[thirdparty/linux.git] / fs / smb / client / transport.c

// SPDX-License-Identifier: LGPL-2.1
/*
 *
 *   Copyright (C) International Business Machines  Corp., 2002,2008
 *   Author(s): Steve French (sfrench@us.ibm.com)
 *   Jeremy Allison (jra@samba.org) 2006.
 *
 */

#include <linux/fs.h>
#include <linux/list.h>
#include <linux/gfp.h>
#include <linux/wait.h>
#include <linux/net.h>
#include <linux/delay.h>
#include <linux/freezer.h>
#include <linux/tcp.h>
#include <linux/bvec.h>
#include <linux/highmem.h>
#include <linux/uaccess.h>
#include <linux/processor.h>
#include <linux/mempool.h>
#include <linux/sched/signal.h>
#include <linux/task_io_accounting_ops.h>
#include "cifspdu.h"
#include "cifsglob.h"
#include "cifsproto.h"
#include "cifs_debug.h"
#include "smb2proto.h"
#include "smbdirect.h"

/* Max number of iovectors we can use off the stack when sending requests. */
#define CIFS_MAX_IOV_SIZE 8

void
cifs_wake_up_task(struct mid_q_entry *mid)
{
        if (mid->mid_state == MID_RESPONSE_RECEIVED)
                mid->mid_state = MID_RESPONSE_READY;
        wake_up_process(mid->callback_data);
}

static struct mid_q_entry *
alloc_mid(const struct smb_hdr *smb_buffer, struct TCP_Server_Info *server)
{
        struct mid_q_entry *temp;

        if (server == NULL) {
                cifs_dbg(VFS, "%s: null TCP session\n", __func__);
                return NULL;
        }

        temp = mempool_alloc(cifs_mid_poolp, GFP_NOFS);
        memset(temp, 0, sizeof(struct mid_q_entry));
        kref_init(&temp->refcount);
        temp->mid = get_mid(smb_buffer);
        temp->pid = current->pid;
        temp->command = cpu_to_le16(smb_buffer->Command);
        cifs_dbg(FYI, "For smb_command %d\n", smb_buffer->Command);
        /* easier to use jiffies */
        /* when mid allocated can be before when sent */
        temp->when_alloc = jiffies;
        temp->server = server;

        /*
         * The default is for the mid to be synchronous, so the
         * default callback just wakes up the current task.
         */
        get_task_struct(current);
        temp->creator = current;
        temp->callback = cifs_wake_up_task;
        temp->callback_data = current;

        atomic_inc(&mid_count);
        temp->mid_state = MID_REQUEST_ALLOCATED;
        return temp;
}

void __release_mid(struct kref *refcount)
{
        struct mid_q_entry *midEntry =
                        container_of(refcount, struct mid_q_entry, refcount);
#ifdef CONFIG_CIFS_STATS2
        __le16 command = midEntry->server->vals->lock_cmd;
        __u16 smb_cmd = le16_to_cpu(midEntry->command);
        unsigned long now;
        unsigned long roundtrip_time;
#endif
        struct TCP_Server_Info *server = midEntry->server;

        if (midEntry->resp_buf && (midEntry->mid_flags & MID_WAIT_CANCELLED) &&
            (midEntry->mid_state == MID_RESPONSE_RECEIVED ||
             midEntry->mid_state == MID_RESPONSE_READY) &&
            server->ops->handle_cancelled_mid)
                server->ops->handle_cancelled_mid(midEntry, server);

        midEntry->mid_state = MID_FREE;
        atomic_dec(&mid_count);
        if (midEntry->large_buf)
                cifs_buf_release(midEntry->resp_buf);
        else
                cifs_small_buf_release(midEntry->resp_buf);
#ifdef CONFIG_CIFS_STATS2
        now = jiffies;
        if (now < midEntry->when_alloc)
                cifs_server_dbg(VFS, "Invalid mid allocation time\n");
        roundtrip_time = now - midEntry->when_alloc;

        if (smb_cmd < NUMBER_OF_SMB2_COMMANDS) {
                if (atomic_read(&server->num_cmds[smb_cmd]) == 0) {
                        server->slowest_cmd[smb_cmd] = roundtrip_time;
                        server->fastest_cmd[smb_cmd] = roundtrip_time;
                } else {
                        if (server->slowest_cmd[smb_cmd] < roundtrip_time)
                                server->slowest_cmd[smb_cmd] = roundtrip_time;
                        else if (server->fastest_cmd[smb_cmd] > roundtrip_time)
                                server->fastest_cmd[smb_cmd] = roundtrip_time;
                }
                cifs_stats_inc(&server->num_cmds[smb_cmd]);
                server->time_per_cmd[smb_cmd] += roundtrip_time;
        }
        /*
         * commands taking longer than one second (default) can be indications
         * that something is wrong, unless it is quite a slow link or a very
         * busy server. Note that this calc is unlikely or impossible to wrap
         * as long as slow_rsp_threshold is not set way above recommended max
         * value (32767 ie 9 hours) and is generally harmless even if wrong
         * since only affects debug counters - so leaving the calc as simple
         * comparison rather than doing multiple conversions and overflow
         * checks
         */
        if ((slow_rsp_threshold != 0) &&
            time_after(now, midEntry->when_alloc + (slow_rsp_threshold * HZ)) &&
            (midEntry->command != command)) {
                /*
                 * smb2slowcmd[NUMBER_OF_SMB2_COMMANDS] counts by command
                 * NB: le16_to_cpu returns unsigned so can not be negative below
                 */
                if (smb_cmd < NUMBER_OF_SMB2_COMMANDS)
                        cifs_stats_inc(&server->smb2slowcmd[smb_cmd]);

                trace_smb3_slow_rsp(smb_cmd, midEntry->mid, midEntry->pid,
                               midEntry->when_sent, midEntry->when_received);
                if (cifsFYI & CIFS_TIMER) {
                        pr_debug("slow rsp: cmd %d mid %llu",
                                 midEntry->command, midEntry->mid);
                        cifs_info("A: 0x%lx S: 0x%lx R: 0x%lx\n",
                                  now - midEntry->when_alloc,
                                  now - midEntry->when_sent,
                                  now - midEntry->when_received);
                }
        }
#endif
        put_task_struct(midEntry->creator);

        mempool_free(midEntry, cifs_mid_poolp);
}

void
delete_mid(struct mid_q_entry *mid)
{
        spin_lock(&mid->server->mid_lock);
        if (!(mid->mid_flags & MID_DELETED)) {
                list_del_init(&mid->qhead);
                mid->mid_flags |= MID_DELETED;
        }
        spin_unlock(&mid->server->mid_lock);

        release_mid(mid);
}

/*
 * smb_send_kvec - send an array of kvecs to the server
 * @server:     Server to send the data to
 * @smb_msg:    Message to send
 * @sent:       amount of data sent on socket is stored here
 *
 * Our basic "send data to server" function. Should be called with srv_mutex
 * held. The caller is responsible for handling the results.
 */
static int
smb_send_kvec(struct TCP_Server_Info *server, struct msghdr *smb_msg,
              size_t *sent)
{
        int rc = 0;
        int retries = 0;
        struct socket *ssocket = server->ssocket;

