[PATCH] _proc_do_string(): fix short reads

[linux-2.6/linux-loongson.git] / fs / 9p / mux.c

/*
 * linux/fs/9p/mux.c
 *
 * Protocol Multiplexer
 *
 *  Copyright (C) 2004 by Eric Van Hensbergen <ericvh@gmail.com>
 *  Copyright (C) 2004-2005 by Latchesar Ionkov <lucho@ionkov.net>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to:
 *  Free Software Foundation
 *  51 Franklin Street, Fifth Floor
 *  Boston, MA  02111-1301  USA
 *
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/kthread.h>
#include <linux/idr.h>
#include <linux/mutex.h>

#include "debug.h"
#include "v9fs.h"
#include "9p.h"
#include "conv.h"
#include "transport.h"
#include "mux.h"

#define ERREQFLUSH      1
#define SCHED_TIMEOUT   10
#define MAXPOLLWADDR    2

enum {
        Rworksched = 1,         /* read work scheduled or running */
        Rpending = 2,           /* can read */
        Wworksched = 4,         /* write work scheduled or running */
        Wpending = 8,           /* can write */
};

enum {
        None,
        Flushing,
        Flushed,
};

struct v9fs_mux_poll_task;

struct v9fs_req {
        spinlock_t lock;
        int tag;
        struct v9fs_fcall *tcall;
        struct v9fs_fcall *rcall;
        int err;
        v9fs_mux_req_callback cb;
        void *cba;
        int flush;
        struct list_head req_list;
};

struct v9fs_mux_data {
        spinlock_t lock;
        struct list_head mux_list;
        struct v9fs_mux_poll_task *poll_task;
        int msize;
        unsigned char *extended;
        struct v9fs_transport *trans;
        struct v9fs_idpool tagpool;
        int err;
        wait_queue_head_t equeue;
        struct list_head req_list;
        struct list_head unsent_req_list;
        struct v9fs_fcall *rcall;
        int rpos;
        char *rbuf;
        int wpos;
        int wsize;
        char *wbuf;
        wait_queue_t poll_wait[MAXPOLLWADDR];
        wait_queue_head_t *poll_waddr[MAXPOLLWADDR];
        poll_table pt;
        struct work_struct rq;
        struct work_struct wq;
        unsigned long wsched;
};

struct v9fs_mux_poll_task {
        struct task_struct *task;
        struct list_head mux_list;
        int muxnum;
};

struct v9fs_mux_rpc {
        struct v9fs_mux_data *m;
        int err;
        struct v9fs_fcall *tcall;
        struct v9fs_fcall *rcall;
        wait_queue_head_t wqueue;
};

static int v9fs_poll_proc(void *);
static void v9fs_read_work(struct work_struct *work);
static void v9fs_write_work(struct work_struct *work);
static void v9fs_pollwait(struct file *filp, wait_queue_head_t * wait_address,
                          poll_table * p);
static u16 v9fs_mux_get_tag(struct v9fs_mux_data *);
static void v9fs_mux_put_tag(struct v9fs_mux_data *, u16);

static DEFINE_MUTEX(v9fs_mux_task_lock);
static struct workqueue_struct *v9fs_mux_wq;

static int v9fs_mux_num;
static int v9fs_mux_poll_task_num;
static struct v9fs_mux_poll_task v9fs_mux_poll_tasks[100];

int v9fs_mux_global_init(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(v9fs_mux_poll_tasks); i++)
                v9fs_mux_poll_tasks[i].task = NULL;

        v9fs_mux_wq = create_workqueue("v9fs");
        if (!v9fs_mux_wq) {
                printk(KERN_WARNING "v9fs: mux: creating workqueue failed\n");
                return -ENOMEM;
        }

        return 0;
}

void v9fs_mux_global_exit(void)
{
        destroy_workqueue(v9fs_mux_wq);
}

/**
 * v9fs_mux_calc_poll_procs - calculates the number of polling procs
 * based on the number of mounted v9fs filesystems.
 *
 * The current implementation returns sqrt of the number of mounts.
 */
static int v9fs_mux_calc_poll_procs(int muxnum)
{
        int n;

