/*
   *  linux/fs/pipe.c
   *
   *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
   */
  
  #include <linux/mm.h>
  #include <linux/file.h>
  #include <linux/poll.h>
  #include <linux/slab.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/fs.h>

  #include <linux/log2.h>

  #include <linux/mount.h>
  #include <linux/pipe_fs_i.h>
  #include <linux/uio.h>
  #include <linux/highmem.h>

  #include <linux/pagemap.h>

  #include <linux/audit.h>

  #include <linux/syscalls.h>

  #include <linux/fcntl.h>

  
  #include <asm/uaccess.h>
  #include <asm/ioctls.h>
  
  /*

   * The max size that a non-root user is allowed to grow the pipe. Can

   * be set by root in /proc/sys/fs/pipe-max-size

   */

  unsigned int pipe_max_size = 1048576;
  
  /*
   * Minimum pipe size, as required by POSIX
   */
  unsigned int pipe_min_size = PAGE_SIZE;

  
  /*

   * We use a start+len construction, which provides full use of the 
   * allocated memory.
   * -- Florian Coosmann (FGC)
   * 
   * Reads with count = 0 should always return 0.
   * -- Julian Bradfield 1999-06-07.
   *
   * FIFOs and Pipes now generate SIGIO for both readers and writers.
   * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
   *
   * pipe_read & write cleanup
   * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
   */

  static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
  {
  	if (pipe->inode)
  		mutex_lock_nested(&pipe->inode->i_mutex, subclass);
  }
  
  void pipe_lock(struct pipe_inode_info *pipe)
  {
  	/*
  	 * pipe_lock() nests non-pipe inode locks (for writing to a file)
  	 */
  	pipe_lock_nested(pipe, I_MUTEX_PARENT);
  }
  EXPORT_SYMBOL(pipe_lock);
  
  void pipe_unlock(struct pipe_inode_info *pipe)
  {
  	if (pipe->inode)
  		mutex_unlock(&pipe->inode->i_mutex);
  }
  EXPORT_SYMBOL(pipe_unlock);
  
  void pipe_double_lock(struct pipe_inode_info *pipe1,
  		      struct pipe_inode_info *pipe2)
  {
  	BUG_ON(pipe1 == pipe2);
  
  	if (pipe1 < pipe2) {
  		pipe_lock_nested(pipe1, I_MUTEX_PARENT);
  		pipe_lock_nested(pipe2, I_MUTEX_CHILD);
  	} else {

  		pipe_lock_nested(pipe2, I_MUTEX_PARENT);
  		pipe_lock_nested(pipe1, I_MUTEX_CHILD);

  	}
  }

  /* Drop the inode semaphore and wait for a pipe event, atomically */

  void pipe_wait(struct pipe_inode_info *pipe)

  {
  	DEFINE_WAIT(wait);

  	/*
  	 * Pipes are system-local resources, so sleeping on them
  	 * is considered a noninteractive wait:
  	 */

  	prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);

  	pipe_unlock(pipe);

  	schedule();

  	finish_wait(&pipe->wait, &wait);

  	pipe_lock(pipe);

  }

  static int

  pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len,
  			int atomic)

  {
  	unsigned long copy;
  
  	while (len > 0) {
  		while (!iov->iov_len)
  			iov++;
  		copy = min_t(unsigned long, len, iov->iov_len);

  		if (atomic) {
  			if (__copy_from_user_inatomic(to, iov->iov_base, copy))
  				return -EFAULT;
  		} else {
  			if (copy_from_user(to, iov->iov_base, copy))
  				return -EFAULT;
  		}

  		to += copy;
  		len -= copy;
  		iov->iov_base += copy;
  		iov->iov_len -= copy;
  	}
  	return 0;
  }

  static int

  pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len,
  		      int atomic)

  {
  	unsigned long copy;
  
  	while (len > 0) {
  		while (!iov->iov_len)
  			iov++;
  		copy = min_t(unsigned long, len, iov->iov_len);

  		if (atomic) {
  			if (__copy_to_user_inatomic(iov->iov_base, from, copy))
  				return -EFAULT;
  		} else {
  			if (copy_to_user(iov->iov_base, from, copy))
  				return -EFAULT;
  		}

  		from += copy;
  		len -= copy;
  		iov->iov_base += copy;
  		iov->iov_len -= copy;
  	}
  	return 0;
  }

