1 files changed, 782 insertions, 0 deletions

diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
new file mode 100644
index 000000000000..e7b047328a39
--- /dev/null
+++ b/fs/afs/rxrpc.c
@@ -0,0 +1,782 @@
+/* Maintain an RxRPC server socket to do AFS communications through
+ *
+ * Copyright (C) 2007 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 License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <net/sock.h>
+#include <net/af_rxrpc.h>
+#include <rxrpc/packet.h>
+#include "internal.h"
+#include "afs_cm.h"
+
+static struct socket *afs_socket; /* my RxRPC socket */
+static struct workqueue_struct *afs_async_calls;
+static atomic_t afs_outstanding_calls;
+static atomic_t afs_outstanding_skbs;
+
+static void afs_wake_up_call_waiter(struct afs_call *);
+static int afs_wait_for_call_to_complete(struct afs_call *);
+static void afs_wake_up_async_call(struct afs_call *);
+static int afs_dont_wait_for_call_to_complete(struct afs_call *);
+static void afs_process_async_call(struct work_struct *);
+static void afs_rx_interceptor(struct sock *, unsigned long, struct sk_buff *);
+static int afs_deliver_cm_op_id(struct afs_call *, struct sk_buff *, bool);
+
+/* synchronous call management */
+const struct afs_wait_mode afs_sync_call = {
+        .rx_wakeup      = afs_wake_up_call_waiter,
+        .wait           = afs_wait_for_call_to_complete,
+};
+
+/* asynchronous call management */
+const struct afs_wait_mode afs_async_call = {
+        .rx_wakeup      = afs_wake_up_async_call,
+        .wait           = afs_dont_wait_for_call_to_complete,
+};
+
+/* asynchronous incoming call management */
+static const struct afs_wait_mode afs_async_incoming_call = {
+        .rx_wakeup      = afs_wake_up_async_call,
+};
+
+/* asynchronous incoming call initial processing */
+static const struct afs_call_type afs_RXCMxxxx = {
+        .name           = "CB.xxxx",
+        .deliver        = afs_deliver_cm_op_id,
+        .abort_to_error = afs_abort_to_error,
+};
+
+static void afs_collect_incoming_call(struct work_struct *);
+
+static struct sk_buff_head afs_incoming_calls;
+static DECLARE_WORK(afs_collect_incoming_call_work, afs_collect_incoming_call);
+
+/*
+ * open an RxRPC socket and bind it to be a server for callback notifications
+ * - the socket is left in blocking mode and non-blocking ops use MSG_DONTWAIT
+ */
+int afs_open_socket(void)
+{
+        struct sockaddr_rxrpc srx;
+        struct socket *socket;
+        int ret;
+
+        _enter("");
+
+        skb_queue_head_init(&afs_incoming_calls);
+
+        afs_async_calls = create_singlethread_workqueue("kafsd");
+        if (!afs_async_calls) {
+                _leave(" = -ENOMEM [wq]");
+                return -ENOMEM;
+        }
+
+        ret = sock_create_kern(AF_RXRPC, SOCK_DGRAM, PF_INET, &socket);
+        if (ret < 0) {
+                destroy_workqueue(afs_async_calls);
+                _leave(" = %d [socket]", ret);
+                return ret;
+        }
+
+        socket->sk->sk_allocation = GFP_NOFS;
+
+        /* bind the callback manager's address to make this a server socket */
+        srx.srx_family                  = AF_RXRPC;
+        srx.srx_service                 = CM_SERVICE;
+        srx.transport_type              = SOCK_DGRAM;
+        srx.transport_len               = sizeof(srx.transport.sin);
+        srx.transport.sin.sin_family    = AF_INET;
+        srx.transport.sin.sin_port      = htons(AFS_CM_PORT);
+        memset(&srx.transport.sin.sin_addr, 0,
+               sizeof(srx.transport.sin.sin_addr));
+
+        ret = kernel_bind(socket, (struct sockaddr *) &srx, sizeof(srx));
+        if (ret < 0) {
+                sock_release(socket);
+                _leave(" = %d [bind]", ret);
+                return ret;
+        }
+
+        rxrpc_kernel_intercept_rx_messages(socket, afs_rx_interceptor);
+
+        afs_socket = socket;
+        _leave(" = 0");
+        return 0;
+}
+
+/*
+ * close the RxRPC socket AFS was using
+ */
+void afs_close_socket(void)
+{
+        _enter("");
+
+        sock_release(afs_socket);
+
+        _debug("dework");
+        destroy_workqueue(afs_async_calls);
+
+        ASSERTCMP(atomic_read(&afs_outstanding_skbs), ==, 0);
+        ASSERTCMP(atomic_read(&afs_outstanding_calls), ==, 0);
