nuttx/mm/shm/shmctl.c

/****************************************************************************
 * mm/shm/shmctl.c
 *
 * 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 <sys/ipc.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#include <assert.h>

#include <nuttx/mm/shm.h>
#include <nuttx/pgalloc.h>

#include "shm/shm.h"

#ifdef CONFIG_MM_SHM

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

/****************************************************************************
 * Name: shmctl
 *
 * Description:
 *   The shmctl() function provides a variety of shared memory control
 *   operations as specified by cmd. The following values for cmd are
 *   available:
 *
 *     - IPC_STAT
 *       Place the current value of each member of the shmid_ds data
 *       structure associated with shmid into the structure pointed to by
 *       buf.
 *     - IPC_SET
 *       Set the value of the shm_perm.mode member of the shmid_ds data
 *       structure associated with shmid to the corresponding value found
 *       in the structure pointed to by buf.
 *     - IPC_RMID
 *       Remove the shared memory identifier specified by shmid from the
 *       system and destroy the shared memory segment and shmid_ds data
 *       structure associated with it.
 *
 * Input Parameters:
 *   shmid - Shared memory identifier
 *   cmd - shmctl() command
 *   buf - Data associated with the shmctl() command
 *
 * Returned Value:
 *   Upon successful completion, shmctl() will return 0; otherwise, it will
 *   return -1 and set errno to indicate the error.
 *
 *     - EACCES
 *       The argument cmd is equal to IPC_STAT and the calling process does
 *       not have read permission.
 *     - EINVAL
 *       The value of shmid is not a valid shared memory identifier, or the
 *       value of cmd is not a valid command.
 *     - EPERM
 *       The argument cmd is equal to IPC_RMID or IPC_SET and the effective
 *       user ID of the calling process is not equal to that of a process
 *       with appropriate privileges and it is not equal to the value of
 *       shm_perm.cuid or shm_perm.uid in the data structure associated with
 *       shmid.
 *     - EOVERFLOW
 *       The cmd argument is IPC_STAT and the gid or uid value is too large
 *       to be stored in the structure pointed to by the buf argument.
 *
 * POSIX Deviations:
 *     - IPC_SET.  Does not set the shm_perm.uid or shm_perm.gid
 *       members of the shmid_ds data structure associated with shmid
 *       because user and group IDs are not yet supported by NuttX
 *     - IPC_SET.  Does not restrict the operation to processes with
 *       appropriate privileges or matching user IDs in shmid_ds data
 *       structure associated with shmid.  Again because user IDs and
 *       user/group privileges are are not yet supported by NuttX
 *     - IPC_RMID.  Does not restrict the operation to processes with
 *       appropriate privileges or matching user IDs in shmid_ds data
 *       structure associated with shmid.  Again because user IDs and
 *       user/group privileges are are not yet supported by NuttX
 *
 ****************************************************************************/

int shmctl(int shmid, int cmd, struct shmid_ds *buf)
{
  FAR struct shm_region_s *region;
  int ret;

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

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

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

  /* Handle the request according to the received cmd */

  switch (cmd)
    {
      case IPC_STAT:
        {
          /* Place the current value of each member of the shmid_ds data
           * structure associated with shmid into the structure pointed to
           * by buf.
           */

          DEBUGASSERT(buf);
          memcpy(buf, &region->sr_ds, sizeof(struct shmid_ds));
        }
        break;

      case IPC_SET:
        {
          /* Set the value of the shm_perm.mode member of the shmid_ds
           * data structure associated with shmid to the corresponding
           * value found in the structure pointed to by buf.
           */

          region->sr_ds.shm_perm.mode = buf->shm_perm.mode;
        }
        break;

      case IPC_RMID:
        {
          /* Are any processes attached to the region? */

          if (region->sr_ds.shm_nattch > 0)
            {
              /* Yes.. just set the UNLINKED flag.  The region will be
               * removed when there are no longer any processes attached to
               * it.
               */

               region->sr_flags |= SRFLAG_UNLINKED;
            }
          else
            {
              /* No.. free the entry now */

              shm_destroy(shmid);

              /* Don't try anything further on the deleted region */

              return OK;
            }
        }
        break;

      default:
        shmerr("ERROR: Unrecognized command: %d\n", cmd);
        ret = -EINVAL;
        goto errout_with_semaphore;
    }

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

  region = &g_shminfo.si_region[shmid];
  region->sr_ds.shm_lpid = getpid();

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

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

  /* Release our lock on the entry */

  nxsem_post(&region->sr_sem);
  return ret;

errout_with_semaphore:
  nxsem_post(&region->sr_sem);

errout_with_ret:
  set_errno(-ret);
  return ERROR;
}

/****************************************************************************
 * Name: shm_destroy
 *
 * Description:
 *   Destroy a memory region.  This function is called:
 *
 *   - On certain conditions when shmget() is not successful in instantiating
 *     the full memory region and we need to clean up and free a table entry.
 *   - When shmctl() is called with cmd == IPC_RMID and there are no
 *     processes attached to the memory region.
 *   - When shmdt() is called after the last process detaches from memory
 *     region after it was previously marked for deletion by shmctl().
 *
 * Input Parameters:
 *   shmid - Shared memory identifier
 *
 * Returned Value:
 *   None
 *
 * Assumption:
 *   The caller holds either the region table semaphore or else the
 *   semaphore on the particular entry being deleted.
 *
 ****************************************************************************/

void shm_destroy(int shmid)
{
  FAR struct shm_region_s *region =  &g_shminfo.si_region[shmid];
  int i;

  /* Free all of the allocated physical pages */

  for (i = 0; i < CONFIG_ARCH_SHM_NPAGES && region->sr_pages[i] != 0; i++)
    {
      mm_pgfree(region->sr_pages[i], 1);
    }

  /* Reset the region entry to its initial state */

  nxsem_destroy(&region->sr_sem);
  memset(region, 0, sizeof(struct shm_region_s));
}

#endif /* CONFIG_MM_SHM */