[DLM] dlm: user locks

This changes the way the dlm handles user locks.  The core dlm is now
aware of user locks so they can be dealt with more efficiently.  There is
no more dlm_device module which previously managed its own duplicate copy
of every user lock.

Signed-off-by: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 769 insertions, 0 deletions

diff --git a/fs/dlm/user.c b/fs/dlm/user.c
new file mode 100644
index 000000000000..1f05960a916f
--- /dev/null
+++ b/fs/dlm/user.c
@@ -0,0 +1,769 @@
+/*
+ * Copyright (C) 2006 Red Hat, Inc.  All rights reserved.
+ *
+ * This copyrighted material is made available to anyone wishing to use,
+ * modify, copy, or redistribute it subject to the terms and conditions
+ * of the GNU General Public License v.2.
+ */
+
+#include <linux/miscdevice.h>
+#include <linux/init.h>
+#include <linux/wait.h>
+#include <linux/module.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/poll.h>
+#include <linux/signal.h>
+#include <linux/spinlock.h>
+#include <linux/dlm.h>
+#include <linux/dlm_device.h>
+
+#include "dlm_internal.h"
+#include "lockspace.h"
+#include "lock.h"
+#include "lvb_table.h"
+
+static const char *name_prefix="dlm";
+static struct miscdevice ctl_device;
+static struct file_operations device_fops;
+
+#ifdef CONFIG_COMPAT
+
+struct dlm_lock_params32 {
+        __u8 mode;
+        __u8 namelen;
+        __u16 flags;
+        __u32 lkid;
+        __u32 parent;
+
+        __u32 castparam;
+        __u32 castaddr;
+        __u32 bastparam;
+        __u32 bastaddr;
+        __u32 lksb;
+
+        char lvb[DLM_USER_LVB_LEN];
+        char name[0];
+};
+
+struct dlm_write_request32 {
+        __u32 version[3];
+        __u8 cmd;
+        __u8 is64bit;
+        __u8 unused[2];
+
+        union  {
+                struct dlm_lock_params32 lock;
+                struct dlm_lspace_params lspace;
+        } i;
+};
+
+struct dlm_lksb32 {
+        __u32 sb_status;
+        __u32 sb_lkid;
+        __u8 sb_flags;
+        __u32 sb_lvbptr;
+};
+
+struct dlm_lock_result32 {
+        __u32 length;
+        __u32 user_astaddr;
+        __u32 user_astparam;
+        __u32 user_lksb;
+        struct dlm_lksb32 lksb;
+        __u8 bast_mode;
+        __u8 unused[3];
+        /* Offsets may be zero if no data is present */
+        __u32 lvb_offset;
+};
+
+static void compat_input(struct dlm_write_request *kb,
+                         struct dlm_write_request32 *kb32)
+{
+        kb->version[0] = kb32->version[0];
+        kb->version[1] = kb32->version[1];
+        kb->version[2] = kb32->version[2];
+
+        kb->cmd = kb32->cmd;
+        kb->is64bit = kb32->is64bit;
+        if (kb->cmd == DLM_USER_CREATE_LOCKSPACE ||
+            kb->cmd == DLM_USER_REMOVE_LOCKSPACE) {
+                kb->i.lspace.flags = kb32->i.lspace.flags;
+                kb->i.lspace.minor = kb32->i.lspace.minor;
+                strcpy(kb->i.lspace.name, kb32->i.lspace.name);
+        } else {
+                kb->i.lock.mode = kb32->i.lock.mode;
+                kb->i.lock.namelen = kb32->i.lock.namelen;
+                kb->i.lock.flags = kb32->i.lock.flags;
+                kb->i.lock.lkid = kb32->i.lock.lkid;
+                kb->i.lock.parent = kb32->i.lock.parent;
+                kb->i.lock.castparam = (void *)(long)kb32->i.lock.castparam;
+                kb->i.lock.castaddr = (void *)(long)kb32->i.lock.castaddr;
+                kb->i.lock.bastparam = (void *)(long)kb32->i.lock.bastparam;
+                kb->i.lock.bastaddr = (void *)(long)kb32->i.lock.bastaddr;
+                kb->i.lock.lksb = (void *)(long)kb32->i.lock.lksb;
+                memcpy(kb->i.lock.lvb, kb32->i.lock.lvb, DLM_USER_LVB_LEN);
+                memcpy(kb->i.lock.name, kb32->i.lock.name, kb->i.lock.namelen);
+        }
+}
+
+static void compat_output(struct dlm_lock_result *res,
+                          struct dlm_lock_result32 *res32)
+{
+        res32->length = res->length - (sizeof(struct dlm_lock_result) -
+                                       sizeof(struct dlm_lock_result32));
+        res32->user_astaddr = (__u32)(long)res->user_astaddr;
+        res32->user_astparam = (__u32)(long)res->user_astparam;
