clntproc.c

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/*
 * linux/fs/lockd/clntproc.c
 *
 * RPC procedures for the client side NLM implementation
 *
 * Copyright (C) 1996, Olaf Kirch <[email protected]>
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/nfs_fs.h>
#include <linux/utsname.h>
#include <linux/freezer.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/svc.h>
#include <linux/lockd/lockd.h>

#define NLMDBG_FACILITY     NLMDBG_CLIENT
#define NLMCLNT_GRACE_WAIT  (5*HZ)
#define NLMCLNT_POLL_TIMEOUT    (30*HZ)
#define NLMCLNT_MAX_RETRIES 3

static int  nlmclnt_test(struct nlm_rqst *, struct file_lock *);
static int  nlmclnt_lock(struct nlm_rqst *, struct file_lock *);
static int  nlmclnt_unlock(struct nlm_rqst *, struct file_lock *);
static int  nlm_stat_to_errno(__be32 stat);
static void nlmclnt_locks_init_private(struct file_lock *fl, struct nlm_host *host);
static int  nlmclnt_cancel(struct nlm_host *, int , struct file_lock *);

static const struct rpc_call_ops nlmclnt_unlock_ops;
static const struct rpc_call_ops nlmclnt_cancel_ops;

/*
 * Cookie counter for NLM requests
 */
static atomic_t nlm_cookie = ATOMIC_INIT(0x1234);

void nlmclnt_next_cookie(struct nlm_cookie *c)
{
    u32 cookie = atomic_inc_return(&nlm_cookie);

    memcpy(c->data, &cookie, 4);
    c->len=4;
}

static struct nlm_lockowner *nlm_get_lockowner(struct nlm_lockowner *lockowner)
{
    atomic_inc(&lockowner->count);
    return lockowner;
}

static void nlm_put_lockowner(struct nlm_lockowner *lockowner)
{
    if (!atomic_dec_and_lock(&lockowner->count, &lockowner->host->h_lock))
        return;
    list_del(&lockowner->list);
    spin_unlock(&lockowner->host->h_lock);
    nlmclnt_release_host(lockowner->host);
    kfree(lockowner);
}

static inline int nlm_pidbusy(struct nlm_host *host, uint32_t pid)
{
    struct nlm_lockowner *lockowner;
    list_for_each_entry(lockowner, &host->h_lockowners, list) {
        if (lockowner->pid == pid)
            return -EBUSY;
    }
    return 0;
}

static inline uint32_t __nlm_alloc_pid(struct nlm_host *host)
{
    uint32_t res;
    do {
        res = host->h_pidcount++;
    } while (nlm_pidbusy(host, res) < 0);
    return res;
}

static struct nlm_lockowner *__nlm_find_lockowner(struct nlm_host *host, fl_owner_t owner)
{
    struct nlm_lockowner *lockowner;
    list_for_each_entry(lockowner, &host->h_lockowners, list) {
        if (lockowner->owner != owner)
            continue;
        return nlm_get_lockowner(lockowner);
    }
    return NULL;
}

static struct nlm_lockowner *nlm_find_lockowner(struct nlm_host *host, fl_owner_t owner)
{
    struct nlm_lockowner *res, *new = NULL;

    spin_lock(&host->h_lock);
    res = __nlm_find_lockowner(host, owner);
    if (res == NULL) {
        spin_unlock(&host->h_lock);
        new = kmalloc(sizeof(*new), GFP_KERNEL);
        spin_lock(&host->h_lock);
        res = __nlm_find_lockowner(host, owner);
        if (res == NULL && new != NULL) {
            res = new;
            atomic_set(&new->count, 1);
            new->owner = owner;
            new->pid = __nlm_alloc_pid(host);
            new->host = nlm_get_host(host);
            list_add(&new->list, &host->h_lockowners);
            new = NULL;
        }
    }
    spin_unlock(&host->h_lock);
    kfree(new);
    return res;
}

