Linux 4.8-rc8

[linux/fpc-iii.git] / fs / cifs / transport.c

/*
 *   fs/cifs/transport.c
 *
 *   Copyright (C) International Business Machines  Corp., 2002,2008
 *   Author(s): Steve French (sfrench@us.ibm.com)
 *   Jeremy Allison (jra@samba.org) 2006.
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Lesser General Public License as published
 *   by the Free Software Foundation; either version 2.1 of the License, or
 *   (at your option) any later version.
 *
 *   This library is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
 *   the GNU Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public License
 *   along with this library; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#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/highmem.h>
#include <asm/uaccess.h>
#include <asm/processor.h>
#include <linux/mempool.h>
#include "cifspdu.h"
#include "cifsglob.h"
#include "cifsproto.h"
#include "cifs_debug.h"

void
cifs_wake_up_task(struct mid_q_entry *mid)
{
        wake_up_process(mid->callback_data);
}

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

        if (server == NULL) {
                cifs_dbg(VFS, "Null TCP session in AllocMidQEntry\n");
                return NULL;
        }

        temp = mempool_alloc(cifs_mid_poolp, GFP_NOFS);
        if (temp == NULL)
                return temp;
        else {
                memset(temp, 0, sizeof(struct mid_q_entry));
                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);
        /*      do_gettimeofday(&temp->when_sent);*/ /* 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.
                 */
                temp->callback = cifs_wake_up_task;
                temp->callback_data = current;
        }

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

void
DeleteMidQEntry(struct mid_q_entry *midEntry)
{
#ifdef CONFIG_CIFS_STATS2
        __le16 command = midEntry->server->vals->lock_cmd;
        unsigned long now;
#endif
        midEntry->mid_state = MID_FREE;
        atomic_dec(&midCount);
        if (midEntry->large_buf)
                cifs_buf_release(midEntry->resp_buf);
        else
                cifs_small_buf_release(midEntry->resp_buf);
#ifdef CONFIG_CIFS_STATS2
        now = jiffies;
        /* commands taking longer than one second are indications that
           something is wrong, unless it is quite a slow link or server */
        if ((now - midEntry->when_alloc) > HZ) {
                if ((cifsFYI & CIFS_TIMER) && (midEntry->command != command)) {
                        pr_debug(" CIFS slow rsp: cmd %d mid %llu",
                               midEntry->command, midEntry->mid);
                        pr_info(" A: 0x%lx S: 0x%lx R: 0x%lx\n",
                               now - midEntry->when_alloc,
                               now - midEntry->when_sent,
                               now - midEntry->when_received);
                }
        }
#endif
        mempool_free(midEntry, cifs_mid_poolp);
}

void
cifs_delete_mid(struct mid_q_entry *mid)
{
        spin_lock(&GlobalMid_Lock);
        list_del(&mid->qhead);
        spin_unlock(&GlobalMid_Lock);

        DeleteMidQEntry(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;

        smb_msg->msg_name = (struct sockaddr *) &server->dstaddr;
        smb_msg->msg_namelen = sizeof(struct sockaddr);
        smb_msg->msg_control = NULL;
        smb_msg->msg_controllen = 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_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_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;
}

static unsigned long
rqst_len(struct smb_rqst *rqst)
{
        unsigned int i;
        struct kvec *iov = rqst->rq_iov;
        unsigned long buflen = 0;

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

        /* add in the page array if there is one */
        if (rqst->rq_npages) {
                buflen += rqst->rq_pagesz * (rqst->rq_npages - 1);
                buflen += rqst->rq_tailsz;
        }

        return buflen;
}

static int
smb_send_rqst(struct TCP_Server_Info *server, struct smb_rqst *rqst)
{
        int rc;
        struct kvec *iov = rqst->rq_iov;
        int n_vec = rqst->rq_nvec;
        unsigned int smb_buf_length = get_rfc1002_length(iov[0].iov_base);
        unsigned long send_length;
        unsigned int i;
        size_t total_len = 0, sent, size;
        struct socket *ssocket = server->ssocket;
        struct msghdr smb_msg;
        int val = 1;

        if (ssocket == NULL)
                return -ENOTSOCK;