+        res32->user_lksb = (__u32)(long)res->user_lksb;
+        res32->bast_mode = res->bast_mode;
+
+        res32->lvb_offset = res->lvb_offset;
+        res32->length = res->length;
+
+        res32->lksb.sb_status = res->lksb.sb_status;
+        res32->lksb.sb_flags = res->lksb.sb_flags;
+        res32->lksb.sb_lkid = res->lksb.sb_lkid;
+        res32->lksb.sb_lvbptr = (__u32)(long)res->lksb.sb_lvbptr;
+}
+#endif
+
+
+void dlm_user_add_ast(struct dlm_lkb *lkb, int type)
+{
+        struct dlm_ls *ls;
+        struct dlm_user_args *ua;
+        struct dlm_user_proc *proc;
+
+        /* dlm_clear_proc_locks() sets ORPHAN/DEAD flag on each
+           lkb before dealing with it.  We need to check this
+           flag before taking ls_clear_proc_locks mutex because if
+           it's set, dlm_clear_proc_locks() holds the mutex. */
+
+        if (lkb->lkb_flags & (DLM_IFL_ORPHAN | DLM_IFL_DEAD)) {
+                /* log_print("user_add_ast skip1 %x", lkb->lkb_flags); */
+                return;
+        }
+
+        ls = lkb->lkb_resource->res_ls;
+        mutex_lock(&ls->ls_clear_proc_locks);
+
+        /* If ORPHAN/DEAD flag is set, it means the process is dead so an ast
+           can't be delivered.  For ORPHAN's, dlm_clear_proc_locks() freed
+           lkb->ua so we can't try to use it. */
+
+        if (lkb->lkb_flags & (DLM_IFL_ORPHAN | DLM_IFL_DEAD)) {
+                /* log_print("user_add_ast skip2 %x", lkb->lkb_flags); */
+                goto out;
+        }
+
+        DLM_ASSERT(lkb->lkb_astparam, dlm_print_lkb(lkb););
+        ua = (struct dlm_user_args *)lkb->lkb_astparam;
+        proc = ua->proc;
+
+        if (type == AST_BAST && ua->bastaddr == NULL)
+                goto out;
+
+        spin_lock(&proc->asts_spin);
+        if (!(lkb->lkb_ast_type & (AST_COMP | AST_BAST))) {
+                kref_get(&lkb->lkb_ref);
+                list_add_tail(&lkb->lkb_astqueue, &proc->asts);
+                lkb->lkb_ast_type |= type;
+                wake_up_interruptible(&proc->wait);
+        }
+
+        /* We want to copy the lvb to userspace when the completion
+           ast is read if the status is 0, the lock has an lvb and
+           lvb_ops says we should.  We could probably have set_lvb_lock()
+           set update_user_lvb instead and not need old_mode */
+
+        if ((lkb->lkb_ast_type & AST_COMP) &&
+            (lkb->lkb_lksb->sb_status == 0) &&
+            lkb->lkb_lksb->sb_lvbptr &&
+            dlm_lvb_operations[ua->old_mode + 1][lkb->lkb_grmode + 1])
+                ua->update_user_lvb = 1;
+        else
+                ua->update_user_lvb = 0;
+
+        spin_unlock(&proc->asts_spin);
+ out:
+        mutex_unlock(&ls->ls_clear_proc_locks);
+}
+
+static int device_user_lock(struct dlm_user_proc *proc,
+                            struct dlm_lock_params *params)
+{
+        struct dlm_ls *ls;
+        struct dlm_user_args *ua;
+        int error = -ENOMEM;
+
+        ls = dlm_find_lockspace_local(proc->lockspace);
+        if (!ls)
+                return -ENOENT;
+
+        if (!params->castaddr || !params->lksb) {
+                error = -EINVAL;
+                goto out;
+        }
+
+        ua = kzalloc(sizeof(struct dlm_user_args), GFP_KERNEL);
+        if (!ua)
+                goto out;
+        ua->proc = proc;
+        ua->user_lksb = params->lksb;
+        ua->castparam = params->castparam;
+        ua->castaddr = params->castaddr;
+        ua->bastparam = params->bastparam;
+        ua->bastaddr = params->bastaddr;
+
+        if (params->flags & DLM_LKF_CONVERT)
+                error = dlm_user_convert(ls, ua,
+                                         params->mode, params->flags,
+                                         params->lkid, params->lvb);
+        else {
+                error = dlm_user_request(ls, ua,
+                                         params->mode, params->flags,
+                                         params->name, params->namelen,
+                                         params->parent);
+                if (!error)
+                        error = ua->lksb.sb_lkid;
+        }
+ out:
+        dlm_put_lockspace(ls);
+        return error;
+}
+
+static int device_user_unlock(struct dlm_user_proc *proc,
+                              struct dlm_lock_params *params)
+{
+        struct dlm_ls *ls;
+        struct dlm_user_args *ua;
+        int error = -ENOMEM;
+
+        ls = dlm_find_lockspace_local(proc->lockspace);
+        if (!ls)
+                return -ENOENT;
+
+        ua = kzalloc(sizeof(struct dlm_user_args), GFP_KERNEL);
+        if (!ua)
+                goto out;
+        ua->proc = proc;
+        ua->user_lksb = params->lksb;
+        ua->castparam = params->castparam;
+        ua->castaddr = params->castaddr;
+
+        if (params->flags & DLM_LKF_CANCEL)
+                error = dlm_user_cancel(ls, ua, params->flags, params->lkid);
+        else
+                error = dlm_user_unlock(ls, ua, params->flags, params->lkid,
+                                        params->lvb);
+ out:
+        dlm_put_lockspace(ls);
+        return error;
+}
+
+static int device_create_lockspace(struct dlm_lspace_params *params)
+{
+        dlm_lockspace_t *lockspace;
+        struct dlm_ls *ls;
+        int error, len;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        error = dlm_new_lockspace(params->name, strlen(params->name),
+                                  &lockspace, 0, DLM_USER_LVB_LEN);
+        if (error)
+                return error;
+
+        ls = dlm_find_lockspace_local(lockspace);
+        if (!ls)
+                return -ENOENT;
+
+        error = -ENOMEM;
+        len = strlen(params->name) + strlen(name_prefix) + 2;
+        ls->ls_device.name = kzalloc(len, GFP_KERNEL);
+        if (!ls->ls_device.name)
+                goto fail;
+        snprintf((char *)ls->ls_device.name, len, "%s_%s", name_prefix,
+                 params->name);
+        ls->ls_device.fops = &device_fops;
+        ls->ls_device.minor = MISC_DYNAMIC_MINOR;
+
+        error = misc_register(&ls->ls_device);
+        if (error) {
+                kfree(ls->ls_device.name);
+                goto fail;
+        }
+
+        error = ls->ls_device.minor;
+        dlm_put_lockspace(ls);
+        return error;
+
+ fail:
+        dlm_put_lockspace(ls);
+        dlm_release_lockspace(lockspace, 0);
+        return error;
+}
+
+static int device_remove_lockspace(struct dlm_lspace_params *params)
+{
+        dlm_lockspace_t *lockspace;
+        struct dlm_ls *ls;
+        int error;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        ls = dlm_find_lockspace_device(params->minor);
+        if (!ls)
+                return -ENOENT;
+
+        error = misc_deregister(&ls->ls_device);
+        if (error) {
+                dlm_put_lockspace(ls);
+                goto out;
+        }
+        kfree(ls->ls_device.name);
+
+        lockspace = ls->ls_local_handle;
+
+        /* dlm_release_lockspace waits for references to go to zero,
+           so all processes will need to close their device for the ls
+           before the release will procede */
+
+        dlm_put_lockspace(ls);
+        error = dlm_release_lockspace(lockspace, 0);
+out:
+        return error;
+}
+
+/* Check the user's version matches ours */
+static int check_version(struct dlm_write_request *req)
+{
+        if (req->version[0] != DLM_DEVICE_VERSION_MAJOR ||
+            (req->version[0] == DLM_DEVICE_VERSION_MAJOR &&
+             req->version[1] > DLM_DEVICE_VERSION_MINOR)) {
+
+                printk(KERN_DEBUG "dlm: process %s (%d) version mismatch "
+                       "user (%d.%d.%d) kernel (%d.%d.%d)\n",
+                       current->comm,
+                       current->pid,
+                       req->version[0],
+                       req->version[1],
+                       req->version[2],
+                       DLM_DEVICE_VERSION_MAJOR,
+                       DLM_DEVICE_VERSION_MINOR,
+                       DLM_DEVICE_VERSION_PATCH);
+                return -EINVAL;
+        }
+        return 0;
+}
+
+/*
+ * device_write
+ *
+ *   device_user_lock
+ *     dlm_user_request -> request_lock
+ *     dlm_user_convert -> convert_lock
+ *
+ *   device_user_unlock
+ *     dlm_user_unlock -> unlock_lock
