text: /*
   * "splice": joining two ropes together by interweaving their strands.
   *
   * This is the "extended pipe" functionality, where a pipe is used as
   * an arbitrary in-memory buffer. Think of a pipe as a small kernel
   * buffer that you can use to transfer data from one end to the other.
   *
   * The traditional unix read/write is extended with a "splice()" operation
   * that transfers data buffers to or from a pipe buffer.
   *
   * Named by Larry McVoy, original implementation from Linus, extended by
   * Jens to support splicing to files, network, direct splicing, etc and
   * fixing lots of bugs.
   *
   * Copyright (C) 2005-2006 Jens Axboe <axboe@kernel.dk>
   * Copyright (C) 2005-2006 Linus Torvalds <torvalds@osdl.org>
   * Copyright (C) 2006 Ingo Molnar <mingo@elte.hu>
   *
   */
  #include <linux/bvec.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/pagemap.h>
  #include <linux/splice.h>
  #include <linux/memcontrol.h>
  #include <linux/mm_inline.h>
  #include <linux/swap.h>
  #include <linux/writeback.h>
  #include <linux/export.h>
  #include <linux/syscalls.h>
  #include <linux/uio.h>
  #include <linux/security.h>
  #include <linux/gfp.h>
  #include <linux/socket.h>
  #include <linux/compat.h>
  #include <linux/sched/signal.h>
  
  #include "internal.h"
  
  /*
   * Attempt to steal a page from a pipe buffer. This should perhaps go into
   * a vm helper function, it's already simplified quite a bit by the
   * addition of remove_mapping(). If success is returned, the caller may
   * attempt to reuse this page for another destination.
   */
  static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
  				     struct pipe_buffer *buf)
  {
  	struct page *page = buf->page;
  	struct address_space *mapping;
  
  	lock_page(page);
  
  	mapping = page_mapping(page);
  	if (mapping) {
  		WARN_ON(!PageUptodate(page));
  
  		/*
  		 * At least for ext2 with nobh option, we need to wait on
  		 * writeback completing on this page, since we'll remove it
  		 * from the pagecache.  Otherwise truncate wont wait on the
  		 * page, allowing the disk blocks to be reused by someone else
  		 * before we actually wrote our data to them. fs corruption
  		 * ensues.
  		 */
  		wait_on_page_writeback(page);
  
  		if (page_has_private(page) &&
  		    !try_to_release_page(page, GFP_KERNEL))
  			goto out_unlock;
  
  		/*
  		 * If we succeeded in removing the mapping, set LRU flag
  		 * and return good.
  		 */
  		if (remove_mapping(mapping, page)) {
  			buf->flags |= PIPE_BUF_FLAG_LRU;
  			return 0;
  		}
  	}
  
  	/*
  	 * Raced with truncate or failed to remove page from current
  	 * address space, unlock and return failure.
  	 */
  out_unlock:
  	unlock_page(page);
  	return 1;
  }
  
  static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
  					struct pipe_buffer *buf)
  {
  	put_page(buf->page);
  	buf->flags &= ~PIPE_BUF_FLAG_LRU;
  }
  
  /*
   * Check whether the contents of buf is OK to access. Since the content
   * is a page cache page, IO may be in flight.
   */
  static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
  				       struct pipe_buffer *buf)
  {
  	struct page *page = buf->page;
  	int err;
  
  	if (!PageUptodate(page)) {
  		lock_page(page);
  
  		/*
  		 * Page got truncated/unhashed. This will cause a 0-byte
  		 * splice, if this is the first page.
  		 */
  		if (!page->mapping) {
  			err = -ENODATA;
  			goto error;
  		}
  
  		/*
  		 * Uh oh, read-error from disk.
  		 */
  		if (!PageUptodate(page)) {
  			err = -EIO;
  			goto error;
  		}
  
  		/*
  		 * Page is ok afterall, we are done.
  		 */
  		unlock_page(page);
  	}
  
  	return 0;
  error:
  	unlock_page(page);
  	return err;
  }
  
  const struct pipe_buf_operations page_cache_pipe_buf_ops = {
  	.can_merge = 0,
  	.confirm = page_cache_pipe_buf_confirm,
  	.release = page_cache_pipe_buf_release,
  	.steal = page_cache_pipe_buf_steal,
  	.get = generic_pipe_buf_get,
  };
  
  static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
  				    struct pipe_buffer *buf)
  {
  	if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
  		return 1;
  
  	buf->flags |= PIPE_BUF_FLAG_LRU;
  	return generic_pipe_buf_steal(pipe, buf);
  }
  
  static const struct pipe_buf_operations user_page_pipe_buf_ops = {
  	.can_merge = 0,
  	.confirm = generic_pipe_buf_confirm,
  	.release = page_cache_pipe_buf_release,
  	.steal = user_page_pipe_buf_steal,
  	.get = generic_pipe_buf_get,
  };
  
  static void wakeup_pipe_readers(struct pipe_inode_info *pipe)
  {
  	smp_mb();
  	if (waitqueue_active(&pipe->wait))
  		wake_up_interruptible(&pipe->wait);
  	kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
  }
  
