// SPDX-License-Identifier: GPL-2.0

  /*
   *  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/pseudo_fs.h>

  #include <linux/magic.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 <linux/memcontrol.h>

  #include <linux/watch_queue.h>

  #include <linux/uaccess.h>

  #include <asm/ioctls.h>

  #include "internal.h"

  /*

   * New pipe buffers will be restricted to this size while the user is exceeding
   * their pipe buffer quota. The general pipe use case needs at least two
   * buffers: one for data yet to be read, and one for new data. If this is less
   * than two, then a write to a non-empty pipe may block even if the pipe is not
   * full. This can occur with GNU make jobserver or similar uses of pipes as
   * semaphores: multiple processes may be waiting to write tokens back to the
   * pipe before reading tokens: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/.
   *
   * Users can reduce their pipe buffers with F_SETPIPE_SZ below this at their
   * own risk, namely: pipe writes to non-full pipes may block until the pipe is
   * emptied.
   */
  #define PIPE_MIN_DEF_BUFFERS 2
  
  /*

   * 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;

  /* Maximum allocatable pages per user. Hard limit is unset by default, soft
   * matches default values.
   */
  unsigned long pipe_user_pages_hard;
  unsigned long pipe_user_pages_soft = PIPE_DEF_BUFFERS * INR_OPEN_CUR;

  /*

   * We use head and tail indices that aren't masked off, except at the point of
   * dereference, but rather they're allowed to wrap naturally.  This means there
   * isn't a dead spot in the buffer, but the ring has to be a power of two and
   * <= 2^31.
   * -- David Howells 2019-09-23.
   *

   * 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->files)

  		mutex_lock_nested(&pipe->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->files)

  		mutex_unlock(&pipe->mutex);

  }
  EXPORT_SYMBOL(pipe_unlock);

  static inline void __pipe_lock(struct pipe_inode_info *pipe)
  {
  	mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
  }
  
  static inline void __pipe_unlock(struct pipe_inode_info *pipe)
  {
  	mutex_unlock(&pipe->mutex);
  }

  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);

  	}
  }

  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

  		put_page(page);

  }

  static bool anon_pipe_buf_try_steal(struct pipe_inode_info *pipe,
  		struct pipe_buffer *buf)

  {
  	struct page *page = buf->page;

  	if (page_count(page) != 1)
  		return false;
  	memcg_kmem_uncharge_page(page, 0);
  	__SetPageLocked(page);
  	return true;

  }

  /**

   * generic_pipe_buf_try_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.
   */

  bool generic_pipe_buf_try_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 true;

  	}

  	return false;

  }

  EXPORT_SYMBOL(generic_pipe_buf_try_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

   *	the tee() system call, when we duplicate the buffers in one

   *	pipe into another.
   */

  bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)

  {

  	return try_get_page(buf->page);

  }

  EXPORT_SYMBOL(generic_pipe_buf_get);

  /**

   * 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)
  {

  	put_page(buf->page);

  }

  EXPORT_SYMBOL(generic_pipe_buf_release);

  static const struct pipe_buf_operations anon_pipe_buf_ops = {

  	.release	= anon_pipe_buf_release,
  	.try_steal	= anon_pipe_buf_try_steal,
  	.get		= generic_pipe_buf_get,

  };

  /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
  static inline bool pipe_readable(const struct pipe_inode_info *pipe)
  {
  	unsigned int head = READ_ONCE(pipe->head);
  	unsigned int tail = READ_ONCE(pipe->tail);
  	unsigned int writers = READ_ONCE(pipe->writers);
  
  	return !pipe_empty(head, tail) || !writers;
  }

  static ssize_t

  pipe_read(struct kiocb *iocb, struct iov_iter *to)

  {

  	size_t total_len = iov_iter_count(to);

  	struct file *filp = iocb->ki_filp;

  	struct pipe_inode_info *pipe = filp->private_data;

  	bool was_full, wake_next_reader = false;

  	ssize_t ret;

  	/* Null read succeeds. */
  	if (unlikely(total_len == 0))
  		return 0;

  	ret = 0;

  	__pipe_lock(pipe);

  
  	/*
  	 * We only wake up writers if the pipe was full when we started
  	 * reading in order to avoid unnecessary wakeups.
  	 *
  	 * But when we do wake up writers, we do so using a sync wakeup
  	 * (WF_SYNC), because we want them to get going and generate more
  	 * data for us.
  	 */
  	was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);

  	for (;;) {

  		/* Read ->head with a barrier vs post_one_notification() */
  		unsigned int head = smp_load_acquire(&pipe->head);

  		unsigned int tail = pipe->tail;
  		unsigned int mask = pipe->ring_size - 1;