  /*
   * Attempt to pre-fault in the user memory, so we can use atomic copies.
   * Returns the number of bytes not faulted in.
   */
  static int iov_fault_in_pages_write(struct iovec *iov, unsigned long len)
  {
  	while (!iov->iov_len)
  		iov++;
  
  	while (len > 0) {
  		unsigned long this_len;
  
  		this_len = min_t(unsigned long, len, iov->iov_len);
  		if (fault_in_pages_writeable(iov->iov_base, this_len))
  			break;
  
  		len -= this_len;
  		iov++;
  	}
  
  	return len;
  }
  
  /*
   * Pre-fault in the user memory, so we can use atomic copies.
   */
  static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
  {
  	while (!iov->iov_len)
  		iov++;
  
  	while (len > 0) {
  		unsigned long this_len;
  
  		this_len = min_t(unsigned long, len, iov->iov_len);
  		fault_in_pages_readable(iov->iov_base, this_len);
  		len -= this_len;
  		iov++;
  	}
  }

  static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
  				  struct pipe_buffer *buf)

  {
  	struct page *page = buf->page;

  	/*
  	 * If nobody else uses this page, and we don't already have a
  	 * temporary page, let's keep track of it as a one-deep

  	 * allocation cache. (Otherwise just release our reference to it)

  	 */

  	if (page_count(page) == 1 && !pipe->tmp_page)

  		pipe->tmp_page = page;

  	else
  		page_cache_release(page);

  }

  /**
   * generic_pipe_buf_map - virtually map a pipe buffer
   * @pipe:	the pipe that the buffer belongs to
   * @buf:	the buffer that should be mapped
   * @atomic:	whether to use an atomic map
   *
   * Description:
   *	This function returns a kernel virtual address mapping for the

   *	pipe_buffer passed in @buf. If @atomic is set, an atomic map is provided

   *	and the caller has to be careful not to fault before calling
   *	the unmap function.
   *
   *	Note that this function occupies KM_USER0 if @atomic != 0.
   */

  void *generic_pipe_buf_map(struct pipe_inode_info *pipe,

  			   struct pipe_buffer *buf, int atomic)

  {

  	if (atomic) {
  		buf->flags |= PIPE_BUF_FLAG_ATOMIC;
  		return kmap_atomic(buf->page, KM_USER0);
  	}

  	return kmap(buf->page);
  }

  EXPORT_SYMBOL(generic_pipe_buf_map);

  /**
   * generic_pipe_buf_unmap - unmap a previously mapped pipe buffer
   * @pipe:	the pipe that the buffer belongs to
   * @buf:	the buffer that should be unmapped
   * @map_data:	the data that the mapping function returned
   *
   * Description:
   *	This function undoes the mapping that ->map() provided.
   */

  void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,

  			    struct pipe_buffer *buf, void *map_data)

  {

  	if (buf->flags & PIPE_BUF_FLAG_ATOMIC) {
  		buf->flags &= ~PIPE_BUF_FLAG_ATOMIC;
  		kunmap_atomic(map_data, KM_USER0);
  	} else
  		kunmap(buf->page);

  }

  EXPORT_SYMBOL(generic_pipe_buf_unmap);

  /**

   * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer

   * @pipe:	the pipe that the buffer belongs to
   * @buf:	the buffer to attempt to steal
   *
   * Description:

   *	This function attempts to steal the &struct page attached to

   *	@buf. If successful, this function returns 0 and returns with
   *	the page locked. The caller may then reuse the page for whatever

   *	he wishes; the typical use is insertion into a different file

   *	page cache.
   */

  int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
  			   struct pipe_buffer *buf)

  {

  	struct page *page = buf->page;

  	/*
  	 * A reference of one is golden, that means that the owner of this
  	 * page is the only one holding a reference to it. lock the page
  	 * and return OK.
  	 */

  	if (page_count(page) == 1) {

  		lock_page(page);
  		return 0;
  	}
  
  	return 1;

  }

  EXPORT_SYMBOL(generic_pipe_buf_steal);

  /**

   * generic_pipe_buf_get - get a reference to a &struct pipe_buffer

   * @pipe:	the pipe that the buffer belongs to
   * @buf:	the buffer to get a reference to
   *
   * Description:
   *	This function grabs an extra reference to @buf. It's used in
   *	in the tee() system call, when we duplicate the buffers in one
   *	pipe into another.
   */
  void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)

  {
  	page_cache_get(buf->page);
  }

  EXPORT_SYMBOL(generic_pipe_buf_get);

  /**
   * generic_pipe_buf_confirm - verify contents of the pipe buffer

   * @info:	the pipe that the buffer belongs to

   * @buf:	the buffer to confirm
   *
   * Description:
   *	This function does nothing, because the generic pipe code uses
   *	pages that are always good when inserted into the pipe.
   */

  int generic_pipe_buf_confirm(struct pipe_inode_info *info,
  			     struct pipe_buffer *buf)