  /**
   * splice_to_pipe - fill passed data into a pipe
   * @pipe:	pipe to fill
   * @spd:	data to fill
   *
   * Description:
   *    @spd contains a map of pages and len/offset tuples, along with
   *    the struct pipe_buf_operations associated with these pages. This
   *    function will link that data to the pipe.
   *
   */
  ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
  		       struct splice_pipe_desc *spd)
  {
  	unsigned int spd_pages = spd->nr_pages;
  	int ret = 0, page_nr = 0;
  
  	if (!spd_pages)
  		return 0;
  
  	if (unlikely(!pipe->readers)) {
  		send_sig(SIGPIPE, current, 0);
  		ret = -EPIPE;
  		goto out;
  	}
  
  	while (pipe->nrbufs < pipe->buffers) {
  		int newbuf = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
  		struct pipe_buffer *buf = pipe->bufs + newbuf;
  
  		buf->page = spd->pages[page_nr];
  		buf->offset = spd->partial[page_nr].offset;
  		buf->len = spd->partial[page_nr].len;
  		buf->private = spd->partial[page_nr].private;
  		buf->ops = spd->ops;
  		buf->flags = 0;
  
  		pipe->nrbufs++;
  		page_nr++;
  		ret += buf->len;
  
  		if (!--spd->nr_pages)
  			break;
  	}
  
  	if (!ret)
  		ret = -EAGAIN;
  
  out:
  	while (page_nr < spd_pages)
  		spd->spd_release(spd, page_nr++);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(splice_to_pipe);
  
  ssize_t add_to_pipe(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
  {
  	int ret;
  
  	if (unlikely(!pipe->readers)) {
  		send_sig(SIGPIPE, current, 0);
  		ret = -EPIPE;
  	} else if (pipe->nrbufs == pipe->buffers) {
  		ret = -EAGAIN;
  	} else {
  		int newbuf = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
  		pipe->bufs[newbuf] = *buf;
  		pipe->nrbufs++;
  		return buf->len;
  	}
  	pipe_buf_release(pipe, buf);
  	return ret;
  }
  EXPORT_SYMBOL(add_to_pipe);
  
  /*
   * Check if we need to grow the arrays holding pages and partial page
   * descriptions.
   */
  int splice_grow_spd(const struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
  {
  	unsigned int buffers = READ_ONCE(pipe->buffers);
  
  	spd->nr_pages_max = buffers;
  	if (buffers <= PIPE_DEF_BUFFERS)
  		return 0;
  
  	spd->pages = kmalloc_array(buffers, sizeof(struct page *), GFP_KERNEL);
  	spd->partial = kmalloc_array(buffers, sizeof(struct partial_page),
  				     GFP_KERNEL);
  
  	if (spd->pages && spd->partial)
  		return 0;
  
  	kfree(spd->pages);
  	kfree(spd->partial);
  	return -ENOMEM;
  }
  
  void splice_shrink_spd(struct splice_pipe_desc *spd)
  {
  	if (spd->nr_pages_max <= PIPE_DEF_BUFFERS)
  		return;
  
  	kfree(spd->pages);
  	kfree(spd->partial);
  }
  
  /**
   * generic_file_splice_read - splice data from file to a pipe
   * @in:		file to splice from
   * @ppos:	position in @in
   * @pipe:	pipe to splice to
   * @len:	number of bytes to splice
   * @flags:	splice modifier flags
   *
   * Description:
   *    Will read pages from given file and fill them into a pipe. Can be
   *    used as long as it has more or less sane ->read_iter().
   *
   */
  ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
  				 struct pipe_inode_info *pipe, size_t len,
  				 unsigned int flags)
  {
  	struct iov_iter to;
  	struct kiocb kiocb;
  	int idx, ret;
  
