/****************************************************************************
 * mm/shm/shmdt.c
 *
 *   Copyright (C) 2014 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <sys/shm.h>
#include <errno.h>

#include <nuttx/arch.h>
#include <nuttx/sched.h>
#include <nuttx/mm/shm.h>

#include "shm/shm.h"

#ifdef CONFIG_MM_SHM

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/****************************************************************************
 * Private Types
 ****************************************************************************/

/****************************************************************************
 * Private Data
 ****************************************************************************/

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: shmdt
 *
 * Description:
 *   The shmdt() function detaches the shared memory segment located at the
 *   address specified by shmaddr from the address space of the calling
 *   process.
 *
 * Input Parameters:
 *   shmid - Shared memory identifier
 *
 * Returned Value:
 *   Upon successful completion, shmdt() will decrement the value of
 *   shm_nattch in the data structure associated with the shared memory ID
 *   of the attached shared memory segment and return 0.
 *
 *   Otherwise, the shared memory segment will not be detached, shmdt()
 &   will return -1, and errno will be set to indicate the error.
 *
 *   - EINVAL
 *     The value of shmaddr is not the data segment start address of a
 *     shared memory segment.
 *
 ****************************************************************************/

int shmdt(FAR const void *shmaddr)
{
  FAR struct shm_region_s *region;
  FAR struct task_group_s *group;
  FAR struct tcb_s *tcb;
  unsigned int npages;
  int shmid;
  int ret;

  /* Get the TCB and group containing our virtual memory allocator */

  tcb = sched_self();
  DEBUGASSERT(tcb && tcb->group);
  group = tcb->group;
  DEBUGASSERT(group->tg_shm.gs_handle != NULL);

  /* Perform the reverse lookup to get the shmid corresponding to this
   * shmaddr.
   */

  for (shmid = 0;
       shmid < CONFIG_ARCH_SHM_MAXREGIONS &&
       group->tg_shm.gs_vaddr[shmid] != (uintptr_t)shmaddr;
       shmid++);

  if (shmid >= CONFIG_ARCH_SHM_MAXREGIONS)
    {
      shmdbg("No region matching this virtual address: %p\n", shmaddr);
      ret = -EINVAL;
      goto errout_with_errno;
    }

  /* Get the region associated with the shmid */

  region =  &g_shminfo.si_region[shmid];
  DEBUGASSERT((region->sr_flags & SRFLAG_INUSE) != 0);

  /* Get exclusive access to the region data structure */

  ret = sem_wait(&region->sr_sem);
  if (ret < 0)
    {
      shmdbg("sem_wait failed: %d\n", ret);
      goto errout;
    }

  /* Free the virtual address space */

  gran_free(group->tg_shm.gs_handle, (FAR void *)shmaddr,
            region->sr_ds.shm_segsz);

  /* Convert the region size to pages */

  npages = MM_PGALIGNUP(region->sr_ds.shm_segsz);

  /* Detach, i.e, unmap, on shared memory region from a user virtual
   * address.
   */

  ret = up_shmdt((uintptr_t)shmaddr, npages);
  if (ret < 0)
    {
      shmdbg("up_shmdt() failed\n");
    }

  /* Indicate that there is no longer any mapping for this region. */

  group->tg_shm.gs_vaddr[shmid] = 0;

  /* Decrement the count of processes attached to this region.
   * If the count decrements to zero and there is a pending unlink,
   * then destroy the shared memory region now and stop any further
   * operations on it.
   */

  DEBUGASSERT(region->sr_ds.shm_nattch > 0);
  if (region->sr_ds.shm_nattch <= 1)
    {
      region->sr_ds.shm_nattch = 0;
      if ((region->sr_flags & SRFLAG_UNLINKED) != 0)
        {
          shm_destroy(shmid);
          return OK;
        }
    }
  else
    {
      /* Just decrement the number of processes attached to the shared
       * memory region.
       */

      region->sr_ds.shm_nattch--;
    }

  /* Save the process ID of the the last operation */

  region->sr_ds.shm_lpid = tcb->pid;

  /* Save the time of the last shmdt() */

  region->sr_ds.shm_dtime = time(NULL);

  /* Release our lock on the entry */

  sem_post(&region->sr_sem);
  return OK;

errout_with_errno:
  set_errno(-ret);
errout:
  return ERROR;
}

#endif /* CONFIG_MM_SHM */