        if (v9fs_mux_poll_task_num)
                n = muxnum / v9fs_mux_poll_task_num +
                    (muxnum % v9fs_mux_poll_task_num ? 1 : 0);
        else
                n = 1;

        if (n > ARRAY_SIZE(v9fs_mux_poll_tasks))
                n = ARRAY_SIZE(v9fs_mux_poll_tasks);

        return n;
}

static int v9fs_mux_poll_start(struct v9fs_mux_data *m)
{
        int i, n;
        struct v9fs_mux_poll_task *vpt, *vptlast;
        struct task_struct *pproc;

        dprintk(DEBUG_MUX, "mux %p muxnum %d procnum %d\n", m, v9fs_mux_num,
                v9fs_mux_poll_task_num);
        mutex_lock(&v9fs_mux_task_lock);

        n = v9fs_mux_calc_poll_procs(v9fs_mux_num + 1);
        if (n > v9fs_mux_poll_task_num) {
                for (i = 0; i < ARRAY_SIZE(v9fs_mux_poll_tasks); i++) {
                        if (v9fs_mux_poll_tasks[i].task == NULL) {
                                vpt = &v9fs_mux_poll_tasks[i];
                                dprintk(DEBUG_MUX, "create proc %p\n", vpt);
                                pproc = kthread_create(v9fs_poll_proc, vpt,
                                                   "v9fs-poll");

                                if (!IS_ERR(pproc)) {
                                        vpt->task = pproc;
                                        INIT_LIST_HEAD(&vpt->mux_list);
                                        vpt->muxnum = 0;
                                        v9fs_mux_poll_task_num++;
                                        wake_up_process(vpt->task);
                                }
                                break;
                        }
                }

                if (i >= ARRAY_SIZE(v9fs_mux_poll_tasks))
                        dprintk(DEBUG_ERROR, "warning: no free poll slots\n");
        }

        n = (v9fs_mux_num + 1) / v9fs_mux_poll_task_num +
            ((v9fs_mux_num + 1) % v9fs_mux_poll_task_num ? 1 : 0);

        vptlast = NULL;
        for (i = 0; i < ARRAY_SIZE(v9fs_mux_poll_tasks); i++) {
                vpt = &v9fs_mux_poll_tasks[i];
                if (vpt->task != NULL) {
                        vptlast = vpt;
                        if (vpt->muxnum < n) {
                                dprintk(DEBUG_MUX, "put in proc %d\n", i);
                                list_add(&m->mux_list, &vpt->mux_list);
                                vpt->muxnum++;
                                m->poll_task = vpt;
                                memset(&m->poll_waddr, 0, sizeof(m->poll_waddr));
                                init_poll_funcptr(&m->pt, v9fs_pollwait);
                                break;
                        }
                }
        }

        if (i >= ARRAY_SIZE(v9fs_mux_poll_tasks)) {
                if (vptlast == NULL)
                        return -ENOMEM;

                dprintk(DEBUG_MUX, "put in proc %d\n", i);
                list_add(&m->mux_list, &vptlast->mux_list);
                vptlast->muxnum++;
                m->poll_task = vptlast;
                memset(&m->poll_waddr, 0, sizeof(m->poll_waddr));
                init_poll_funcptr(&m->pt, v9fs_pollwait);
        }

        v9fs_mux_num++;
        mutex_unlock(&v9fs_mux_task_lock);

        return 0;
}

static void v9fs_mux_poll_stop(struct v9fs_mux_data *m)
{
        int i;
        struct v9fs_mux_poll_task *vpt;

        mutex_lock(&v9fs_mux_task_lock);
        vpt = m->poll_task;
        list_del(&m->mux_list);
        for(i = 0; i < ARRAY_SIZE(m->poll_waddr); i++) {
                if (m->poll_waddr[i] != NULL) {
                        remove_wait_queue(m->poll_waddr[i], &m->poll_wait[i]);
                        m->poll_waddr[i] = NULL;
                }
        }
        vpt->muxnum--;
        if (!vpt->muxnum) {
                dprintk(DEBUG_MUX, "destroy proc %p\n", vpt);
                send_sig(SIGKILL, vpt->task, 1);
                vpt->task = NULL;
                v9fs_mux_poll_task_num--;
        }
        v9fs_mux_num--;
        mutex_unlock(&v9fs_mux_task_lock);
}