  #ifdef CONFIG_WATCH_QUEUE
  		if (pipe->note_loss) {
  			struct watch_notification n;
  
  			if (total_len < 8) {
  				if (ret == 0)
  					ret = -ENOBUFS;
  				break;
  			}
  
  			n.type = WATCH_TYPE_META;
  			n.subtype = WATCH_META_LOSS_NOTIFICATION;
  			n.info = watch_sizeof(n);
  			if (copy_to_iter(&n, sizeof(n), to) != sizeof(n)) {
  				if (ret == 0)
  					ret = -EFAULT;
  				break;
  			}
  			ret += sizeof(n);
  			total_len -= sizeof(n);
  			pipe->note_loss = false;
  		}
  #endif

  		if (!pipe_empty(head, tail)) {
  			struct pipe_buffer *buf = &pipe->bufs[tail & mask];

  			size_t chars = buf->len;

  			size_t written;
  			int error;

  			if (chars > total_len) {
  				if (buf->flags & PIPE_BUF_FLAG_WHOLE) {
  					if (ret == 0)
  						ret = -ENOBUFS;
  					break;
  				}

  				chars = total_len;

  			}

  			error = pipe_buf_confirm(pipe, buf);

  			if (error) {

  				if (!ret)

  					ret = error;

  				break;
  			}

  			written = copy_page_to_iter(buf->page, buf->offset, chars, to);

  			if (unlikely(written < chars)) {

  				if (!ret)

  					ret = -EFAULT;

  				break;
  			}
  			ret += chars;
  			buf->offset += chars;
  			buf->len -= chars;

  
  			/* Was it a packet buffer? Clean up and exit */
  			if (buf->flags & PIPE_BUF_FLAG_PACKET) {
  				total_len = chars;
  				buf->len = 0;
  			}

  			if (!buf->len) {

  				pipe_buf_release(pipe, buf);

  				spin_lock_irq(&pipe->rd_wait.lock);

  #ifdef CONFIG_WATCH_QUEUE
  				if (buf->flags & PIPE_BUF_FLAG_LOSS)
  					pipe->note_loss = true;
  #endif

  				tail++;
  				pipe->tail = tail;

  				spin_unlock_irq(&pipe->rd_wait.lock);

  			}
  			total_len -= chars;
  			if (!total_len)
  				break;	/* common path: read succeeded */

  			if (!pipe_empty(head, tail))	/* More to do? */
  				continue;

  		}

  		if (!pipe->writers)

  			break;

  		if (ret)
  			break;
  		if (filp->f_flags & O_NONBLOCK) {
  			ret = -EAGAIN;
  			break;

  		}

  		__pipe_unlock(pipe);

  
  		/*
  		 * We only get here if we didn't actually read anything.
  		 *
  		 * However, we could have seen (and removed) a zero-sized
  		 * pipe buffer, and might have made space in the buffers
  		 * that way.
  		 *
  		 * You can't make zero-sized pipe buffers by doing an empty
  		 * write (not even in packet mode), but they can happen if
  		 * the writer gets an EFAULT when trying to fill a buffer
  		 * that already got allocated and inserted in the buffer
  		 * array.
  		 *
  		 * So we still need to wake up any pending writers in the
  		 * _very_ unlikely case that the pipe was full, but we got
  		 * no data.
  		 */

  		if (unlikely(was_full))

  			wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);

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

  
  		/*
  		 * But because we didn't read anything, at this point we can
  		 * just return directly with -ERESTARTSYS if we're interrupted,
  		 * since we've done any required wakeups and there's no need
  		 * to mark anything accessed. And we've dropped the lock.
  		 */

  		if (wait_event_interruptible_exclusive(pipe->rd_wait, pipe_readable(pipe)) < 0)

  			return -ERESTARTSYS;

  		__pipe_lock(pipe);

  		was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);

  		wake_next_reader = true;

  	}

  	if (pipe_empty(pipe->head, pipe->tail))
  		wake_next_reader = false;

  	__pipe_unlock(pipe);

  	if (was_full)

  		wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);

  	if (wake_next_reader)
  		wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);

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

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

  static inline int is_packetized(struct file *file)
  {
  	return (file->f_flags & O_DIRECT) != 0;
  }

  /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
  static inline bool pipe_writable(const struct pipe_inode_info *pipe)
  {
  	unsigned int head = READ_ONCE(pipe->head);
  	unsigned int tail = READ_ONCE(pipe->tail);
  	unsigned int max_usage = READ_ONCE(pipe->max_usage);
  
  	return !pipe_full(head, tail, max_usage) ||
  		!READ_ONCE(pipe->readers);
  }

  static ssize_t

  pipe_write(struct kiocb *iocb, struct iov_iter *from)