        *sent = 0;

        if (server->noblocksnd)
                smb_msg->msg_flags = MSG_DONTWAIT + MSG_NOSIGNAL;
        else
                smb_msg->msg_flags = MSG_NOSIGNAL;

        while (msg_data_left(smb_msg)) {
                /*
                 * If blocking send, we try 3 times, since each can block
                 * for 5 seconds. For nonblocking  we have to try more
                 * but wait increasing amounts of time allowing time for
                 * socket to clear.  The overall time we wait in either
                 * case to send on the socket is about 15 seconds.
                 * Similarly we wait for 15 seconds for a response from
                 * the server in SendReceive[2] for the server to send
                 * a response back for most types of requests (except
                 * SMB Write past end of file which can be slow, and
                 * blocking lock operations). NFS waits slightly longer
                 * than CIFS, but this can make it take longer for
                 * nonresponsive servers to be detected and 15 seconds
                 * is more than enough time for modern networks to
                 * send a packet.  In most cases if we fail to send
                 * after the retries we will kill the socket and
                 * reconnect which may clear the network problem.
                 */
                rc = sock_sendmsg(ssocket, smb_msg);
                if (rc == -EAGAIN) {
                        retries++;
                        if (retries >= 14 ||
                            (!server->noblocksnd && (retries > 2))) {
                                cifs_server_dbg(VFS, "sends on sock %p stuck for 15 seconds\n",
                                         ssocket);
                                return -EAGAIN;
                        }
                        msleep(1 << retries);
                        continue;
                }

                if (rc < 0)
                        return rc;

                if (rc == 0) {
                        /* should never happen, letting socket clear before
                           retrying is our only obvious option here */
                        cifs_server_dbg(VFS, "tcp sent no data\n");
                        msleep(500);
                        continue;
                }

                /* send was at least partially successful */
                *sent += rc;
                retries = 0; /* in case we get ENOSPC on the next send */
        }
        return 0;
}

unsigned long
smb_rqst_len(struct TCP_Server_Info *server, struct smb_rqst *rqst)
{
        unsigned int i;
        struct kvec *iov;
        int nvec;
        unsigned long buflen = 0;

        if (!is_smb1(server) && rqst->rq_nvec >= 2 &&
            rqst->rq_iov[0].iov_len == 4) {
                iov = &rqst->rq_iov[1];
                nvec = rqst->rq_nvec - 1;
        } else {
                iov = rqst->rq_iov;
                nvec = rqst->rq_nvec;
        }

        /* total up iov array first */
        for (i = 0; i < nvec; i++)
                buflen += iov[i].iov_len;

        buflen += iov_iter_count(&rqst->rq_iter);
        return buflen;
}

static int
__smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
                struct smb_rqst *rqst)
{
        int rc;
        struct kvec *iov;
        int n_vec;
        unsigned int send_length = 0;
        unsigned int i, j;
        sigset_t mask, oldmask;
        size_t total_len = 0, sent, size;
        struct socket *ssocket = server->ssocket;
        struct msghdr smb_msg = {};
        __be32 rfc1002_marker;

        cifs_in_send_inc(server);
        if (cifs_rdma_enabled(server)) {
                /* return -EAGAIN when connecting or reconnecting */
                rc = -EAGAIN;
                if (server->smbd_conn)
                        rc = smbd_send(server, num_rqst, rqst);
                goto smbd_done;
        }

        rc = -EAGAIN;
        if (ssocket == NULL)
                goto out;

        rc = -ERESTARTSYS;
        if (fatal_signal_pending(current)) {
                cifs_dbg(FYI, "signal pending before send request\n");
                goto out;
        }

        rc = 0;
        /* cork the socket */
        tcp_sock_set_cork(ssocket->sk, true);

        for (j = 0; j < num_rqst; j++)
                send_length += smb_rqst_len(server, &rqst[j]);
        rfc1002_marker = cpu_to_be32(send_length);

        /*
         * We should not allow signals to interrupt the network send because
         * any partial send will cause session reconnects thus increasing
         * latency of system calls and overload a server with unnecessary
         * requests.
         */

        sigfillset(&mask);
        sigprocmask(SIG_BLOCK, &mask, &oldmask);

        /* Generate a rfc1002 marker for SMB2+ */
        if (!is_smb1(server)) {
                struct kvec hiov = {
                        .iov_base = &rfc1002_marker,
                        .iov_len  = 4
                };
                iov_iter_kvec(&smb_msg.msg_iter, ITER_SOURCE, &hiov, 1, 4);
                rc = smb_send_kvec(server, &smb_msg, &sent);
                if (rc < 0)
                        goto unmask;

                total_len += sent;
                send_length += 4;
        }

        cifs_dbg(FYI, "Sending smb: smb_len=%u\n", send_length);

        for (j = 0; j < num_rqst; j++) {
                iov = rqst[j].rq_iov;
                n_vec = rqst[j].rq_nvec;

                size = 0;
                for (i = 0; i < n_vec; i++) {
                        dump_smb(iov[i].iov_base, iov[i].iov_len);
                        size += iov[i].iov_len;
                }

                iov_iter_kvec(&smb_msg.msg_iter, ITER_SOURCE, iov, n_vec, size);

                rc = smb_send_kvec(server, &smb_msg, &sent);
                if (rc < 0)
                        goto unmask;

                total_len += sent;

                if (iov_iter_count(&rqst[j].rq_iter) > 0) {
                        smb_msg.msg_iter = rqst[j].rq_iter;
                        rc = smb_send_kvec(server, &smb_msg, &sent);
                        if (rc < 0)
                                break;
                        total_len += sent;
                }

}

unmask:
        sigprocmask(SIG_SETMASK, &oldmask, NULL);

        /*
         * If signal is pending but we have already sent the whole packet to
         * the server we need to return success status to allow a corresponding
         * mid entry to be kept in the pending requests queue thus allowing
         * to handle responses from the server by the client.
         *
         * If only part of the packet has been sent there is no need to hide
         * interrupt because the session will be reconnected anyway, so there
         * won't be any response from the server to handle.
         */

        if (signal_pending(current) && (total_len != send_length)) {
                cifs_dbg(FYI, "signal is pending after attempt to send\n");
                rc = -ERESTARTSYS;
        }

        /* uncork it */
        tcp_sock_set_cork(ssocket->sk, false);

        if ((total_len > 0) && (total_len != send_length)) {
                cifs_dbg(FYI, "partial send (wanted=%u sent=%zu): terminating session\n",
                         send_length, total_len);
                /*
                 * If we have only sent part of an SMB then the next SMB could
                 * be taken as the remainder of this one. We need to kill the
                 * socket so the server throws away the partial SMB
                 */
                cifs_signal_cifsd_for_reconnect(server, false);
                trace_smb3_partial_send_reconnect(server->CurrentMid,
                                                  server->conn_id, server->hostname);
        }
smbd_done:
        if (rc < 0 && rc != -EINTR)
                cifs_server_dbg(VFS, "Error %d sending data on socket to server\n",
                         rc);
        else if (rc > 0)
                rc = 0;
out:
        cifs_in_send_dec(server);
        return rc;
}

struct send_req_vars {
        struct smb2_transform_hdr tr_hdr;
        struct smb_rqst rqst[MAX_COMPOUND];
        struct kvec iov;
};

static int
smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
              struct smb_rqst *rqst, int flags)
{
        struct send_req_vars *vars;
        struct smb_rqst *cur_rqst;
        struct kvec *iov;
        int rc;

        if (!(flags & CIFS_TRANSFORM_REQ))
                return __smb_send_rqst(server, num_rqst, rqst);

        if (num_rqst > MAX_COMPOUND - 1)
                return -ENOMEM;

        if (!server->ops->init_transform_rq) {
                cifs_server_dbg(VFS, "Encryption requested but transform callback is missing\n");
                return -EIO;
        }

        vars = kzalloc(sizeof(*vars), GFP_NOFS);
        if (!vars)
                return -ENOMEM;
        cur_rqst = vars->rqst;
        iov = &vars->iov;