/**
 * v9fs_mux_init - allocate and initialize the per-session mux data
 * Creates the polling task if this is the first session.
 *
 * @trans - transport structure
 * @msize - maximum message size
 * @extended - pointer to the extended flag
 */
struct v9fs_mux_data *v9fs_mux_init(struct v9fs_transport *trans, int msize,
                                    unsigned char *extended)
{
        int i, n;
        struct v9fs_mux_data *m, *mtmp;

        dprintk(DEBUG_MUX, "transport %p msize %d\n", trans, msize);
        m = kmalloc(sizeof(struct v9fs_mux_data), GFP_KERNEL);
        if (!m)
                return ERR_PTR(-ENOMEM);

        spin_lock_init(&m->lock);
        INIT_LIST_HEAD(&m->mux_list);
        m->msize = msize;
        m->extended = extended;
        m->trans = trans;
        idr_init(&m->tagpool.pool);
        init_MUTEX(&m->tagpool.lock);
        m->err = 0;
        init_waitqueue_head(&m->equeue);
        INIT_LIST_HEAD(&m->req_list);
        INIT_LIST_HEAD(&m->unsent_req_list);
        m->rcall = NULL;
        m->rpos = 0;
        m->rbuf = NULL;
        m->wpos = m->wsize = 0;
        m->wbuf = NULL;
        INIT_WORK(&m->rq, v9fs_read_work);
        INIT_WORK(&m->wq, v9fs_write_work);
        m->wsched = 0;
        memset(&m->poll_waddr, 0, sizeof(m->poll_waddr));
        m->poll_task = NULL;
        n = v9fs_mux_poll_start(m);
        if (n)
                return ERR_PTR(n);

        n = trans->poll(trans, &m->pt);
        if (n & POLLIN) {
                dprintk(DEBUG_MUX, "mux %p can read\n", m);
                set_bit(Rpending, &m->wsched);
        }

        if (n & POLLOUT) {
                dprintk(DEBUG_MUX, "mux %p can write\n", m);
                set_bit(Wpending, &m->wsched);
        }

        for(i = 0; i < ARRAY_SIZE(m->poll_waddr); i++) {
                if (IS_ERR(m->poll_waddr[i])) {
                        v9fs_mux_poll_stop(m);
                        mtmp = (void *)m->poll_waddr;   /* the error code */
                        kfree(m);
                        m = mtmp;
                        break;
                }
        }

        return m;
}

/**
 * v9fs_mux_destroy - cancels all pending requests and frees mux resources
 */
void v9fs_mux_destroy(struct v9fs_mux_data *m)
{
        dprintk(DEBUG_MUX, "mux %p prev %p next %p\n", m,
                m->mux_list.prev, m->mux_list.next);
        v9fs_mux_cancel(m, -ECONNRESET);

        if (!list_empty(&m->req_list)) {
                /* wait until all processes waiting on this session exit */
                dprintk(DEBUG_MUX, "mux %p waiting for empty request queue\n",
                        m);
                wait_event_timeout(m->equeue, (list_empty(&m->req_list)), 5000);
                dprintk(DEBUG_MUX, "mux %p request queue empty: %d\n", m,
                        list_empty(&m->req_list));
        }

        v9fs_mux_poll_stop(m);
        m->trans = NULL;

        kfree(m);
}

/**
 * v9fs_pollwait - called by files poll operation to add v9fs-poll task
 *      to files wait queue
 */
static void
v9fs_pollwait(struct file *filp, wait_queue_head_t * wait_address,
              poll_table * p)
{
        int i;
        struct v9fs_mux_data *m;

        m = container_of(p, struct v9fs_mux_data, pt);
        for(i = 0; i < ARRAY_SIZE(m->poll_waddr); i++)
                if (m->poll_waddr[i] == NULL)
                        break;

        if (i >= ARRAY_SIZE(m->poll_waddr)) {
                dprintk(DEBUG_ERROR, "not enough wait_address slots\n");
                return;
        }

        m->poll_waddr[i] = wait_address;

        if (!wait_address) {
                dprintk(DEBUG_ERROR, "no wait_address\n");
                m->poll_waddr[i] = ERR_PTR(-EIO);
                return;
        }

        init_waitqueue_entry(&m->poll_wait[i], m->poll_task->task);
        add_wait_queue(wait_address, &m->poll_wait[i]);
}