  {

  	struct file *filp = iocb->ki_filp;

  	struct pipe_inode_info *pipe = filp->private_data;

  	unsigned int head;

  	ssize_t ret = 0;

  	size_t total_len = iov_iter_count(from);

  	ssize_t chars;

  	bool was_empty = false;

  	bool wake_next_writer = false;

  	/* Null write succeeds. */
  	if (unlikely(total_len == 0))
  		return 0;

  	__pipe_lock(pipe);

  	if (!pipe->readers) {

  		send_sig(SIGPIPE, current, 0);
  		ret = -EPIPE;
  		goto out;
  	}

  #ifdef CONFIG_WATCH_QUEUE
  	if (pipe->watch_queue) {
  		ret = -EXDEV;
  		goto out;
  	}
  #endif

  	/*

  	 * If it wasn't empty we try to merge new data into
  	 * the last buffer.
  	 *
  	 * That naturally merges small writes, but it also

  	 * page-aligns the rest of the writes for large writes

  	 * spanning multiple pages.
  	 */

  	head = pipe->head;

  	was_empty = pipe_empty(head, pipe->tail);

  	chars = total_len & (PAGE_SIZE-1);

  	if (chars && !was_empty) {

  		unsigned int mask = pipe->ring_size - 1;

  		struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];

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

  		if ((buf->flags & PIPE_BUF_FLAG_CAN_MERGE) &&
  		    offset + chars <= PAGE_SIZE) {

  			ret = pipe_buf_confirm(pipe, buf);

  			if (ret)

  				goto out;

  			ret = copy_page_from_iter(buf->page, offset, chars, from);
  			if (unlikely(ret < chars)) {

  				ret = -EFAULT;

  				goto out;

  			}

  			buf->len += ret;

  			if (!iov_iter_count(from))

  				goto out;
  		}
  	}
  
  	for (;;) {

  		if (!pipe->readers) {

  			send_sig(SIGPIPE, current, 0);

  			if (!ret)
  				ret = -EPIPE;

  			break;
  		}

  		head = pipe->head;

  		if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
  			unsigned int mask = pipe->ring_size - 1;

  			struct pipe_buffer *buf = &pipe->bufs[head & mask];

  			struct page *page = pipe->tmp_page;

  			int copied;

  
  			if (!page) {

  				page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);

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

  				pipe->tmp_page = page;

  			}

  
  			/* Allocate a slot in the ring in advance and attach an
  			 * empty buffer.  If we fault or otherwise fail to use
  			 * it, either the reader will consume it or it'll still
  			 * be there for the next write.
  			 */

  			spin_lock_irq(&pipe->rd_wait.lock);

  
  			head = pipe->head;

  			if (pipe_full(head, pipe->tail, pipe->max_usage)) {

  				spin_unlock_irq(&pipe->rd_wait.lock);

  				continue;
  			}

  			pipe->head = head + 1;

  			spin_unlock_irq(&pipe->rd_wait.lock);

  
  			/* Insert it into the buffer array */

  			buf = &pipe->bufs[head & mask];

  			buf->page = page;
  			buf->ops = &anon_pipe_buf_ops;
  			buf->offset = 0;

  			buf->len = 0;

  			if (is_packetized(filp))

  				buf->flags = PIPE_BUF_FLAG_PACKET;

  			else
  				buf->flags = PIPE_BUF_FLAG_CAN_MERGE;

  			pipe->tmp_page = NULL;

  			copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
  			if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
  				if (!ret)
  					ret = -EFAULT;
  				break;
  			}
  			ret += copied;
  			buf->offset = 0;
  			buf->len = copied;

  			if (!iov_iter_count(from))

  				break;
  		}

  		if (!pipe_full(head, pipe->tail, pipe->max_usage))

  			continue;

  
  		/* Wait for buffer space to become available. */

  		if (filp->f_flags & O_NONBLOCK) {

  			if (!ret)
  				ret = -EAGAIN;

  			break;
  		}
  		if (signal_pending(current)) {

  			if (!ret)
  				ret = -ERESTARTSYS;

  			break;
  		}

  
  		/*
  		 * We're going to release the pipe lock and wait for more
  		 * space. We wake up any readers if necessary, and then
  		 * after waiting we need to re-check whether the pipe
  		 * become empty while we dropped the lock.
  		 */

  		__pipe_unlock(pipe);

  		if (was_empty)

  			wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);

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

  		wait_event_interruptible_exclusive(pipe->wr_wait, pipe_writable(pipe));

  		__pipe_lock(pipe);

  		was_empty = pipe_empty(pipe->head, pipe->tail);

  		wake_next_writer = true;

  	}
  out:

  	if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
  		wake_next_writer = false;

  	__pipe_unlock(pipe);

  
  	/*
  	 * If we do do a wakeup event, we do a 'sync' wakeup, because we
  	 * want the reader to start processing things asap, rather than
  	 * leave the data pending.
  	 *
  	 * This is particularly important for small writes, because of
  	 * how (for example) the GNU make jobserver uses small writes to
  	 * wake up pending jobs

  	 *
  	 * Epoll nonsensically wants a wakeup whether the pipe
  	 * was already empty or not.

