diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c
index fc0010d..8cf8d10 100644
--- a/fs/afs/cmservice.c
+++ b/fs/afs/cmservice.c
@@ -16,6 +16,7 @@
 #include <linux/ip.h>
 #include "internal.h"
 #include "afs_cm.h"
+#include "protocol_yfs.h"
 
 static int afs_deliver_cb_init_call_back_state(struct afs_call *);
 static int afs_deliver_cb_init_call_back_state3(struct afs_call *);
@@ -30,6 +31,8 @@ static void SRXAFSCB_Probe(struct work_struct *);
 static void SRXAFSCB_ProbeUuid(struct work_struct *);
 static void SRXAFSCB_TellMeAboutYourself(struct work_struct *);
 
+static int afs_deliver_yfs_cb_callback(struct afs_call *);
+
 #define CM_NAME(name) \
 	const char afs_SRXCB##name##_name[] __tracepoint_string =	\
 		"CB." #name
@@ -101,12 +104,23 @@ static const struct afs_call_type afs_SRXCBTellMeAboutYourself = {
 };
 
 /*
+ * YFS CB.CallBack operation type
+ */
+static CM_NAME(YFS_CallBack);
+static const struct afs_call_type afs_SRXYFSCB_CallBack = {
+	.name		= afs_SRXCBYFS_CallBack_name,
+	.deliver	= afs_deliver_yfs_cb_callback,
+	.destructor	= afs_cm_destructor,
+	.work		= SRXAFSCB_CallBack,
+};
+
+/*
  * route an incoming cache manager call
  * - return T if supported, F if not
  */
 bool afs_cm_incoming_call(struct afs_call *call)
 {
-	_enter("{CB.OP %u}", call->operation_ID);
+	_enter("{%u, CB.OP %u}", call->service_id, call->operation_ID);
 
 	switch (call->operation_ID) {
 	case CBCallBack:
@@ -127,6 +141,11 @@ bool afs_cm_incoming_call(struct afs_call *call)
 	case CBTellMeAboutYourself:
 		call->type = &afs_SRXCBTellMeAboutYourself;
 		return true;
+	case YFSCBCallBack:
+		if (call->service_id != YFS_CM_SERVICE)
+			return false;
+		call->type = &afs_SRXYFSCB_CallBack;
+		return true;
 	default:
 		return false;
 	}
@@ -570,3 +589,85 @@ static int afs_deliver_cb_tell_me_about_yourself(struct afs_call *call)
 
