6 files changed, 40 insertions, 7 deletions

diff --git a/Documentation/filesystems/nfs/nfs41-server.txt b/Documentation/filesystems/nfs/nfs41-server.txt
index 092fad92a3f0..f5ddff2da302 100644
--- a/Documentation/filesystems/nfs/nfs41-server.txt
+++ b/Documentation/filesystems/nfs/nfs41-server.txt
@@ -39,11 +39,6 @@ interoperability problems with future clients.  Known issues:
           from a linux client are possible, but we aren't really
           conformant with the spec (for example, we don't use kerberos
           on the backchannel correctly).
-        - Incomplete backchannel support: incomplete backchannel gss
-          support and no support for BACKCHANNEL_CTL mean that
-          callbacks (hence delegations and layouts) may not be
-          available and clients confused by the incomplete
-          implementation may fail.
         - We do not support SSV, which provides security for shared
           client-server state (thus preventing unauthorized tampering
           with locks and opens, for example).  It is mandatory for
@@ -89,7 +84,7 @@ Operations
    |                      | MNI        | or OPT)      |                |
    +----------------------+------------+--------------+----------------+
    | ACCESS               | REQ        |              | Section 18.1   |
-NS | BACKCHANNEL_CTL      | REQ        |              | Section 18.33  |
+I  | BACKCHANNEL_CTL      | REQ        |              | Section 18.33  |
 I  | BIND_CONN_TO_SESSION | REQ        |              | Section 18.34  |
    | CLOSE                | REQ        |              | Section 18.2   |
    | COMMIT               | REQ        |              | Section 18.3   |
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 6c9a4b291dba..f955176f1b6f 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1666,6 +1666,12 @@ static struct nfsd4_operation nfsd4_ops[] = {
                 .op_name = "OP_EXCHANGE_ID",
                 .op_rsize_bop = (nfsd4op_rsize)nfsd4_exchange_id_rsize,
         },
+        [OP_BACKCHANNEL_CTL] = {
+                .op_func = (nfsd4op_func)nfsd4_backchannel_ctl,
+                .op_flags = ALLOWED_WITHOUT_FH | OP_MODIFIES_SOMETHING,
+                .op_name = "OP_BACKCHANNEL_CTL",
+                .op_rsize_bop = (nfsd4op_rsize)nfsd4_only_status_rsize,
+        },
         [OP_BIND_CONN_TO_SESSION] = {
                 .op_func = (nfsd4op_func)nfsd4_bind_conn_to_session,
                 .op_flags = ALLOWED_WITHOUT_FH | ALLOWED_AS_FIRST_OP
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index dbbbd2fe5236..4023e77687ee 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1865,6 +1865,20 @@ static __be32 nfsd4_map_bcts_dir(u32 *dir)
         return nfserr_inval;
 }
 
+__be32 nfsd4_backchannel_ctl(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, struct nfsd4_backchannel_ctl *bc)
+{
+        struct nfsd4_session *session = cstate->session;
+
+        spin_lock(&client_lock);
+        session->se_cb_prog = bc->bc_cb_program;
+        session->se_cb_sec = bc->bc_cb_sec;
+        spin_unlock(&client_lock);
+
+        nfsd4_probe_callback(session->se_client);
+
+        return nfs_ok;
+}
+
 __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
                      struct nfsd4_compound_state *cstate,
                      struct nfsd4_bind_conn_to_session *bcts)
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 511f980b605c..d7e7c110246e 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -483,6 +483,17 @@ static __be32 nfsd4_decode_cb_sec(struct nfsd4_compoundargs *argp, struct nfsd4_
         DECODE_TAIL;
 }
 
+static __be32 nfsd4_decode_backchannel_ctl(struct nfsd4_compoundargs *argp, struct nfsd4_backchannel_ctl *bc)
+{
+        DECODE_HEAD;
+
+        READ_BUF(4);
+        READ32(bc->bc_cb_program);
+        nfsd4_decode_cb_sec(argp, &bc->bc_cb_sec);
+
+        DECODE_TAIL;
+}
+
 static __be32 nfsd4_decode_bind_conn_to_session(struct nfsd4_compoundargs *argp, struct nfsd4_bind_conn_to_session *bcts)
 {
         DECODE_HEAD;
@@ -1536,7 +1547,7 @@ static nfsd4_dec nfsd41_dec_ops[] = {
         [OP_RELEASE_LOCKOWNER]  = (nfsd4_dec)nfsd4_decode_notsupp,
 
         /* new operations for NFSv4.1 */
-        [OP_BACKCHANNEL_CTL]    = (nfsd4_dec)nfsd4_decode_notsupp,
+        [OP_BACKCHANNEL_CTL]    = (nfsd4_dec)nfsd4_decode_backchannel_ctl,
         [OP_BIND_CONN_TO_SESSION]= (nfsd4_dec)nfsd4_decode_bind_conn_to_session,
         [OP_EXCHANGE_ID]        = (nfsd4_dec)nfsd4_decode_exchange_id,
         [OP_CREATE_SESSION]     = (nfsd4_dec)nfsd4_decode_create_session,
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index bff856c34a32..758bc9c2646b 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -166,6 +166,11 @@ struct nfsd4_create_session {
         struct nfsd4_cb_sec             cb_sec;
 };
 
+struct nfsd4_backchannel_ctl {
+        u32     bc_cb_program;
+        struct nfsd4_cb_sec             bc_cb_sec;
+};
+
 struct nfsd4_bind_conn_to_session {
         struct nfs4_sessionid           sessionid;
         u32                             dir;
diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
index acd127d4ee82..71c5c47f2750 100644
--- a/fs/nfsd/xdr4.h
+++ b/fs/nfsd/xdr4.h
@@ -462,6 +462,7 @@ struct nfsd4_op {
 
                 /* NFSv4.1 */
                 struct nfsd4_exchange_id        exchange_id;
+                struct nfsd4_backchannel_ctl    backchannel_ctl;
                 struct nfsd4_bind_conn_to_session bind_conn_to_session;
                 struct nfsd4_create_session     create_session;
                 struct nfsd4_destroy_session    destroy_session;
@@ -566,6 +567,7 @@ extern __be32 nfsd4_replay_cache_entry(struct nfsd4_compoundres *resp,
                 struct nfsd4_sequence *seq);
 extern __be32 nfsd4_exchange_id(struct svc_rqst *rqstp,
                 struct nfsd4_compound_state *, struct nfsd4_exchange_id *);
+extern __be32 nfsd4_backchannel_ctl(struct svc_rqst *, struct nfsd4_compound_state *, struct nfsd4_backchannel_ctl *);
 extern __be32 nfsd4_bind_conn_to_session(struct svc_rqst *, struct nfsd4_compound_state *, struct nfsd4_bind_conn_to_session *);
 extern __be32 nfsd4_create_session(struct svc_rqst *,
                 struct nfsd4_compound_state *,