  {
  	return 0;
  }

  EXPORT_SYMBOL(generic_pipe_buf_confirm);

  /**
   * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
   * @pipe:	the pipe that the buffer belongs to
   * @buf:	the buffer to put a reference to
   *
   * Description:
   *	This function releases a reference to @buf.
   */
  void generic_pipe_buf_release(struct pipe_inode_info *pipe,
  			      struct pipe_buffer *buf)
  {
  	page_cache_release(buf->page);
  }

  EXPORT_SYMBOL(generic_pipe_buf_release);

  static const struct pipe_buf_operations anon_pipe_buf_ops = {

  	.can_merge = 1,

  	.map = generic_pipe_buf_map,
  	.unmap = generic_pipe_buf_unmap,

  	.confirm = generic_pipe_buf_confirm,

  	.release = anon_pipe_buf_release,

  	.steal = generic_pipe_buf_steal,

  	.get = generic_pipe_buf_get,

  };
  
  static ssize_t

  pipe_read(struct kiocb *iocb, const struct iovec *_iov,
  	   unsigned long nr_segs, loff_t pos)

  {

  	struct file *filp = iocb->ki_filp;

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	struct pipe_inode_info *pipe;

  	int do_wakeup;
  	ssize_t ret;
  	struct iovec *iov = (struct iovec *)_iov;
  	size_t total_len;
  
  	total_len = iov_length(iov, nr_segs);
  	/* Null read succeeds. */
  	if (unlikely(total_len == 0))
  		return 0;
  
  	do_wakeup = 0;
  	ret = 0;

  	mutex_lock(&inode->i_mutex);

  	pipe = inode->i_pipe;

  	for (;;) {

  		int bufs = pipe->nrbufs;

  		if (bufs) {

  			int curbuf = pipe->curbuf;
  			struct pipe_buffer *buf = pipe->bufs + curbuf;

  			const struct pipe_buf_operations *ops = buf->ops;

  			void *addr;
  			size_t chars = buf->len;

  			int error, atomic;

  
  			if (chars > total_len)
  				chars = total_len;

  			error = ops->confirm(pipe, buf);

  			if (error) {

  				if (!ret)

  					ret = error;

  				break;
  			}

  			atomic = !iov_fault_in_pages_write(iov, chars);
  redo:
  			addr = ops->map(pipe, buf, atomic);
  			error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars, atomic);
  			ops->unmap(pipe, buf, addr);

  			if (unlikely(error)) {

  				/*
  				 * Just retry with the slow path if we failed.
  				 */
  				if (atomic) {
  					atomic = 0;
  					goto redo;
  				}

  				if (!ret)

  					ret = error;

  				break;
  			}
  			ret += chars;
  			buf->offset += chars;
  			buf->len -= chars;
  			if (!buf->len) {
  				buf->ops = NULL;

  				ops->release(pipe, buf);

  				curbuf = (curbuf + 1) & (pipe->buffers - 1);

  				pipe->curbuf = curbuf;
  				pipe->nrbufs = --bufs;

  				do_wakeup = 1;
  			}
  			total_len -= chars;
  			if (!total_len)
  				break;	/* common path: read succeeded */
  		}
  		if (bufs)	/* More to do? */
  			continue;

  		if (!pipe->writers)

  			break;

  		if (!pipe->waiting_writers) {

  			/* syscall merging: Usually we must not sleep
  			 * if O_NONBLOCK is set, or if we got some data.
  			 * But if a writer sleeps in kernel space, then
  			 * we can wait for that data without violating POSIX.
  			 */
  			if (ret)
  				break;
  			if (filp->f_flags & O_NONBLOCK) {
  				ret = -EAGAIN;
  				break;
  			}
  		}
  		if (signal_pending(current)) {

  			if (!ret)
  				ret = -ERESTARTSYS;

  			break;
  		}
  		if (do_wakeup) {

  			wake_up_interruptible_sync_poll(&pipe->wait, POLLOUT | POLLWRNORM);

   			kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);

  		}

  		pipe_wait(pipe);

  	}

  	mutex_unlock(&inode->i_mutex);

  
  	/* Signal writers asynchronously that there is more room. */

  	if (do_wakeup) {

  		wake_up_interruptible_sync_poll(&pipe->wait, POLLOUT | POLLWRNORM);

  		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);

  	}
  	if (ret > 0)
  		file_accessed(filp);
  	return ret;
  }
  
  static ssize_t

  pipe_write(struct kiocb *iocb, const struct iovec *_iov,
  	    unsigned long nr_segs, loff_t ppos)