+        _leave("");
+}
+
+/*
+ * note that the data in a socket buffer is now delivered and that the buffer
+ * should be freed
+ */
+static void afs_data_delivered(struct sk_buff *skb)
+{
+        if (!skb) {
+                _debug("DLVR NULL [%d]", atomic_read(&afs_outstanding_skbs));
+                dump_stack();
+        } else {
+                _debug("DLVR %p{%u} [%d]",
+                       skb, skb->mark, atomic_read(&afs_outstanding_skbs));
+                if (atomic_dec_return(&afs_outstanding_skbs) == -1)
+                        BUG();
+                rxrpc_kernel_data_delivered(skb);
+        }
+}
+
+/*
+ * free a socket buffer
+ */
+static void afs_free_skb(struct sk_buff *skb)
+{
+        if (!skb) {
+                _debug("FREE NULL [%d]", atomic_read(&afs_outstanding_skbs));
+                dump_stack();
+        } else {
+                _debug("FREE %p{%u} [%d]",
+                       skb, skb->mark, atomic_read(&afs_outstanding_skbs));
+                if (atomic_dec_return(&afs_outstanding_skbs) == -1)
+                        BUG();
+                rxrpc_kernel_free_skb(skb);
+        }
+}
+
+/*
+ * free a call
+ */
+static void afs_free_call(struct afs_call *call)
+{
+        _debug("DONE %p{%s} [%d]",
+               call, call->type->name, atomic_read(&afs_outstanding_calls));
+        if (atomic_dec_return(&afs_outstanding_calls) == -1)
+                BUG();
+
+        ASSERTCMP(call->rxcall, ==, NULL);
+        ASSERT(!work_pending(&call->async_work));
+        ASSERT(skb_queue_empty(&call->rx_queue));
+        ASSERT(call->type->name != NULL);
+
+        kfree(call->request);
+        kfree(call);
+}
+
+/*
+ * allocate a call with flat request and reply buffers
+ */
+struct afs_call *afs_alloc_flat_call(const struct afs_call_type *type,
+                                     size_t request_size, size_t reply_size)
+{
+        struct afs_call *call;
+
+        call = kzalloc(sizeof(*call), GFP_NOFS);
+        if (!call)
+                goto nomem_call;
+
+        _debug("CALL %p{%s} [%d]",
+               call, type->name, atomic_read(&afs_outstanding_calls));
+        atomic_inc(&afs_outstanding_calls);
+
+        call->type = type;
+        call->request_size = request_size;
+        call->reply_max = reply_size;
+
+        if (request_size) {
+                call->request = kmalloc(request_size, GFP_NOFS);
+                if (!call->request)
+                        goto nomem_free;
+        }
+
+        if (reply_size) {
+                call->buffer = kmalloc(reply_size, GFP_NOFS);
+                if (!call->buffer)
+                        goto nomem_free;
+        }
+
+        init_waitqueue_head(&call->waitq);
+        skb_queue_head_init(&call->rx_queue);
+        return call;
+
+nomem_free:
+        afs_free_call(call);
+nomem_call:
+        return NULL;
+}
+
+/*
+ * clean up a call with flat buffer
+ */
+void afs_flat_call_destructor(struct afs_call *call)
+{
+        _enter("");
+
+        kfree(call->request);
+        call->request = NULL;
+        kfree(call->buffer);
+        call->buffer = NULL;
+}
+
+/*
+ * initiate a call
+ */
+int afs_make_call(struct in_addr *addr, struct afs_call *call, gfp_t gfp,
+                  const struct afs_wait_mode *wait_mode)
+{
+        struct sockaddr_rxrpc srx;
+        struct rxrpc_call *rxcall;
+        struct msghdr msg;
+        struct kvec iov[1];
+        int ret;
+
+        _enter("%x,{%d},", addr->s_addr, ntohs(call->port));
+
+        ASSERT(call->type != NULL);
+        ASSERT(call->type->name != NULL);
+
+        _debug("MAKE %p{%s} [%d]",
+               call, call->type->name, atomic_read(&afs_outstanding_calls));
+
+        call->wait_mode = wait_mode;
+        INIT_WORK(&call->async_work, afs_process_async_call);
+
+        memset(&srx, 0, sizeof(srx));
+        srx.srx_family = AF_RXRPC;
+        srx.srx_service = call->service_id;
+        srx.transport_type = SOCK_DGRAM;
+        srx.transport_len = sizeof(srx.transport.sin);
+        srx.transport.sin.sin_family = AF_INET;
+        srx.transport.sin.sin_port = call->port;
+        memcpy(&srx.transport.sin.sin_addr, addr, 4);
+
+        /* create a call */
+        rxcall = rxrpc_kernel_begin_call(afs_socket, &srx, call->key,