  	iov_iter_pipe(&to, READ, pipe, len);
  	idx = to.idx;
  	init_sync_kiocb(&kiocb, in);
  	kiocb.ki_pos = *ppos;
  	ret = call_read_iter(in, &kiocb, &to);
  	if (ret > 0) {
  		*ppos = kiocb.ki_pos;
  		file_accessed(in);
  	} else if (ret < 0) {
  		to.idx = idx;
  		to.iov_offset = 0;
  		iov_iter_advance(&to, 0); /* to free what was emitted */
  		/*
  		 * callers of ->splice_read() expect -EAGAIN on
  		 * "can't put anything in there", rather than -EFAULT.
  		 */
  		if (ret == -EFAULT)
  			ret = -EAGAIN;
  	}
  
  	return ret;
  }
  EXPORT_SYMBOL(generic_file_splice_read);
  
  const struct pipe_buf_operations default_pipe_buf_ops = {
  	.can_merge = 0,
  	.confirm = generic_pipe_buf_confirm,
  	.release = generic_pipe_buf_release,
  	.steal = generic_pipe_buf_steal,
  	.get = generic_pipe_buf_get,
  };
  
  static int generic_pipe_buf_nosteal(struct pipe_inode_info *pipe,
  				    struct pipe_buffer *buf)
  {
  	return 1;
  }
  
  /* Pipe buffer operations for a socket and similar. */
  const struct pipe_buf_operations nosteal_pipe_buf_ops = {
  	.can_merge = 0,
  	.confirm = generic_pipe_buf_confirm,
  	.release = generic_pipe_buf_release,
  	.steal = generic_pipe_buf_nosteal,
  	.get = generic_pipe_buf_get,
  };
  EXPORT_SYMBOL(nosteal_pipe_buf_ops);
  
  static ssize_t kernel_readv(struct file *file, const struct kvec *vec,
  			    unsigned long vlen, loff_t offset)
  {
  	mm_segment_t old_fs;
  	loff_t pos = offset;
  	ssize_t res;
  
  	old_fs = get_fs();
  	set_fs(get_ds());
  	/* The cast to a user pointer is valid due to the set_fs() */
  	res = vfs_readv(file, (const struct iovec __user *)vec, vlen, &pos, 0);
  	set_fs(old_fs);
  
  	return res;
  }
  
  static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
  				 struct pipe_inode_info *pipe, size_t len,
  				 unsigned int flags)
  {
  	struct kvec *vec, __vec[PIPE_DEF_BUFFERS];
  	struct iov_iter to;
  	struct page **pages;
  	unsigned int nr_pages;
  	size_t offset, base, copied = 0;
  	ssize_t res;
  	int i;
  
  	if (pipe->nrbufs == pipe->buffers)
  		return -EAGAIN;
  
  	/*
  	 * Try to keep page boundaries matching to source pagecache ones -
  	 * it probably won't be much help, but...
  	 */
  	offset = *ppos & ~PAGE_MASK;
  
  	iov_iter_pipe(&to, READ, pipe, len + offset);
  
  	res = iov_iter_get_pages_alloc(&to, &pages, len + offset, &base);
  	if (res <= 0)
  		return -ENOMEM;
  
  	nr_pages = DIV_ROUND_UP(res + base, PAGE_SIZE);
  
  	vec = __vec;
  	if (nr_pages > PIPE_DEF_BUFFERS) {
  		vec = kmalloc_array(nr_pages, sizeof(struct kvec), GFP_KERNEL);
  		if (unlikely(!vec)) {
  			res = -ENOMEM;
  			goto out;
  		}
  	}
  
  	pipe->bufs[to.idx].offset = offset;
  	pipe->bufs[to.idx].len -= offset;
  
  	for (i = 0; i < nr_pages; i++) {
  		size_t this_len = min_t(size_t, len, PAGE_SIZE - offset);
  		vec[i].iov_base = page_address(pages[i]) + offset;
  		vec[i].iov_len = this_len;
  		len -= this_len;
  		offset = 0;
  	}
  
  	res = kernel_readv(in, vec, nr_pages, *ppos);
  	if (res > 0) {
  		copied = res;
  		*ppos += res;
  	}
  
  	if (vec != __vec)
  		kfree(vec);
  out:
  	for (i = 0; i < nr_pages; i++)
  		put_page(pages[i]);
  	kvfree(pages);
  	iov_iter_advance(&to, copied);	/* truncates and discards */
  	return res;
  }
  
  /*
   * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
   * using sendpage(). Return the number of bytes sent.
   */
  static int pipe_to_sendpage(struct pipe_inode_info *pipe,
  			    struct pipe_buffer *buf, struct splice_desc *sd)
  {
  	struct file *file = sd->u.file;
  	loff_t pos = sd->pos;
  	int more;
  
  	if (!likely(file->f_op->sendpage))
  		return -EINVAL;
  
  	more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
  
  	if (sd->len < sd->total_len && pipe->nrbufs > 1)
  		more |= MSG_SENDPAGE_NOTLAST;
  
  	return file->f_op->sendpage(file, buf->page, buf->offset,
  				    sd->len, &pos, more);
  }
  
  static void wakeup_pipe_writers(struct pipe_inode_info *pipe)
  {
  	smp_mb();
  	if (waitqueue_active(&pipe->wait))
  		wake_up_interruptible(&pipe->wait);
  	kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
  }
  