/**
 * v9fs_poll_mux - polls a mux and schedules read or write works if necessary
 */
static void v9fs_poll_mux(struct v9fs_mux_data *m)
{
        int n;

        if (m->err < 0)
                return;

        n = m->trans->poll(m->trans, NULL);
        if (n < 0 || n & (POLLERR | POLLHUP | POLLNVAL)) {
                dprintk(DEBUG_MUX, "error mux %p err %d\n", m, n);
                if (n >= 0)
                        n = -ECONNRESET;
                v9fs_mux_cancel(m, n);
        }

        if (n & POLLIN) {
                set_bit(Rpending, &m->wsched);
                dprintk(DEBUG_MUX, "mux %p can read\n", m);
                if (!test_and_set_bit(Rworksched, &m->wsched)) {
                        dprintk(DEBUG_MUX, "schedule read work mux %p\n", m);
                        queue_work(v9fs_mux_wq, &m->rq);
                }
        }

        if (n & POLLOUT) {
                set_bit(Wpending, &m->wsched);
                dprintk(DEBUG_MUX, "mux %p can write\n", m);
                if ((m->wsize || !list_empty(&m->unsent_req_list))
                    && !test_and_set_bit(Wworksched, &m->wsched)) {
                        dprintk(DEBUG_MUX, "schedule write work mux %p\n", m);
                        queue_work(v9fs_mux_wq, &m->wq);
                }
        }
}

/**
 * v9fs_poll_proc - polls all v9fs transports for new events and queues
 *      the appropriate work to the work queue
 */
static int v9fs_poll_proc(void *a)
{
        struct v9fs_mux_data *m, *mtmp;
        struct v9fs_mux_poll_task *vpt;

        vpt = a;
        dprintk(DEBUG_MUX, "start %p %p\n", current, vpt);
        allow_signal(SIGKILL);
        while (!kthread_should_stop()) {
                set_current_state(TASK_INTERRUPTIBLE);
                if (signal_pending(current))
                        break;

                list_for_each_entry_safe(m, mtmp, &vpt->mux_list, mux_list) {
                        v9fs_poll_mux(m);
                }

                dprintk(DEBUG_MUX, "sleeping...\n");
                schedule_timeout(SCHED_TIMEOUT * HZ);
        }

        __set_current_state(TASK_RUNNING);
        dprintk(DEBUG_MUX, "finish\n");
        return 0;
}

/**
 * v9fs_write_work - called when a transport can send some data
 */
static void v9fs_write_work(struct work_struct *work)
{
        int n, err;
        struct v9fs_mux_data *m;
        struct v9fs_req *req;

        m = container_of(work, struct v9fs_mux_data, wq);

        if (m->err < 0) {
                clear_bit(Wworksched, &m->wsched);
                return;
        }

        if (!m->wsize) {
                if (list_empty(&m->unsent_req_list)) {
                        clear_bit(Wworksched, &m->wsched);
                        return;
                }

                spin_lock(&m->lock);
again:
                req = list_entry(m->unsent_req_list.next, struct v9fs_req,
                               req_list);
                list_move_tail(&req->req_list, &m->req_list);
                if (req->err == ERREQFLUSH)
                        goto again;

                m->wbuf = req->tcall->sdata;
                m->wsize = req->tcall->size;
                m->wpos = 0;
                dump_data(m->wbuf, m->wsize);
                spin_unlock(&m->lock);
        }

        dprintk(DEBUG_MUX, "mux %p pos %d size %d\n", m, m->wpos, m->wsize);
        clear_bit(Wpending, &m->wsched);
        err = m->trans->write(m->trans, m->wbuf + m->wpos, m->wsize - m->wpos);
        dprintk(DEBUG_MUX, "mux %p sent %d bytes\n", m, err);
        if (err == -EAGAIN) {
                clear_bit(Wworksched, &m->wsched);
                return;
        }

