On 3/19/25 2:46 PM, NeilBrown wrote:
On Thu, 20 Mar 2025, Dai Ngo wrote:
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.
This is easily achieved with
echo /path/to/filesystem > /proc/fs/nfsd/unlock_filesystem
Do this after unexporting and before unmounting.
Yes, this works!
All state for NFSv4 exports, and all NLM locks for NFSv2/3 exports, will
be invalidated and files closed. NFSv4 clients will get
NFS4ERR_ADMIN_REVOKED when they attempt to use any state that was on
that filesystem.
In my test, client gets NFS4ERR_STALE for the PUTFH in the GETATTR compound
which is expected.
(I don't think this flushes the NFSv3 file cache, so a short delay might
be needed before the unmount when v3 is used. That should be fixed)
Thank you very much Neil!
-Dai
NeilBrown
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
