/* Allocate a memory region shared across processes.

   Copyright (C) 2017-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <errno.h>

#include <stddef.h>

#include <support/support.h>

#include <support/xunistd.h>

#include <sys/mman.h>

/* Header for the allocation.  It contains the size of the allocation

   for subsequent unmapping.  */

struct header

{

  size_t total_size;

  char data[] __attribute__ ((aligned (__alignof__ (max_align_t))));

};

void *

support_shared_allocate (size_t size)

{

  size_t total_size = size + offsetof (struct header, data);

  if (total_size < size)

    {

      errno = ENOMEM;

      oom_error (__func__, size);

      return NULL;

    }

  else

    {

      struct header *result = xmmap (NULL, total_size, PROT_READ | PROT_WRITE,

                                     MAP_ANONYMOUS | MAP_SHARED, -1);

      result->total_size = total_size;

      return &result->data;

    }

}

void

support_shared_free (void *data)

{

  struct header *header = data - offsetof (struct header, data);

  xmunmap (header, header->total_size);

}