  	 */

  	if (was_empty || pipe->poll_usage)

  		wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);

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

  	if (wake_next_writer)
  		wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);

  	if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {

  		int err = file_update_time(filp);
  		if (err)
  			ret = err;

  		sb_end_write(file_inode(filp)->i_sb);

  	}

  	return ret;
  }

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

  {

  	struct pipe_inode_info *pipe = filp->private_data;

  	int count, head, tail, mask;

  
  	switch (cmd) {

  	case FIONREAD:
  		__pipe_lock(pipe);
  		count = 0;
  		head = pipe->head;
  		tail = pipe->tail;
  		mask = pipe->ring_size - 1;

  		while (tail != head) {
  			count += pipe->bufs[tail & mask].len;
  			tail++;
  		}
  		__pipe_unlock(pipe);

  		return put_user(count, (int __user *)arg);

  #ifdef CONFIG_WATCH_QUEUE
  	case IOC_WATCH_QUEUE_SET_SIZE: {
  		int ret;
  		__pipe_lock(pipe);
  		ret = watch_queue_set_size(pipe, arg);
  		__pipe_unlock(pipe);
  		return ret;
  	}
  
  	case IOC_WATCH_QUEUE_SET_FILTER:
  		return watch_queue_set_filter(
  			pipe, (struct watch_notification_filter __user *)arg);
  #endif
  
  	default:
  		return -ENOIOCTLCMD;

  	}
  }

  /* No kernel lock held - fine */

  static __poll_t
  pipe_poll(struct file *filp, poll_table *wait)

  {

  	__poll_t mask;

  	struct pipe_inode_info *pipe = filp->private_data;

  	unsigned int head, tail;

  	/* Epoll has some historical nasty semantics, this enables them */

  	WRITE_ONCE(pipe->poll_usage, true);

  	/*

  	 * Reading pipe state only -- no need for acquiring the semaphore.

  	 *
  	 * But because this is racy, the code has to add the
  	 * entry to the poll table _first_ ..
  	 */

  	if (filp->f_mode & FMODE_READ)
  		poll_wait(filp, &pipe->rd_wait, wait);
  	if (filp->f_mode & FMODE_WRITE)
  		poll_wait(filp, &pipe->wr_wait, wait);

  	/*
  	 * .. and only then can you do the racy tests. That way,
  	 * if something changes and you got it wrong, the poll
  	 * table entry will wake you up and fix it.
  	 */
  	head = READ_ONCE(pipe->head);
  	tail = READ_ONCE(pipe->tail);

  	mask = 0;

  	if (filp->f_mode & FMODE_READ) {

  		if (!pipe_empty(head, tail))
  			mask |= EPOLLIN | EPOLLRDNORM;

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

  			mask |= EPOLLHUP;

  	}
  
  	if (filp->f_mode & FMODE_WRITE) {

  		if (!pipe_full(head, tail, pipe->max_usage))

  			mask |= EPOLLOUT | EPOLLWRNORM;

  		/*

  		 * Most Unices do not set EPOLLERR for FIFOs but on Linux they

  		 * behave exactly like pipes for poll().
  		 */

  		if (!pipe->readers)

  			mask |= EPOLLERR;

  	}
  
  	return mask;
  }

  static void put_pipe_info(struct inode *inode, struct pipe_inode_info *pipe)
  {
  	int kill = 0;
  
  	spin_lock(&inode->i_lock);
  	if (!--pipe->files) {
  		inode->i_pipe = NULL;
  		kill = 1;
  	}
  	spin_unlock(&inode->i_lock);
  
  	if (kill)
  		free_pipe_info(pipe);
  }

  static int

  pipe_release(struct inode *inode, struct file *file)

  {

  	struct pipe_inode_info *pipe = file->private_data;

  	__pipe_lock(pipe);

  	if (file->f_mode & FMODE_READ)
  		pipe->readers--;
  	if (file->f_mode & FMODE_WRITE)
  		pipe->writers--;