  /**
   * splice_from_pipe_feed - feed available data from a pipe to a file
   * @pipe:	pipe to splice from
   * @sd:		information to @actor
   * @actor:	handler that splices the data
   *
   * Description:
   *    This function loops over the pipe and calls @actor to do the
   *    actual moving of a single struct pipe_buffer to the desired
   *    destination.  It returns when there's no more buffers left in
   *    the pipe or if the requested number of bytes (@sd->total_len)
   *    have been copied.  It returns a positive number (one) if the
   *    pipe needs to be filled with more data, zero if the required
   *    number of bytes have been copied and -errno on error.
   *
   *    This, together with splice_from_pipe_{begin,end,next}, may be
   *    used to implement the functionality of __splice_from_pipe() when
   *    locking is required around copying the pipe buffers to the
   *    destination.
   */
  static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_desc *sd,
  			  splice_actor *actor)
  {
  	int ret;
  
  	while (pipe->nrbufs) {
  		struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
  
  		sd->len = buf->len;
  		if (sd->len > sd->total_len)
  			sd->len = sd->total_len;
  
  		ret = pipe_buf_confirm(pipe, buf);
  		if (unlikely(ret)) {
  			if (ret == -ENODATA)
  				ret = 0;
  			return ret;
  		}
  
  		ret = actor(pipe, buf, sd);
  		if (ret <= 0)
  			return ret;
  
  		buf->offset += ret;
  		buf->len -= ret;
  
  		sd->num_spliced += ret;
  		sd->len -= ret;
  		sd->pos += ret;
  		sd->total_len -= ret;
  
  		if (!buf->len) {
  			pipe_buf_release(pipe, buf);
  			pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
  			pipe->nrbufs--;
  			if (pipe->files)
  				sd->need_wakeup = true;
  		}
  
  		if (!sd->total_len)
  			return 0;
  	}
  
  	return 1;
  }
  
  /**
   * splice_from_pipe_next - wait for some data to splice from
   * @pipe:	pipe to splice from
   * @sd:		information about the splice operation
   *
   * Description:
   *    This function will wait for some data and return a positive
   *    value (one) if pipe buffers are available.  It will return zero
   *    or -errno if no more data needs to be spliced.
   */
  static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
  {
  	/*
  	 * Check for signal early to make process killable when there are
  	 * always buffers available
  	 */
  	if (signal_pending(current))
  		return -ERESTARTSYS;
  
  	while (!pipe->nrbufs) {
  		if (!pipe->writers)
  			return 0;
  
  		if (!pipe->waiting_writers && sd->num_spliced)
  			return 0;
  
  		if (sd->flags & SPLICE_F_NONBLOCK)
  			return -EAGAIN;
  
  		if (signal_pending(current))
  			return -ERESTARTSYS;
  
  		if (sd->need_wakeup) {
  			wakeup_pipe_writers(pipe);
  			sd->need_wakeup = false;
  		}
  
  		pipe_wait(pipe);
  	}
  
  	return 1;
  }
  
  /**
   * splice_from_pipe_begin - start splicing from pipe
   * @sd:		information about the splice operation
   *
   * Description:
   *    This function should be called before a loop containing
   *    splice_from_pipe_next() and splice_from_pipe_feed() to
   *    initialize the necessary fields of @sd.
   */
  static void splice_from_pipe_begin(struct splice_desc *sd)
  {
  	sd->num_spliced = 0;
  	sd->need_wakeup = false;
  }
  
  /**
   * splice_from_pipe_end - finish splicing from pipe
   * @pipe:	pipe to splice from
   * @sd:		information about the splice operation
   *
   * Description:
   *    This function will wake up pipe writers if necessary.  It should
   *    be called after a loop containing splice_from_pipe_next() and
   *    splice_from_pipe_feed().
   */
  static void splice_from_pipe_end(struct pipe_inode_info *pipe, struct splice_desc *sd)
  {
  	if (sd->need_wakeup)
  		wakeup_pipe_writers(pipe);
  }
  