 	return afs_queue_call_work(call);
 }
+
+/*
+ * deliver request data to a YFS CB.CallBack call
+ */
+static int afs_deliver_yfs_cb_callback(struct afs_call *call)
+{
+	struct afs_callback_break *cb;
+	struct sockaddr_rxrpc srx;
+	struct yfs_xdr_YFSFid *bp;
+	size_t size;
+	int ret, loop;
+
+	_enter("{%u}", call->unmarshall);
+
+	switch (call->unmarshall) {
+	case 0:
+		afs_extract_to_tmp(call);
+		call->unmarshall++;
+
+		/* extract the FID array and its count in two steps */
+	case 1:
+		_debug("extract FID count");
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		call->count = ntohl(call->tmp);
+		_debug("FID count: %u", call->count);
+		if (call->count > YFSCBMAX)
+			return afs_protocol_error(call, -EBADMSG,
+						  afs_eproto_cb_fid_count);
+
+		size = array_size(call->count, sizeof(struct yfs_xdr_YFSFid));
+		call->buffer = kmalloc(size, GFP_KERNEL);
+		if (!call->buffer)
+			return -ENOMEM;
+		afs_extract_to_buf(call, size);
+		call->unmarshall++;
+
+	case 2:
+		_debug("extract FID array");
+		ret = afs_extract_data(call, false);
+		if (ret < 0)
+			return ret;
+
+		_debug("unmarshall FID array");
+		call->request = kcalloc(call->count,
+					sizeof(struct afs_callback_break),
+					GFP_KERNEL);
+		if (!call->request)
+			return -ENOMEM;
+
+		cb = call->request;
+		bp = call->buffer;
+		for (loop = call->count; loop > 0; loop--, cb++) {
+			cb->fid.vid	= xdr_to_u64(bp->volume);
+			cb->fid.vnode	= xdr_to_u64(bp->vnode.lo);
+			cb->fid.vnode_hi = ntohl(bp->vnode.hi);
+			cb->fid.unique	= ntohl(bp->vnode.unique);
+			bp++;
+		}
+
+		afs_extract_to_tmp(call);
+		call->unmarshall++;
+
+	case 3:
+		break;
+	}
+
+	if (!afs_check_call_state(call, AFS_CALL_SV_REPLYING))
+		return afs_io_error(call, afs_io_error_cm_reply);
+
+	/* We'll need the file server record as that tells us which set of
+	 * vnodes to operate upon.
+	 */
+	rxrpc_kernel_get_peer(call->net->socket, call->rxcall, &srx);
+	call->cm_server = afs_find_server(call->net, &srx);
+	if (!call->cm_server)
+		trace_afs_cm_no_server(call, &srx);
+
+	return afs_queue_call_work(call);
+}
diff --git a/fs/afs/protocol_yfs.h b/fs/afs/protocol_yfs.h
new file mode 100644
index 0000000..b7b211d
--- /dev/null
+++ b/fs/afs/protocol_yfs.h
@@ -0,0 +1,57 @@
+/* YFS protocol bits
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define YFS_FS_SERVICE	2500
+#define YFS_CM_SERVICE	2501
+
+#define YFSCBMAX 1024
+
+enum YFS_CM_Operations {
+	YFSCBProbe		= 206,	/* probe client */
+	YFSCBGetLock		= 207,	/* get contents of CM lock table */
+	YFSCBXStatsVersion	= 209,	/* get version of extended statistics */
+	YFSCBGetXStats		= 210,	/* get contents of extended statistics data */
+	YFSCBInitCallBackState3	= 213,	/* initialise callback state, version 3 */
+	YFSCBProbeUuid		= 214,	/* check the client hasn't rebooted */
+	YFSCBGetServerPrefs	= 215,
+	YFSCBGetCellServDV	= 216,
+	YFSCBGetLocalCell	= 217,
+	YFSCBGetCacheConfig	= 218,
+	YFSCBGetCellByNum	= 65537,
+	YFSCBTellMeAboutYourself = 65538, /* get client capabilities */
+	YFSCBCallBack		= 64204,
+};
+
+struct yfs_xdr_u64 {
+	__be32			msw;
+	__be32			lsw;
+} __packed;
+
+static inline u64 xdr_to_u64(const struct yfs_xdr_u64 x)
+{
+	return ((u64)ntohl(x.msw) << 32) | ntohl(x.lsw);
+}
+
+static inline struct yfs_xdr_u64 u64_to_xdr(const u64 x)
+{
+	return (struct yfs_xdr_u64){ .msw = htonl(x >> 32), .lsw = htonl(x) };
+}
+
+struct yfs_xdr_vnode {
+	struct yfs_xdr_u64	lo;
+	__be32			hi;
+	__be32			unique;
+} __packed;
+
+struct yfs_xdr_YFSFid {
+	struct yfs_xdr_u64	volume;
+	struct yfs_xdr_vnode	vnode;
+} __packed;
diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index e6ab824..ce98e13 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -16,6 +16,7 @@
 #include <net/af_rxrpc.h>
 #include "internal.h"
 #include "afs_cm.h"
+#include "protocol_yfs.h"
 
 struct workqueue_struct *afs_async_calls;
 
@@ -42,6 +43,7 @@ int afs_open_socket(struct afs_net *net)
 	struct sockaddr_rxrpc srx;
 	struct socket *socket;
 	unsigned int min_level;
+	u16 service_upgrade[2];
 	int ret;
 
 	_enter("");
@@ -75,6 +77,19 @@ int afs_open_socket(struct afs_net *net)
 	if (ret < 0)
 		goto error_2;
 
+	srx.srx_service = YFS_CM_SERVICE;
+	ret = kernel_bind(socket, (struct sockaddr *) &srx, sizeof(srx));
+	if (ret < 0)
+		goto error_2;
+
+	service_upgrade[0] = CM_SERVICE;
+	service_upgrade[1] = YFS_CM_SERVICE;
+	ret = kernel_setsockopt(socket, SOL_RXRPC, RXRPC_UPGRADEABLE_SERVICE,
+				(void *)service_upgrade, sizeof(service_upgrade));
+	if (ret < 0)
+		goto error_2;
+
+
 	rxrpc_kernel_new_call_notification(socket, afs_rx_new_call,
 					   afs_rx_discard_new_call);