/*
 * Initialize arguments for TEST/LOCK/UNLOCK/CANCEL calls
 */
static void nlmclnt_setlockargs(struct nlm_rqst *req, struct file_lock *fl)
{
    struct nlm_args *argp = &req->a_args;
    struct nlm_lock *lock = &argp->lock;

    nlmclnt_next_cookie(&argp->cookie);
    memcpy(&lock->fh, NFS_FH(fl->fl_file->f_path.dentry->d_inode), sizeof(struct nfs_fh));
    lock->caller  = utsname()->nodename;
    lock->oh.data = req->a_owner;
    lock->oh.len  = snprintf(req->a_owner, sizeof(req->a_owner), "%u@%s",
                (unsigned int)fl->fl_u.nfs_fl.owner->pid,
                utsname()->nodename);
    lock->svid = fl->fl_u.nfs_fl.owner->pid;
    lock->fl.fl_start = fl->fl_start;
    lock->fl.fl_end = fl->fl_end;
    lock->fl.fl_type = fl->fl_type;
}

static void nlmclnt_release_lockargs(struct nlm_rqst *req)
{
    BUG_ON(req->a_args.lock.fl.fl_ops != NULL);
}

int nlmclnt_proc(struct nlm_host *host, int cmd, struct file_lock *fl)
{
    struct nlm_rqst     *call;
    int         status;

    call = nlm_alloc_call(host);
    if (call == NULL)
        return -ENOMEM;

    nlmclnt_locks_init_private(fl, host);
    if (!fl->fl_u.nfs_fl.owner) {
        /* lockowner allocation has failed */
        nlmclnt_release_call(call);
        return -ENOMEM;
    }
    /* Set up the argument struct */
    nlmclnt_setlockargs(call, fl);

    if (IS_SETLK(cmd) || IS_SETLKW(cmd)) {
        if (fl->fl_type != F_UNLCK) {
            call->a_args.block = IS_SETLKW(cmd) ? 1 : 0;
            status = nlmclnt_lock(call, fl);
        } else
            status = nlmclnt_unlock(call, fl);
    } else if (IS_GETLK(cmd))
        status = nlmclnt_test(call, fl);
    else
        status = -EINVAL;
    fl->fl_ops->fl_release_private(fl);
    fl->fl_ops = NULL;

    dprintk("lockd: clnt proc returns %d\n", status);
    return status;
}
EXPORT_SYMBOL_GPL(nlmclnt_proc);

/*
 * Allocate an NLM RPC call struct
 */
struct nlm_rqst *nlm_alloc_call(struct nlm_host *host)
{
    struct nlm_rqst *call;

    for(;;) {
        call = kzalloc(sizeof(*call), GFP_KERNEL);
        if (call != NULL) {
            atomic_set(&call->a_count, 1);
            locks_init_lock(&call->a_args.lock.fl);
            locks_init_lock(&call->a_res.lock.fl);
            call->a_host = nlm_get_host(host);
            return call;
        }
        if (signalled())
            break;
        printk("nlm_alloc_call: failed, waiting for memory\n");
        schedule_timeout_interruptible(5*HZ);
    }
    return NULL;
}

void nlmclnt_release_call(struct nlm_rqst *call)
{
    if (!atomic_dec_and_test(&call->a_count))
        return;
    nlmclnt_release_host(call->a_host);
    nlmclnt_release_lockargs(call);
    kfree(call);
}

static void nlmclnt_rpc_release(void *data)
{
    nlmclnt_release_call(data);
}

static int nlm_wait_on_grace(wait_queue_head_t *queue)
{
    DEFINE_WAIT(wait);
    int status = -EINTR;

    prepare_to_wait(queue, &wait, TASK_INTERRUPTIBLE);
    if (!signalled ()) {
        schedule_timeout(NLMCLNT_GRACE_WAIT);
        try_to_freeze();
        if (!signalled ())
            status = 0;
    }
    finish_wait(queue, &wait);
    return status;
}