  /**
   * __splice_from_pipe - splice data from a pipe to given actor
   * @pipe:	pipe to splice from
   * @sd:		information to @actor
   * @actor:	handler that splices the data
   *
   * Description:
   *    This function does little more than loop over the pipe and call
   *    @actor to do the actual moving of a single struct pipe_buffer to
   *    the desired destination. See pipe_to_file, pipe_to_sendpage, or
   *    pipe_to_user.
   *
   */
  ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
  			   splice_actor *actor)
  {
  	int ret;
  
  	splice_from_pipe_begin(sd);
  	do {
  		cond_resched();
  		ret = splice_from_pipe_next(pipe, sd);
  		if (ret > 0)
  			ret = splice_from_pipe_feed(pipe, sd, actor);
  	} while (ret > 0);
  	splice_from_pipe_end(pipe, sd);
  
  	return sd->num_spliced ? sd->num_spliced : ret;
  }
  EXPORT_SYMBOL(__splice_from_pipe);
  
  /**
   * splice_from_pipe - splice data from a pipe to a file
   * @pipe:	pipe to splice from
   * @out:	file to splice to
   * @ppos:	position in @out
   * @len:	how many bytes to splice
   * @flags:	splice modifier flags
   * @actor:	handler that splices the data
   *
   * Description:
   *    See __splice_from_pipe. This function locks the pipe inode,
   *    otherwise it's identical to __splice_from_pipe().
   *
   */
  ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
  			 loff_t *ppos, size_t len, unsigned int flags,
  			 splice_actor *actor)
  {
  	ssize_t ret;
  	struct splice_desc sd = {
  		.total_len = len,
  		.flags = flags,
  		.pos = *ppos,
  		.u.file = out,
  	};
  
  	pipe_lock(pipe);
  	ret = __splice_from_pipe(pipe, &sd, actor);
  	pipe_unlock(pipe);
  
  	return ret;
  }
  
  /**
   * iter_file_splice_write - splice data from a pipe to a file
   * @pipe:	pipe info
   * @out:	file to write to
   * @ppos:	position in @out
   * @len:	number of bytes to splice
   * @flags:	splice modifier flags
   *
   * Description:
   *    Will either move or copy pages (determined by @flags options) from
   *    the given pipe inode to the given file.
   *    This one is ->write_iter-based.
   *
   */
  ssize_t
  iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
  			  loff_t *ppos, size_t len, unsigned int flags)
  {
  	struct splice_desc sd = {
  		.total_len = len,
  		.flags = flags,
  		.pos = *ppos,
  		.u.file = out,
  	};
  	int nbufs = pipe->buffers;
  	struct bio_vec *array = kcalloc(nbufs, sizeof(struct bio_vec),
  					GFP_KERNEL);
  	ssize_t ret;
  
  	if (unlikely(!array))
  		return -ENOMEM;
  
  	pipe_lock(pipe);
  
  	splice_from_pipe_begin(&sd);
  	while (sd.total_len) {
  		struct iov_iter from;
  		size_t left;
  		int n, idx;
  
  		ret = splice_from_pipe_next(pipe, &sd);
  		if (ret <= 0)
  			break;
  
  		if (unlikely(nbufs < pipe->buffers)) {
  			kfree(array);
  			nbufs = pipe->buffers;
  			array = kcalloc(nbufs, sizeof(struct bio_vec),
  					GFP_KERNEL);
  			if (!array) {
  				ret = -ENOMEM;
  				break;
  			}
  		}
  
  		/* build the vector */
  		left = sd.total_len;
  		for (n = 0, idx = pipe->curbuf; left && n < pipe->nrbufs; n++, idx++) {
  			struct pipe_buffer *buf = pipe->bufs + idx;
  			size_t this_len = buf->len;
  
  			if (this_len > left)
  				this_len = left;
  
  			if (idx == pipe->buffers - 1)
  				idx = -1;
  
  			ret = pipe_buf_confirm(pipe, buf);
  			if (unlikely(ret)) {
  				if (ret == -ENODATA)
  					ret = 0;
  				goto done;
  			}
  
  			array[n].bv_page = buf->page;
  			array[n].bv_len = this_len;
  			array[n].bv_offset = buf->offset;
  			left -= this_len;
  		}
  
  		iov_iter_bvec(&from, WRITE, array, n, sd.total_len - left);
  		ret = vfs_iter_write(out, &from, &sd.pos, 0);
  		if (ret <= 0)
  			break;
  
  		sd.num_spliced += ret;
  		sd.total_len -= ret;
  		*ppos = sd.pos;
  
