lockd: unlock lockd locks associated with a given server ip

For high-availability NFS service, we generally need to be able to drop
file locks held on the exported filesystem before moving clients to a
new server.  Currently the only way to do that is by shutting down lockd
entirely, which is often undesireable (for example, if you want to
continue exporting other filesystems).

This patch allows the administrator to release all locks held by clients
accessing the client through a given server ip address, by echoing that
address to a new file, /proc/fs/nfsd/unlock_ip, as in:

shell> echo 10.1.1.2 > /proc/fs/nfsd/unlock_ip

The expected sequence of events can be:
1. Tear down the IP address
2. Unexport the path
3. Write IP to /proc/fs/nfsd/unlock_ip to unlock files
4. Signal peer to begin take-over.

For now we only support IPv4 addresses and NFSv2/v3 (NFSv4 locks are not
affected).

Also, if unmounting the filesystem is required, we assume at step 3 that
clients using the given server ip are the only clients holding locks on
the given filesystem; otherwise, an additional patch is required to
allow revoking all locks held by lockd on a given filesystem.

Signed-off-by: S. Wendy Cheng <wcheng@redhat.com>
Cc: Lon Hohberger  <lhh@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

 fs/lockd/svcsubs.c          |   66 +++++++++++++++++++++++++++++++++++++++-----
 fs/nfsd/nfsctl.c            |   65 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/lockd/lockd.h |    7 ++++
 3 files changed, 131 insertions(+), 7 deletions(-)

1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index 94649a8da014..bcb93fc1fce7 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -194,7 +194,7 @@ void		  nsm_release(struct nsm_handle *);
  * This is used in garbage collection and resource reclaim
  * A return value != 0 means destroy the lock/block/share
  */
-typedef int	  (*nlm_host_match_fn_t)(struct nlm_host *cur, struct nlm_host *ref);
+typedef int	  (*nlm_host_match_fn_t)(void *cur, struct nlm_host *ref);
 
 /*
  * Server-side lock handling
@@ -220,6 +220,11 @@ void		  nlmsvc_mark_resources(void);
 void		  nlmsvc_free_host_resources(struct nlm_host *);
 void		  nlmsvc_invalidate_all(void);
 
+/*
+ * Cluster failover support
+ */
+int           nlmsvc_unlock_all_by_ip(__be32 server_addr);
+
 static inline struct inode *nlmsvc_file_inode(struct nlm_file *file)
 {
 	return file->f_file->f_path.dentry->d_inode;