        /* sanity check send length */
        send_length = rqst_len(rqst);
        if (send_length != smb_buf_length + 4) {
                WARN(1, "Send length mismatch(send_length=%lu smb_buf_length=%u)\n",
                        send_length, smb_buf_length);
                return -EIO;
        }

        cifs_dbg(FYI, "Sending smb: smb_len=%u\n", smb_buf_length);
        dump_smb(iov[0].iov_base, iov[0].iov_len);

        /* cork the socket */
        kernel_setsockopt(ssocket, SOL_TCP, TCP_CORK,
                                (char *)&val, sizeof(val));

        size = 0;
        for (i = 0; i < n_vec; i++)
                size += iov[i].iov_len;

        iov_iter_kvec(&smb_msg.msg_iter, WRITE | ITER_KVEC, iov, n_vec, size);

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

        total_len += sent;

        /* now walk the page array and send each page in it */
        for (i = 0; i < rqst->rq_npages; i++) {
                size_t len = i == rqst->rq_npages - 1
                                ? rqst->rq_tailsz
                                : rqst->rq_pagesz;
                struct bio_vec bvec = {
                        .bv_page = rqst->rq_pages[i],
                        .bv_len = len
                };
                iov_iter_bvec(&smb_msg.msg_iter, WRITE | ITER_BVEC,
                              &bvec, 1, len);
                rc = smb_send_kvec(server, &smb_msg, &sent);
                if (rc < 0)
                        break;

                total_len += sent;
        }

uncork:
        /* uncork it */
        val = 0;
        kernel_setsockopt(ssocket, SOL_TCP, TCP_CORK,
                                (char *)&val, sizeof(val));

        if ((total_len > 0) && (total_len != smb_buf_length + 4)) {
                cifs_dbg(FYI, "partial send (wanted=%u sent=%zu): terminating session\n",
                         smb_buf_length + 4, 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
                 */
                server->tcpStatus = CifsNeedReconnect;
        }

        if (rc < 0 && rc != -EINTR)
                cifs_dbg(VFS, "Error %d sending data on socket to server\n",
                         rc);
        else
                rc = 0;

        return rc;
}

static int
smb_sendv(struct TCP_Server_Info *server, struct kvec *iov, int n_vec)
{
        struct smb_rqst rqst = { .rq_iov = iov,
                                 .rq_nvec = n_vec };

        return smb_send_rqst(server, &rqst);
}

int
smb_send(struct TCP_Server_Info *server, struct smb_hdr *smb_buffer,
         unsigned int smb_buf_length)
{
        struct kvec iov;

        iov.iov_base = smb_buffer;
        iov.iov_len = smb_buf_length + 4;

        return smb_sendv(server, &iov, 1);
}

static int
wait_for_free_credits(struct TCP_Server_Info *server, const int timeout,
                      int *credits)
{
        int rc;

        spin_lock(&server->req_lock);
        if (timeout == CIFS_ASYNC_OP) {
                /* oplock breaks must not be held up */
                server->in_flight++;
                *credits -= 1;
                spin_unlock(&server->req_lock);
                return 0;
        }

        while (1) {
                if (*credits <= 0) {
                        spin_unlock(&server->req_lock);
                        cifs_num_waiters_inc(server);
                        rc = wait_event_killable(server->request_q,
                                                 has_credits(server, credits));
                        cifs_num_waiters_dec(server);
                        if (rc)
                                return rc;
                        spin_lock(&server->req_lock);
                } else {
                        if (server->tcpStatus == CifsExiting) {
                                spin_unlock(&server->req_lock);
                                return -ENOENT;
                        }

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

                        /* update # of requests on the wire to server */
                        if (timeout != CIFS_BLOCKING_OP) {
                                *credits -= 1;
                                server->in_flight++;
                        }
                        spin_unlock(&server->req_lock);
                        break;
                }
        }
        return 0;
}

static int
wait_for_free_request(struct TCP_Server_Info *server, const int timeout,
                      const int optype)
{
        int *val;

