nuttx/drivers/dev_null.c

/****************************************************************************
 * drivers/dev_null.c
 *
 *   Copyright (C) 2007, 2008, 2013, 2016 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/types.h>
#include <stdbool.h>
#include <string.h>
#include <poll.h>
#include <errno.h>

#include <nuttx/semaphore.h>
#include <nuttx/fs/fs.h>
#include <nuttx/drivers/drivers.h>

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

static ssize_t devnull_read(FAR struct file *filep, FAR char *buffer,
                 size_t buflen);
static ssize_t devnull_write(FAR struct file *filep, FAR const char *buffer,
                 size_t buflen);
static int     devnull_poll(FAR struct file *filep, FAR struct pollfd *fds,
                 bool setup);

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

static const struct file_operations devnull_fops =
{
  NULL,          /* open */
  NULL,          /* close */
  devnull_read,  /* read */
  devnull_write, /* write */
  NULL,          /* seek */
  NULL,          /* ioctl */
  devnull_poll   /* poll */
#ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
  , NULL         /* unlink */
#endif
};

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

/****************************************************************************
 * Name: devnull_read
 ****************************************************************************/

static ssize_t devnull_read(FAR struct file *filep, FAR char *buffer,
                            size_t len)
{
  return 0; /* Return EOF */
}

/****************************************************************************
 * Name: devnull_write
 ****************************************************************************/

static ssize_t devnull_write(FAR struct file *filep, FAR const char *buffer,
                             size_t len)
{
  return len; /* Say that everything was written */
}

/****************************************************************************
 * Name: devnull_poll
 ****************************************************************************/

static int devnull_poll(FAR struct file *filep, FAR struct pollfd *fds,
                        bool setup)
{
  if (setup)
    {
      fds->revents |= (fds->events & (POLLIN | POLLOUT));
      if (fds->revents != 0)
        {
          nxsem_post(fds->sem);
        }
    }

  return OK;
}

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

/****************************************************************************
 * Name: devnull_register
 *
 * Description:
 *   Register /dev/null
 *
 ****************************************************************************/

void devnull_register(void)
{
  (void)register_driver("/dev/null", &devnull_fops, 0666, NULL);
}