  {

  	struct file *filp = iocb->ki_filp;

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	struct pipe_inode_info *pipe;

  	ssize_t ret;
  	int do_wakeup;
  	struct iovec *iov = (struct iovec *)_iov;
  	size_t total_len;
  	ssize_t chars;
  
  	total_len = iov_length(iov, nr_segs);
  	/* Null write succeeds. */
  	if (unlikely(total_len == 0))
  		return 0;
  
  	do_wakeup = 0;
  	ret = 0;

  	mutex_lock(&inode->i_mutex);

  	pipe = inode->i_pipe;

  	if (!pipe->readers) {

  		send_sig(SIGPIPE, current, 0);
  		ret = -EPIPE;
  		goto out;
  	}
  
  	/* We try to merge small writes */
  	chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */

  	if (pipe->nrbufs && chars != 0) {

  		int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &

  							(pipe->buffers - 1);

  		struct pipe_buffer *buf = pipe->bufs + lastbuf;

  		const struct pipe_buf_operations *ops = buf->ops;

  		int offset = buf->offset + buf->len;

  		if (ops->can_merge && offset + chars <= PAGE_SIZE) {

  			int error, atomic = 1;

  			void *addr;

  			error = ops->confirm(pipe, buf);

  			if (error)

  				goto out;

  			iov_fault_in_pages_read(iov, chars);
  redo1:
  			addr = ops->map(pipe, buf, atomic);

  			error = pipe_iov_copy_from_user(offset + addr, iov,

  							chars, atomic);
  			ops->unmap(pipe, buf, addr);

  			ret = error;
  			do_wakeup = 1;

  			if (error) {
  				if (atomic) {
  					atomic = 0;
  					goto redo1;
  				}

  				goto out;

  			}

  			buf->len += chars;
  			total_len -= chars;
  			ret = chars;
  			if (!total_len)
  				goto out;
  		}
  	}
  
  	for (;;) {
  		int bufs;

  		if (!pipe->readers) {

  			send_sig(SIGPIPE, current, 0);

  			if (!ret)
  				ret = -EPIPE;

  			break;
  		}

  		bufs = pipe->nrbufs;

  		if (bufs < pipe->buffers) {
  			int newbuf = (pipe->curbuf + bufs) & (pipe->buffers-1);

  			struct pipe_buffer *buf = pipe->bufs + newbuf;
  			struct page *page = pipe->tmp_page;

  			char *src;
  			int error, atomic = 1;

  
  			if (!page) {
  				page = alloc_page(GFP_HIGHUSER);
  				if (unlikely(!page)) {
  					ret = ret ? : -ENOMEM;
  					break;
  				}

  				pipe->tmp_page = page;

  			}

  			/* Always wake up, even if the copy fails. Otherwise

  			 * we lock up (O_NONBLOCK-)readers that sleep due to
  			 * syscall merging.
  			 * FIXME! Is this really true?
  			 */
  			do_wakeup = 1;
  			chars = PAGE_SIZE;
  			if (chars > total_len)
  				chars = total_len;

  			iov_fault_in_pages_read(iov, chars);
  redo2:
  			if (atomic)
  				src = kmap_atomic(page, KM_USER0);
  			else
  				src = kmap(page);
  
  			error = pipe_iov_copy_from_user(src, iov, chars,
  							atomic);
  			if (atomic)
  				kunmap_atomic(src, KM_USER0);
  			else
  				kunmap(page);

  			if (unlikely(error)) {

  				if (atomic) {
  					atomic = 0;
  					goto redo2;
  				}

  				if (!ret)

  					ret = error;

  				break;
  			}
  			ret += chars;
  
  			/* Insert it into the buffer array */
  			buf->page = page;
  			buf->ops = &anon_pipe_buf_ops;
  			buf->offset = 0;
  			buf->len = chars;

  			pipe->nrbufs = ++bufs;
  			pipe->tmp_page = NULL;

  
  			total_len -= chars;
  			if (!total_len)
  				break;
  		}

  		if (bufs < pipe->buffers)

  			continue;
  		if (filp->f_flags & O_NONBLOCK) {

  			if (!ret)
  				ret = -EAGAIN;

  			break;
  		}
  		if (signal_pending(current)) {

  			if (!ret)
  				ret = -ERESTARTSYS;

  			break;
  		}
  		if (do_wakeup) {

  			wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM);

  			kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);

  			do_wakeup = 0;
  		}

  		pipe->waiting_writers++;
  		pipe_wait(pipe);
  		pipe->waiting_writers--;

  	}
  out:

  	mutex_unlock(&inode->i_mutex);

  	if (do_wakeup) {

  		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM);