+                                         (unsigned long) call, gfp);
+        call->key = NULL;
+        if (IS_ERR(rxcall)) {
+                ret = PTR_ERR(rxcall);
+                goto error_kill_call;
+        }
+
+        call->rxcall = rxcall;
+
+        /* send the request */
+        iov[0].iov_base = call->request;
+        iov[0].iov_len  = call->request_size;
+
+        msg.msg_name            = NULL;
+        msg.msg_namelen         = 0;
+        msg.msg_iov             = (struct iovec *) iov;
+        msg.msg_iovlen          = 1;
+        msg.msg_control         = NULL;
+        msg.msg_controllen      = 0;
+        msg.msg_flags           = 0;
+
+        /* have to change the state *before* sending the last packet as RxRPC
+         * might give us the reply before it returns from sending the
+         * request */
+        call->state = AFS_CALL_AWAIT_REPLY;
+        ret = rxrpc_kernel_send_data(rxcall, &msg, call->request_size);
+        if (ret < 0)
+                goto error_do_abort;
+
+        /* at this point, an async call may no longer exist as it may have
+         * already completed */
+        return wait_mode->wait(call);
+
+error_do_abort:
+        rxrpc_kernel_abort_call(rxcall, RX_USER_ABORT);
+        rxrpc_kernel_end_call(rxcall);
+        call->rxcall = NULL;
+error_kill_call:
+        call->type->destructor(call);
+        afs_free_call(call);
+        _leave(" = %d", ret);
+        return ret;
+}
+
+/*
+ * handles intercepted messages that were arriving in the socket's Rx queue
+ * - called with the socket receive queue lock held to ensure message ordering
+ * - called with softirqs disabled
+ */
+static void afs_rx_interceptor(struct sock *sk, unsigned long user_call_ID,
+                               struct sk_buff *skb)
+{
+        struct afs_call *call = (struct afs_call *) user_call_ID;
+
+        _enter("%p,,%u", call, skb->mark);
+
+        _debug("ICPT %p{%u} [%d]",
+               skb, skb->mark, atomic_read(&afs_outstanding_skbs));
+
+        ASSERTCMP(sk, ==, afs_socket->sk);
+        atomic_inc(&afs_outstanding_skbs);
+
+        if (!call) {
+                /* its an incoming call for our callback service */
+                skb_queue_tail(&afs_incoming_calls, skb);
+                schedule_work(&afs_collect_incoming_call_work);
+        } else {
+                /* route the messages directly to the appropriate call */
+                skb_queue_tail(&call->rx_queue, skb);
+                call->wait_mode->rx_wakeup(call);
+        }
+
+        _leave("");
+}
+
+/*
+ * deliver messages to a call
+ */
+static void afs_deliver_to_call(struct afs_call *call)
+{
+        struct sk_buff *skb;
+        bool last;
+        u32 abort_code;
+        int ret;
+
+        _enter("");
+
+        while ((call->state == AFS_CALL_AWAIT_REPLY ||
+                call->state == AFS_CALL_AWAIT_OP_ID ||
+                call->state == AFS_CALL_AWAIT_REQUEST ||
+                call->state == AFS_CALL_AWAIT_ACK) &&
+               (skb = skb_dequeue(&call->rx_queue))) {
+                switch (skb->mark) {
+                case RXRPC_SKB_MARK_DATA:
+                        _debug("Rcv DATA");
+                        last = rxrpc_kernel_is_data_last(skb);
+                        ret = call->type->deliver(call, skb, last);
+                        switch (ret) {
+                        case 0:
+                                if (last &&
+                                    call->state == AFS_CALL_AWAIT_REPLY)
+                                        call->state = AFS_CALL_COMPLETE;
+                                break;
+                        case -ENOTCONN:
+                                abort_code = RX_CALL_DEAD;
+                                goto do_abort;
+                        case -ENOTSUPP:
+                                abort_code = RX_INVALID_OPERATION;
+                                goto do_abort;
+                        default:
+                                abort_code = RXGEN_CC_UNMARSHAL;
+                                if (call->state != AFS_CALL_AWAIT_REPLY)
+                                        abort_code = RXGEN_SS_UNMARSHAL;
+                        do_abort:
+                                rxrpc_kernel_abort_call(call->rxcall,
+                                                        abort_code);
+                                call->error = ret;
+                                call->state = AFS_CALL_ERROR;
+                                break;
+                        }
+                        afs_data_delivered(skb);
+                        skb = NULL;
+                        continue;
+                case RXRPC_SKB_MARK_FINAL_ACK:
+                        _debug("Rcv ACK");
+                        call->state = AFS_CALL_COMPLETE;
+                        break;
+                case RXRPC_SKB_MARK_BUSY:
+                        _debug("Rcv BUSY");
+                        call->error = -EBUSY;
+                        call->state = AFS_CALL_BUSY;
+                        break;
+                case RXRPC_SKB_MARK_REMOTE_ABORT:
+                        abort_code = rxrpc_kernel_get_abort_code(skb);
+                        call->error = call->type->abort_to_error(abort_code);
+                        call->state = AFS_CALL_ABORTED;
+                        _debug("Rcv ABORT %u -> %d", abort_code, call->error);
+                        break;
+                case RXRPC_SKB_MARK_NET_ERROR:
+                        call->error = -rxrpc_kernel_get_error_number(skb);
+                        call->state = AFS_CALL_ERROR;
+                        _debug("Rcv NET ERROR %d", call->error);
+                        break;
+                case RXRPC_SKB_MARK_LOCAL_ERROR:
+                        call->error = -rxrpc_kernel_get_error_number(skb);
+                        call->state = AFS_CALL_ERROR;
+                        _debug("Rcv LOCAL ERROR %d", call->error);
+                        break;
+                default:
+                        BUG();
+                        break;
+                }
+
+                afs_free_skb(skb);
+        }
+
+        /* make sure the queue is empty if the call is done with (we might have
+         * aborted the call early because of an unmarshalling error) */
+        if (call->state >= AFS_CALL_COMPLETE) {
+                while ((skb = skb_dequeue(&call->rx_queue)))
+                        afs_free_skb(skb);
+                if (call->incoming) {
+                        rxrpc_kernel_end_call(call->rxcall);
+                        call->rxcall = NULL;
+                        call->type->destructor(call);
+                        afs_free_call(call);
+                }
+        }
+
+        _leave("");
+}
+
+/*
+ * wait synchronously for a call to complete
+ */
+static int afs_wait_for_call_to_complete(struct afs_call *call)
+{
+        struct sk_buff *skb;
+        int ret;
+
+        DECLARE_WAITQUEUE(myself, current);
+
+        _enter("");
+
+        add_wait_queue(&call->waitq, &myself);
+        for (;;) {
+                set_current_state(TASK_INTERRUPTIBLE);
+
+                /* deliver any messages that are in the queue */
+                if (!skb_queue_empty(&call->rx_queue)) {
+                        __set_current_state(TASK_RUNNING);
+                        afs_deliver_to_call(call);
+                        continue;
+                }
+
+                ret = call->error;
+                if (call->state >= AFS_CALL_COMPLETE)
+                        break;
+                ret = -EINTR;
+                if (signal_pending(current))
+                        break;
+                schedule();
+        }
+
+        remove_wait_queue(&call->waitq, &myself);
+        __set_current_state(TASK_RUNNING);
+
+        /* kill the call */
+        if (call->state < AFS_CALL_COMPLETE) {
+                _debug("call incomplete");
+                rxrpc_kernel_abort_call(call->rxcall, RX_CALL_DEAD);
+                while ((skb = skb_dequeue(&call->rx_queue)))
+                        afs_free_skb(skb);
+        }
+
+        _debug("call complete");
+        rxrpc_kernel_end_call(call->rxcall);
+        call->rxcall = NULL;
+        call->type->destructor(call);
+        afs_free_call(call);
+        _leave(" = %d", ret);
+        return ret;
+}
+
+/*
+ * wake up a waiting call
+ */
+static void afs_wake_up_call_waiter(struct afs_call *call)
+{
+        wake_up(&call->waitq);
+}
+
+/*
+ * wake up an asynchronous call