/*
 * Generic NLM call
 */
static int
nlmclnt_call(struct rpc_cred *cred, struct nlm_rqst *req, u32 proc)
{
    struct nlm_host *host = req->a_host;
    struct rpc_clnt *clnt;
    struct nlm_args *argp = &req->a_args;
    struct nlm_res  *resp = &req->a_res;
    struct rpc_message msg = {
        .rpc_argp   = argp,
        .rpc_resp   = resp,
        .rpc_cred   = cred,
    };
    int     status;

    dprintk("lockd: call procedure %d on %s\n",
            (int)proc, host->h_name);

    do {
        if (host->h_reclaiming && !argp->reclaim)
            goto in_grace_period;

        /* If we have no RPC client yet, create one. */
        if ((clnt = nlm_bind_host(host)) == NULL)
            return -ENOLCK;
        msg.rpc_proc = &clnt->cl_procinfo[proc];

        /* Perform the RPC call. If an error occurs, try again */
        if ((status = rpc_call_sync(clnt, &msg, 0)) < 0) {
            dprintk("lockd: rpc_call returned error %d\n", -status);
            switch (status) {
            case -EPROTONOSUPPORT:
                status = -EINVAL;
                break;
            case -ECONNREFUSED:
            case -ETIMEDOUT:
            case -ENOTCONN:
                nlm_rebind_host(host);
                status = -EAGAIN;
                break;
            case -ERESTARTSYS:
                return signalled () ? -EINTR : status;
            default:
                break;
            }
            break;
        } else
        if (resp->status == nlm_lck_denied_grace_period) {
            dprintk("lockd: server in grace period\n");
            if (argp->reclaim) {
                printk(KERN_WARNING
                     "lockd: spurious grace period reject?!\n");
                return -ENOLCK;
            }
        } else {
            if (!argp->reclaim) {
                /* We appear to be out of the grace period */
                wake_up_all(&host->h_gracewait);
            }
            dprintk("lockd: server returns status %d\n",
                ntohl(resp->status));
            return 0;   /* Okay, call complete */
        }

in_grace_period:
        /*
         * The server has rebooted and appears to be in the grace
         * period during which locks are only allowed to be
         * reclaimed.
         * We can only back off and try again later.
         */
        status = nlm_wait_on_grace(&host->h_gracewait);
    } while (status == 0);

    return status;
}

/*
 * Generic NLM call, async version.
 */
static struct rpc_task *__nlm_async_call(struct nlm_rqst *req, u32 proc, struct rpc_message *msg, const struct rpc_call_ops *tk_ops)
{
    struct nlm_host *host = req->a_host;
    struct rpc_clnt *clnt;
    struct rpc_task_setup task_setup_data = {
        .rpc_message = msg,
        .callback_ops = tk_ops,
        .callback_data = req,
        .flags = RPC_TASK_ASYNC,
    };

    dprintk("lockd: call procedure %d on %s (async)\n",
            (int)proc, host->h_name);

    /* If we have no RPC client yet, create one. */
    clnt = nlm_bind_host(host);
    if (clnt == NULL)
        goto out_err;
    msg->rpc_proc = &clnt->cl_procinfo[proc];
    task_setup_data.rpc_client = clnt;

        /* bootstrap and kick off the async RPC call */
    return rpc_run_task(&task_setup_data);
out_err:
    tk_ops->rpc_release(req);
    return ERR_PTR(-ENOLCK);
}

static int nlm_do_async_call(struct nlm_rqst *req, u32 proc, struct rpc_message *msg, const struct rpc_call_ops *tk_ops)
{
    struct rpc_task *task;

    task = __nlm_async_call(req, proc, msg, tk_ops);
    if (IS_ERR(task))
        return PTR_ERR(task);
    rpc_put_task(task);
    return 0;
}

/*
 * NLM asynchronous call.
 */
int nlm_async_call(struct nlm_rqst *req, u32 proc, const struct rpc_call_ops *tk_ops)
{
    struct rpc_message msg = {
        .rpc_argp   = &req->a_args,
        .rpc_resp   = &req->a_res,
    };
    return nlm_do_async_call(req, proc, &msg, tk_ops);
}

int nlm_async_reply(struct nlm_rqst *req, u32 proc, const struct rpc_call_ops *tk_ops)
{
    struct rpc_message msg = {
        .rpc_argp   = &req->a_res,
    };
    return nlm_do_async_call(req, proc, &msg, tk_ops);
}