        if (err <= 0)
                goto error;

        m->wpos += err;
        if (m->wpos == m->wsize)
                m->wpos = m->wsize = 0;

        if (m->wsize == 0 && !list_empty(&m->unsent_req_list)) {
                if (test_and_clear_bit(Wpending, &m->wsched))
                        n = POLLOUT;
                else
                        n = m->trans->poll(m->trans, NULL);

                if (n & POLLOUT) {
                        dprintk(DEBUG_MUX, "schedule write work mux %p\n", m);
                        queue_work(v9fs_mux_wq, &m->wq);
                } else
                        clear_bit(Wworksched, &m->wsched);
        } else
                clear_bit(Wworksched, &m->wsched);

        return;

      error:
        v9fs_mux_cancel(m, err);
        clear_bit(Wworksched, &m->wsched);
}

static void process_request(struct v9fs_mux_data *m, struct v9fs_req *req)
{
        int ecode;
        struct v9fs_str *ename;

        if (!req->err && req->rcall->id == RERROR) {
                ecode = req->rcall->params.rerror.errno;
                ename = &req->rcall->params.rerror.error;

                dprintk(DEBUG_MUX, "Rerror %.*s\n", ename->len, ename->str);

                if (*m->extended)
                        req->err = -ecode;

                if (!req->err) {
                        req->err = v9fs_errstr2errno(ename->str, ename->len);

                        if (!req->err) {        /* string match failed */
                                PRINT_FCALL_ERROR("unknown error", req->rcall);
                        }

                        if (!req->err)
                                req->err = -ESERVERFAULT;
                }
        } else if (req->tcall && req->rcall->id != req->tcall->id + 1) {
                dprintk(DEBUG_ERROR, "fcall mismatch: expected %d, got %d\n",
                        req->tcall->id + 1, req->rcall->id);
                if (!req->err)
                        req->err = -EIO;
        }
}

/**
 * v9fs_read_work - called when there is some data to be read from a transport
 */
static void v9fs_read_work(struct work_struct *work)
{
        int n, err;
        struct v9fs_mux_data *m;
        struct v9fs_req *req, *rptr, *rreq;
        struct v9fs_fcall *rcall;
        char *rbuf;

        m = container_of(work, struct v9fs_mux_data, rq);

        if (m->err < 0)
                return;

        rcall = NULL;
        dprintk(DEBUG_MUX, "start mux %p pos %d\n", m, m->rpos);

        if (!m->rcall) {
                m->rcall =
                    kmalloc(sizeof(struct v9fs_fcall) + m->msize, GFP_KERNEL);
                if (!m->rcall) {
                        err = -ENOMEM;
                        goto error;
                }

                m->rbuf = (char *)m->rcall + sizeof(struct v9fs_fcall);
                m->rpos = 0;
        }

        clear_bit(Rpending, &m->wsched);
        err = m->trans->read(m->trans, m->rbuf + m->rpos, m->msize - m->rpos);
        dprintk(DEBUG_MUX, "mux %p got %d bytes\n", m, err);
        if (err == -EAGAIN) {
                clear_bit(Rworksched, &m->wsched);
                return;
        }

        if (err <= 0)
                goto error;

        m->rpos += err;
        while (m->rpos > 4) {
                n = le32_to_cpu(*(__le32 *) m->rbuf);
                if (n >= m->msize) {
                        dprintk(DEBUG_ERROR,
                                "requested packet size too big: %d\n", n);
                        err = -EIO;
                        goto error;
                }

                if (m->rpos < n)
                        break;

                dump_data(m->rbuf, n);
                err =
                    v9fs_deserialize_fcall(m->rbuf, n, m->rcall, *m->extended);
                if (err < 0) {
                        goto error;
                }

                if ((v9fs_debug_level&DEBUG_FCALL) == DEBUG_FCALL) {
                        char buf[150];