  		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);

  	}
  	if (ret > 0)

  		file_update_time(filp);

  	return ret;
  }
  
  static ssize_t

  bad_pipe_r(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
  {
  	return -EBADF;
  }
  
  static ssize_t

  bad_pipe_w(struct file *filp, const char __user *buf, size_t count,
  	   loff_t *ppos)

  {
  	return -EBADF;
  }

  static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)

  {

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	struct pipe_inode_info *pipe;

  	int count, buf, nrbufs;
  
  	switch (cmd) {
  		case FIONREAD:

  			mutex_lock(&inode->i_mutex);

  			pipe = inode->i_pipe;

  			count = 0;

  			buf = pipe->curbuf;
  			nrbufs = pipe->nrbufs;

  			while (--nrbufs >= 0) {

  				count += pipe->bufs[buf].len;

  				buf = (buf+1) & (pipe->buffers - 1);

  			}

  			mutex_unlock(&inode->i_mutex);

  			return put_user(count, (int __user *)arg);
  		default:
  			return -EINVAL;
  	}
  }
  
  /* No kernel lock held - fine */
  static unsigned int
  pipe_poll(struct file *filp, poll_table *wait)
  {
  	unsigned int mask;

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	struct pipe_inode_info *pipe = inode->i_pipe;

  	int nrbufs;

  	poll_wait(filp, &pipe->wait, wait);

  
  	/* Reading only -- no need for acquiring the semaphore.  */

  	nrbufs = pipe->nrbufs;

  	mask = 0;
  	if (filp->f_mode & FMODE_READ) {
  		mask = (nrbufs > 0) ? POLLIN | POLLRDNORM : 0;

  		if (!pipe->writers && filp->f_version != pipe->w_counter)

  			mask |= POLLHUP;
  	}
  
  	if (filp->f_mode & FMODE_WRITE) {

  		mask |= (nrbufs < pipe->buffers) ? POLLOUT | POLLWRNORM : 0;

  		/*
  		 * Most Unices do not set POLLERR for FIFOs but on Linux they
  		 * behave exactly like pipes for poll().
  		 */

  		if (!pipe->readers)

  			mask |= POLLERR;
  	}
  
  	return mask;
  }

  static int
  pipe_release(struct inode *inode, int decr, int decw)
  {

  	struct pipe_inode_info *pipe;

  	mutex_lock(&inode->i_mutex);

  	pipe = inode->i_pipe;
  	pipe->readers -= decr;
  	pipe->writers -= decw;

  	if (!pipe->readers && !pipe->writers) {

  		free_pipe_info(inode);
  	} else {

  		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM | POLLERR | POLLHUP);

  		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
  		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);

  	}

  	mutex_unlock(&inode->i_mutex);

  
  	return 0;
  }
  
  static int
  pipe_read_fasync(int fd, struct file *filp, int on)
  {

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	int retval;

  	mutex_lock(&inode->i_mutex);
  	retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_readers);
  	mutex_unlock(&inode->i_mutex);

  	return retval;

  }
  
  
  static int
  pipe_write_fasync(int fd, struct file *filp, int on)
  {

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	int retval;

  	mutex_lock(&inode->i_mutex);
  	retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_writers);
  	mutex_unlock(&inode->i_mutex);

  	return retval;

  }
  
  
  static int
  pipe_rdwr_fasync(int fd, struct file *filp, int on)
  {

  	struct inode *inode = filp->f_path.dentry->d_inode;

  	struct pipe_inode_info *pipe = inode->i_pipe;

  	int retval;

  	mutex_lock(&inode->i_mutex);

  	retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);

  	if (retval >= 0) {

  		retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);

  		if (retval < 0) /* this can happen only if on == T */
  			fasync_helper(-1, filp, 0, &pipe->fasync_readers);
  	}

  	mutex_unlock(&inode->i_mutex);

  	return retval;

  }
  
  
  static int
  pipe_read_release(struct inode *inode, struct file *filp)
  {

  	return pipe_release(inode, 1, 0);
  }
  
  static int
  pipe_write_release(struct inode *inode, struct file *filp)
  {

  	return pipe_release(inode, 0, 1);
  }
  
  static int
  pipe_rdwr_release(struct inode *inode, struct file *filp)
  {
  	int decr, decw;

  	decr = (filp->f_mode & FMODE_READ) != 0;
  	decw = (filp->f_mode & FMODE_WRITE) != 0;
  	return pipe_release(inode, decr, decw);
  }
  
  static int
  pipe_read_open(struct inode *inode, struct file *filp)
  {

  	int ret = -ENOENT;

  	mutex_lock(&inode->i_mutex);

  
  	if (inode->i_pipe) {
  		ret = 0;
  		inode->i_pipe->readers++;
  	}

  	mutex_unlock(&inode->i_mutex);

  	return ret;