/*
 * NLM client asynchronous call.
 *
 * Note that although the calls are asynchronous, and are therefore
 *      guaranteed to complete, we still always attempt to wait for
 *      completion in order to be able to correctly track the lock
 *      state.
 */
static int nlmclnt_async_call(struct rpc_cred *cred, struct nlm_rqst *req, u32 proc, const struct rpc_call_ops *tk_ops)
{
    struct rpc_message msg = {
        .rpc_argp   = &req->a_args,
        .rpc_resp   = &req->a_res,
        .rpc_cred   = cred,
    };
    struct rpc_task *task;
    int err;

    task = __nlm_async_call(req, proc, &msg, tk_ops);
    if (IS_ERR(task))
        return PTR_ERR(task);
    err = rpc_wait_for_completion_task(task);
    rpc_put_task(task);
    return err;
}

/*
 * TEST for the presence of a conflicting lock
 */
static int
nlmclnt_test(struct nlm_rqst *req, struct file_lock *fl)
{
    int status;

    status = nlmclnt_call(nfs_file_cred(fl->fl_file), req, NLMPROC_TEST);
    if (status < 0)
        goto out;

    switch (req->a_res.status) {
        case nlm_granted:
            fl->fl_type = F_UNLCK;
            break;
        case nlm_lck_denied:
            /*
             * Report the conflicting lock back to the application.
             */
            fl->fl_start = req->a_res.lock.fl.fl_start;
            fl->fl_end = req->a_res.lock.fl.fl_end;
            fl->fl_type = req->a_res.lock.fl.fl_type;
            fl->fl_pid = 0;
            break;
        default:
            status = nlm_stat_to_errno(req->a_res.status);
    }
out:
    nlmclnt_release_call(req);
    return status;
}

static void nlmclnt_locks_copy_lock(struct file_lock *new, struct file_lock *fl)
{
    spin_lock(&fl->fl_u.nfs_fl.owner->host->h_lock);
    new->fl_u.nfs_fl.state = fl->fl_u.nfs_fl.state;
    new->fl_u.nfs_fl.owner = nlm_get_lockowner(fl->fl_u.nfs_fl.owner);
    list_add_tail(&new->fl_u.nfs_fl.list, &fl->fl_u.nfs_fl.owner->host->h_granted);
    spin_unlock(&fl->fl_u.nfs_fl.owner->host->h_lock);
}

static void nlmclnt_locks_release_private(struct file_lock *fl)
{
    spin_lock(&fl->fl_u.nfs_fl.owner->host->h_lock);
    list_del(&fl->fl_u.nfs_fl.list);
    spin_unlock(&fl->fl_u.nfs_fl.owner->host->h_lock);
    nlm_put_lockowner(fl->fl_u.nfs_fl.owner);
}

static const struct file_lock_operations nlmclnt_lock_ops = {
    .fl_copy_lock = nlmclnt_locks_copy_lock,
    .fl_release_private = nlmclnt_locks_release_private,
};

static void nlmclnt_locks_init_private(struct file_lock *fl, struct nlm_host *host)
{
    BUG_ON(fl->fl_ops != NULL);
    fl->fl_u.nfs_fl.state = 0;
    fl->fl_u.nfs_fl.owner = nlm_find_lockowner(host, fl->fl_owner);
    INIT_LIST_HEAD(&fl->fl_u.nfs_fl.list);
    fl->fl_ops = &nlmclnt_lock_ops;
}

static int do_vfs_lock(struct file_lock *fl)
{
    int res = 0;
    switch (fl->fl_flags & (FL_POSIX|FL_FLOCK)) {
        case FL_POSIX:
            res = posix_lock_file_wait(fl->fl_file, fl);
            break;
        case FL_FLOCK:
            res = flock_lock_file_wait(fl->fl_file, fl);
            break;
        default:
            BUG();
    }
    return res;
}