  	/* Was that the last reader or writer, but not the other side? */
  	if (!pipe->readers != !pipe->writers) {
  		wake_up_interruptible_all(&pipe->rd_wait);
  		wake_up_interruptible_all(&pipe->wr_wait);

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

  	}

  	__pipe_unlock(pipe);

  	put_pipe_info(inode, pipe);

  	return 0;
  }
  
  static int

  pipe_fasync(int fd, struct file *filp, int on)

  {

  	struct pipe_inode_info *pipe = filp->private_data;

  	int retval = 0;

  	__pipe_lock(pipe);

  	if (filp->f_mode & FMODE_READ)
  		retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
  	if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {

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

  		if (retval < 0 && (filp->f_mode & FMODE_READ))
  			/* this can happen only if on == T */

  			fasync_helper(-1, filp, 0, &pipe->fasync_readers);
  	}

  	__pipe_unlock(pipe);

  	return retval;

  }

  unsigned long account_pipe_buffers(struct user_struct *user,
  				   unsigned long old, unsigned long new)

  {

  	return atomic_long_add_return(new - old, &user->pipe_bufs);

  }

  bool too_many_pipe_buffers_soft(unsigned long user_bufs)

  {

  	unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
  
  	return soft_limit && user_bufs > soft_limit;

  }

  bool too_many_pipe_buffers_hard(unsigned long user_bufs)

  {

  	unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
  
  	return hard_limit && user_bufs > hard_limit;

  }

  bool pipe_is_unprivileged_user(void)

  {
  	return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
  }

  struct pipe_inode_info *alloc_pipe_info(void)

  {

  	struct pipe_inode_info *pipe;

  	unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
  	struct user_struct *user = get_current_user();

  	unsigned long user_bufs;

  	unsigned int max_size = READ_ONCE(pipe_max_size);

  	pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);

  	if (pipe == NULL)
  		goto out_free_uid;

  	if (pipe_bufs * PAGE_SIZE > max_size && !capable(CAP_SYS_RESOURCE))
  		pipe_bufs = max_size >> PAGE_SHIFT;

  	user_bufs = account_pipe_buffers(user, 0, pipe_bufs);

  	if (too_many_pipe_buffers_soft(user_bufs) && pipe_is_unprivileged_user()) {

  		user_bufs = account_pipe_buffers(user, pipe_bufs, PIPE_MIN_DEF_BUFFERS);
  		pipe_bufs = PIPE_MIN_DEF_BUFFERS;

  	}

  	if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())

  		goto out_revert_acct;
  
  	pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
  			     GFP_KERNEL_ACCOUNT);

  	if (pipe->bufs) {

  		init_waitqueue_head(&pipe->rd_wait);
  		init_waitqueue_head(&pipe->wr_wait);

  		pipe->r_counter = pipe->w_counter = 1;

  		pipe->max_usage = pipe_bufs;

  		pipe->ring_size = pipe_bufs;

  		pipe->nr_accounted = pipe_bufs;

  		pipe->user = user;

  		mutex_init(&pipe->mutex);
  		return pipe;

  	}

  out_revert_acct:

  	(void) account_pipe_buffers(user, pipe_bufs, 0);

  	kfree(pipe);
  out_free_uid:
  	free_uid(user);

  	return NULL;

  }

  void free_pipe_info(struct pipe_inode_info *pipe)

  {
  	int i;

  #ifdef CONFIG_WATCH_QUEUE

  	if (pipe->watch_queue)

  		watch_queue_clear(pipe->watch_queue);

  #endif
  
  	(void) account_pipe_buffers(pipe->user, pipe->nr_accounted, 0);

  	free_uid(pipe->user);

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

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

  		if (buf->ops)

  			pipe_buf_release(pipe, buf);

  	}

  #ifdef CONFIG_WATCH_QUEUE
  	if (pipe->watch_queue)
  		put_watch_queue(pipe->watch_queue);
  #endif

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

  	kfree(pipe->bufs);

  	kfree(pipe);

  }

  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]",

  				d_inode(dentry)->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();

  	if (!pipe)

  		goto fail_iput;

  	inode->i_pipe = pipe;
  	pipe->files = 2;

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

  	inode->i_fop = &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(inode);

  	return inode;
  
  fail_iput:
  	iput(inode);

  fail_inode:
  	return NULL;
  }

  int create_pipe_files(struct file **res, int flags)

  {

  	struct inode *inode = get_pipe_inode();

  	struct file *f;

  	int error;

  	if (!inode)

  		return -ENFILE;

  	if (flags & O_NOTIFICATION_PIPE) {

  		error = watch_queue_init(inode->i_pipe);
  		if (error) {
  			free_pipe_info(inode->i_pipe);

  			iput(inode);

  			return error;

