nuttx/drivers/pipes/fifo.c

/****************************************************************************
 * drivers/pipes/fifo.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/types.h>
#include <sys/stat.h>
#include <stdint.h>
#include <errno.h>

#include <nuttx/fs/fs.h>

#include "pipe_common.h"

#if CONFIG_DEV_FIFO_SIZE > 0

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

static const struct file_operations fifo_fops =
{
  pipecommon_open,     /* open */
  pipecommon_close,    /* close */
  pipecommon_read,     /* read */
  pipecommon_write,    /* write */
  NULL,                /* seek */
  pipecommon_ioctl,    /* ioctl */
  pipecommon_poll      /* poll */
#ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
  , pipecommon_unlink  /* unlink */
#endif
};

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

/****************************************************************************
 * Name: nx_mkfifo
 *
 * Description:
 *   nx_mkfifo() makes a FIFO device driver file with name 'pathname.' Unlike
 *   Linux, a NuttX FIFO is not a special file type but simply a device
 *   driver instance.  'mode' specifies the FIFO's permissions.
 *
 *   Once the FIFO has been created by nx_mkfifo(), any thread can open it
 *   for reading or writing, in the same way as an ordinary file. However, it
 *   must have been opened from both reading and writing before input or
 *   output can be performed.  This FIFO implementation will block all
 *   attempts to open a FIFO read-only until at least one thread has opened
 *   the FIFO for  writing.
 *
 *   If all threads that write to the FIFO have closed, subsequent calls to
 *   read() on the FIFO will return 0 (end-of-file).
 *
 *   NOTE: nx_mkfifo is a special, non-standard, NuttX-only interface.  Since
 *   the NuttX FIFOs are based in in-memory, circular buffers, the ability
 *   to control the size of those buffers is critical for system tuning.
 *
 * Input Parameters:
 *   pathname - The full path to the FIFO instance to attach to or to create
 *     (if not already created).
 *   mode - Ignored for now
 *   bufsize - The size of the in-memory, circular buffer in bytes.
 *
 * Returned Value:
 *   0 is returned on success; a negated errno value is returned on a
 *   failure.
 *
 ****************************************************************************/

int nx_mkfifo(FAR const char *pathname, mode_t mode, size_t bufsize)
{
  FAR struct pipe_dev_s *dev;
  int ret;

  /* Allocate and initialize a new device structure instance */

  dev = pipecommon_allocdev(bufsize);
  if (!dev)
    {
      return -ENOMEM;
    }

  ret = register_driver(pathname, &fifo_fops, mode, (FAR void *)dev);
  if (ret != 0)
    {
      pipecommon_freedev(dev);
    }

  return ret;
}

#endif /* CONFIG_DEV_FIFO_SIZE > 0 */