  		/* dismiss the fully eaten buffers, adjust the partial one */
  		while (ret) {
  			struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
  			if (ret >= buf->len) {
  				ret -= buf->len;
  				buf->len = 0;
  				pipe_buf_release(pipe, buf);
  				pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
  				pipe->nrbufs--;
  				if (pipe->files)
  					sd.need_wakeup = true;
  			} else {
  				buf->offset += ret;
  				buf->len -= ret;
  				ret = 0;
  			}
  		}
  	}
  done:
  	kfree(array);
  	splice_from_pipe_end(pipe, &sd);
  
  	pipe_unlock(pipe);
  
  	if (sd.num_spliced)
  		ret = sd.num_spliced;
  
  	return ret;
  }
  
  EXPORT_SYMBOL(iter_file_splice_write);
  
  static int write_pipe_buf(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
  			  struct splice_desc *sd)
  {
  	int ret;
  	void *data;
  	loff_t tmp = sd->pos;
  
  	data = kmap(buf->page);
  	ret = __kernel_write(sd->u.file, data + buf->offset, sd->len, &tmp);
  	kunmap(buf->page);
  
  	return ret;
  }
  
  static ssize_t default_file_splice_write(struct pipe_inode_info *pipe,
  					 struct file *out, loff_t *ppos,
  					 size_t len, unsigned int flags)
  {
  	ssize_t ret;
  
  	ret = splice_from_pipe(pipe, out, ppos, len, flags, write_pipe_buf);
  	if (ret > 0)
  		*ppos += ret;
  
  	return ret;
  }
  
  /**
   * generic_splice_sendpage - splice data from a pipe to a socket
   * @pipe:	pipe to splice from
   * @out:	socket to write to
   * @ppos:	position in @out
   * @len:	number of bytes to splice
   * @flags:	splice modifier flags
   *
   * Description:
   *    Will send @len bytes from the pipe to a network socket. No data copying
   *    is involved.
   *
   */
  ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
  				loff_t *ppos, size_t len, unsigned int flags)
  {
  	return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
  }
  
  EXPORT_SYMBOL(generic_splice_sendpage);
  
  /*
   * Attempt to initiate a splice from pipe to file.
   */
  static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
  			   loff_t *ppos, size_t len, unsigned int flags)
  {
  	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *,
  				loff_t *, size_t, unsigned int);
  
  	if (out->f_op->splice_write)
  		splice_write = out->f_op->splice_write;
  	else
  		splice_write = default_file_splice_write;
  
  	return splice_write(pipe, out, ppos, len, flags);
  }
  
  /*
   * Attempt to initiate a splice from a file to a pipe.
   */
  static long do_splice_to(struct file *in, loff_t *ppos,
  			 struct pipe_inode_info *pipe, size_t len,
  			 unsigned int flags)
  {
  	ssize_t (*splice_read)(struct file *, loff_t *,
  			       struct pipe_inode_info *, size_t, unsigned int);
  	int ret;
  
  	if (unlikely(!(in->f_mode & FMODE_READ)))
  		return -EBADF;
  
  	ret = rw_verify_area(READ, in, ppos, len);
  	if (unlikely(ret < 0))
  		return ret;
  
  	if (unlikely(len > MAX_RW_COUNT))
  		len = MAX_RW_COUNT;
  
  	if (in->f_op->splice_read)
  		splice_read = in->f_op->splice_read;
  	else
  		splice_read = default_file_splice_read;
  
  	return splice_read(in, ppos, pipe, len, flags);
  }
  
  /**
   * splice_direct_to_actor - splices data directly between two non-pipes
   * @in:		file to splice from
   * @sd:		actor information on where to splice to
   * @actor:	handles the data splicing
   *
   * Description:
   *    This is a special case helper to splice directly between two
   *    points, without requiring an explicit pipe. Internally an allocated
   *    pipe is cached in the process, and reused during the lifetime of
   *    that process.
   *
   */
  ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
  			       splice_direct_actor *actor)
  {
  	struct pipe_inode_info *pipe;
  	long ret, bytes;
  	umode_t i_mode;
  	size_t len;
  	int i, flags, more;
  
  	/*
  	 * We require the input being a regular file, as we don't want to
  	 * randomly drop data for eg socket -> socket splicing. Use the
  	 * piped splicing for that!
  	 */
  	i_mode = file_inode(in)->i_mode;
  	if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
  		return -EINVAL;
  
  	/*
  	 * neither in nor out is a pipe, setup an internal pipe attached to
  	 * 'out' and transfer the wanted data from 'in' to 'out' through that
  	 */
  	pipe = current->splice_pipe;
  	if (unlikely(!pipe)) {
  		pipe = alloc_pipe_info();
  		if (!pipe)
  			return -ENOMEM;
  