+ *     dlm_user_cancel -> cancel_lock
+ *
+ *   device_create_lockspace
+ *     dlm_new_lockspace
+ *
+ *   device_remove_lockspace
+ *     dlm_release_lockspace
+ */
+
+/* a write to a lockspace device is a lock or unlock request, a write
+   to the control device is to create/remove a lockspace */
+
+static ssize_t device_write(struct file *file, const char __user *buf,
+                            size_t count, loff_t *ppos)
+{
+        struct dlm_user_proc *proc = file->private_data;
+        struct dlm_write_request *kbuf;
+        sigset_t tmpsig, allsigs;
+        int error;
+
+#ifdef CONFIG_COMPAT
+        if (count < sizeof(struct dlm_write_request32))
+#else
+        if (count < sizeof(struct dlm_write_request))
+#endif
+                return -EINVAL;
+
+        kbuf = kmalloc(count, GFP_KERNEL);
+        if (!kbuf)
+                return -ENOMEM;
+
+        if (copy_from_user(kbuf, buf, count)) {
+                error = -EFAULT;
+                goto out_free;
+        }
+
+        if (check_version(kbuf)) {
+                error = -EBADE;
+                goto out_free;
+        }
+
+#ifdef CONFIG_COMPAT
+        if (!kbuf->is64bit) {
+                struct dlm_write_request32 *k32buf;
+                k32buf = (struct dlm_write_request32 *)kbuf;
+                kbuf = kmalloc(count + (sizeof(struct dlm_write_request) -
+                               sizeof(struct dlm_write_request32)), GFP_KERNEL);
+                if (!kbuf)
+                        return -ENOMEM;
+
+                if (proc)
+                        set_bit(DLM_PROC_FLAGS_COMPAT, &proc->flags);
+                compat_input(kbuf, k32buf);
+                kfree(k32buf);
+        }
+#endif
+
+        /* do we really need this? can a write happen after a close? */
+        if ((kbuf->cmd == DLM_USER_LOCK || kbuf->cmd == DLM_USER_UNLOCK) &&
+            test_bit(DLM_PROC_FLAGS_CLOSING, &proc->flags))
+                return -EINVAL;
+
+        sigfillset(&allsigs);
+        sigprocmask(SIG_BLOCK, &allsigs, &tmpsig);
+
+        error = -EINVAL;
+
+        switch (kbuf->cmd)
+        {
+        case DLM_USER_LOCK:
+                if (!proc) {
+                        log_print("no locking on control device");
+                        goto out_sig;
+                }
+                error = device_user_lock(proc, &kbuf->i.lock);
+                break;
+
+        case DLM_USER_UNLOCK:
+                if (!proc) {
+                        log_print("no locking on control device");
+                        goto out_sig;
+                }
+                error = device_user_unlock(proc, &kbuf->i.lock);
+                break;
+
+        case DLM_USER_CREATE_LOCKSPACE:
+                if (proc) {
+                        log_print("create/remove only on control device");
+                        goto out_sig;
+                }
+                error = device_create_lockspace(&kbuf->i.lspace);
+                break;
+
+        case DLM_USER_REMOVE_LOCKSPACE:
+                if (proc) {
+                        log_print("create/remove only on control device");
+                        goto out_sig;
+                }
+                error = device_remove_lockspace(&kbuf->i.lspace);
+                break;
+
+        default:
+                log_print("Unknown command passed to DLM device : %d\n",
+                          kbuf->cmd);
+        }
+
+ out_sig:
+        sigprocmask(SIG_SETMASK, &tmpsig, NULL);
+        recalc_sigpending();
+ out_free:
+        kfree(kbuf);
+        return error;
+}
+
+/* Every process that opens the lockspace device has its own "proc" structure
+   hanging off the open file that's used to keep track of locks owned by the
+   process and asts that need to be delivered to the process. */
+
+static int device_open(struct inode *inode, struct file *file)
+{
+        struct dlm_user_proc *proc;
+        struct dlm_ls *ls;
+
+        ls = dlm_find_lockspace_device(iminor(inode));
+        if (!ls)
+                return -ENOENT;
+
+        proc = kzalloc(sizeof(struct dlm_user_proc), GFP_KERNEL);
+        if (!proc) {
+                dlm_put_lockspace(ls);