        iov->iov_base = &vars->tr_hdr;
        iov->iov_len = sizeof(vars->tr_hdr);
        cur_rqst[0].rq_iov = iov;
        cur_rqst[0].rq_nvec = 1;

        rc = server->ops->init_transform_rq(server, num_rqst + 1,
                                            &cur_rqst[0], rqst);
        if (rc)
                goto out;

        rc = __smb_send_rqst(server, num_rqst + 1, &cur_rqst[0]);
        smb3_free_compound_rqst(num_rqst, &cur_rqst[1]);
out:
        kfree(vars);
        return rc;
}

int
smb_send(struct TCP_Server_Info *server, struct smb_hdr *smb_buffer,
         unsigned int smb_buf_length)
{
        struct kvec iov[2];
        struct smb_rqst rqst = { .rq_iov = iov,
                                 .rq_nvec = 2 };

        iov[0].iov_base = smb_buffer;
        iov[0].iov_len = 4;
        iov[1].iov_base = (char *)smb_buffer + 4;
        iov[1].iov_len = smb_buf_length;

        return __smb_send_rqst(server, 1, &rqst);
}

static int
wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
                      const int timeout, const int flags,
                      unsigned int *instance)
{
        long rc;
        int *credits;
        int optype;
        long int t;
        int scredits, in_flight;

        if (timeout < 0)
                t = MAX_JIFFY_OFFSET;
        else
                t = msecs_to_jiffies(timeout);

        optype = flags & CIFS_OP_MASK;

        *instance = 0;

        credits = server->ops->get_credits_field(server, optype);
        /* Since an echo is already inflight, no need to wait to send another */
        if (*credits <= 0 && optype == CIFS_ECHO_OP)
                return -EAGAIN;

        spin_lock(&server->req_lock);
        if ((flags & CIFS_TIMEOUT_MASK) == CIFS_NON_BLOCKING) {
                /* oplock breaks must not be held up */
                server->in_flight++;
                if (server->in_flight > server->max_in_flight)
                        server->max_in_flight = server->in_flight;
                *credits -= 1;
                *instance = server->reconnect_instance;
                scredits = *credits;
                in_flight = server->in_flight;
                spin_unlock(&server->req_lock);

                trace_smb3_nblk_credits(server->CurrentMid,
                                server->conn_id, server->hostname, scredits, -1, in_flight);
                cifs_dbg(FYI, "%s: remove %u credits total=%d\n",
                                __func__, 1, scredits);

                return 0;
        }

        while (1) {
                spin_unlock(&server->req_lock);

                spin_lock(&server->srv_lock);
                if (server->tcpStatus == CifsExiting) {
                        spin_unlock(&server->srv_lock);
                        return -ENOENT;
                }
                spin_unlock(&server->srv_lock);

                spin_lock(&server->req_lock);
                if (*credits < num_credits) {
                        scredits = *credits;
                        spin_unlock(&server->req_lock);

                        cifs_num_waiters_inc(server);
                        rc = wait_event_killable_timeout(server->request_q,
                                has_credits(server, credits, num_credits), t);
                        cifs_num_waiters_dec(server);
                        if (!rc) {
                                spin_lock(&server->req_lock);
                                scredits = *credits;
                                in_flight = server->in_flight;
                                spin_unlock(&server->req_lock);

                                trace_smb3_credit_timeout(server->CurrentMid,
                                                server->conn_id, server->hostname, scredits,
                                                num_credits, in_flight);
                                cifs_server_dbg(VFS, "wait timed out after %d ms\n",
                                                timeout);
                                return -EBUSY;
                        }
                        if (rc == -ERESTARTSYS)
                                return -ERESTARTSYS;
                        spin_lock(&server->req_lock);
                } else {
                        /*
                         * For normal commands, reserve the last MAX_COMPOUND
                         * credits to compound requests.
                         * Otherwise these compounds could be permanently
                         * starved for credits by single-credit requests.
                         *
                         * To prevent spinning CPU, block this thread until
                         * there are >MAX_COMPOUND credits available.
                         * But only do this is we already have a lot of
                         * credits in flight to avoid triggering this check
                         * for servers that are slow to hand out credits on
                         * new sessions.
                         */
                        if (!optype && num_credits == 1 &&
                            server->in_flight > 2 * MAX_COMPOUND &&
                            *credits <= MAX_COMPOUND) {
                                spin_unlock(&server->req_lock);

                                cifs_num_waiters_inc(server);
                                rc = wait_event_killable_timeout(
                                        server->request_q,
                                        has_credits(server, credits,
                                                    MAX_COMPOUND + 1),
                                        t);
                                cifs_num_waiters_dec(server);
                                if (!rc) {
                                        spin_lock(&server->req_lock);
                                        scredits = *credits;
                                        in_flight = server->in_flight;
                                        spin_unlock(&server->req_lock);

                                        trace_smb3_credit_timeout(
                                                        server->CurrentMid,
                                                        server->conn_id, server->hostname,
                                                        scredits, num_credits, in_flight);
                                        cifs_server_dbg(VFS, "wait timed out after %d ms\n",
                                                        timeout);
                                        return -EBUSY;
                                }
                                if (rc == -ERESTARTSYS)
                                        return -ERESTARTSYS;
                                spin_lock(&server->req_lock);
                                continue;
                        }

                        /*
                         * Can not count locking commands against total
                         * as they are allowed to block on server.
                         */

                        /* update # of requests on the wire to server */
                        if ((flags & CIFS_TIMEOUT_MASK) != CIFS_BLOCKING_OP) {
                                *credits -= num_credits;
                                server->in_flight += num_credits;
                                if (server->in_flight > server->max_in_flight)
                                        server->max_in_flight = server->in_flight;
                                *instance = server->reconnect_instance;
                        }
                        scredits = *credits;
                        in_flight = server->in_flight;
                        spin_unlock(&server->req_lock);

                        trace_smb3_waitff_credits(server->CurrentMid,
                                        server->conn_id, server->hostname, scredits,
                                        -(num_credits), in_flight);
                        cifs_dbg(FYI, "%s: remove %u credits total=%d\n",
                                        __func__, num_credits, scredits);
                        break;
                }
        }
        return 0;
}

static int
wait_for_free_request(struct TCP_Server_Info *server, const int flags,
                      unsigned int *instance)
{
        return wait_for_free_credits(server, 1, -1, flags,
                                     instance);
}

static int
wait_for_compound_request(struct TCP_Server_Info *server, int num,
                          const int flags, unsigned int *instance)
{
        int *credits;
        int scredits, in_flight;

        credits = server->ops->get_credits_field(server, flags & CIFS_OP_MASK);

        spin_lock(&server->req_lock);
        scredits = *credits;
        in_flight = server->in_flight;

        if (*credits < num) {
                /*
                 * If the server is tight on resources or just gives us less
                 * credits for other reasons (e.g. requests are coming out of
                 * order and the server delays granting more credits until it
                 * processes a missing mid) and we exhausted most available
                 * credits there may be situations when we try to send
                 * a compound request but we don't have enough credits. At this
                 * point the client needs to decide if it should wait for
                 * additional credits or fail the request. If at least one
                 * request is in flight there is a high probability that the
                 * server will return enough credits to satisfy this compound
                 * request.
                 *
                 * Return immediately if no requests in flight since we will be
                 * stuck on waiting for credits.
                 */
                if (server->in_flight == 0) {
                        spin_unlock(&server->req_lock);
                        trace_smb3_insufficient_credits(server->CurrentMid,
                                        server->conn_id, server->hostname, scredits,
                                        num, in_flight);
                        cifs_dbg(FYI, "%s: %d requests in flight, needed %d total=%d\n",
                                        __func__, in_flight, num, scredits);
                        return -EDEADLK;
                }
        }
        spin_unlock(&server->req_lock);