/*
 * LOCK: Try to create a lock
 *
 *          Programmer Harassment Alert
 *
 * When given a blocking lock request in a sync RPC call, the HPUX lockd
 * will faithfully return LCK_BLOCKED but never cares to notify us when
 * the lock could be granted. This way, our local process could hang
 * around forever waiting for the callback.
 *
 *  Solution A: Implement busy-waiting
 *  Solution B: Use the async version of the call (NLM_LOCK_{MSG,RES})
 *
 * For now I am implementing solution A, because I hate the idea of
 * re-implementing lockd for a third time in two months. The async
 * calls shouldn't be too hard to do, however.
 *
 * This is one of the lovely things about standards in the NFS area:
 * they're so soft and squishy you can't really blame HP for doing this.
 */
static int
nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
{
    struct rpc_cred *cred = nfs_file_cred(fl->fl_file);
    struct nlm_host *host = req->a_host;
    struct nlm_res  *resp = &req->a_res;
    struct nlm_wait *block = NULL;
    unsigned char fl_flags = fl->fl_flags;
    unsigned char fl_type;
    int status = -ENOLCK;

    if (nsm_monitor(host) < 0)
        goto out;
    req->a_args.state = nsm_local_state;

    fl->fl_flags |= FL_ACCESS;
    status = do_vfs_lock(fl);
    fl->fl_flags = fl_flags;
    if (status < 0)
        goto out;

    block = nlmclnt_prepare_block(host, fl);
again:
    /*
     * Initialise resp->status to a valid non-zero value,
     * since 0 == nlm_lck_granted
     */
    resp->status = nlm_lck_blocked;
    for(;;) {
        /* Reboot protection */
        fl->fl_u.nfs_fl.state = host->h_state;
        status = nlmclnt_call(cred, req, NLMPROC_LOCK);
        if (status < 0)
            break;
        /* Did a reclaimer thread notify us of a server reboot? */
        if (resp->status ==  nlm_lck_denied_grace_period)
            continue;
        if (resp->status != nlm_lck_blocked)
            break;
        /* Wait on an NLM blocking lock */
        status = nlmclnt_block(block, req, NLMCLNT_POLL_TIMEOUT);
        if (status < 0)
            break;
        if (resp->status != nlm_lck_blocked)
            break;
    }

    /* if we were interrupted while blocking, then cancel the lock request
     * and exit
     */
    if (resp->status == nlm_lck_blocked) {
        if (!req->a_args.block)
            goto out_unlock;
        if (nlmclnt_cancel(host, req->a_args.block, fl) == 0)
            goto out_unblock;
    }

    if (resp->status == nlm_granted) {
        down_read(&host->h_rwsem);
        /* Check whether or not the server has rebooted */
        if (fl->fl_u.nfs_fl.state != host->h_state) {
            up_read(&host->h_rwsem);
            goto again;
        }
        /* Ensure the resulting lock will get added to granted list */
        fl->fl_flags |= FL_SLEEP;
        if (do_vfs_lock(fl) < 0)
            printk(KERN_WARNING "%s: VFS is out of sync with lock manager!\n", __func__);
        up_read(&host->h_rwsem);
        fl->fl_flags = fl_flags;
        status = 0;
    }
    if (status < 0)
        goto out_unlock;
    /*
     * EAGAIN doesn't make sense for sleeping locks, and in some
     * cases NLM_LCK_DENIED is returned for a permanent error.  So
     * turn it into an ENOLCK.
     */
    if (resp->status == nlm_lck_denied && (fl_flags & FL_SLEEP))
        status = -ENOLCK;
    else
        status = nlm_stat_to_errno(resp->status);
out_unblock:
    nlmclnt_finish_block(block);
out:
    nlmclnt_release_call(req);
    return status;
out_unlock:
    /* Fatal error: ensure that we remove the lock altogether */
    dprintk("lockd: lock attempt ended in fatal error.\n"
        "       Attempting to unlock.\n");
    nlmclnt_finish_block(block);
    fl_type = fl->fl_type;
    fl->fl_type = F_UNLCK;
    down_read(&host->h_rwsem);
    do_vfs_lock(fl);
    up_read(&host->h_rwsem);
    fl->fl_type = fl_type;
    fl->fl_flags = fl_flags;
    nlmclnt_async_call(cred, req, NLMPROC_UNLOCK, &nlmclnt_unlock_ops);
    return status;
}

