drivers/pipes/pipe.c

/****************************************************************************
 * drivers/pipes/pipe.c
 *
 *   Copyright (C) 2008-2009 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.
 *
 ****************************************************************************/

/****************************************************************************
 * Compilation Switches
 ****************************************************************************/

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

#include <nuttx/config.h>

#include <sys/types.h>
#include <nuttx/fs/fs.h>
#include <stdio.h>
#include <unistd.h>
#include <semaphore.h>
#include <fcntl.h>
#include <errno.h>

#include "pipe_common.h"

#if CONFIG_DEV_PIPE_SIZE > 0

/****************************************************************************
 * Definitions
 ****************************************************************************/

#define MAX_PIPES 32

/****************************************************************************
 * Private Types
 ****************************************************************************/

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

static int pipe_close(FAR struct file *filep);

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

static const struct file_operations pipe_fops =
{
  pipecommon_open,   /* open */
  pipe_close,        /* close */
  pipecommon_read,   /* read */
  pipecommon_write,  /* write */
  0,                 /* seek */
  0                  /* ioctl */
#ifndef CONFIG_DISABLE_POLL
  , pipecommon_poll  /* poll */
#endif
};

static sem_t  g_pipesem       = SEM_INITIALIZER(1);
static uint32_t g_pipeset     = 0;
static uint32_t g_pipecreated = 0;

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

/****************************************************************************
 * Name: pipe_allocate
 ****************************************************************************/

static inline int pipe_allocate(void)
{
  int pipeno;
  int ret = -ENFILE;

  for (pipeno = 0; pipeno < MAX_PIPES; pipeno++)
    {
      if ((g_pipeset & (1 << pipeno)) == 0)
        {
          g_pipeset |= (1 << pipeno);
          ret = pipeno;
          break;
        }
    }

  return ret;
}

/****************************************************************************
 * Name: pipe_free
 ****************************************************************************/

static inline void pipe_free(int pipeno)
{
  int ret = sem_wait(&g_pipesem);
  if (ret == 0)
    {
      g_pipeset &= ~(1 << pipeno);
      (void)sem_post(&g_pipesem);
    }
}

/****************************************************************************
 * Name: pipe_close
 ****************************************************************************/

static int pipe_close(FAR struct file *filep)
{
  struct inode      *inode = filep->f_inode;
  struct pipe_dev_s *dev   = inode->i_private;
  int                ret;

  /* Some sanity checking */
#if CONFIG_DEBUG
  if (!dev)
    {
      return -EBADF;
    }
#endif

  /* Perform common close operations */

  ret =  pipecommon_close(filep);
  if (ret == 0 && dev->d_refs == 0)
    {
      /* Release the pipe when there are no further open references to it. */

      pipe_free(dev->d_pipeno);
    }

  return ret;
}

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

/****************************************************************************
 * Name: pipe
 *
 * Description:
 *   pipe() creates a pair of file descriptors, pointing to a pipe inode, and
 *   places them in the array pointed to by 'fd'. fd[0] is for reading,
 *   fd[1] is for writing.
 *
 * Inputs:
 *   fd[2] - The user provided array in which to catch the pipe file
 *   descriptors
 *
 * Return:
 *   0 is returned on success; otherwise, -1 is returned with errno set
 *   appropriately.
 *
 ****************************************************************************/

int pipe(int fd[2])
{
  struct pipe_dev_s *dev = NULL;
  char devname[16];
  int pipeno;
  int err;
  int ret;

  /* Get exclusive access to the pipe allocation data */

  ret = sem_wait(&g_pipesem);
  if (ret < 0)
    {
      /* sem_wait() will have already set errno */

      return ERROR;
    }

  /* Allocate a minor number for the pipe device */

  pipeno = pipe_allocate();
  if (pipeno < 0)
    {
      (void)sem_post(&g_pipesem);
      err = -pipeno;
      goto errout;
    }

  /* Create a pathname to the pipe device */

  sprintf(devname, "/dev/pipe%d", pipeno);

  /* Check if the pipe device has already been created */

  if ((g_pipecreated & (1 << pipeno)) == 0)
    {
      /* No.. Allocate and initialize a new device structure instance */

      dev = pipecommon_allocdev();
      if (!dev)
        {
          (void)sem_post(&g_pipesem);
          err = ENOMEM;
          goto errout_with_pipe;
        }

      dev->d_pipeno = pipeno;

      /* Register the pipe device */

      ret = register_driver(devname, &pipe_fops, 0666, (void*)dev);
      if (ret != 0)
        {
          (void)sem_post(&g_pipesem);
          err = -ret;
          goto errout_with_dev;
        }

      /* Remember that we created this device */

       g_pipecreated |= (1 << pipeno);
    }

  (void)sem_post(&g_pipesem);

  /* Get a write file descriptor */

  fd[1] = open(devname, O_WRONLY);
  if (fd[1] < 0)
    {
      err = -fd[1];
      goto errout_with_driver;
    }

  /* Get a read file descriptor */

  fd[0] = open(devname, O_RDONLY);
  if (fd[0] < 0)
    {
      err = -fd[0];
      goto errout_with_wrfd;
    }

  return OK;

errout_with_wrfd:
  close(fd[1]);
errout_with_driver:
  unregister_driver(devname);
errout_with_dev:
  pipecommon_freedev(dev);
errout_with_pipe:
  pipe_free(pipeno);
errout:
  errno = err;
  return ERROR;
}

#endif /* CONFIG_DEV_PIPE_SIZE > 0 */