        return wait_for_free_credits(server, num, 60000, flags,
                                     instance);
}

int
cifs_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,
                      unsigned int *num, struct cifs_credits *credits)
{
        *num = size;
        credits->value = 0;
        credits->instance = server->reconnect_instance;
        return 0;
}

static int allocate_mid(struct cifs_ses *ses, struct smb_hdr *in_buf,
                        struct mid_q_entry **ppmidQ)
{
        spin_lock(&ses->ses_lock);
        if (ses->ses_status == SES_NEW) {
                if ((in_buf->Command != SMB_COM_SESSION_SETUP_ANDX) &&
                        (in_buf->Command != SMB_COM_NEGOTIATE)) {
                        spin_unlock(&ses->ses_lock);
                        return -EAGAIN;
                }
                /* else ok - we are setting up session */
        }

        if (ses->ses_status == SES_EXITING) {
                /* check if SMB session is bad because we are setting it up */
                if (in_buf->Command != SMB_COM_LOGOFF_ANDX) {
                        spin_unlock(&ses->ses_lock);
                        return -EAGAIN;
                }
                /* else ok - we are shutting down session */
        }
        spin_unlock(&ses->ses_lock);

        *ppmidQ = alloc_mid(in_buf, ses->server);
        if (*ppmidQ == NULL)
                return -ENOMEM;
        spin_lock(&ses->server->mid_lock);
        list_add_tail(&(*ppmidQ)->qhead, &ses->server->pending_mid_q);
        spin_unlock(&ses->server->mid_lock);
        return 0;
}

static int
wait_for_response(struct TCP_Server_Info *server, struct mid_q_entry *midQ)
{
        int error;

        error = wait_event_state(server->response_q,
                                 midQ->mid_state != MID_REQUEST_SUBMITTED &&
                                 midQ->mid_state != MID_RESPONSE_RECEIVED,
                                 (TASK_KILLABLE|TASK_FREEZABLE_UNSAFE));
        if (error < 0)
                return -ERESTARTSYS;

        return 0;
}

struct mid_q_entry *
cifs_setup_async_request(struct TCP_Server_Info *server, struct smb_rqst *rqst)
{
        int rc;
        struct smb_hdr *hdr = (struct smb_hdr *)rqst->rq_iov[0].iov_base;
        struct mid_q_entry *mid;

        if (rqst->rq_iov[0].iov_len != 4 ||
            rqst->rq_iov[0].iov_base + 4 != rqst->rq_iov[1].iov_base)
                return ERR_PTR(-EIO);

        /* enable signing if server requires it */
        if (server->sign)
                hdr->Flags2 |= SMBFLG2_SECURITY_SIGNATURE;

        mid = alloc_mid(hdr, server);
        if (mid == NULL)
                return ERR_PTR(-ENOMEM);

        rc = cifs_sign_rqst(rqst, server, &mid->sequence_number);
        if (rc) {
                release_mid(mid);
                return ERR_PTR(rc);
        }

        return mid;
}

/*
 * Send a SMB request and set the callback function in the mid to handle
 * the result. Caller is responsible for dealing with timeouts.
 */
int
cifs_call_async(struct TCP_Server_Info *server, struct smb_rqst *rqst,
                mid_receive_t *receive, mid_callback_t *callback,
                mid_handle_t *handle, void *cbdata, const int flags,
                const struct cifs_credits *exist_credits)
{
        int rc;
        struct mid_q_entry *mid;
        struct cifs_credits credits = { .value = 0, .instance = 0 };
        unsigned int instance;
        int optype;

        optype = flags & CIFS_OP_MASK;

        if ((flags & CIFS_HAS_CREDITS) == 0) {
                rc = wait_for_free_request(server, flags, &instance);
                if (rc)
                        return rc;
                credits.value = 1;
                credits.instance = instance;
        } else
                instance = exist_credits->instance;

        cifs_server_lock(server);

        /*
         * We can't use credits obtained from the previous session to send this
         * request. Check if there were reconnects after we obtained credits and
         * return -EAGAIN in such cases to let callers handle it.
         */
        if (instance != server->reconnect_instance) {
                cifs_server_unlock(server);
                add_credits_and_wake_if(server, &credits, optype);
                return -EAGAIN;
        }

        mid = server->ops->setup_async_request(server, rqst);
        if (IS_ERR(mid)) {
                cifs_server_unlock(server);
                add_credits_and_wake_if(server, &credits, optype);
                return PTR_ERR(mid);
        }

        mid->receive = receive;
        mid->callback = callback;
        mid->callback_data = cbdata;
        mid->handle = handle;
        mid->mid_state = MID_REQUEST_SUBMITTED;

        /* put it on the pending_mid_q */
        spin_lock(&server->mid_lock);
        list_add_tail(&mid->qhead, &server->pending_mid_q);
        spin_unlock(&server->mid_lock);

        /*
         * Need to store the time in mid before calling I/O. For call_async,
         * I/O response may come back and free the mid entry on another thread.
         */
        cifs_save_when_sent(mid);
        rc = smb_send_rqst(server, 1, rqst, flags);

        if (rc < 0) {
                revert_current_mid(server, mid->credits);
                server->sequence_number -= 2;
                delete_mid(mid);
        }

        cifs_server_unlock(server);

        if (rc == 0)
                return 0;

        add_credits_and_wake_if(server, &credits, optype);
        return rc;
}

/*
 *
 * Send an SMB Request.  No response info (other than return code)
 * needs to be parsed.
 *
 * flags indicate the type of request buffer and how long to wait
 * and whether to log NT STATUS code (error) before mapping it to POSIX error
 *
 */
int
SendReceiveNoRsp(const unsigned int xid, struct cifs_ses *ses,
                 char *in_buf, int flags)
{
        int rc;
        struct kvec iov[1];
        struct kvec rsp_iov;
        int resp_buf_type;

        iov[0].iov_base = in_buf;
        iov[0].iov_len = get_rfc1002_length(in_buf) + 4;
        flags |= CIFS_NO_RSP_BUF;
        rc = SendReceive2(xid, ses, iov, 1, &resp_buf_type, flags, &rsp_iov);
        cifs_dbg(NOISY, "SendRcvNoRsp flags %d rc %d\n", flags, rc);

        return rc;
}

static int
cifs_sync_mid_result(struct mid_q_entry *mid, struct TCP_Server_Info *server)
{
        int rc = 0;

        cifs_dbg(FYI, "%s: cmd=%d mid=%llu state=%d\n",
                 __func__, le16_to_cpu(mid->command), mid->mid, mid->mid_state);

        spin_lock(&server->mid_lock);
        switch (mid->mid_state) {
        case MID_RESPONSE_READY:
                spin_unlock(&server->mid_lock);
                return rc;
        case MID_RETRY_NEEDED:
                rc = -EAGAIN;
                break;
        case MID_RESPONSE_MALFORMED:
                rc = -EIO;
                break;
        case MID_SHUTDOWN:
                rc = -EHOSTDOWN;
                break;
        default:
                if (!(mid->mid_flags & MID_DELETED)) {
                        list_del_init(&mid->qhead);
                        mid->mid_flags |= MID_DELETED;
                }
                cifs_server_dbg(VFS, "%s: invalid mid state mid=%llu state=%d\n",
                         __func__, mid->mid, mid->mid_state);
                rc = -EIO;
        }
        spin_unlock(&server->mid_lock);

        release_mid(mid);
        return rc;
}

static inline int
send_cancel(struct TCP_Server_Info *server, struct smb_rqst *rqst,
            struct mid_q_entry *mid)
{
        return server->ops->send_cancel ?
                                server->ops->send_cancel(server, rqst, mid) : 0;
}

int
cifs_check_receive(struct mid_q_entry *mid, struct TCP_Server_Info *server,
                   bool log_error)
{
        unsigned int len = get_rfc1002_length(mid->resp_buf) + 4;

        dump_smb(mid->resp_buf, min_t(u32, 92, len));

