[Cluster-devel] [PATCH 1/2] NLM failover unlock commands

[Wendy Cheng <wcheng@redhat.com>]

We've implemented two new NFSD procfs files:

o /proc/fs/nfsd/unlock_ip
o /proc/fs/nfsd/unlock_filesystem

They are intended to allow admin or user mode script to release NLM 
locks based on either a path name or a server in-bound ip address (ipv4 
for now)
as;

shell> echo 10.1.1.2 > /proc/fs/nfsd/unlock_ip
shell> echo /mnt/sfs1 > /proc/fs/nfsd/unlock_filesystem

The expected usage is for High Availability (HA) environment where nfs 
servers are clustered together to provide either load balancing or take 
over upon server failure. The task is normally started by transferring a 
floating IP address from serverA to serverB with the following sequences:

ServerA:
1. Tear down the IP address
2. Unexport the path
3. Write IP to /proc/fs/nfsd/unlock_ip to unlock files
4. If unmount required,
      write path name to /proc/fs/nfsd/unlock_filesystem, then unmount.
5. Signal peer to begin take-over.

For details, check out:
http://people.redhat.com/wcheng/Patches/NFS/NLM/004.txt

Acknowledgment goes to Neil Brown who has been offered support and 
guidance during our prototype efforts.

-- Wendy

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