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

int
cifs_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,
                      unsigned int *num, unsigned int *credits)
{
        *num = size;
        *credits = 0;
        return 0;
}

static int allocate_mid(struct cifs_ses *ses, struct smb_hdr *in_buf,
                        struct mid_q_entry **ppmidQ)
{
        if (ses->server->tcpStatus == CifsExiting) {
                return -ENOENT;
        }

        if (ses->server->tcpStatus == CifsNeedReconnect) {
                cifs_dbg(FYI, "tcp session dead - return to caller to retry\n");
                return -EAGAIN;
        }

        if (ses->status == CifsNew) {
                if ((in_buf->Command != SMB_COM_SESSION_SETUP_ANDX) &&
                        (in_buf->Command != SMB_COM_NEGOTIATE))
                        return -EAGAIN;
                /* else ok - we are setting up session */
        }

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

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

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

        error = wait_event_freezekillable_unsafe(server->response_q,
                                    midQ->mid_state != MID_REQUEST_SUBMITTED);
        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;

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

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

        rc = cifs_sign_rqst(rqst, server, &mid->sequence_number);
        if (rc) {
                DeleteMidQEntry(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,
                void *cbdata, const int flags)
{
        int rc, timeout, optype;
        struct mid_q_entry *mid;
        unsigned int credits = 0;

        timeout = flags & CIFS_TIMEOUT_MASK;
        optype = flags & CIFS_OP_MASK;

        if ((flags & CIFS_HAS_CREDITS) == 0) {
                rc = wait_for_free_request(server, timeout, optype);
                if (rc)
                        return rc;
                credits = 1;
        }

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

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

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


        cifs_in_send_inc(server);
        rc = smb_send_rqst(server, rqst);
        cifs_in_send_dec(server);
        cifs_save_when_sent(mid);

        if (rc < 0) {
                server->sequence_number -= 2;
                cifs_delete_mid(mid);
        }

        mutex_unlock(&server->srv_mutex);

        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];
        int resp_buf_type;

        iov[0].iov_base = in_buf;
        iov[0].iov_len = get_rfc1002_length(in_buf) + 4;
        flags |= CIFS_NO_RESP;
        rc = SendReceive2(xid, ses, iov, 1, &resp_buf_type, flags);
        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(&GlobalMid_Lock);
        switch (mid->mid_state) {
        case MID_RESPONSE_RECEIVED:
                spin_unlock(&GlobalMid_Lock);
                return rc;
        case MID_RETRY_NEEDED:
                rc = -EAGAIN;
                break;
        case MID_RESPONSE_MALFORMED:
                rc = -EIO;
                break;
        case MID_SHUTDOWN:
                rc = -EHOSTDOWN;
                break;
        default:
                list_del_init(&mid->qhead);
                cifs_dbg(VFS, "%s: invalid mid state mid=%llu state=%d\n",
                         __func__, mid->mid, mid->mid_state);
                rc = -EIO;
        }
        spin_unlock(&GlobalMid_Lock);

        mutex_lock(&server->srv_mutex);
        DeleteMidQEntry(mid);
        mutex_unlock(&server->srv_mutex);
        return rc;
}

static inline int
send_cancel(struct TCP_Server_Info *server, void *buf, struct mid_q_entry *mid)
{
        return server->ops->send_cancel ?
                                server->ops->send_cancel(server, buf, 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;
                int rc = 0;
                struct smb_rqst rqst = { .rq_iov = &iov,
                                         .rq_nvec = 1 };

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

        /* BB special case reconnect tid and uid here? */
        return map_smb_to_linux_error(mid->resp_buf, log_error);
}

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

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

int
SendReceive2(const unsigned int xid, struct cifs_ses *ses,
             struct kvec *iov, int n_vec, int *resp_buf_type /* ret */,
             const int flags)
{
        int rc = 0;
        int timeout, optype;
        struct mid_q_entry *midQ;
        char *buf = iov[0].iov_base;
        unsigned int credits = 1;
        struct smb_rqst rqst = { .rq_iov = iov,
                                 .rq_nvec = n_vec };

        timeout = flags & CIFS_TIMEOUT_MASK;
        optype = flags & CIFS_OP_MASK;