        /* convert the length into a more usable form */
        if (server->sign) {
                struct kvec iov[2];
                int rc = 0;
                struct smb_rqst rqst = { .rq_iov = iov,
                                         .rq_nvec = 2 };

                iov[0].iov_base = mid->resp_buf;
                iov[0].iov_len = 4;
                iov[1].iov_base = (char *)mid->resp_buf + 4;
                iov[1].iov_len = len - 4;
                /* FIXME: add code to kill session */
                rc = cifs_verify_signature(&rqst, server,
                                           mid->sequence_number);
                if (rc)
                        cifs_server_dbg(VFS, "SMB signature verification returned error = %d\n",
                                 rc);
        }

        /* BB special case reconnect tid and uid here? */
        return map_and_check_smb_error(mid, log_error);
}

struct mid_q_entry *
cifs_setup_request(struct cifs_ses *ses, struct TCP_Server_Info *ignored,
                   struct smb_rqst *rqst)
{
        int rc;
        struct smb_hdr *hdr = (struct smb_hdr *)rqst->rq_iov[0].iov_base;
        struct mid_q_entry *mid;

        if (rqst->rq_iov[0].iov_len != 4 ||
            rqst->rq_iov[0].iov_base + 4 != rqst->rq_iov[1].iov_base)
                return ERR_PTR(-EIO);

        rc = allocate_mid(ses, hdr, &mid);
        if (rc)
                return ERR_PTR(rc);
        rc = cifs_sign_rqst(rqst, ses->server, &mid->sequence_number);
        if (rc) {
                delete_mid(mid);
                return ERR_PTR(rc);
        }
        return mid;
}

static void
cifs_compound_callback(struct mid_q_entry *mid)
{
        struct TCP_Server_Info *server = mid->server;
        struct cifs_credits credits;

        credits.value = server->ops->get_credits(mid);
        credits.instance = server->reconnect_instance;

        add_credits(server, &credits, mid->optype);

        if (mid->mid_state == MID_RESPONSE_RECEIVED)
                mid->mid_state = MID_RESPONSE_READY;
}

static void
cifs_compound_last_callback(struct mid_q_entry *mid)
{
        cifs_compound_callback(mid);
        cifs_wake_up_task(mid);
}

static void
cifs_cancelled_callback(struct mid_q_entry *mid)
{
        cifs_compound_callback(mid);
        release_mid(mid);
}

/*
 * Return a channel (master if none) of @ses that can be used to send
 * regular requests.
 *
 * If we are currently binding a new channel (negprot/sess.setup),
 * return the new incomplete channel.
 */
struct TCP_Server_Info *cifs_pick_channel(struct cifs_ses *ses)
{
        uint index = 0;
        unsigned int min_in_flight = UINT_MAX, max_in_flight = 0;
        struct TCP_Server_Info *server = NULL;
        int i;

        if (!ses)
                return NULL;

        spin_lock(&ses->chan_lock);
        for (i = 0; i < ses->chan_count; i++) {
                server = ses->chans[i].server;
                if (!server)
                        continue;

                /*
                 * strictly speaking, we should pick up req_lock to read
                 * server->in_flight. But it shouldn't matter much here if we
                 * race while reading this data. The worst that can happen is
                 * that we could use a channel that's not least loaded. Avoiding
                 * taking the lock could help reduce wait time, which is
                 * important for this function
                 */
                if (server->in_flight < min_in_flight) {
                        min_in_flight = server->in_flight;
                        index = i;
                }
                if (server->in_flight > max_in_flight)
                        max_in_flight = server->in_flight;
        }

        /* if all channels are equally loaded, fall back to round-robin */
        if (min_in_flight == max_in_flight) {
                index = (uint)atomic_inc_return(&ses->chan_seq);
                index %= ses->chan_count;
        }
        spin_unlock(&ses->chan_lock);

        return ses->chans[index].server;
}

int
compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
                   struct TCP_Server_Info *server,
                   const int flags, const int num_rqst, struct smb_rqst *rqst,
                   int *resp_buf_type, struct kvec *resp_iov)
{
        int i, j, optype, rc = 0;
        struct mid_q_entry *midQ[MAX_COMPOUND];
        bool cancelled_mid[MAX_COMPOUND] = {false};
        struct cifs_credits credits[MAX_COMPOUND] = {
                { .value = 0, .instance = 0 }
        };
        unsigned int instance;
        char *buf;

        optype = flags & CIFS_OP_MASK;

        for (i = 0; i < num_rqst; i++)
                resp_buf_type[i] = CIFS_NO_BUFFER;  /* no response buf yet */

        if (!ses || !ses->server || !server) {
                cifs_dbg(VFS, "Null session\n");
                return -EIO;
        }

        spin_lock(&server->srv_lock);
        if (server->tcpStatus == CifsExiting) {
                spin_unlock(&server->srv_lock);
                return -ENOENT;
        }
        spin_unlock(&server->srv_lock);

        /*
         * Wait for all the requests to become available.
         * This approach still leaves the possibility to be stuck waiting for
         * credits if the server doesn't grant credits to the outstanding
         * requests and if the client is completely idle, not generating any
         * other requests.
         * This can be handled by the eventual session reconnect.
         */
        rc = wait_for_compound_request(server, num_rqst, flags,
                                       &instance);
        if (rc)
                return rc;

        for (i = 0; i < num_rqst; i++) {
                credits[i].value = 1;
                credits[i].instance = instance;
        }

        /*
         * Make sure that we sign in the same order that we send on this socket
         * and avoid races inside tcp sendmsg code that could cause corruption
         * of smb data.
         */

        cifs_server_lock(server);

        /*
         * All the parts of the compound chain belong obtained credits from the
         * same session. We can not use credits obtained from the previous
         * session to send this request. Check if there were reconnects after
         * we obtained credits and return -EAGAIN in such cases to let callers
         * handle it.
         */
        if (instance != server->reconnect_instance) {
                cifs_server_unlock(server);
                for (j = 0; j < num_rqst; j++)
                        add_credits(server, &credits[j], optype);
                return -EAGAIN;
        }

        for (i = 0; i < num_rqst; i++) {
                midQ[i] = server->ops->setup_request(ses, server, &rqst[i]);
                if (IS_ERR(midQ[i])) {
                        revert_current_mid(server, i);
                        for (j = 0; j < i; j++)
                                delete_mid(midQ[j]);
                        cifs_server_unlock(server);

                        /* Update # of requests on wire to server */
                        for (j = 0; j < num_rqst; j++)
                                add_credits(server, &credits[j], optype);
                        return PTR_ERR(midQ[i]);
                }

                midQ[i]->mid_state = MID_REQUEST_SUBMITTED;
                midQ[i]->optype = optype;
                /*
                 * Invoke callback for every part of the compound chain
                 * to calculate credits properly. Wake up this thread only when
                 * the last element is received.
                 */
                if (i < num_rqst - 1)
                        midQ[i]->callback = cifs_compound_callback;
                else
                        midQ[i]->callback = cifs_compound_last_callback;
        }
        rc = smb_send_rqst(server, num_rqst, rqst, flags);

        for (i = 0; i < num_rqst; i++)
                cifs_save_when_sent(midQ[i]);

        if (rc < 0) {
                revert_current_mid(server, num_rqst);
                server->sequence_number -= 2;
        }

        cifs_server_unlock(server);