  }
  
  static int
  pipe_write_open(struct inode *inode, struct file *filp)
  {

  	int ret = -ENOENT;

  	mutex_lock(&inode->i_mutex);

  
  	if (inode->i_pipe) {
  		ret = 0;
  		inode->i_pipe->writers++;
  	}

  	mutex_unlock(&inode->i_mutex);

  	return ret;

  }
  
  static int
  pipe_rdwr_open(struct inode *inode, struct file *filp)
  {

  	int ret = -ENOENT;

  	mutex_lock(&inode->i_mutex);

  
  	if (inode->i_pipe) {
  		ret = 0;
  		if (filp->f_mode & FMODE_READ)
  			inode->i_pipe->readers++;
  		if (filp->f_mode & FMODE_WRITE)
  			inode->i_pipe->writers++;
  	}

  	mutex_unlock(&inode->i_mutex);

  	return ret;

  }
  
  /*
   * The file_operations structs are not static because they
   * are also used in linux/fs/fifo.c to do operations on FIFOs.

   *
   * Pipes reuse fifos' file_operations structs.

   */

  const struct file_operations read_pipefifo_fops = {

  	.llseek		= no_llseek,

  	.read		= do_sync_read,
  	.aio_read	= pipe_read,

  	.write		= bad_pipe_w,
  	.poll		= pipe_poll,

  	.unlocked_ioctl	= pipe_ioctl,

  	.open		= pipe_read_open,
  	.release	= pipe_read_release,
  	.fasync		= pipe_read_fasync,
  };

  const struct file_operations write_pipefifo_fops = {

  	.llseek		= no_llseek,
  	.read		= bad_pipe_r,

  	.write		= do_sync_write,
  	.aio_write	= pipe_write,

  	.poll		= pipe_poll,

  	.unlocked_ioctl	= pipe_ioctl,

  	.open		= pipe_write_open,
  	.release	= pipe_write_release,
  	.fasync		= pipe_write_fasync,
  };

  const struct file_operations rdwr_pipefifo_fops = {

  	.llseek		= no_llseek,

  	.read		= do_sync_read,
  	.aio_read	= pipe_read,
  	.write		= do_sync_write,
  	.aio_write	= pipe_write,

  	.poll		= pipe_poll,

  	.unlocked_ioctl	= pipe_ioctl,

  	.open		= pipe_rdwr_open,
  	.release	= pipe_rdwr_release,
  	.fasync		= pipe_rdwr_fasync,
  };

  struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
  {

  	struct pipe_inode_info *pipe;

  	pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
  	if (pipe) {

  		pipe->bufs = kzalloc(sizeof(struct pipe_buffer) * PIPE_DEF_BUFFERS, GFP_KERNEL);
  		if (pipe->bufs) {
  			init_waitqueue_head(&pipe->wait);
  			pipe->r_counter = pipe->w_counter = 1;
  			pipe->inode = inode;
  			pipe->buffers = PIPE_DEF_BUFFERS;
  			return pipe;
  		}
  		kfree(pipe);

  	}

  	return NULL;

  }

  void __free_pipe_info(struct pipe_inode_info *pipe)

  {
  	int i;

  	for (i = 0; i < pipe->buffers; i++) {

  		struct pipe_buffer *buf = pipe->bufs + i;

  		if (buf->ops)

  			buf->ops->release(pipe, buf);

  	}

  	if (pipe->tmp_page)
  		__free_page(pipe->tmp_page);

  	kfree(pipe->bufs);

  	kfree(pipe);

  }

  void free_pipe_info(struct inode *inode)
  {
  	__free_pipe_info(inode->i_pipe);
  	inode->i_pipe = NULL;
  }

  static struct vfsmount *pipe_mnt __read_mostly;

  /*
   * pipefs_dname() is called from d_path().
   */
  static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
  {
  	return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
  				dentry->d_inode->i_ino);
  }

  static const struct dentry_operations pipefs_dentry_operations = {

  	.d_dname	= pipefs_dname,

  };
  
  static struct inode * get_pipe_inode(void)
  {

  	struct inode *inode = new_inode_pseudo(pipe_mnt->mnt_sb);

  	struct pipe_inode_info *pipe;

  
  	if (!inode)
  		goto fail_inode;

  	inode->i_ino = get_next_ino();

  	pipe = alloc_pipe_info(inode);
  	if (!pipe)

  		goto fail_iput;

  	inode->i_pipe = pipe;

  	pipe->readers = pipe->writers = 1;

  	inode->i_fop = &rdwr_pipefifo_fops;

