/*

 * Copyright (c) 2020 Red Hat, Inc.

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 * 

 * 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 the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

 * 02110-1301, USA. 

 *

 * $Id: //eng/vdo-releases/aluminum/src/c++/vdo/kernel/workQueueHandle.h#1 $

 */

#ifndef WORK_QUEUE_HANDLE_H

#define WORK_QUEUE_HANDLE_H

#include <linux/version.h>

#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,11,0)

#include <linux/sched/task_stack.h>

#else

#include <linux/sched.h>

#endif

#include "workQueueInternals.h"

/*

 * Layout of a special structure stored at a consistent place on the

 * stack in work queue threads.

 */

typedef struct workQueueStackHandle {

  unsigned long    nonce;

  SimpleWorkQueue *queue;

} WorkQueueStackHandle;

typedef struct workQueueStackHandleGlobals {

  /*

   * Location in the stack, relative to the task structure which is

   * contained in the same memory allocation.

   */

  long          offset;

  /*

   * A lock is used to guard against multiple updaters, but once an

   * update is done, the offset variable will be read-only.

   */

  spinlock_t    offsetLock;

  /*

   * A nonce chosen differently each time the module is loaded, used

   * as a marker so we can check that the current thread really is a

   * work queue thread. Set at module initialization time, before any

   * work queues are created.

   */

  unsigned long nonce;

} WorkQueueStackHandleGlobals;

extern WorkQueueStackHandleGlobals workQueueStackHandleGlobals;

/**

 * Initialize a stack handle associated with a work queue.

 *

 * @param [out] handle  The handle to be initialized

 * @param [in]  queue   The work queue pointer

 **/

void initializeWorkQueueStackHandle(WorkQueueStackHandle *handle,

                                    SimpleWorkQueue      *queue);

/**

 * Return the work queue pointer recorded at initialization time in

 * the work-queue stack handle initialized on the stack of the current

 * thread, if any.

 *

 * @return   the work queue pointer, or NULL

 **/

static inline SimpleWorkQueue *getCurrentThreadWorkQueue(void)

{

  WorkQueueStackHandle *handle

    = (WorkQueueStackHandle *)(task_stack_page(current)

                               + workQueueStackHandleGlobals.offset);

  if (likely(handle->nonce == workQueueStackHandleGlobals.nonce)) {

    return handle->queue;

  } else {

    return NULL;

  }

}

/**

 * Initialize the global state used by the work-queue stack-handle

 * code.

 **/

void initWorkQueueStackHandleOnce(void);

#endif // WORK_QUEUE_HANDLE_H