                        v9fs_printfcall(buf, sizeof(buf), m->rcall,
                                *m->extended);
                        printk(KERN_NOTICE ">>> %p %s\n", m, buf);
                }

                rcall = m->rcall;
                rbuf = m->rbuf;
                if (m->rpos > n) {
                        m->rcall = kmalloc(sizeof(struct v9fs_fcall) + m->msize,
                                           GFP_KERNEL);
                        if (!m->rcall) {
                                err = -ENOMEM;
                                goto error;
                        }

                        m->rbuf = (char *)m->rcall + sizeof(struct v9fs_fcall);
                        memmove(m->rbuf, rbuf + n, m->rpos - n);
                        m->rpos -= n;
                } else {
                        m->rcall = NULL;
                        m->rbuf = NULL;
                        m->rpos = 0;
                }

                dprintk(DEBUG_MUX, "mux %p fcall id %d tag %d\n", m, rcall->id,
                        rcall->tag);

                req = NULL;
                spin_lock(&m->lock);
                list_for_each_entry_safe(rreq, rptr, &m->req_list, req_list) {
                        if (rreq->tag == rcall->tag) {
                                req = rreq;
                                if (req->flush != Flushing)
                                        list_del(&req->req_list);
                                break;
                        }
                }
                spin_unlock(&m->lock);

                if (req) {
                        req->rcall = rcall;
                        process_request(m, req);

                        if (req->flush != Flushing) {
                                if (req->cb)
                                        (*req->cb) (req, req->cba);
                                else
                                        kfree(req->rcall);

                                wake_up(&m->equeue);
                        }
                } else {
                        if (err >= 0 && rcall->id != RFLUSH)
                                dprintk(DEBUG_ERROR,
                                        "unexpected response mux %p id %d tag %d\n",
                                        m, rcall->id, rcall->tag);
                        kfree(rcall);
                }
        }

        if (!list_empty(&m->req_list)) {
                if (test_and_clear_bit(Rpending, &m->wsched))
                        n = POLLIN;
                else
                        n = m->trans->poll(m->trans, NULL);

                if (n & POLLIN) {
                        dprintk(DEBUG_MUX, "schedule read work mux %p\n", m);
                        queue_work(v9fs_mux_wq, &m->rq);
                } else
                        clear_bit(Rworksched, &m->wsched);
        } else
                clear_bit(Rworksched, &m->wsched);

        return;

      error:
        v9fs_mux_cancel(m, err);
        clear_bit(Rworksched, &m->wsched);
}

/**
 * v9fs_send_request - send 9P request
 * The function can sleep until the request is scheduled for sending.
 * The function can be interrupted. Return from the function is not
 * a guarantee that the request is sent successfully. Can return errors
 * that can be retrieved by PTR_ERR macros.
 *
 * @m: mux data
 * @tc: request to be sent
 * @cb: callback function to call when response is received
 * @cba: parameter to pass to the callback function
 */
static struct v9fs_req *v9fs_send_request(struct v9fs_mux_data *m,
                                          struct v9fs_fcall *tc,
                                          v9fs_mux_req_callback cb, void *cba)
{
        int n;
        struct v9fs_req *req;

        dprintk(DEBUG_MUX, "mux %p task %p tcall %p id %d\n", m, current,
                tc, tc->id);
        if (m->err < 0)
                return ERR_PTR(m->err);

        req = kmalloc(sizeof(struct v9fs_req), GFP_KERNEL);
        if (!req)
                return ERR_PTR(-ENOMEM);

        if (tc->id == TVERSION)
                n = V9FS_NOTAG;
        else
                n = v9fs_mux_get_tag(m);

        if (n < 0)
                return ERR_PTR(-ENOMEM);

        v9fs_set_tag(tc, n);
        if ((v9fs_debug_level&DEBUG_FCALL) == DEBUG_FCALL) {
                char buf[150];

                v9fs_printfcall(buf, sizeof(buf), tc, *m->extended);
                printk(KERN_NOTICE "<<< %p %s\n", m, buf);
        }

        spin_lock_init(&req->lock);
        req->tag = n;
        req->tcall = tc;
        req->rcall = NULL;
        req->err = 0;
        req->cb = cb;
        req->cba = cba;
        req->flush = None;