/*
 * RECLAIM: Try to reclaim a lock
 */
int
nlmclnt_reclaim(struct nlm_host *host, struct file_lock *fl)
{
    struct nlm_rqst reqst, *req;
    int     status;

    req = &reqst;
    memset(req, 0, sizeof(*req));
    locks_init_lock(&req->a_args.lock.fl);
    locks_init_lock(&req->a_res.lock.fl);
    req->a_host  = host;
    req->a_flags = 0;

    /* Set up the argument struct */
    nlmclnt_setlockargs(req, fl);
    req->a_args.reclaim = 1;

    status = nlmclnt_call(nfs_file_cred(fl->fl_file), req, NLMPROC_LOCK);
    if (status >= 0 && req->a_res.status == nlm_granted)
        return 0;

    printk(KERN_WARNING "lockd: failed to reclaim lock for pid %d "
                "(errno %d, status %d)\n", fl->fl_pid,
                status, ntohl(req->a_res.status));

    /*
     * FIXME: This is a serious failure. We can
     *
     *  a.  Ignore the problem
     *  b.  Send the owning process some signal (Linux doesn't have
     *  SIGLOST, though...)
     *  c.  Retry the operation
     *
     * Until someone comes up with a simple implementation
     * for b or c, I'll choose option a.
     */

    return -ENOLCK;
}

/*
 * UNLOCK: remove an existing lock
 */
static int
nlmclnt_unlock(struct nlm_rqst *req, struct file_lock *fl)
{
    struct nlm_host *host = req->a_host;
    struct nlm_res  *resp = &req->a_res;
    int status;
    unsigned char fl_flags = fl->fl_flags;

    /*
     * Note: the server is supposed to either grant us the unlock
     * request, or to deny it with NLM_LCK_DENIED_GRACE_PERIOD. In either
     * case, we want to unlock.
     */
    fl->fl_flags |= FL_EXISTS;
    down_read(&host->h_rwsem);
    status = do_vfs_lock(fl);
    up_read(&host->h_rwsem);
    fl->fl_flags = fl_flags;
    if (status == -ENOENT) {
        status = 0;
        goto out;
    }

    atomic_inc(&req->a_count);
    status = nlmclnt_async_call(nfs_file_cred(fl->fl_file), req,
            NLMPROC_UNLOCK, &nlmclnt_unlock_ops);
    if (status < 0)
        goto out;

    if (resp->status == nlm_granted)
        goto out;

    if (resp->status != nlm_lck_denied_nolocks)
        printk("lockd: unexpected unlock status: %d\n",
            ntohl(resp->status));
    /* What to do now? I'm out of my depth... */
    status = -ENOLCK;
out:
    nlmclnt_release_call(req);
    return status;
}

static void nlmclnt_unlock_callback(struct rpc_task *task, void *data)
{
    struct nlm_rqst *req = data;
    u32 status = ntohl(req->a_res.status);

    if (RPC_ASSASSINATED(task))
        goto die;

    if (task->tk_status < 0) {
        dprintk("lockd: unlock failed (err = %d)\n", -task->tk_status);
        switch (task->tk_status) {
        case -EACCES:
        case -EIO:
            goto die;
        default:
            goto retry_rebind;
        }
    }
    if (status == NLM_LCK_DENIED_GRACE_PERIOD) {
        rpc_delay(task, NLMCLNT_GRACE_WAIT);
        goto retry_unlock;
    }
    if (status != NLM_LCK_GRANTED)
        printk(KERN_WARNING "lockd: unexpected unlock status: %d\n", status);
die:
    return;
 retry_rebind:
    nlm_rebind_host(req->a_host);
 retry_unlock:
    rpc_restart_call(task);
}

static const struct rpc_call_ops nlmclnt_unlock_ops = {
    .rpc_call_done = nlmclnt_unlock_callback,
    .rpc_release = nlmclnt_rpc_release,
};