  		}

  	}

  	f = alloc_file_pseudo(inode, pipe_mnt, "",
  				O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT)),
  				&pipefifo_fops);

  	if (IS_ERR(f)) {

  		free_pipe_info(inode->i_pipe);
  		iput(inode);
  		return PTR_ERR(f);

  	}

  	f->private_data = inode->i_pipe;

  	res[0] = alloc_file_clone(f, O_RDONLY | (flags & O_NONBLOCK),
  				  &pipefifo_fops);

  	if (IS_ERR(res[0])) {

  		put_pipe_info(inode, inode->i_pipe);
  		fput(f);
  		return PTR_ERR(res[0]);

  	}

  	res[0]->private_data = inode->i_pipe;

  	res[1] = f;

  	stream_open(inode, res[0]);
  	stream_open(inode, res[1]);

  	return 0;

  }

  static int __do_pipe_flags(int *fd, struct file **files, int flags)

  {

  	int error;
  	int fdw, fdr;

  	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT | O_NOTIFICATION_PIPE))

  		return -EINVAL;

  	error = create_pipe_files(files, flags);
  	if (error)
  		return error;

  	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[0] = fdr;
  	fd[1] = fdw;

  	return 0;
  
   err_fdr:
  	put_unused_fd(fdr);
   err_read_pipe:

  	fput(files[0]);
  	fput(files[1]);

  	return error;

  }

  int do_pipe_flags(int *fd, int flags)
  {
  	struct file *files[2];
  	int error = __do_pipe_flags(fd, files, flags);
  	if (!error) {
  		fd_install(fd[0], files[0]);
  		fd_install(fd[1], files[1]);
  	}
  	return error;
  }

  /*

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

  static int do_pipe2(int __user *fildes, int flags)

  {

  	struct file *files[2];

  	int fd[2];
  	int error;

  	error = __do_pipe_flags(fd, files, flags);

  	if (!error) {

  		if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
  			fput(files[0]);
  			fput(files[1]);
  			put_unused_fd(fd[0]);
  			put_unused_fd(fd[1]);

  			error = -EFAULT;

  		} else {
  			fd_install(fd[0], files[0]);
  			fd_install(fd[1], files[1]);

  		}

  	}
  	return error;
  }

  SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
  {
  	return do_pipe2(fildes, flags);
  }

  SYSCALL_DEFINE1(pipe, int __user *, fildes)

  {

  	return do_pipe2(fildes, 0);

  }

  /*
   * This is the stupid "wait for pipe to be readable or writable"
   * model.
   *
   * See pipe_read/write() for the proper kind of exclusive wait,
   * but that requires that we wake up any other readers/writers
   * if we then do not end up reading everything (ie the whole
   * "wake_next_reader/writer" logic in pipe_read/write()).
   */
  void pipe_wait_readable(struct pipe_inode_info *pipe)
  {
  	pipe_unlock(pipe);
  	wait_event_interruptible(pipe->rd_wait, pipe_readable(pipe));
  	pipe_lock(pipe);
  }
  
  void pipe_wait_writable(struct pipe_inode_info *pipe)
  {
  	pipe_unlock(pipe);
  	wait_event_interruptible(pipe->wr_wait, pipe_writable(pipe));
  	pipe_lock(pipe);
  }
  
  /*
   * This depends on both the wait (here) and the wakeup (wake_up_partner)
   * holding the pipe lock, so "*cnt" is stable and we know a wakeup cannot
   * race with the count check and waitqueue prep.
   *
   * Normally in order to avoid races, you'd do the prepare_to_wait() first,
   * then check the condition you're waiting for, and only then sleep. But
   * because of the pipe lock, we can check the condition before being on
   * the wait queue.
   *
   * We use the 'rd_wait' waitqueue for pipe partner waiting.
   */

  static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)

  {

  	DEFINE_WAIT(rdwait);

  	int cur = *cnt;

  
  	while (cur == *cnt) {

  		prepare_to_wait(&pipe->rd_wait, &rdwait, TASK_INTERRUPTIBLE);
  		pipe_unlock(pipe);
  		schedule();
  		finish_wait(&pipe->rd_wait, &rdwait);
  		pipe_lock(pipe);

  		if (signal_pending(current))
  			break;
  	}
  	return cur == *cnt ? -ERESTARTSYS : 0;
  }

  static void wake_up_partner(struct pipe_inode_info *pipe)

  {

  	wake_up_interruptible_all(&pipe->rd_wait);