        spin_lock(&m->lock);
        list_add_tail(&req->req_list, &m->unsent_req_list);
        spin_unlock(&m->lock);

        if (test_and_clear_bit(Wpending, &m->wsched))
                n = POLLOUT;
        else
                n = m->trans->poll(m->trans, NULL);

        if (n & POLLOUT && !test_and_set_bit(Wworksched, &m->wsched))
                queue_work(v9fs_mux_wq, &m->wq);

        return req;
}

static void v9fs_mux_free_request(struct v9fs_mux_data *m, struct v9fs_req *req)
{
        v9fs_mux_put_tag(m, req->tag);
        kfree(req);
}

static void v9fs_mux_flush_cb(struct v9fs_req *freq, void *a)
{
        v9fs_mux_req_callback cb;
        int tag;
        struct v9fs_mux_data *m;
        struct v9fs_req *req, *rreq, *rptr;

        m = a;
        dprintk(DEBUG_MUX, "mux %p tc %p rc %p err %d oldtag %d\n", m,
                freq->tcall, freq->rcall, freq->err,
                freq->tcall->params.tflush.oldtag);

        spin_lock(&m->lock);
        cb = NULL;
        tag = freq->tcall->params.tflush.oldtag;
        req = NULL;
        list_for_each_entry_safe(rreq, rptr, &m->req_list, req_list) {
                if (rreq->tag == tag) {
                        req = rreq;
                        list_del(&req->req_list);
                        break;
                }
        }
        spin_unlock(&m->lock);

        if (req) {
                spin_lock(&req->lock);
                req->flush = Flushed;
                spin_unlock(&req->lock);

                if (req->cb)
                        (*req->cb) (req, req->cba);
                else
                        kfree(req->rcall);

                wake_up(&m->equeue);
        }

        kfree(freq->tcall);
        kfree(freq->rcall);
        v9fs_mux_free_request(m, freq);
}

static int
v9fs_mux_flush_request(struct v9fs_mux_data *m, struct v9fs_req *req)
{
        struct v9fs_fcall *fc;
        struct v9fs_req *rreq, *rptr;

        dprintk(DEBUG_MUX, "mux %p req %p tag %d\n", m, req, req->tag);

        /* if a response was received for a request, do nothing */
        spin_lock(&req->lock);
        if (req->rcall || req->err) {
                spin_unlock(&req->lock);
                dprintk(DEBUG_MUX, "mux %p req %p response already received\n", m, req);
                return 0;
        }

        req->flush = Flushing;
        spin_unlock(&req->lock);

        spin_lock(&m->lock);
        /* if the request is not sent yet, just remove it from the list */
        list_for_each_entry_safe(rreq, rptr, &m->unsent_req_list, req_list) {
                if (rreq->tag == req->tag) {
                        dprintk(DEBUG_MUX, "mux %p req %p request is not sent yet\n", m, req);
                        list_del(&rreq->req_list);
                        req->flush = Flushed;
                        spin_unlock(&m->lock);
                        if (req->cb)
                                (*req->cb) (req, req->cba);
                        return 0;
                }
        }
        spin_unlock(&m->lock);

        clear_thread_flag(TIF_SIGPENDING);
        fc = v9fs_create_tflush(req->tag);
        v9fs_send_request(m, fc, v9fs_mux_flush_cb, m);
        return 1;
}

static void
v9fs_mux_rpc_cb(struct v9fs_req *req, void *a)
{
        struct v9fs_mux_rpc *r;

        dprintk(DEBUG_MUX, "req %p r %p\n", req, a);
        r = a;
        r->rcall = req->rcall;
        r->err = req->err;

        if (req->flush!=None && !req->err)
                r->err = -ERESTARTSYS;

        wake_up(&r->wqueue);
}

/**
 * v9fs_mux_rpc - sends 9P request and waits until a response is available.
 *      The function can be interrupted.
 * @m: mux data
 * @tc: request to be sent
 * @rc: pointer where a pointer to the response is stored
 */
int
v9fs_mux_rpc(struct v9fs_mux_data *m, struct v9fs_fcall *tc,
             struct v9fs_fcall **rc)
{
        int err, sigpending;
        unsigned long flags;
        struct v9fs_req *req;
        struct v9fs_mux_rpc r;