        *resp_buf_type = CIFS_NO_BUFFER;  /* no response buf yet */

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

        if (ses->server->tcpStatus == CifsExiting) {
                cifs_small_buf_release(buf);
                return -ENOENT;
        }

        /*
         * 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.
         */

        rc = wait_for_free_request(ses->server, timeout, optype);
        if (rc) {
                cifs_small_buf_release(buf);
                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.
         */

        mutex_lock(&ses->server->srv_mutex);

        midQ = ses->server->ops->setup_request(ses, &rqst);
        if (IS_ERR(midQ)) {
                mutex_unlock(&ses->server->srv_mutex);
                cifs_small_buf_release(buf);
                /* Update # of requests on wire to server */
                add_credits(ses->server, 1, optype);
                return PTR_ERR(midQ);
        }

        midQ->mid_state = MID_REQUEST_SUBMITTED;
        cifs_in_send_inc(ses->server);
        rc = smb_sendv(ses->server, iov, n_vec);
        cifs_in_send_dec(ses->server);
        cifs_save_when_sent(midQ);

        if (rc < 0)
                ses->server->sequence_number -= 2;
        mutex_unlock(&ses->server->srv_mutex);

        if (rc < 0) {
                cifs_small_buf_release(buf);
                goto out;
        }

        if (timeout == CIFS_ASYNC_OP) {
                cifs_small_buf_release(buf);
                goto out;
        }

        rc = wait_for_response(ses->server, midQ);
        if (rc != 0) {
                send_cancel(ses->server, buf, midQ);
                spin_lock(&GlobalMid_Lock);
                if (midQ->mid_state == MID_REQUEST_SUBMITTED) {
                        midQ->callback = DeleteMidQEntry;
                        spin_unlock(&GlobalMid_Lock);
                        cifs_small_buf_release(buf);
                        add_credits(ses->server, 1, optype);
                        return rc;
                }
                spin_unlock(&GlobalMid_Lock);
        }

        cifs_small_buf_release(buf);

        rc = cifs_sync_mid_result(midQ, ses->server);
        if (rc != 0) {
                add_credits(ses->server, 1, optype);
                return rc;
        }

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

        buf = (char *)midQ->resp_buf;
        iov[0].iov_base = buf;
        iov[0].iov_len = get_rfc1002_length(buf) + 4;
        if (midQ->large_buf)
                *resp_buf_type = CIFS_LARGE_BUFFER;
        else
                *resp_buf_type = CIFS_SMALL_BUFFER;

        credits = ses->server->ops->get_credits(midQ);

        rc = ses->server->ops->check_receive(midQ, ses->server,
                                             flags & CIFS_LOG_ERROR);

        /* mark it so buf will not be freed by cifs_delete_mid */
        if ((flags & CIFS_NO_RESP) == 0)
                midQ->resp_buf = NULL;
out:
        cifs_delete_mid(midQ);
        add_credits(ses->server, credits, optype);

        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 timeout)
{
        int rc = 0;
        struct mid_q_entry *midQ;

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

        if (ses->server->tcpStatus == CifsExiting)
                return -ENOENT;

        /* 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 (be32_to_cpu(in_buf->smb_buf_length) > CIFSMaxBufSize +
                        MAX_CIFS_HDR_SIZE - 4) {
                cifs_dbg(VFS, "Illegal length, greater than maximum frame, %d\n",
                         be32_to_cpu(in_buf->smb_buf_length));
                return -EIO;
        }

        rc = wait_for_free_request(ses->server, timeout, 0);
        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 */

        mutex_lock(&ses->server->srv_mutex);

        rc = allocate_mid(ses, in_buf, &midQ);
        if (rc) {
                mutex_unlock(&ses->server->srv_mutex);
                /* Update # of requests on wire to server */
                add_credits(ses->server, 1, 0);
                return rc;
        }