  }
  
  static int fifo_open(struct inode *inode, struct file *filp)
  {
  	struct pipe_inode_info *pipe;

  	bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;

  	int ret;

  	filp->f_version = 0;
  
  	spin_lock(&inode->i_lock);
  	if (inode->i_pipe) {
  		pipe = inode->i_pipe;
  		pipe->files++;
  		spin_unlock(&inode->i_lock);
  	} else {
  		spin_unlock(&inode->i_lock);

  		pipe = alloc_pipe_info();

  		if (!pipe)

  			return -ENOMEM;
  		pipe->files = 1;
  		spin_lock(&inode->i_lock);
  		if (unlikely(inode->i_pipe)) {
  			inode->i_pipe->files++;
  			spin_unlock(&inode->i_lock);

  			free_pipe_info(pipe);

  			pipe = inode->i_pipe;
  		} else {
  			inode->i_pipe = pipe;
  			spin_unlock(&inode->i_lock);
  		}

  	}

  	filp->private_data = pipe;

  	/* OK, we have a pipe and it's pinned down */

  	__pipe_lock(pipe);

  
  	/* We can only do regular read/write on fifos */

  	stream_open(inode, filp);

  	switch (filp->f_mode & (FMODE_READ | FMODE_WRITE)) {

  	case FMODE_READ:
  	/*
  	 *  O_RDONLY
  	 *  POSIX.1 says that O_NONBLOCK means return with the FIFO
  	 *  opened, even when there is no process writing the FIFO.
  	 */

  		pipe->r_counter++;
  		if (pipe->readers++ == 0)

  			wake_up_partner(pipe);

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

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

  				/* suppress EPOLLHUP until we have

  				 * seen a writer */
  				filp->f_version = pipe->w_counter;
  			} else {

  				if (wait_for_partner(pipe, &pipe->w_counter))

  					goto err_rd;
  			}
  		}
  		break;

  	case FMODE_WRITE:
  	/*
  	 *  O_WRONLY
  	 *  POSIX.1 says that O_NONBLOCK means return -1 with
  	 *  errno=ENXIO when there is no process reading the FIFO.
  	 */
  		ret = -ENXIO;

  		if (!is_pipe && (filp->f_flags & O_NONBLOCK) && !pipe->readers)

  			goto err;

  		pipe->w_counter++;
  		if (!pipe->writers++)

  			wake_up_partner(pipe);

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

  			if (wait_for_partner(pipe, &pipe->r_counter))

  				goto err_wr;
  		}
  		break;

  	case FMODE_READ | FMODE_WRITE:
  	/*
  	 *  O_RDWR
  	 *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
  	 *  This implementation will NEVER block on a O_RDWR open, since
  	 *  the process can at least talk to itself.
  	 */

  
  		pipe->readers++;
  		pipe->writers++;
  		pipe->r_counter++;
  		pipe->w_counter++;
  		if (pipe->readers == 1 || pipe->writers == 1)

  			wake_up_partner(pipe);

  		break;
  
  	default:
  		ret = -EINVAL;
  		goto err;
  	}
  
  	/* Ok! */

  	__pipe_unlock(pipe);

  	return 0;
  
  err_rd:
  	if (!--pipe->readers)

  		wake_up_interruptible(&pipe->wr_wait);

  	ret = -ERESTARTSYS;
  	goto err;
  
  err_wr:
  	if (!--pipe->writers)

  		wake_up_interruptible_all(&pipe->rd_wait);

  	ret = -ERESTARTSYS;
  	goto err;
  
  err:

  	__pipe_unlock(pipe);

  
  	put_pipe_info(inode, pipe);

  	return ret;
  }

  const struct file_operations pipefifo_fops = {
  	.open		= fifo_open,
  	.llseek		= no_llseek,

  	.read_iter	= pipe_read,

  	.write_iter	= pipe_write,

  	.poll		= pipe_poll,

  	.unlocked_ioctl	= pipe_ioctl,
  	.release	= pipe_release,
  	.fasync		= pipe_fasync,

  	.splice_write	= iter_file_splice_write,

  };

  /*

   * Currently we rely on the pipe array holding a power-of-2 number

   * of pages. Returns 0 on error.

   */

  unsigned int round_pipe_size(unsigned long size)

  {

  	if (size > (1U << 31))

  		return 0;

  	/* Minimum pipe size, as required by POSIX */
  	if (size < PAGE_SIZE)

  		return PAGE_SIZE;

  	return roundup_pow_of_two(size);

  }
  
  /*

   * Resize the pipe ring to a number of slots.

   *
   * Note the pipe can be reduced in capacity, but only if the current
   * occupancy doesn't exceed nr_slots; if it does, EBUSY will be
   * returned instead.