  		/*
  		 * We don't have an immediate reader, but we'll read the stuff
  		 * out of the pipe right after the splice_to_pipe(). So set
  		 * PIPE_READERS appropriately.
  		 */
  		pipe->readers = 1;
  
  		current->splice_pipe = pipe;
  	}
  
  	/*
  	 * Do the splice.
  	 */
  	ret = 0;
  	bytes = 0;
  	len = sd->total_len;
  	flags = sd->flags;
  
  	/*
  	 * Don't block on output, we have to drain the direct pipe.
  	 */
  	sd->flags &= ~SPLICE_F_NONBLOCK;
  	more = sd->flags & SPLICE_F_MORE;
  
  	while (len) {
  		size_t read_len;
  		loff_t pos = sd->pos, prev_pos = pos;
  
  		ret = do_splice_to(in, &pos, pipe, len, flags);
  		if (unlikely(ret <= 0))
  			goto out_release;
  
  		read_len = ret;
  		sd->total_len = read_len;
  
  		/*
  		 * If more data is pending, set SPLICE_F_MORE
  		 * If this is the last data and SPLICE_F_MORE was not set
  		 * initially, clears it.
  		 */
  		if (read_len < len)
  			sd->flags |= SPLICE_F_MORE;
  		else if (!more)
  			sd->flags &= ~SPLICE_F_MORE;
  		/*
  		 * NOTE: nonblocking mode only applies to the input. We
  		 * must not do the output in nonblocking mode as then we
  		 * could get stuck data in the internal pipe:
  		 */
  		ret = actor(pipe, sd);
  		if (unlikely(ret <= 0)) {
  			sd->pos = prev_pos;
  			goto out_release;
  		}
  
  		bytes += ret;
  		len -= ret;
  		sd->pos = pos;
  
  		if (ret < read_len) {
  			sd->pos = prev_pos + ret;
  			goto out_release;
  		}
  	}
  
  done:
  	pipe->nrbufs = pipe->curbuf = 0;
  	file_accessed(in);
  	return bytes;
  
  out_release:
  	/*
  	 * If we did an incomplete transfer we must release
  	 * the pipe buffers in question:
  	 */
  	for (i = 0; i < pipe->buffers; i++) {
  		struct pipe_buffer *buf = pipe->bufs + i;
  
  		if (buf->ops)
  			pipe_buf_release(pipe, buf);
  	}
  
  	if (!bytes)
  		bytes = ret;
  
  	goto done;
  }
  EXPORT_SYMBOL(splice_direct_to_actor);
  
  static int direct_splice_actor(struct pipe_inode_info *pipe,
  			       struct splice_desc *sd)
  {
  	struct file *file = sd->u.file;
  
  	return do_splice_from(pipe, file, sd->opos, sd->total_len,
  			      sd->flags);
  }
  
  /**
   * do_splice_direct - splices data directly between two files
   * @in:		file to splice from
   * @ppos:	input file offset
   * @out:	file to splice to
   * @opos:	output file offset
   * @len:	number of bytes to splice
   * @flags:	splice modifier flags
   *
   * Description:
   *    For use by do_sendfile(). splice can easily emulate sendfile, but
   *    doing it in the application would incur an extra system call
   *    (splice in + splice out, as compared to just sendfile()). So this helper
   *    can splice directly through a process-private pipe.
   *
   */
  long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
  		      loff_t *opos, size_t len, unsigned int flags)
  {
  	struct splice_desc sd = {
  		.len		= len,
  		.total_len	= len,
  		.flags		= flags,
  		.pos		= *ppos,
  		.u.file		= out,
  		.opos		= opos,
  	};
  	long ret;
  
  	if (unlikely(!(out->f_mode & FMODE_WRITE)))
  		return -EBADF;
  
  	if (unlikely(out->f_flags & O_APPEND))
  		return -EINVAL;
  
  	ret = rw_verify_area(WRITE, out, opos, len);
  	if (unlikely(ret < 0))
  		return ret;
  
  	ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
  	if (ret > 0)
  		*ppos = sd.pos;
  
  	return ret;
  }
  EXPORT_SYMBOL(do_splice_direct);
  
  static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
  {
  	for (;;) {
  		if (unlikely(!pipe->readers)) {
  			send_sig(SIGPIPE, current, 0);
  			return -EPIPE;
  		}
  		if (pipe->nrbufs != pipe->buffers)
  			return 0;
  		if (flags & SPLICE_F_NONBLOCK)
  			return -EAGAIN;
  		if (signal_pending(current))
  			return -ERESTARTSYS;
  		pipe->waiting_writers++;
  		pipe_wait(pipe);
  		pipe->waiting_writers--;
  	}
  }
  
  static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
  			       struct pipe_inode_info *opipe,
  			       size_t len, unsigned int flags);
  