+ */
+static void afs_wake_up_async_call(struct afs_call *call)
+{
+        _enter("");
+        queue_work(afs_async_calls, &call->async_work);
+}
+
+/*
+ * put a call into asynchronous mode
+ * - mustn't touch the call descriptor as the call my have completed by the
+ *   time we get here
+ */
+static int afs_dont_wait_for_call_to_complete(struct afs_call *call)
+{
+        _enter("");
+        return -EINPROGRESS;
+}
+
+/*
+ * delete an asynchronous call
+ */
+static void afs_delete_async_call(struct work_struct *work)
+{
+        struct afs_call *call =
+                container_of(work, struct afs_call, async_work);
+
+        _enter("");
+
+        afs_free_call(call);
+
+        _leave("");
+}
+
+/*
+ * perform processing on an asynchronous call
+ * - on a multiple-thread workqueue this work item may try to run on several
+ *   CPUs at the same time
+ */
+static void afs_process_async_call(struct work_struct *work)
+{
+        struct afs_call *call =
+                container_of(work, struct afs_call, async_work);
+
+        _enter("");
+
+        if (!skb_queue_empty(&call->rx_queue))
+                afs_deliver_to_call(call);
+
+        if (call->state >= AFS_CALL_COMPLETE && call->wait_mode) {
+                if (call->wait_mode->async_complete)
+                        call->wait_mode->async_complete(call->reply,
+                                                        call->error);
+                call->reply = NULL;
+
+                /* kill the call */
+                rxrpc_kernel_end_call(call->rxcall);
+                call->rxcall = NULL;
+                if (call->type->destructor)
+                        call->type->destructor(call);
+
+                /* we can't just delete the call because the work item may be
+                 * queued */
+                PREPARE_WORK(&call->async_work, afs_delete_async_call);
+                queue_work(afs_async_calls, &call->async_work);
+        }
+
+        _leave("");
+}
+
+/*
+ * empty a socket buffer into a flat reply buffer
+ */
+void afs_transfer_reply(struct afs_call *call, struct sk_buff *skb)
+{
+        size_t len = skb->len;
+
+        if (skb_copy_bits(skb, 0, call->buffer + call->reply_size, len) < 0)
+                BUG();
+        call->reply_size += len;
+}
+
+/*
+ * accept the backlog of incoming calls
+ */
+static void afs_collect_incoming_call(struct work_struct *work)
+{
+        struct rxrpc_call *rxcall;
+        struct afs_call *call = NULL;
+        struct sk_buff *skb;
+
+        while ((skb = skb_dequeue(&afs_incoming_calls))) {
+                _debug("new call");
+
+                /* don't need the notification */
+                afs_free_skb(skb);
+
+                if (!call) {
+                        call = kzalloc(sizeof(struct afs_call), GFP_KERNEL);
+                        if (!call) {
+                                rxrpc_kernel_reject_call(afs_socket);
+                                return;
+                        }
+
+                        INIT_WORK(&call->async_work, afs_process_async_call);
+                        call->wait_mode = &afs_async_incoming_call;
+                        call->type = &afs_RXCMxxxx;
+                        init_waitqueue_head(&call->waitq);
+                        skb_queue_head_init(&call->rx_queue);
+                        call->state = AFS_CALL_AWAIT_OP_ID;
+
+                        _debug("CALL %p{%s} [%d]",
+                               call, call->type->name,
+                               atomic_read(&afs_outstanding_calls));
+                        atomic_inc(&afs_outstanding_calls);
+                }
+
+                rxcall = rxrpc_kernel_accept_call(afs_socket,
+                                                  (unsigned long) call);
+                if (!IS_ERR(rxcall)) {
+                        call->rxcall = rxcall;
+                        call = NULL;
+                }
+        }
+
+        if (call)
+                afs_free_call(call);
+}
+
+/*
+ * grab the operation ID from an incoming cache manager call
+ */
+static int afs_deliver_cm_op_id(struct afs_call *call, struct sk_buff *skb,
+                                bool last)
+{
+        size_t len = skb->len;
+        void *oibuf = (void *) &call->operation_ID;