+                return -ENOMEM;
+        }
+
+        proc->lockspace = ls->ls_local_handle;
+        INIT_LIST_HEAD(&proc->asts);
+        INIT_LIST_HEAD(&proc->locks);
+        spin_lock_init(&proc->asts_spin);
+        spin_lock_init(&proc->locks_spin);
+        init_waitqueue_head(&proc->wait);
+        file->private_data = proc;
+
+        return 0;
+}
+
+static int device_close(struct inode *inode, struct file *file)
+{
+        struct dlm_user_proc *proc = file->private_data;
+        struct dlm_ls *ls;
+        sigset_t tmpsig, allsigs;
+
+        ls = dlm_find_lockspace_local(proc->lockspace);
+        if (!ls)
+                return -ENOENT;
+
+        sigfillset(&allsigs);
+        sigprocmask(SIG_BLOCK, &allsigs, &tmpsig);
+
+        set_bit(DLM_PROC_FLAGS_CLOSING, &proc->flags);
+
+        dlm_clear_proc_locks(ls, proc);
+
+        /* at this point no more lkb's should exist for this lockspace,
+           so there's no chance of dlm_user_add_ast() being called and
+           looking for lkb->ua->proc */
+
+        kfree(proc);
+        file->private_data = NULL;
+
+        dlm_put_lockspace(ls);
+        dlm_put_lockspace(ls);  /* for the find in device_open() */
+
+        /* FIXME: AUTOFREE: if this ls is no longer used do
+           device_remove_lockspace() */
+
+        sigprocmask(SIG_SETMASK, &tmpsig, NULL);
+        recalc_sigpending();
+
+        return 0;
+}
+
+static int copy_result_to_user(struct dlm_user_args *ua, int compat, int type,
+                               int bmode, char __user *buf, size_t count)
+{
+#ifdef CONFIG_COMPAT
+        struct dlm_lock_result32 result32;
+#endif
+        struct dlm_lock_result result;
+        void *resultptr;
+        int error=0;
+        int len;
+        int struct_len;
+
+        memset(&result, 0, sizeof(struct dlm_lock_result));
+        memcpy(&result.lksb, &ua->lksb, sizeof(struct dlm_lksb));
+        result.user_lksb = ua->user_lksb;
+
+        /* FIXME: dlm1 provides for the user's bastparam/addr to not be updated
+           in a conversion unless the conversion is successful.  See code
+           in dlm_user_convert() for updating ua from ua_tmp.  OpenVMS, though,
+           notes that a new blocking AST address and parameter are set even if
+           the conversion fails, so maybe we should just do that. */
+
+        if (type == AST_BAST) {
+                result.user_astaddr = ua->bastaddr;
+                result.user_astparam = ua->bastparam;
+                result.bast_mode = bmode;
+        } else {
+                result.user_astaddr = ua->castaddr;
+                result.user_astparam = ua->castparam;
+        }
+
+#ifdef CONFIG_COMPAT
+        if (compat)
+                len = sizeof(struct dlm_lock_result32);
+        else
+#endif
+                len = sizeof(struct dlm_lock_result);
+        struct_len = len;
+
+        /* copy lvb to userspace if there is one, it's been updated, and
+           the user buffer has space for it */
+
+        if (ua->update_user_lvb && ua->lksb.sb_lvbptr &&
+            count >= len + DLM_USER_LVB_LEN) {
+                if (copy_to_user(buf+len, ua->lksb.sb_lvbptr,
+                                 DLM_USER_LVB_LEN)) {
+                        error = -EFAULT;
+                        goto out;
+                }
+
+                result.lvb_offset = len;
+                len += DLM_USER_LVB_LEN;
+        }
+
+        result.length = len;
+        resultptr = &result;
+#ifdef CONFIG_COMPAT
+        if (compat) {
+                compat_output(&result, &result32);
+                resultptr = &result32;
+        }
+#endif
+
+        if (copy_to_user(buf, resultptr, struct_len))
+                error = -EFAULT;
+        else
+                error = len;
+ out:
+        return error;
+}
+
+/* a read returns a single ast described in a struct dlm_lock_result */
+
+static ssize_t device_read(struct file *file, char __user *buf, size_t count,
+                           loff_t *ppos)
+{
+        struct dlm_user_proc *proc = file->private_data;
+        struct dlm_lkb *lkb;
+        struct dlm_user_args *ua;
+        DECLARE_WAITQUEUE(wait, current);