   */

  int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)

  {
  	struct pipe_buffer *bufs;

  	unsigned int head, tail, mask, n;

  	bufs = kcalloc(nr_slots, sizeof(*bufs),

  		       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);

  	if (unlikely(!bufs))
  		return -ENOMEM;

  	spin_lock_irq(&pipe->rd_wait.lock);
  	mask = pipe->ring_size - 1;
  	head = pipe->head;
  	tail = pipe->tail;
  
  	n = pipe_occupancy(head, tail);
  	if (nr_slots < n) {
  		spin_unlock_irq(&pipe->rd_wait.lock);
  		kfree(bufs);
  		return -EBUSY;
  	}

  	/*
  	 * The pipe array wraps around, so just start the new one at zero

  	 * and adjust the indices.

  	 */

  	if (n > 0) {
  		unsigned int h = head & mask;
  		unsigned int t = tail & mask;
  		if (h > t) {
  			memcpy(bufs, pipe->bufs + t,
  			       n * sizeof(struct pipe_buffer));
  		} else {
  			unsigned int tsize = pipe->ring_size - t;
  			if (h > 0)
  				memcpy(bufs + tsize, pipe->bufs,
  				       h * sizeof(struct pipe_buffer));
  			memcpy(bufs, pipe->bufs + t,
  			       tsize * sizeof(struct pipe_buffer));
  		}

  	}

  	head = n;
  	tail = 0;

  	kfree(pipe->bufs);
  	pipe->bufs = bufs;

  	pipe->ring_size = nr_slots;

  	if (pipe->max_usage > nr_slots)
  		pipe->max_usage = nr_slots;

  	pipe->tail = tail;
  	pipe->head = head;

  	spin_unlock_irq(&pipe->rd_wait.lock);

  	/* This might have made more room for writers */
  	wake_up_interruptible(&pipe->wr_wait);

  	return 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 arg)
  {
  	unsigned long user_bufs;
  	unsigned int nr_slots, size;
  	long ret = 0;
  
  #ifdef CONFIG_WATCH_QUEUE
  	if (pipe->watch_queue)
  		return -EBUSY;
  #endif
  
  	size = round_pipe_size(arg);
  	nr_slots = size >> PAGE_SHIFT;
  
  	if (!nr_slots)
  		return -EINVAL;
  
  	/*
  	 * If trying to increase the pipe capacity, check that an
  	 * unprivileged user is not trying to exceed various limits
  	 * (soft limit check here, hard limit check just below).
  	 * Decreasing the pipe capacity is always permitted, even
  	 * if the user is currently over a limit.
  	 */
  	if (nr_slots > pipe->max_usage &&
  			size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
  		return -EPERM;
  
  	user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_slots);
  
  	if (nr_slots > pipe->max_usage &&
  			(too_many_pipe_buffers_hard(user_bufs) ||
  			 too_many_pipe_buffers_soft(user_bufs)) &&
  			pipe_is_unprivileged_user()) {
  		ret = -EPERM;
  		goto out_revert_acct;
  	}
  
  	ret = pipe_resize_ring(pipe, nr_slots);
  	if (ret < 0)
  		goto out_revert_acct;
  
  	pipe->max_usage = nr_slots;
  	pipe->nr_accounted = nr_slots;

  	return pipe->max_usage * PAGE_SIZE;

  
  out_revert_acct:

  	(void) account_pipe_buffers(pipe->user, nr_slots, pipe->nr_accounted);

  	return ret;

  }

  /*

   * Note that i_pipe and 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, bool for_splice)

  {

  	struct pipe_inode_info *pipe = file->private_data;
  
  	if (file->f_op != &pipefifo_fops || !pipe)
  		return NULL;
  #ifdef CONFIG_WATCH_QUEUE
  	if (for_splice && pipe->watch_queue)
  		return NULL;
  #endif
  	return pipe;

  }

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

  	pipe = get_pipe_info(file, false);

  	if (!pipe)
  		return -EBADF;

  	__pipe_lock(pipe);

  
  	switch (cmd) {

  	case F_SETPIPE_SZ:
  		ret = pipe_set_size(pipe, arg);

  		break;
  	case F_GETPIPE_SZ:

  		ret = pipe->max_usage * PAGE_SIZE;

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

  	__pipe_unlock(pipe);

  	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 int pipefs_init_fs_context(struct fs_context *fc)

  {

  	struct pseudo_fs_context *ctx = init_pseudo(fc, PIPEFS_MAGIC);
  	if (!ctx)
  		return -ENOMEM;
  	ctx->ops = &pipefs_ops;
  	ctx->dops = &pipefs_dentry_operations;
  	return 0;

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

  	.init_fs_context = pipefs_init_fs_context,

  	.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);