        /*
         * If sending failed for some reason or it is an oplock break that we
         * will not receive a response to - return credits back
         */
        if (rc < 0 || (flags & CIFS_NO_SRV_RSP)) {
                for (i = 0; i < num_rqst; i++)
                        add_credits(server, &credits[i], optype);
                goto out;
        }

        /*
         * At this point the request is passed to the network stack - we assume
         * that any credits taken from the server structure on the client have
         * been spent and we can't return them back. Once we receive responses
         * we will collect credits granted by the server in the mid callbacks
         * and add those credits to the server structure.
         */

        /*
         * Compounding is never used during session establish.
         */
        spin_lock(&ses->ses_lock);
        if ((ses->ses_status == SES_NEW) || (optype & CIFS_NEG_OP) || (optype & CIFS_SESS_OP)) {
                spin_unlock(&ses->ses_lock);

                cifs_server_lock(server);
                smb311_update_preauth_hash(ses, server, rqst[0].rq_iov, rqst[0].rq_nvec);
                cifs_server_unlock(server);

                spin_lock(&ses->ses_lock);
        }
        spin_unlock(&ses->ses_lock);

        for (i = 0; i < num_rqst; i++) {
                rc = wait_for_response(server, midQ[i]);
                if (rc != 0)
                        break;
        }
        if (rc != 0) {
                for (; i < num_rqst; i++) {
                        cifs_server_dbg(FYI, "Cancelling wait for mid %llu cmd: %d\n",
                                 midQ[i]->mid, le16_to_cpu(midQ[i]->command));
                        send_cancel(server, &rqst[i], midQ[i]);
                        spin_lock(&server->mid_lock);
                        midQ[i]->mid_flags |= MID_WAIT_CANCELLED;
                        if (midQ[i]->mid_state == MID_REQUEST_SUBMITTED ||
                            midQ[i]->mid_state == MID_RESPONSE_RECEIVED) {
                                midQ[i]->callback = cifs_cancelled_callback;
                                cancelled_mid[i] = true;
                                credits[i].value = 0;
                        }
                        spin_unlock(&server->mid_lock);
                }
        }

        for (i = 0; i < num_rqst; i++) {
                if (rc < 0)
                        goto out;

                rc = cifs_sync_mid_result(midQ[i], server);
                if (rc != 0) {
                        /* mark this mid as cancelled to not free it below */
                        cancelled_mid[i] = true;
                        goto out;
                }

                if (!midQ[i]->resp_buf ||
                    midQ[i]->mid_state != MID_RESPONSE_READY) {
                        rc = -EIO;
                        cifs_dbg(FYI, "Bad MID state?\n");
                        goto out;
                }

                buf = (char *)midQ[i]->resp_buf;
                resp_iov[i].iov_base = buf;
                resp_iov[i].iov_len = midQ[i]->resp_buf_size +
                        HEADER_PREAMBLE_SIZE(server);

                if (midQ[i]->large_buf)
                        resp_buf_type[i] = CIFS_LARGE_BUFFER;
                else
                        resp_buf_type[i] = CIFS_SMALL_BUFFER;

                rc = server->ops->check_receive(midQ[i], server,
                                                     flags & CIFS_LOG_ERROR);

                /* mark it so buf will not be freed by delete_mid */
                if ((flags & CIFS_NO_RSP_BUF) == 0)
                        midQ[i]->resp_buf = NULL;

        }

        /*
         * Compounding is never used during session establish.
         */
        spin_lock(&ses->ses_lock);
        if ((ses->ses_status == SES_NEW) || (optype & CIFS_NEG_OP) || (optype & CIFS_SESS_OP)) {
                struct kvec iov = {
                        .iov_base = resp_iov[0].iov_base,
                        .iov_len = resp_iov[0].iov_len
                };
                spin_unlock(&ses->ses_lock);
                cifs_server_lock(server);
                smb311_update_preauth_hash(ses, server, &iov, 1);
                cifs_server_unlock(server);
                spin_lock(&ses->ses_lock);
        }
        spin_unlock(&ses->ses_lock);

out:
        /*
         * This will dequeue all mids. After this it is important that the
         * demultiplex_thread will not process any of these mids any futher.
         * This is prevented above by using a noop callback that will not
         * wake this thread except for the very last PDU.
         */
        for (i = 0; i < num_rqst; i++) {
                if (!cancelled_mid[i])
                        delete_mid(midQ[i]);
        }

        return rc;
}

int
cifs_send_recv(const unsigned int xid, struct cifs_ses *ses,
               struct TCP_Server_Info *server,
               struct smb_rqst *rqst, int *resp_buf_type, const int flags,
               struct kvec *resp_iov)
{
        return compound_send_recv(xid, ses, server, flags, 1,
                                  rqst, resp_buf_type, resp_iov);
}

int
SendReceive2(const unsigned int xid, struct cifs_ses *ses,
             struct kvec *iov, int n_vec, int *resp_buf_type /* ret */,
             const int flags, struct kvec *resp_iov)
{
        struct smb_rqst rqst;
        struct kvec s_iov[CIFS_MAX_IOV_SIZE], *new_iov;
        int rc;

        if (n_vec + 1 > CIFS_MAX_IOV_SIZE) {
                new_iov = kmalloc_array(n_vec + 1, sizeof(struct kvec),
                                        GFP_KERNEL);
                if (!new_iov) {
                        /* otherwise cifs_send_recv below sets resp_buf_type */
                        *resp_buf_type = CIFS_NO_BUFFER;
                        return -ENOMEM;
                }
        } else
                new_iov = s_iov;

        /* 1st iov is a RFC1001 length followed by the rest of the packet */
        memcpy(new_iov + 1, iov, (sizeof(struct kvec) * n_vec));

        new_iov[0].iov_base = new_iov[1].iov_base;
        new_iov[0].iov_len = 4;
        new_iov[1].iov_base += 4;
        new_iov[1].iov_len -= 4;

        memset(&rqst, 0, sizeof(struct smb_rqst));
        rqst.rq_iov = new_iov;
        rqst.rq_nvec = n_vec + 1;

        rc = cifs_send_recv(xid, ses, ses->server,
                            &rqst, resp_buf_type, flags, resp_iov);
        if (n_vec + 1 > CIFS_MAX_IOV_SIZE)
                kfree(new_iov);
        return rc;
}

int
SendReceive(const unsigned int xid, struct cifs_ses *ses,
            struct smb_hdr *in_buf, struct smb_hdr *out_buf,
            int *pbytes_returned, const int flags)
{
        int rc = 0;
        struct mid_q_entry *midQ;
        unsigned int len = be32_to_cpu(in_buf->smb_buf_length);
        struct kvec iov = { .iov_base = in_buf, .iov_len = len };
        struct smb_rqst rqst = { .rq_iov = &iov, .rq_nvec = 1 };
        struct cifs_credits credits = { .value = 1, .instance = 0 };
        struct TCP_Server_Info *server;

        if (ses == NULL) {
                cifs_dbg(VFS, "Null smb session\n");
                return -EIO;
        }
        server = ses->server;
        if (server == NULL) {
                cifs_dbg(VFS, "Null tcp session\n");
                return -EIO;
        }

        spin_lock(&server->srv_lock);
        if (server->tcpStatus == CifsExiting) {
                spin_unlock(&server->srv_lock);
                return -ENOENT;
        }
        spin_unlock(&server->srv_lock);