+        int error, type=0, bmode=0, removed = 0;
+
+#ifdef CONFIG_COMPAT
+        if (count < sizeof(struct dlm_lock_result32))
+#else
+        if (count < sizeof(struct dlm_lock_result))
+#endif
+                return -EINVAL;
+
+        /* do we really need this? can a read happen after a close? */
+        if (test_bit(DLM_PROC_FLAGS_CLOSING, &proc->flags))
+                return -EINVAL;
+
+        spin_lock(&proc->asts_spin);
+        if (list_empty(&proc->asts)) {
+                if (file->f_flags & O_NONBLOCK) {
+                        spin_unlock(&proc->asts_spin);
+                        return -EAGAIN;
+                }
+
+                add_wait_queue(&proc->wait, &wait);
+
+        repeat:
+                set_current_state(TASK_INTERRUPTIBLE);
+                if (list_empty(&proc->asts) && !signal_pending(current)) {
+                        spin_unlock(&proc->asts_spin);
+                        schedule();
+                        spin_lock(&proc->asts_spin);
+                        goto repeat;
+                }
+                set_current_state(TASK_RUNNING);
+                remove_wait_queue(&proc->wait, &wait);
+
+                if (signal_pending(current)) {
+                        spin_unlock(&proc->asts_spin);
+                        return -ERESTARTSYS;
+                }
+        }
+
+        if (list_empty(&proc->asts)) {
+                spin_unlock(&proc->asts_spin);
+                return -EAGAIN;
+        }
+
+        /* there may be both completion and blocking asts to return for
+           the lkb, don't remove lkb from asts list unless no asts remain */
+
+        lkb = list_entry(proc->asts.next, struct dlm_lkb, lkb_astqueue);
+
+        if (lkb->lkb_ast_type & AST_COMP) {
+                lkb->lkb_ast_type &= ~AST_COMP;
+                type = AST_COMP;
+        } else if (lkb->lkb_ast_type & AST_BAST) {
+                lkb->lkb_ast_type &= ~AST_BAST;
+                type = AST_BAST;
+                bmode = lkb->lkb_bastmode;
+        }
+
+        if (!lkb->lkb_ast_type) {
+                list_del(&lkb->lkb_astqueue);
+                removed = 1;
+        }
+        spin_unlock(&proc->asts_spin);
+
+        ua = (struct dlm_user_args *)lkb->lkb_astparam;
+        error = copy_result_to_user(ua,
+                                test_bit(DLM_PROC_FLAGS_COMPAT, &proc->flags),
+                                type, bmode, buf, count);
+
+        /* removes reference for the proc->asts lists added by
+           dlm_user_add_ast() and may result in the lkb being freed */
+        if (removed)
+                dlm_put_lkb(lkb);
+
+        return error;
+}
+
+static unsigned int device_poll(struct file *file, poll_table *wait)
+{
+        struct dlm_user_proc *proc = file->private_data;
+
+        poll_wait(file, &proc->wait, wait);
+
+        spin_lock(&proc->asts_spin);
+        if (!list_empty(&proc->asts)) {
+                spin_unlock(&proc->asts_spin);
+                return POLLIN | POLLRDNORM;
+        }
+        spin_unlock(&proc->asts_spin);
+        return 0;
+}
+
+static int ctl_device_open(struct inode *inode, struct file *file)
+{
+        file->private_data = NULL;
+        return 0;
+}
+
+static int ctl_device_close(struct inode *inode, struct file *file)
+{
+        return 0;
+}
+
+static struct file_operations device_fops = {
+        .open    = device_open,
+        .release = device_close,
+        .read    = device_read,
+        .write   = device_write,
+        .poll    = device_poll,
+        .owner   = THIS_MODULE,
+};
+
+static struct file_operations ctl_device_fops = {
+        .open    = ctl_device_open,
+        .release = ctl_device_close,
+        .write   = device_write,
+        .owner   = THIS_MODULE,
+};
+
+int dlm_user_init(void)
+{
+        int error;
+
+        ctl_device.name = "dlm-control";
+        ctl_device.fops = &ctl_device_fops;
+        ctl_device.minor = MISC_DYNAMIC_MINOR;
+
+        error = misc_register(&ctl_device);
+        if (error)
+                log_print("misc_register failed for control device");
+
+        return error;
+}
+
+void dlm_user_exit(void)
+{
+        misc_deregister(&ctl_device);
+}
+