/* 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;
}

/*
 * attach the data from a bunch of pages on an inode to a call
 */
static int afs_send_pages(struct afs_call *call, struct msghdr *msg,
                          struct kvec *iov)
{
        struct page *pages[8];
        unsigned count, n, loop, offset, to;
        pgoff_t first = call->first, last = call->last;
        int ret;

        _enter("");

        offset = call->first_offset;
        call->first_offset = 0;

        do {
                _debug("attach %lx-%lx", first, last);

                count = last - first + 1;
                if (count > ARRAY_SIZE(pages))
                        count = ARRAY_SIZE(pages);
                n = find_get_pages_contig(call->mapping, first, count, pages);
                ASSERTCMP(n, ==, count);

                loop = 0;
                do {
                        msg->msg_flags = 0;
                        to = PAGE_SIZE;
                        if (first + loop >= last)
                                to = call->last_to;
                        else
                                msg->msg_flags = MSG_MORE;
                        iov->iov_base = kmap(pages[loop]) + offset;
                        iov->iov_len = to - offset;
                        offset = 0;

                        _debug("- range %u-%u%s",
                               offset, to, msg->msg_flags ? " [more]" : "");
                        msg->msg_iov = (struct iovec *) iov;
                        msg->msg_iovlen = 1;

                        /* have to change the state *before* sending the last
                         * packet as RxRPC might give us the reply before it
                         * returns from sending the request */
                        if (first + loop >= last)
                                call->state = AFS_CALL_AWAIT_REPLY;
                        ret = rxrpc_kernel_send_data(call->rxcall, msg,
                                                     to - offset);
                        kunmap(pages[loop]);
                        if (ret < 0)
                                break;
                } while (++loop < count);
                first += count;

                for (loop = 0; loop < count; loop++)
                        put_page(pages[loop]);
                if (ret < 0)
                        break;
        } while (first <= last);

        _leave(" = %d", ret);
        return ret;
}

/*
 * 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,%x} [%d]____",
               call, call->type->name, key_serial(call->key),
               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           = (call->send_pages ? MSG_MORE : 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 */
        if (!call->send_pages)
                call->state = AFS_CALL_AWAIT_REPLY;
        ret = rxrpc_kernel_send_data(rxcall, &msg, call->request_size);
        if (ret < 0)
                goto error_do_abort;

        if (call->send_pages) {
                ret = afs_send_pages(call, &msg, iov);
                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];
        int n;

        _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;
        n = rxrpc_kernel_send_data(call->rxcall, &msg, len);
        if (n >= 0) {
                _leave(" [replied]");
                return;
        }
        if (n == -ENOMEM) {
                _debug("oom");
                rxrpc_kernel_abort_call(call->rxcall, RX_USER_ABORT);
        }
        rxrpc_kernel_end_call(call->rxcall);
        call->rxcall = NULL;
        call->type->destructor(call);
        afs_free_call(call);
        _leave(" [error]");
}

/*
 * 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 < %zu]", call->offset, count);
                        return -EBADMSG;
                }
                _leave(" = -EAGAIN");
                return -EAGAIN;
        }
        return 0;
}