nfsd: set the server_scope during service startup

Currently, nfsd4_encode_exchange_id() encodes the utsname nodename
string in the server_scope field.  In a multi-host container
environemnt, if an nfsd container is restarted on a different host than
it was originally running on, clients will see a server_scope mismatch
and will not attempt to reclaim opens.

Instead, set the server_scope while we're in a process context during
service startup, so we get the utsname nodename of the current process
and store that in nfsd_net.
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
[bfields: fix up major_id too]
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/netns.h

@@ -172,6 +172,8 @@ struct nfsd_net {
 	unsigned int             longest_chain_cachesize;
 
 	struct shrinker		nfsd_reply_cache_shrinker;
+	/* utsname taken from the the process that starts the server */
+	char			nfsd_name[UNX_MAXNODENAME+1];
 };
 
 /* Simple check to find out if a given net was properly initialized */

fs/nfsd/nfs4xdr.c

@@ -4005,11 +4005,12 @@ nfsd4_encode_exchange_id(struct nfsd4_compoundres *resp, __be32 nfserr,
 	int major_id_sz;
 	int server_scope_sz;
 	uint64_t minor_id = 0;
+	struct nfsd_net *nn = net_generic(SVC_NET(resp->rqstp), nfsd_net_id);
 
-	major_id = utsname()->nodename;
-	major_id_sz = strlen(major_id);
-	server_scope = utsname()->nodename;
-	server_scope_sz = strlen(server_scope);
+	major_id = nn->nfsd_name;
+	major_id_sz = strlen(nn->nfsd_name);
+	server_scope = nn->nfsd_name;
+	server_scope_sz = strlen(nn->nfsd_name);
 
 	p = xdr_reserve_space(xdr,
 		8 /* eir_clientid */ +

fs/nfsd/nfssvc.c

@@ -749,6 +749,9 @@ nfsd_svc(int nrservs, struct net *net, const struct cred *cred)
 	if (nrservs == 0 && nn->nfsd_serv == NULL)
 		goto out;
 
+	strlcpy(nn->nfsd_name, utsname()->nodename,
+		sizeof(nn->nfsd_name));
+
 	error = nfsd_create_serv(net);
 	if (error)
 		goto out;