+
+        _enter("{%u},{%zu},%d", call->offset, len, last);
+
+        ASSERTCMP(call->offset, <, 4);
+
+        /* the operation ID forms the first four bytes of the request data */
+        len = min_t(size_t, len, 4 - call->offset);
+        if (skb_copy_bits(skb, 0, oibuf + call->offset, len) < 0)
+                BUG();
+        if (!pskb_pull(skb, len))
+                BUG();
+        call->offset += len;
+
+        if (call->offset < 4) {
+                if (last) {
+                        _leave(" = -EBADMSG [op ID short]");
+                        return -EBADMSG;
+                }
+                _leave(" = 0 [incomplete]");
+                return 0;
+        }
+
+        call->state = AFS_CALL_AWAIT_REQUEST;
+
+        /* ask the cache manager to route the call (it'll change the call type
+         * if successful) */
+        if (!afs_cm_incoming_call(call))
+                return -ENOTSUPP;
+
+        /* pass responsibility for the remainer of this message off to the
+         * cache manager op */
+        return call->type->deliver(call, skb, last);
+}
+
+/*
+ * send an empty reply
+ */
+void afs_send_empty_reply(struct afs_call *call)
+{
+        struct msghdr msg;
+        struct iovec iov[1];
+
+        _enter("");
+
+        iov[0].iov_base         = NULL;
+        iov[0].iov_len          = 0;
+        msg.msg_name            = NULL;
+        msg.msg_namelen         = 0;
+        msg.msg_iov             = iov;
+        msg.msg_iovlen          = 0;
+        msg.msg_control         = NULL;
+        msg.msg_controllen      = 0;
+        msg.msg_flags           = 0;
+
+        call->state = AFS_CALL_AWAIT_ACK;
+        switch (rxrpc_kernel_send_data(call->rxcall, &msg, 0)) {
+        case 0:
+                _leave(" [replied]");
+                return;
+
+        case -ENOMEM:
+                _debug("oom");
+                rxrpc_kernel_abort_call(call->rxcall, RX_USER_ABORT);
+        default:
+                rxrpc_kernel_end_call(call->rxcall);
+                call->rxcall = NULL;
+                call->type->destructor(call);
+                afs_free_call(call);
+                _leave(" [error]");
+                return;
+        }
+}
+
+/*
+ * send a simple reply
+ */
+void afs_send_simple_reply(struct afs_call *call, const void *buf, size_t len)
+{
+        struct msghdr msg;
+        struct iovec iov[1];
+
+        _enter("");
+
+        iov[0].iov_base         = (void *) buf;
+        iov[0].iov_len          = len;
+        msg.msg_name            = NULL;
+        msg.msg_namelen         = 0;
+        msg.msg_iov             = iov;
+        msg.msg_iovlen          = 1;
+        msg.msg_control         = NULL;
+        msg.msg_controllen      = 0;
+        msg.msg_flags           = 0;
+
+        call->state = AFS_CALL_AWAIT_ACK;
+        switch (rxrpc_kernel_send_data(call->rxcall, &msg, len)) {
+        case 0:
+                _leave(" [replied]");
+                return;
+
+        case -ENOMEM:
+                _debug("oom");
+                rxrpc_kernel_abort_call(call->rxcall, RX_USER_ABORT);
+        default:
+                rxrpc_kernel_end_call(call->rxcall);
+                call->rxcall = NULL;
+                call->type->destructor(call);
+                afs_free_call(call);
+                _leave(" [error]");
+                return;
+        }
+}
+
+/*
+ * extract a piece of data from the received data socket buffers
+ */
+int afs_extract_data(struct afs_call *call, struct sk_buff *skb,
+                     bool last, void *buf, size_t count)
+{
+        size_t len = skb->len;
+
+        _enter("{%u},{%zu},%d,,%zu", call->offset, len, last, count);
+
+        ASSERTCMP(call->offset, <, count);
+
+        len = min_t(size_t, len, count - call->offset);
+        if (skb_copy_bits(skb, 0, buf + call->offset, len) < 0 ||
+            !pskb_pull(skb, len))
+                BUG();
+        call->offset += len;
+
+        if (call->offset < count) {
+                if (last) {
+                        _leave(" = -EBADMSG [%d < %lu]", call->offset, count);
+                        return -EBADMSG;
+                }
+                _leave(" = -EAGAIN");
+                return -EAGAIN;
+        }
+        return 0;
+}