NFSD: allow callers to pass in scope string to nfsd_svc

Currently admins set this by using unshare to create a new uts
namespace, and then resetting the hostname. With the new netlink
interface we can just pass this in directly. Prepare nfsd_svc for
this change.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfsctl.c

@@ -405,7 +405,7 @@ static ssize_t write_threads(struct file *file, char *buf, size_t size)
 			return -EINVAL;
 		trace_nfsd_ctl_threads(net, newthreads);
 		mutex_lock(&nfsd_mutex);
-		rv = nfsd_svc(newthreads, net, file->f_cred);
+		rv = nfsd_svc(newthreads, net, file->f_cred, NULL);
 		mutex_unlock(&nfsd_mutex);
 		if (rv < 0)
 			return rv;

fs/nfsd/nfsd.h

@@ -103,7 +103,7 @@ bool		nfssvc_encode_voidres(struct svc_rqst *rqstp,
 /*
  * Function prototypes.
  */
-int		nfsd_svc(int nrservs, struct net *net, const struct cred *cred);
+int		nfsd_svc(int nrservs, struct net *net, const struct cred *cred, const char *scope);
 int		nfsd_dispatch(struct svc_rqst *rqstp);
 
 int		nfsd_nrthreads(struct net *);

fs/nfsd/nfssvc.c

@@ -769,7 +769,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
  * this is the first time nrservs is nonzero.
  */
 int
-nfsd_svc(int nrservs, struct net *net, const struct cred *cred)
+nfsd_svc(int nrservs, struct net *net, const struct cred *cred, const char *scope)
 {
 	int	error;
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
@@ -786,7 +786,7 @@ nfsd_svc(int nrservs, struct net *net, const struct cred *cred)
 	if (nrservs == 0 && nn->nfsd_serv == NULL)
 		goto out;
 
-	strscpy(nn->nfsd_name, utsname()->nodename,
+	strscpy(nn->nfsd_name, scope ? scope : utsname()->nodename,
 		sizeof(nn->nfsd_name));
 
 	error = nfsd_create_serv(net);