        r.err = 0;
        r.tcall = tc;
        r.rcall = NULL;
        r.m = m;
        init_waitqueue_head(&r.wqueue);

        if (rc)
                *rc = NULL;

        sigpending = 0;
        if (signal_pending(current)) {
                sigpending = 1;
                clear_thread_flag(TIF_SIGPENDING);
        }

        req = v9fs_send_request(m, tc, v9fs_mux_rpc_cb, &r);
        if (IS_ERR(req)) {
                err = PTR_ERR(req);
                dprintk(DEBUG_MUX, "error %d\n", err);
                return err;
        }

        err = wait_event_interruptible(r.wqueue, r.rcall != NULL || r.err < 0);
        if (r.err < 0)
                err = r.err;

        if (err == -ERESTARTSYS && m->trans->status == Connected && m->err == 0) {
                if (v9fs_mux_flush_request(m, req)) {
                        /* wait until we get response of the flush message */
                        do {
                                clear_thread_flag(TIF_SIGPENDING);
                                err = wait_event_interruptible(r.wqueue,
                                        r.rcall || r.err);
                        } while (!r.rcall && !r.err && err==-ERESTARTSYS &&
                                m->trans->status==Connected && !m->err);

                        err = -ERESTARTSYS;
                }
                sigpending = 1;
        }

        if (sigpending) {
                spin_lock_irqsave(&current->sighand->siglock, flags);
                recalc_sigpending();
                spin_unlock_irqrestore(&current->sighand->siglock, flags);
        }

        if (rc)
                *rc = r.rcall;
        else
                kfree(r.rcall);

        v9fs_mux_free_request(m, req);
        if (err > 0)
                err = -EIO;

        return err;
}

#if 0
/**
 * v9fs_mux_rpcnb - sends 9P request without waiting for response.
 * @m: mux data
 * @tc: request to be sent
 * @cb: callback function to be called when response arrives
 * @cba: value to pass to the callback function
 */
int v9fs_mux_rpcnb(struct v9fs_mux_data *m, struct v9fs_fcall *tc,
                   v9fs_mux_req_callback cb, void *a)
{
        int err;
        struct v9fs_req *req;

        req = v9fs_send_request(m, tc, cb, a);
        if (IS_ERR(req)) {
                err = PTR_ERR(req);
                dprintk(DEBUG_MUX, "error %d\n", err);
                return PTR_ERR(req);
        }

        dprintk(DEBUG_MUX, "mux %p tc %p tag %d\n", m, tc, req->tag);
        return 0;
}
#endif  /*  0  */

/**
 * v9fs_mux_cancel - cancel all pending requests with error
 * @m: mux data
 * @err: error code
 */
void v9fs_mux_cancel(struct v9fs_mux_data *m, int err)
{
        struct v9fs_req *req, *rtmp;
        LIST_HEAD(cancel_list);

        dprintk(DEBUG_ERROR, "mux %p err %d\n", m, err);
        m->err = err;
        spin_lock(&m->lock);
        list_for_each_entry_safe(req, rtmp, &m->req_list, req_list) {
                list_move(&req->req_list, &cancel_list);
        }
        list_for_each_entry_safe(req, rtmp, &m->unsent_req_list, req_list) {
                list_move(&req->req_list, &cancel_list);
        }
        spin_unlock(&m->lock);

        list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
                list_del(&req->req_list);
                if (!req->err)
                        req->err = err;

                if (req->cb)
                        (*req->cb) (req, req->cba);
                else
                        kfree(req->rcall);
        }

        wake_up(&m->equeue);
}

static u16 v9fs_mux_get_tag(struct v9fs_mux_data *m)
{
        int tag;

        tag = v9fs_get_idpool(&m->tagpool);
        if (tag < 0)
                return V9FS_NOTAG;
        else
                return (u16) tag;
}

static void v9fs_mux_put_tag(struct v9fs_mux_data *m, u16 tag)
{
        if (tag != V9FS_NOTAG && v9fs_check_idpool(tag, &m->tagpool))
                v9fs_put_idpool(tag, &m->tagpool);
}