sunrpc/auth: allow lockless (rcu) lookup of credential cache.

The new flag RPCAUTH_LOOKUP_RCU to credential lookup avoids locking,
does not take a reference on the returned credential, and returns
-ECHILD if a simple lookup was not possible.

The returned value can only be used within an rcu_read_lock protected
region.

The main user of this is the new rpc_lookup_cred_nonblock() which
returns a pointer to the current credential which is only rcu-safe (no
ref-count held), and might return -ECHILD if allocation was required.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index c683b9a06913..8e030075fe79 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -103,6 +103,7 @@ struct rpc_auth_create_args {
 
 /* Flags for rpcauth_lookupcred() */
 #define RPCAUTH_LOOKUP_NEW              0x01    /* Accept an uninitialised cred */
+#define RPCAUTH_LOOKUP_RCU              0x02    /* lock-less lookup */
 
 /*
  * Client authentication ops
@@ -154,6 +155,7 @@ void			rpc_destroy_generic_auth(void);
 void                    rpc_destroy_authunix(void);
 
 struct rpc_cred *       rpc_lookup_cred(void);
+struct rpc_cred *       rpc_lookup_cred_nonblock(void);
 struct rpc_cred *       rpc_lookup_machine_cred(const char *service_name);
 int                     rpcauth_register(const struct rpc_authops *);
 int                     rpcauth_unregister(const struct rpc_authops *);