  
  	/*
  	 * Mark the inode dirty from the very beginning,
  	 * that way it will never be moved to the dirty
  	 * list because "mark_inode_dirty()" will think
  	 * that it already _is_ on the dirty list.
  	 */
  	inode->i_state = I_DIRTY;
  	inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;

  	inode->i_uid = current_fsuid();
  	inode->i_gid = current_fsgid();

  	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;

  	return inode;
  
  fail_iput:
  	iput(inode);

  fail_inode:
  	return NULL;
  }

  struct file *create_write_pipe(int flags)

  {

  	int err;
  	struct inode *inode;
  	struct file *f;

  	struct path path;

  	struct qstr name = { .name = "" };

  	err = -ENFILE;

  	inode = get_pipe_inode();
  	if (!inode)

  		goto err;

  	err = -ENOMEM;

  	path.dentry = d_alloc_pseudo(pipe_mnt->mnt_sb, &name);

  	if (!path.dentry)

  		goto err_inode;

  	path.mnt = mntget(pipe_mnt);

  	d_instantiate(path.dentry, inode);

  
  	err = -ENFILE;

  	f = alloc_file(&path, FMODE_WRITE, &write_pipefifo_fops);

  	if (!f)
  		goto err_dentry;

  	f->f_mapping = inode->i_mapping;

  	f->f_flags = O_WRONLY | (flags & O_NONBLOCK);

  	f->f_version = 0;
  
  	return f;

   err_dentry:

  	free_pipe_info(inode);

  	path_put(&path);

  	return ERR_PTR(err);

   err_inode:

  	free_pipe_info(inode);
  	iput(inode);

   err:

  	return ERR_PTR(err);
  }
  
  void free_write_pipe(struct file *f)
  {

  	free_pipe_info(f->f_dentry->d_inode);

  	path_put(&f->f_path);

  	put_filp(f);
  }

  struct file *create_read_pipe(struct file *wrf, int flags)

  {

  	/* Grab pipe from the writer */
  	struct file *f = alloc_file(&wrf->f_path, FMODE_READ,
  				    &read_pipefifo_fops);

  	if (!f)
  		return ERR_PTR(-ENFILE);

  	path_get(&wrf->f_path);

  	f->f_flags = O_RDONLY | (flags & O_NONBLOCK);

  
  	return f;
  }

  int do_pipe_flags(int *fd, int flags)

  {
  	struct file *fw, *fr;
  	int error;
  	int fdw, fdr;

  	if (flags & ~(O_CLOEXEC | O_NONBLOCK))

  		return -EINVAL;

  	fw = create_write_pipe(flags);

  	if (IS_ERR(fw))
  		return PTR_ERR(fw);

  	fr = create_read_pipe(fw, flags);

  	error = PTR_ERR(fr);
  	if (IS_ERR(fr))
  		goto err_write_pipe;

  	error = get_unused_fd_flags(flags);

  	if (error < 0)
  		goto err_read_pipe;
  	fdr = error;

  	error = get_unused_fd_flags(flags);

  	if (error < 0)
  		goto err_fdr;
  	fdw = error;

  	audit_fd_pair(fdr, fdw);

  	fd_install(fdr, fr);
  	fd_install(fdw, fw);
  	fd[0] = fdr;
  	fd[1] = fdw;
  
  	return 0;
  
   err_fdr:
  	put_unused_fd(fdr);
   err_read_pipe:

  	path_put(&fr->f_path);

  	put_filp(fr);
   err_write_pipe:
  	free_write_pipe(fw);
  	return error;

  }
  
  /*

   * sys_pipe() is the normal C calling standard for creating
   * a pipe. It's not the way Unix traditionally does this, though.
   */

  SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)

  {
  	int fd[2];
  	int error;

  	error = do_pipe_flags(fd, flags);

  	if (!error) {

  		if (copy_to_user(fildes, fd, sizeof(fd))) {
  			sys_close(fd[0]);
  			sys_close(fd[1]);

  			error = -EFAULT;

  		}

  	}
  	return error;
  }

  SYSCALL_DEFINE1(pipe, int __user *, fildes)

  {
  	return sys_pipe2(fildes, 0);
  }

  /*

   * Allocate a new array of pipe buffers and copy the info over. Returns the
   * pipe size if successful, or return -ERROR on error.
   */

  static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long nr_pages)

  {
  	struct pipe_buffer *bufs;
  
