/****************************************************************************
 * mm/shm/shmat.c
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

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

#include <nuttx/config.h>

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

#include <nuttx/sched.h>
#include <nuttx/arch.h>
#include <nuttx/pgalloc.h>
#include <nuttx/mm/map.h>

#include "sched/sched.h"
#include "shm/shm.h"

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

static int munmap_shm(FAR struct task_group_s *group,
                      FAR struct mm_map_entry_s *entry,
                      FAR void *start,
                      size_t length)
{
  FAR void *shmaddr = entry->vaddr;
  int shmid = entry->priv.i;
  FAR struct shm_region_s *region;
  pid_t pid;
  unsigned int npages;
  int ret;

  /* Remove the entry from the process' mappings */

  ret = mm_map_remove(get_group_mm(group), entry);
  if (ret < 0)
    {
      return ret;
    }

  /* 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 = nxmutex_lock(&region->sr_lock);
  if (ret < 0)
    {
      shmerr("ERROR: nxsem_wait failed: %d\n", ret);
      return ret;
    }

  if (group)
    {
      /* Free the virtual address space */

      vm_release_region(get_group_mm(group), shmaddr,
                        region->sr_ds.shm_segsz);

      /* Convert the region size to pages */

      npages = MM_NPAGES(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);

      /* Get pid of this process */

      pid = group->tg_pid;
    }
  else
    {
      /* We are in the middle of process destruction and don't know the
       * context
       */

      pid = 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 last operation */

  region->sr_ds.shm_lpid = pid;

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

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

  /* Release our lock on the entry */

  nxmutex_unlock(&region->sr_lock);

  return ret;
}

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

/****************************************************************************
 * Name: shmat
 *
 * Description:
 *   The shmat() function attaches the shared memory segment associated with
 *   the shared memory identifier specified by shmid to the address space of
 *   the calling process. The segment is attached at the address specified
 *   by one of the following criteria:
 *
 *     - If shmaddr is a null pointer, the segment is attached at the first
 *       available address as selected by the system.
 *     - If shmaddr is not a null pointer and (shmflg & SHM_RND) is non-
 *       zero, the segment is attached at the address given by
 *       (shmaddr - ((uintptr_t)shmaddr % SHMLBA)).
 *     - If shmaddr is not a null pointer and (shmflg & SHM_RND) is 0, the
 *       segment is attached at the address given by shmaddr.
 *     - The segment is attached for reading if (shmflg & SHM_RDONLY) is
 *       non-zero and the calling process has read permission; otherwise, if
 *       it is 0 and the calling process has read and write permission, the
 *       segment is attached for reading and writing.
 *
 * Input Parameters:
 *   shmid  - Shared memory identifier
 *   smaddr - Determines mapping of the shared memory region
 *   shmflg - See SHM_* definitions in include/sys/shm.h.  Only SHM_RDONLY
 *            and SHM_RND are supported.
 *
 * Returned Value:
 *   Upon successful completion, shmat() will increment the value of
 *   shm_nattch in the data structure associated with the shared memory ID
 *   of the attached shared memory segment and return the segment's start
 *   address.
 *
 *   Otherwise, the shared memory segment will not be attached, shmat() will
 *   return -1, and errno will be set to indicate the error.
 *
 *     - EACCES
 *       Operation permission is denied to the calling process
 *     - EINVAL
 *       The value of shmid is not a valid shared memory identifier, the
 *       shmaddr is not a null pointer, and the value of
 *       (shmaddr -((uintptr_t)shmaddr % SHMLBA)) is an illegal address for
 *       attaching shared memory; or the shmaddr is not a null pointer,
 *       (shmflg & SHM_RND) is 0, and the value of shmaddr is an illegal
 *       address for attaching shared memory.
 *     - EMFILE
 *       The number of shared memory segments attached to the calling
 *       process would exceed the system-imposed limit.
 *     - ENOMEM
 *       The available data space is not large enough to accommodate the
 *       shared memory segment.
 *
 ****************************************************************************/

FAR void *shmat(int shmid, FAR const void *shmaddr, int shmflg)
{
  FAR struct shm_region_s *region;
  FAR struct task_group_s *group;
  FAR struct tcb_s *tcb;
  FAR void *vaddr;
  unsigned int npages;
  int ret;
  struct mm_map_entry_s entry;

  /* Get the region associated with the shmid */

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

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

  tcb = this_task();
  DEBUGASSERT(tcb && tcb->group);

  group = tcb->group;

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

  ret = nxmutex_lock(&region->sr_lock);
  if (ret < 0)
    {
      shmerr("ERROR: nxsem_wait failed: %d\n", ret);
      goto errout_with_ret;
    }

  /* Set aside a virtual address space to span this physical region */

  vaddr = vm_alloc_region(get_group_mm(group), NULL,
                          region->sr_ds.shm_segsz);
  if (vaddr == NULL)
    {
      shmerr("ERROR: vm_alloc_regioon() failed\n");
      ret = -ENOMEM;
      goto errout_with_lock;
    }

  /* Convert the region size to pages */

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

  /* Attach, i.e, map, on shared memory region to the user virtual address. */

  ret = up_shmat(region->sr_pages, npages, (uintptr_t)vaddr);
  if (ret < 0)
    {
      shmerr("ERROR: up_shmat() failed\n");
      goto errout_with_vaddr;
    }

  /* Save the virtual address of the region.  We will need that in shmdt()
   * to do the reverse lookup:  Give the virtual address of the region to
   * detach, we need to get the region table index.
   */

  entry.vaddr = vaddr;
  entry.length = region->sr_ds.shm_segsz;
  entry.offset = 0;
  entry.munmap = munmap_shm;
  entry.priv.i = shmid;

  ret = mm_map_add(get_current_mm(), &entry);
  if (ret < 0)
    {
      shmerr("ERROR: mm_map_add() failed\n");
      goto errout_with_vaddr;
    }

  /* Increment the count of processes attached to this region */

  region->sr_ds.shm_nattch++;

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

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

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

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

  /* Release our lock on the entry */

  nxmutex_unlock(&region->sr_lock);
  return vaddr;

errout_with_vaddr:
  vm_release_region(get_group_mm(group), vaddr, region->sr_ds.shm_segsz);

errout_with_lock:
  nxmutex_unlock(&region->sr_lock);

errout_with_ret:
  set_errno(-ret);
  return (FAR void *)ERROR;
}