nfsd41: destroy_session operation

Implement the destory_session operation confoming to
http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion1-26

[use sessionid_lock spin lock]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 04a395f..9192e5b 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1422,7 +1422,34 @@
 		      struct nfsd4_compound_state *cstate,
 		      struct nfsd4_destroy_session *sessionid)
 {
-	return -1;	/* stub */
+	struct nfsd4_session *ses;
+	u32 status = nfserr_badsession;
+
+	/* Notes:
+	 * - The confirmed nfs4_client->cl_sessionid holds destroyed sessinid
+	 * - Should we return nfserr_back_chan_busy if waiting for
+	 *   callbacks on to-be-destroyed session?
+	 * - Do we need to clear any callback info from previous session?
+	 */
+
+	dump_sessionid(__func__, &sessionid->sessionid);
+	spin_lock(&sessionid_lock);
+	ses = find_in_sessionid_hashtbl(&sessionid->sessionid);
+	if (!ses) {
+		spin_unlock(&sessionid_lock);
+		goto out;
+	}
+
+	unhash_session(ses);
+	spin_unlock(&sessionid_lock);
+
+	/* wait for callbacks */
+	shutdown_callback_client(ses->se_client);
+	nfsd4_put_session(ses);
+	status = nfs_ok;
+out:
+	dprintk("%s returns %d\n", __func__, ntohl(status));
+	return status;
 }
 
 __be32