  	/*

  	 * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
  	 * expect a lot of shrink+grow operations, just free and allocate
  	 * again like we would do for growing. If the pipe currently
  	 * contains more buffers than arg, then return busy.
  	 */

  	if (nr_pages < pipe->nrbufs)

  		return -EBUSY;

  	bufs = kcalloc(nr_pages, sizeof(*bufs), GFP_KERNEL | __GFP_NOWARN);

  	if (unlikely(!bufs))
  		return -ENOMEM;
  
  	/*
  	 * The pipe array wraps around, so just start the new one at zero
  	 * and adjust the indexes.
  	 */
  	if (pipe->nrbufs) {

  		unsigned int tail;
  		unsigned int head;

  		tail = pipe->curbuf + pipe->nrbufs;
  		if (tail < pipe->buffers)
  			tail = 0;
  		else
  			tail &= (pipe->buffers - 1);
  
  		head = pipe->nrbufs - tail;

  		if (head)
  			memcpy(bufs, pipe->bufs + pipe->curbuf, head * sizeof(struct pipe_buffer));
  		if (tail)

  			memcpy(bufs + head, pipe->bufs, tail * sizeof(struct pipe_buffer));

  	}
  
  	pipe->curbuf = 0;
  	kfree(pipe->bufs);
  	pipe->bufs = bufs;

  	pipe->buffers = nr_pages;
  	return nr_pages * PAGE_SIZE;

  }

  /*
   * Currently we rely on the pipe array holding a power-of-2 number
   * of pages.
   */
  static inline unsigned int round_pipe_size(unsigned int size)
  {
  	unsigned long nr_pages;
  
  	nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
  }
  
  /*
   * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
   * will return an error.
   */
  int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
  		 size_t *lenp, loff_t *ppos)
  {
  	int ret;
  
  	ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
  	if (ret < 0 || !write)
  		return ret;
  
  	pipe_max_size = round_pipe_size(pipe_max_size);
  	return ret;
  }

  /*
   * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
   * location, so checking ->i_pipe is not enough to verify that this is a
   * pipe.
   */
  struct pipe_inode_info *get_pipe_info(struct file *file)
  {
  	struct inode *i = file->f_path.dentry->d_inode;
  
  	return S_ISFIFO(i->i_mode) ? i->i_pipe : NULL;
  }

  long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
  {
  	struct pipe_inode_info *pipe;
  	long ret;

  	pipe = get_pipe_info(file);

  	if (!pipe)
  		return -EBADF;
  
  	mutex_lock(&pipe->inode->i_mutex);
  
  	switch (cmd) {

  	case F_SETPIPE_SZ: {

  		unsigned int size, nr_pages;

  		size = round_pipe_size(arg);
  		nr_pages = size >> PAGE_SHIFT;

  		ret = -EINVAL;
  		if (!nr_pages)
  			goto out;

  		if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {

  			ret = -EPERM;

  			goto out;

  		}

  		ret = pipe_set_size(pipe, nr_pages);

  		break;

  		}

  	case F_GETPIPE_SZ:

  		ret = pipe->buffers * PAGE_SIZE;

  		break;
  	default:
  		ret = -EINVAL;
  		break;
  	}

  out:

  	mutex_unlock(&pipe->inode->i_mutex);
  	return ret;
  }

  static const struct super_operations pipefs_ops = {
  	.destroy_inode = free_inode_nonrcu,

  	.statfs = simple_statfs,

  };

  /*

   * pipefs should _never_ be mounted by userland - too much of security hassle,
   * no real gain from having the whole whorehouse mounted. So we don't need
   * any operations on the root directory. However, we need a non-trivial
   * d_name - pipe: will go nicely and kill the special-casing in procfs.
   */

  static struct dentry *pipefs_mount(struct file_system_type *fs_type,
  			 int flags, const char *dev_name, void *data)

  {

  	return mount_pseudo(fs_type, "pipe:", &pipefs_ops,
  			&pipefs_dentry_operations, PIPEFS_MAGIC);

  }
  
  static struct file_system_type pipe_fs_type = {
  	.name		= "pipefs",

  	.mount		= pipefs_mount,

  	.kill_sb	= kill_anon_super,
  };
  
  static int __init init_pipe_fs(void)
  {
  	int err = register_filesystem(&pipe_fs_type);

  	if (!err) {
  		pipe_mnt = kern_mount(&pipe_fs_type);
  		if (IS_ERR(pipe_mnt)) {
  			err = PTR_ERR(pipe_mnt);
  			unregister_filesystem(&pipe_fs_type);
  		}
  	}
  	return err;
  }

  fs_initcall(init_pipe_fs);