SUNRPC: Add a server-side API for retrieving an RPC's pseudoflavor

NFSD will use this new API to determine whether nfsd_splice_read is
safe to use. This avoids the need to add a dependency to NFSD for
CONFIG_SUNRPC_GSS.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/svcauth.h

@@ -131,8 +131,11 @@ enum svc_auth_status {
  *   This call releases a domain.
  *
  * set_client()
- *   Givens a pending request (struct svc_rqst), finds and assigns
+ *   Given a pending request (struct svc_rqst), finds and assigns
  *   an appropriate 'auth_domain' as the client.
+ *
+ * pseudoflavor()
+ *   Returns RPC_AUTH pseudoflavor in use by @rqstp.
  */
 struct auth_ops {
 	char *	name;
@@ -143,11 +146,13 @@ struct auth_ops {
 	int			(*release)(struct svc_rqst *rqstp);
 	void			(*domain_release)(struct auth_domain *dom);
 	enum svc_auth_status	(*set_client)(struct svc_rqst *rqstp);
+	rpc_authflavor_t	(*pseudoflavor)(struct svc_rqst *rqstp);
 };
 
 struct svc_xprt;
 
 extern enum svc_auth_status svc_authenticate(struct svc_rqst *rqstp);
+extern rpc_authflavor_t svc_auth_flavor(struct svc_rqst *rqstp);
 extern int	svc_authorise(struct svc_rqst *rqstp);
 extern enum svc_auth_status svc_set_client(struct svc_rqst *rqstp);
 extern int	svc_auth_register(rpc_authflavor_t flavor, struct auth_ops *aops);

net/sunrpc/auth_gss/svcauth_gss.c

@@ -2014,6 +2014,11 @@ svcauth_gss_domain_release(struct auth_domain *dom)
 	call_rcu(&dom->rcu_head, svcauth_gss_domain_release_rcu);
 }
 
+static rpc_authflavor_t svcauth_gss_pseudoflavor(struct svc_rqst *rqstp)
+{
+	return svcauth_gss_flavor(rqstp->rq_gssclient);
+}
+
 static struct auth_ops svcauthops_gss = {
 	.name		= "rpcsec_gss",
 	.owner		= THIS_MODULE,
@@ -2022,6 +2027,7 @@ static struct auth_ops svcauthops_gss = {
 	.release	= svcauth_gss_release,
 	.domain_release = svcauth_gss_domain_release,
 	.set_client	= svcauth_gss_set_client,
+	.pseudoflavor	= svcauth_gss_pseudoflavor,
 };
 
 static int rsi_cache_create_net(struct net *net)

net/sunrpc/svcauth.c

@@ -160,6 +160,22 @@ svc_auth_unregister(rpc_authflavor_t flavor)
 }
 EXPORT_SYMBOL_GPL(svc_auth_unregister);
 
+/**
+ * svc_auth_flavor - return RPC transaction's RPC_AUTH flavor
+ * @rqstp: RPC transaction context
+ *
+ * Returns an RPC flavor or GSS pseudoflavor.
+ */
+rpc_authflavor_t svc_auth_flavor(struct svc_rqst *rqstp)
+{
+	struct auth_ops *aops = rqstp->rq_authop;
+
+	if (!aops->pseudoflavor)
+		return aops->flavour;
+	return aops->pseudoflavor(rqstp);
+}
+EXPORT_SYMBOL_GPL(svc_auth_flavor);
+
 /**************************************************
  * 'auth_domains' are stored in a hash table indexed by name.
  * When the last reference to an 'auth_domain' is dropped,