        /* Ensure that we do not send more than 50 overlapping requests
           to the same server. We may make this configurable later or
           use ses->maxReq */

        if (len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE - 4) {
                cifs_server_dbg(VFS, "Invalid length, greater than maximum frame, %d\n",
                                len);
                return -EIO;
        }

        rc = wait_for_free_request(server, flags, &credits.instance);
        if (rc)
                return rc;

        /* make sure that we sign in the same order that we send on this socket
           and avoid races inside tcp sendmsg code that could cause corruption
           of smb data */

        cifs_server_lock(server);

        rc = allocate_mid(ses, in_buf, &midQ);
        if (rc) {
                cifs_server_unlock(server);
                /* Update # of requests on wire to server */
                add_credits(server, &credits, 0);
                return rc;
        }

        rc = cifs_sign_smb(in_buf, server, &midQ->sequence_number);
        if (rc) {
                cifs_server_unlock(server);
                goto out;
        }

        midQ->mid_state = MID_REQUEST_SUBMITTED;

        rc = smb_send(server, in_buf, len);
        cifs_save_when_sent(midQ);

        if (rc < 0)
                server->sequence_number -= 2;

        cifs_server_unlock(server);

        if (rc < 0)
                goto out;

        rc = wait_for_response(server, midQ);
        if (rc != 0) {
                send_cancel(server, &rqst, midQ);
                spin_lock(&server->mid_lock);
                if (midQ->mid_state == MID_REQUEST_SUBMITTED ||
                    midQ->mid_state == MID_RESPONSE_RECEIVED) {
                        /* no longer considered to be "in-flight" */
                        midQ->callback = release_mid;
                        spin_unlock(&server->mid_lock);
                        add_credits(server, &credits, 0);
                        return rc;
                }
                spin_unlock(&server->mid_lock);
        }

        rc = cifs_sync_mid_result(midQ, server);
        if (rc != 0) {
                add_credits(server, &credits, 0);
                return rc;
        }

        if (!midQ->resp_buf || !out_buf ||
            midQ->mid_state != MID_RESPONSE_READY) {
                rc = -EIO;
                cifs_server_dbg(VFS, "Bad MID state?\n");
                goto out;
        }

        *pbytes_returned = get_rfc1002_length(midQ->resp_buf);
        memcpy(out_buf, midQ->resp_buf, *pbytes_returned + 4);
        rc = cifs_check_receive(midQ, server, 0);
out:
        delete_mid(midQ);
        add_credits(server, &credits, 0);

        return rc;
}

/* We send a LOCKINGX_CANCEL_LOCK to cause the Windows
   blocking lock to return. */

static int
send_lock_cancel(const unsigned int xid, struct cifs_tcon *tcon,
                        struct smb_hdr *in_buf,
                        struct smb_hdr *out_buf)
{
        int bytes_returned;
        struct cifs_ses *ses = tcon->ses;
        LOCK_REQ *pSMB = (LOCK_REQ *)in_buf;

        /* We just modify the current in_buf to change
           the type of lock from LOCKING_ANDX_SHARED_LOCK
           or LOCKING_ANDX_EXCLUSIVE_LOCK to
           LOCKING_ANDX_CANCEL_LOCK. */

        pSMB->LockType = LOCKING_ANDX_CANCEL_LOCK|LOCKING_ANDX_LARGE_FILES;
        pSMB->Timeout = 0;
        pSMB->hdr.Mid = get_next_mid(ses->server);

        return SendReceive(xid, ses, in_buf, out_buf,
                        &bytes_returned, 0);
}

int
SendReceiveBlockingLock(const unsigned int xid, struct cifs_tcon *tcon,
            struct smb_hdr *in_buf, struct smb_hdr *out_buf,
            int *pbytes_returned)
{
        int rc = 0;
        int rstart = 0;
        struct mid_q_entry *midQ;
        struct cifs_ses *ses;
        unsigned int len = be32_to_cpu(in_buf->smb_buf_length);
        struct kvec iov = { .iov_base = in_buf, .iov_len = len };
        struct smb_rqst rqst = { .rq_iov = &iov, .rq_nvec = 1 };
        unsigned int instance;
        struct TCP_Server_Info *server;

        if (tcon == NULL || tcon->ses == NULL) {
                cifs_dbg(VFS, "Null smb session\n");
                return -EIO;
        }
        ses = tcon->ses;
        server = ses->server;

        if (server == NULL) {
                cifs_dbg(VFS, "Null tcp session\n");
                return -EIO;
        }

        spin_lock(&server->srv_lock);
        if (server->tcpStatus == CifsExiting) {
                spin_unlock(&server->srv_lock);
                return -ENOENT;
        }
        spin_unlock(&server->srv_lock);

        /* Ensure that we do not send more than 50 overlapping requests
           to the same server. We may make this configurable later or
           use ses->maxReq */

        if (len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE - 4) {
                cifs_tcon_dbg(VFS, "Invalid length, greater than maximum frame, %d\n",
                              len);
                return -EIO;
        }

        rc = wait_for_free_request(server, CIFS_BLOCKING_OP, &instance);
        if (rc)
                return rc;

        /* make sure that we sign in the same order that we send on this socket
           and avoid races inside tcp sendmsg code that could cause corruption
           of smb data */

        cifs_server_lock(server);

        rc = allocate_mid(ses, in_buf, &midQ);
        if (rc) {
                cifs_server_unlock(server);
                return rc;
        }

        rc = cifs_sign_smb(in_buf, server, &midQ->sequence_number);
        if (rc) {
                delete_mid(midQ);
                cifs_server_unlock(server);
                return rc;
        }

        midQ->mid_state = MID_REQUEST_SUBMITTED;
        rc = smb_send(server, in_buf, len);
        cifs_save_when_sent(midQ);

        if (rc < 0)
                server->sequence_number -= 2;

        cifs_server_unlock(server);

        if (rc < 0) {
                delete_mid(midQ);
                return rc;
        }

        /* Wait for a reply - allow signals to interrupt. */
        rc = wait_event_interruptible(server->response_q,
                (!(midQ->mid_state == MID_REQUEST_SUBMITTED ||
                   midQ->mid_state == MID_RESPONSE_RECEIVED)) ||
                ((server->tcpStatus != CifsGood) &&
                 (server->tcpStatus != CifsNew)));

        /* Were we interrupted by a signal ? */
        spin_lock(&server->srv_lock);
        if ((rc == -ERESTARTSYS) &&
                (midQ->mid_state == MID_REQUEST_SUBMITTED ||
                 midQ->mid_state == MID_RESPONSE_RECEIVED) &&
                ((server->tcpStatus == CifsGood) ||
                 (server->tcpStatus == CifsNew))) {
                spin_unlock(&server->srv_lock);

                if (in_buf->Command == SMB_COM_TRANSACTION2) {
                        /* POSIX lock. We send a NT_CANCEL SMB to cause the
                           blocking lock to return. */
                        rc = send_cancel(server, &rqst, midQ);
                        if (rc) {
                                delete_mid(midQ);
                                return rc;
                        }
                } else {
                        /* Windows lock. We send a LOCKINGX_CANCEL_LOCK
                           to cause the blocking lock to return. */

                        rc = send_lock_cancel(xid, tcon, in_buf, out_buf);