/*
 * Cancel a blocked lock request.
 * We always use an async RPC call for this in order not to hang a
 * process that has been Ctrl-C'ed.
 */
static int nlmclnt_cancel(struct nlm_host *host, int block, struct file_lock *fl)
{
    struct nlm_rqst *req;
    int status;

    dprintk("lockd: blocking lock attempt was interrupted by a signal.\n"
        "       Attempting to cancel lock.\n");

    req = nlm_alloc_call(host);
    if (!req)
        return -ENOMEM;
    req->a_flags = RPC_TASK_ASYNC;

    nlmclnt_setlockargs(req, fl);
    req->a_args.block = block;

    atomic_inc(&req->a_count);
    status = nlmclnt_async_call(nfs_file_cred(fl->fl_file), req,
            NLMPROC_CANCEL, &nlmclnt_cancel_ops);
    if (status == 0 && req->a_res.status == nlm_lck_denied)
        status = -ENOLCK;
    nlmclnt_release_call(req);
    return status;
}

static void nlmclnt_cancel_callback(struct rpc_task *task, void *data)
{
    struct nlm_rqst *req = data;
    u32 status = ntohl(req->a_res.status);

    if (RPC_ASSASSINATED(task))
        goto die;

    if (task->tk_status < 0) {
        dprintk("lockd: CANCEL call error %d, retrying.\n",
                    task->tk_status);
        goto retry_cancel;
    }

    dprintk("lockd: cancel status %u (task %u)\n",
            status, task->tk_pid);

    switch (status) {
    case NLM_LCK_GRANTED:
    case NLM_LCK_DENIED_GRACE_PERIOD:
    case NLM_LCK_DENIED:
        /* Everything's good */
        break;
    case NLM_LCK_DENIED_NOLOCKS:
        dprintk("lockd: CANCEL failed (server has no locks)\n");
        goto retry_cancel;
    default:
        printk(KERN_NOTICE "lockd: weird return %d for CANCEL call\n",
            status);
    }

die:
    return;

retry_cancel:
    /* Don't ever retry more than 3 times */
    if (req->a_retries++ >= NLMCLNT_MAX_RETRIES)
        goto die;
    nlm_rebind_host(req->a_host);
    rpc_restart_call(task);
    rpc_delay(task, 30 * HZ);
}

static const struct rpc_call_ops nlmclnt_cancel_ops = {
    .rpc_call_done = nlmclnt_cancel_callback,
    .rpc_release = nlmclnt_rpc_release,
};

/*
 * Convert an NLM status code to a generic kernel errno
 */
static int
nlm_stat_to_errno(__be32 status)
{
    switch(ntohl(status)) {
    case NLM_LCK_GRANTED:
        return 0;
    case NLM_LCK_DENIED:
        return -EAGAIN;
    case NLM_LCK_DENIED_NOLOCKS:
    case NLM_LCK_DENIED_GRACE_PERIOD:
        return -ENOLCK;
    case NLM_LCK_BLOCKED:
        printk(KERN_NOTICE "lockd: unexpected status NLM_BLOCKED\n");
        return -ENOLCK;
#ifdef CONFIG_LOCKD_V4
    case NLM_DEADLCK:
        return -EDEADLK;
    case NLM_ROFS:
        return -EROFS;
    case NLM_STALE_FH:
        return -ESTALE;
    case NLM_FBIG:
        return -EOVERFLOW;
    case NLM_FAILED:
        return -ENOLCK;
#endif
    }
    printk(KERN_NOTICE "lockd: unexpected server status %d\n",
         ntohl(status));
    return -ENOLCK;
}