// 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/uaccess.h>

  #include <asm/ioctls.h>

  #include "internal.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;

  /* 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 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->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);

  	}
  }

  /* 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 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 int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
  			       struct pipe_buffer *buf)
  {
  	struct page *page = buf->page;
  
  	if (page_count(page) == 1) {

  		memcg_kmem_uncharge(page, 0);

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

  /**

   * 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.
   */

  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_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)
  {

  	put_page(buf->page);

  }

  EXPORT_SYMBOL(generic_pipe_buf_release);

  /* New data written to a pipe may be appended to a buffer with this type. */

  static const struct pipe_buf_operations anon_pipe_buf_ops = {

  	.confirm = generic_pipe_buf_confirm,

  	.release = anon_pipe_buf_release,

  	.steal = anon_pipe_buf_steal,

  	.get = generic_pipe_buf_get,

  };

  static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {

  	.confirm = generic_pipe_buf_confirm,

  	.release = anon_pipe_buf_release,

  	.steal = anon_pipe_buf_steal,

  	.get = generic_pipe_buf_get,

  };

  static const struct pipe_buf_operations packet_pipe_buf_ops = {

  	.confirm = generic_pipe_buf_confirm,
  	.release = anon_pipe_buf_release,

  	.steal = anon_pipe_buf_steal,

  	.get = generic_pipe_buf_get,
  };

  /**
   * pipe_buf_mark_unmergeable - mark a &struct pipe_buffer as unmergeable
   * @buf:	the buffer to mark
   *
   * Description:
   *	This function ensures that no future writes will be merged into the
   *	given &struct pipe_buffer. This is necessary when multiple pipe buffers
   *	share the same backing page.
   */

  void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
  {
  	if (buf->ops == &anon_pipe_buf_ops)
  		buf->ops = &anon_pipe_buf_nomerge_ops;
  }

  static bool pipe_buf_can_merge(struct pipe_buffer *buf)
  {
  	return buf->ops == &anon_pipe_buf_ops;
  }

  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;

  	int do_wakeup;
  	ssize_t ret;

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

  	__pipe_lock(pipe);

  	for (;;) {

  		int bufs = pipe->nrbufs;

  		if (bufs) {

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

  			size_t chars = buf->len;

  			size_t written;
  			int error;

  
  			if (chars > total_len)
  				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);

  				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, EPOLLOUT | EPOLLWRNORM);

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

  		}

  		pipe_wait(pipe);

  	}

  	__pipe_unlock(pipe);

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

  	if (do_wakeup) {

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

  		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;
  }

  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;

  	ssize_t ret = 0;
  	int do_wakeup = 0;
  	size_t total_len = iov_iter_count(from);

  	ssize_t chars;

  	/* 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;
  	}
  
  	/* 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;

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

  		if (pipe_buf_can_merge(buf) && 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;

  			}

  			do_wakeup = 1;

  			buf->len += ret;

  			if (!iov_iter_count(from))

  				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;

  			int copied;

  
  			if (!page) {

  				page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);

  				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;

  			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;

  
  			/* Insert it into the buffer array */
  			buf->page = page;
  			buf->ops = &anon_pipe_buf_ops;
  			buf->offset = 0;

  			buf->len = copied;

  			buf->flags = 0;
  			if (is_packetized(filp)) {
  				buf->ops = &packet_pipe_buf_ops;
  				buf->flags = PIPE_BUF_FLAG_PACKET;
  			}

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

  			if (!iov_iter_count(from))

  				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, EPOLLIN | EPOLLRDNORM);

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

  			do_wakeup = 0;
  		}

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

  	}
  out:

  	__pipe_unlock(pipe);

  	if (do_wakeup) {

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

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

  	}

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

  			__pipe_lock(pipe);

  			count = 0;

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

  			while (--nrbufs >= 0) {

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

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

  			}

  			__pipe_unlock(pipe);

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

  	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) ? EPOLLIN | EPOLLRDNORM : 0;

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

  			mask |= EPOLLHUP;

  	}
  
  	if (filp->f_mode & FMODE_WRITE) {

  		mask |= (nrbufs < pipe->buffers) ? EPOLLOUT | EPOLLWRNORM : 0;

  		/*

  		 * 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--;

  	if (pipe->readers || pipe->writers) {

  		wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLOUT | EPOLLRDNORM | EPOLLWRNORM | EPOLLERR | EPOLLHUP);

  		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;

  }

  static 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);

  }

  static 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;

  }

  static 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;

  }

  static bool 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) && is_unprivileged_user()) {

  		user_bufs = account_pipe_buffers(user, pipe_bufs, 1);

  		pipe_bufs = 1;

  	}

  	if (too_many_pipe_buffers_hard(user_bufs) && 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->wait);
  		pipe->r_counter = pipe->w_counter = 1;
  		pipe->buffers = 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;

  	(void) account_pipe_buffers(pipe->user, pipe->buffers, 0);

  	free_uid(pipe->user);

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

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

  		if (buf->ops)

  			pipe_buf_release(pipe, buf);

  	}

  	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;

  	if (!inode)

  		return -ENFILE;

  	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;
  	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))

  		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);

  }

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

  {
  	int cur = *cnt;	
  
  	while (cur == *cnt) {

  		pipe_wait(pipe);

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

  static void wake_up_partner(struct pipe_inode_info *pipe)

  {

  	wake_up_interruptible(&pipe->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 */
  	filp->f_mode &= (FMODE_READ | FMODE_WRITE);
  
  	switch (filp->f_mode) {
  	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->wait);
  	ret = -ERESTARTSYS;
  	goto err;
  
  err_wr:
  	if (!--pipe->writers)
  		wake_up_interruptible(&pipe->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,

  };

  /*

   * 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);

  }
  
  /*

   * 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)

  {
  	struct pipe_buffer *bufs;

  	unsigned int size, nr_pages;

  	unsigned long user_bufs;

  	long ret = 0;

  
  	size = round_pipe_size(arg);
  	nr_pages = size >> PAGE_SHIFT;
  
  	if (!nr_pages)
  		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_pages > pipe->buffers &&
  			size > pipe_max_size && !capable(CAP_SYS_RESOURCE))

  		return -EPERM;

  	user_bufs = account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);

  
  	if (nr_pages > pipe->buffers &&

  			(too_many_pipe_buffers_hard(user_bufs) ||
  			 too_many_pipe_buffers_soft(user_bufs)) &&

  			is_unprivileged_user()) {

  		ret = -EPERM;
  		goto out_revert_acct;
  	}

  
  	/*

  	 * 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) {
  		ret = -EBUSY;
  		goto out_revert_acct;
  	}

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

  	if (unlikely(!bufs)) {
  		ret = -ENOMEM;
  		goto out_revert_acct;
  	}

  
  	/*
  	 * 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;

  
  out_revert_acct:

  	(void) account_pipe_buffers(pipe->user, nr_pages, pipe->buffers);

  	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)
  {

  	return file->f_op == &pipefifo_fops ? file->private_data : 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;

  	__pipe_lock(pipe);

  
  	switch (cmd) {

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

  		break;
  	case F_GETPIPE_SZ:

  		ret = pipe->buffers * 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);