                        /* If we get -ENOLCK back the lock may have
                           already been removed. Don't exit in this case. */
                        if (rc && rc != -ENOLCK) {
                                delete_mid(midQ);
                                return rc;
                        }
                }

                rc = wait_for_response(server, midQ);
                if (rc) {
                        send_cancel(server, &rqst, midQ);
                        spin_lock(&server->mid_lock);
                        if (midQ->mid_state == MID_REQUEST_SUBMITTED ||
                            midQ->mid_state == MID_RESPONSE_RECEIVED) {
                                /* no longer considered to be "in-flight" */
                                midQ->callback = release_mid;
                                spin_unlock(&server->mid_lock);
                                return rc;
                        }
                        spin_unlock(&server->mid_lock);
                }

                /* We got the response - restart system call. */
                rstart = 1;
                spin_lock(&server->srv_lock);
        }
        spin_unlock(&server->srv_lock);

        rc = cifs_sync_mid_result(midQ, server);
        if (rc != 0)
                return rc;

        /* rcvd frame is ok */
        if (out_buf == NULL || midQ->mid_state != MID_RESPONSE_READY) {
                rc = -EIO;
                cifs_tcon_dbg(VFS, "Bad MID state?\n");
                goto out;
        }

        *pbytes_returned = get_rfc1002_length(midQ->resp_buf);
        memcpy(out_buf, midQ->resp_buf, *pbytes_returned + 4);
        rc = cifs_check_receive(midQ, server, 0);
out:
        delete_mid(midQ);
        if (rstart && rc == -EACCES)
                return -ERESTARTSYS;
        return rc;
}

/*
 * Discard any remaining data in the current SMB. To do this, we borrow the
 * current bigbuf.
 */
int
cifs_discard_remaining_data(struct TCP_Server_Info *server)
{
        unsigned int rfclen = server->pdu_size;
        size_t remaining = rfclen + HEADER_PREAMBLE_SIZE(server) -
                server->total_read;

        while (remaining > 0) {
                ssize_t length;

                length = cifs_discard_from_socket(server,
                                min_t(size_t, remaining,
                                      CIFSMaxBufSize + MAX_HEADER_SIZE(server)));
                if (length < 0)
                        return length;
                server->total_read += length;
                remaining -= length;
        }

        return 0;
}

static int
__cifs_readv_discard(struct TCP_Server_Info *server, struct mid_q_entry *mid,
                     bool malformed)
{
        int length;

        length = cifs_discard_remaining_data(server);
        dequeue_mid(mid, malformed);
        mid->resp_buf = server->smallbuf;
        server->smallbuf = NULL;
        return length;
}

static int
cifs_readv_discard(struct TCP_Server_Info *server, struct mid_q_entry *mid)
{
        struct cifs_readdata *rdata = mid->callback_data;

        return  __cifs_readv_discard(server, mid, rdata->result);
}

int
cifs_readv_receive(struct TCP_Server_Info *server, struct mid_q_entry *mid)
{
        int length, len;
        unsigned int data_offset, data_len;
        struct cifs_readdata *rdata = mid->callback_data;
        char *buf = server->smallbuf;
        unsigned int buflen = server->pdu_size + HEADER_PREAMBLE_SIZE(server);
        bool use_rdma_mr = false;

        cifs_dbg(FYI, "%s: mid=%llu offset=%llu bytes=%u\n",
                 __func__, mid->mid, rdata->offset, rdata->bytes);

        /*
         * read the rest of READ_RSP header (sans Data array), or whatever we
         * can if there's not enough data. At this point, we've read down to
         * the Mid.
         */
        len = min_t(unsigned int, buflen, server->vals->read_rsp_size) -
                                                        HEADER_SIZE(server) + 1;

        length = cifs_read_from_socket(server,
                                       buf + HEADER_SIZE(server) - 1, len);
        if (length < 0)
                return length;
        server->total_read += length;

        if (server->ops->is_session_expired &&
            server->ops->is_session_expired(buf)) {
                cifs_reconnect(server, true);
                return -1;
        }

        if (server->ops->is_status_pending &&
            server->ops->is_status_pending(buf, server)) {
                cifs_discard_remaining_data(server);
                return -1;
        }

        /* set up first two iov for signature check and to get credits */
        rdata->iov[0].iov_base = buf;
        rdata->iov[0].iov_len = HEADER_PREAMBLE_SIZE(server);
        rdata->iov[1].iov_base = buf + HEADER_PREAMBLE_SIZE(server);
        rdata->iov[1].iov_len =
                server->total_read - HEADER_PREAMBLE_SIZE(server);
        cifs_dbg(FYI, "0: iov_base=%p iov_len=%zu\n",
                 rdata->iov[0].iov_base, rdata->iov[0].iov_len);
        cifs_dbg(FYI, "1: iov_base=%p iov_len=%zu\n",
                 rdata->iov[1].iov_base, rdata->iov[1].iov_len);

        /* Was the SMB read successful? */
        rdata->result = server->ops->map_error(buf, false);
        if (rdata->result != 0) {
                cifs_dbg(FYI, "%s: server returned error %d\n",
                         __func__, rdata->result);
                /* normal error on read response */
                return __cifs_readv_discard(server, mid, false);
        }

        /* Is there enough to get to the rest of the READ_RSP header? */
        if (server->total_read < server->vals->read_rsp_size) {
                cifs_dbg(FYI, "%s: server returned short header. got=%u expected=%zu\n",
                         __func__, server->total_read,
                         server->vals->read_rsp_size);
                rdata->result = -EIO;
                return cifs_readv_discard(server, mid);
        }

        data_offset = server->ops->read_data_offset(buf) +
                HEADER_PREAMBLE_SIZE(server);
        if (data_offset < server->total_read) {
                /*
                 * win2k8 sometimes sends an offset of 0 when the read
                 * is beyond the EOF. Treat it as if the data starts just after
                 * the header.
                 */
                cifs_dbg(FYI, "%s: data offset (%u) inside read response header\n",
                         __func__, data_offset);
                data_offset = server->total_read;
        } else if (data_offset > MAX_CIFS_SMALL_BUFFER_SIZE) {
                /* data_offset is beyond the end of smallbuf */
                cifs_dbg(FYI, "%s: data offset (%u) beyond end of smallbuf\n",
                         __func__, data_offset);
                rdata->result = -EIO;
                return cifs_readv_discard(server, mid);
        }

        cifs_dbg(FYI, "%s: total_read=%u data_offset=%u\n",
                 __func__, server->total_read, data_offset);

        len = data_offset - server->total_read;
        if (len > 0) {
                /* read any junk before data into the rest of smallbuf */
                length = cifs_read_from_socket(server,
                                               buf + server->total_read, len);
                if (length < 0)
                        return length;
                server->total_read += length;
        }

        /* how much data is in the response? */
#ifdef CONFIG_CIFS_SMB_DIRECT
        use_rdma_mr = rdata->mr;
#endif
        data_len = server->ops->read_data_length(buf, use_rdma_mr);
        if (!use_rdma_mr && (data_offset + data_len > buflen)) {
                /* data_len is corrupt -- discard frame */
                rdata->result = -EIO;
                return cifs_readv_discard(server, mid);
        }

#ifdef CONFIG_CIFS_SMB_DIRECT
        if (rdata->mr)
                length = data_len; /* An RDMA read is already done. */
        else
#endif
                length = cifs_read_iter_from_socket(server, &rdata->iter,
                                                    data_len);
        if (length > 0)
                rdata->got_bytes += length;
        server->total_read += length;

        cifs_dbg(FYI, "total_read=%u buflen=%u remaining=%u\n",
                 server->total_read, buflen, data_len);

        /* discard anything left over */
        if (server->total_read < buflen)
                return cifs_readv_discard(server, mid);

        dequeue_mid(mid, false);
        mid->resp_buf = server->smallbuf;
        server->smallbuf = NULL;
        return length;
}