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

        midQ->mid_state = MID_REQUEST_SUBMITTED;

        cifs_in_send_inc(ses->server);
        rc = smb_send(ses->server, in_buf, be32_to_cpu(in_buf->smb_buf_length));
        cifs_in_send_dec(ses->server);
        cifs_save_when_sent(midQ);

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

        mutex_unlock(&ses->server->srv_mutex);

        if (rc < 0)
                goto out;

        if (timeout == CIFS_ASYNC_OP)
                goto out;

        rc = wait_for_response(ses->server, midQ);
        if (rc != 0) {
                send_cancel(ses->server, in_buf, midQ);
                spin_lock(&GlobalMid_Lock);
                if (midQ->mid_state == MID_REQUEST_SUBMITTED) {
                        /* no longer considered to be "in-flight" */
                        midQ->callback = DeleteMidQEntry;
                        spin_unlock(&GlobalMid_Lock);
                        add_credits(ses->server, 1, 0);
                        return rc;
                }
                spin_unlock(&GlobalMid_Lock);
        }

        rc = cifs_sync_mid_result(midQ, ses->server);
        if (rc != 0) {
                add_credits(ses->server, 1, 0);
                return rc;
        }

        if (!midQ->resp_buf || !out_buf ||
            midQ->mid_state != MID_RESPONSE_RECEIVED) {
                rc = -EIO;
                cifs_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, ses->server, 0);
out:
        cifs_delete_mid(midQ);
        add_credits(ses->server, 1, 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;

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

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

        if (ses->server->tcpStatus == CifsExiting)
                return -ENOENT;

        /* 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 (be32_to_cpu(in_buf->smb_buf_length) > CIFSMaxBufSize +
                        MAX_CIFS_HDR_SIZE - 4) {
                cifs_dbg(VFS, "Illegal length, greater than maximum frame, %d\n",
                         be32_to_cpu(in_buf->smb_buf_length));
                return -EIO;
        }

        rc = wait_for_free_request(ses->server, CIFS_BLOCKING_OP, 0);
        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 */

        mutex_lock(&ses->server->srv_mutex);

        rc = allocate_mid(ses, in_buf, &midQ);
        if (rc) {
                mutex_unlock(&ses->server->srv_mutex);
                return rc;
        }

        rc = cifs_sign_smb(in_buf, ses->server, &midQ->sequence_number);
        if (rc) {
                cifs_delete_mid(midQ);
                mutex_unlock(&ses->server->srv_mutex);
                return rc;
        }

        midQ->mid_state = MID_REQUEST_SUBMITTED;
        cifs_in_send_inc(ses->server);
        rc = smb_send(ses->server, in_buf, be32_to_cpu(in_buf->smb_buf_length));
        cifs_in_send_dec(ses->server);
        cifs_save_when_sent(midQ);

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

        mutex_unlock(&ses->server->srv_mutex);

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

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

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

                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(ses->server, in_buf, midQ);
                        if (rc) {
                                cifs_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) {
                                cifs_delete_mid(midQ);
                                return rc;
                        }
                }

                rc = wait_for_response(ses->server, midQ);
                if (rc) {
                        send_cancel(ses->server, in_buf, midQ);
                        spin_lock(&GlobalMid_Lock);
                        if (midQ->mid_state == MID_REQUEST_SUBMITTED) {
                                /* no longer considered to be "in-flight" */
                                midQ->callback = DeleteMidQEntry;
                                spin_unlock(&GlobalMid_Lock);
                                return rc;
                        }
                        spin_unlock(&GlobalMid_Lock);
                }

                /* We got the response - restart system call. */
                rstart = 1;
        }

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

        /* rcvd frame is ok */
        if (out_buf == NULL || midQ->mid_state != MID_RESPONSE_RECEIVED) {
                rc = -EIO;
                cifs_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, ses->server, 0);
out:
        cifs_delete_mid(midQ);
        if (rstart && rc == -EACCES)
                return -ERESTARTSYS;
        return rc;
}