS layer
to notify the upper protocols; NFS and SMB, to release its states on this file
system for the umount to complete.

Is there any existing mechanism to allow NFSD to release its states automatically
on unmount?

Unmount is not a frequent operation. Is it justifiable to add a bunch of complex
code for something is not frequently needed?

I appreciate any opinions on this issue.

Thanks,
-Dai