  /*
   * Determine where to splice to/from.
   */
  static long do_splice(struct file *in, loff_t __user *off_in,
  		      struct file *out, loff_t __user *off_out,
  		      size_t len, unsigned int flags)
  {
  	struct pipe_inode_info *ipipe;
  	struct pipe_inode_info *opipe;
  	loff_t offset;
  	long ret;
  
  	ipipe = get_pipe_info(in);
  	opipe = get_pipe_info(out);
  
  	if (ipipe && opipe) {
  		if (off_in || off_out)
  			return -ESPIPE;
  
  		if (!(in->f_mode & FMODE_READ))
  			return -EBADF;
  
  		if (!(out->f_mode & FMODE_WRITE))
  			return -EBADF;
  
  		/* Splicing to self would be fun, but... */
  		if (ipipe == opipe)
  			return -EINVAL;
  
  		return splice_pipe_to_pipe(ipipe, opipe, len, flags);
  	}
  
  	if (ipipe) {
  		if (off_in)
  			return -ESPIPE;
  		if (off_out) {
  			if (!(out->f_mode & FMODE_PWRITE))
  				return -EINVAL;
  			if (copy_from_user(&offset, off_out, sizeof(loff_t)))
  				return -EFAULT;
  		} else {
  			offset = out->f_pos;
  		}
  
  		if (unlikely(!(out->f_mode & FMODE_WRITE)))
  			return -EBADF;
  
  		if (unlikely(out->f_flags & O_APPEND))
  			return -EINVAL;
  
  		ret = rw_verify_area(WRITE, out, &offset, len);
  		if (unlikely(ret < 0))
  			return ret;
  
  		file_start_write(out);
  		ret = do_splice_from(ipipe, out, &offset, len, flags);
  		file_end_write(out);
  
  		if (!off_out)
  			out->f_pos = offset;
  		else if (copy_to_user(off_out, &offset, sizeof(loff_t)))
  			ret = -EFAULT;
  
  		return ret;
  	}
  
  	if (opipe) {
  		if (off_out)
  			return -ESPIPE;
  		if (off_in) {
  			if (!(in->f_mode & FMODE_PREAD))
  				return -EINVAL;
  			if (copy_from_user(&offset, off_in, sizeof(loff_t)))
  				return -EFAULT;
  		} else {
  			offset = in->f_pos;
  		}
  
  		pipe_lock(opipe);
  		ret = wait_for_space(opipe, flags);
  		if (!ret)
  			ret = do_splice_to(in, &offset, opipe, len, flags);
  		pipe_unlock(opipe);
  		if (ret > 0)
  			wakeup_pipe_readers(opipe);
  		if (!off_in)
  			in->f_pos = offset;
  		else if (copy_to_user(off_in, &offset, sizeof(loff_t)))
  			ret = -EFAULT;
  
  		return ret;
  	}
  
  	return -EINVAL;
  }
  
  static int iter_to_pipe(struct iov_iter *from,
  			struct pipe_inode_info *pipe,
  			unsigned flags)
  {
  	struct pipe_buffer buf = {
  		.ops = &user_page_pipe_buf_ops,
  		.flags = flags
  	};
  	size_t total = 0;
  	int ret = 0;
  	bool failed = false;
  
  	while (iov_iter_count(from) && !failed) {
  		struct page *pages[16];
  		ssize_t copied;
  		size_t start;
  		int n;
  
  		copied = iov_iter_get_pages(from, pages, ~0UL, 16, &start);
  		if (copied <= 0) {
  			ret = copied;
  			break;
  		}
  
  		for (n = 0; copied; n++, start = 0) {
  			int size = min_t(int, copied, PAGE_SIZE - start);
  			if (!failed) {
  				buf.page = pages[n];
  				buf.offset = start;
  				buf.len = size;
  				ret = add_to_pipe(pipe, &buf);
  				if (unlikely(ret < 0)) {
  					failed = true;
  				} else {
  					iov_iter_advance(from, ret);
  					total += ret;
  				}
  			} else {
  				put_page(pages[n]);
  			}
  			copied -= size;
  		}
  	}
  	return total ? total : ret;
  }
  
  static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
  			struct splice_desc *sd)
  {
  	int n = copy_page_to_iter(buf->page, buf->offset, sd->len, sd->u.data);
  	return n == sd->len ? n : -EFAULT;
  }
  
  /*
   * For lack of a better implementation, implement vmsplice() to userspace
   * as a simple copy of the pipes pages to the user iov.
   */
  static long vmsplice_to_user(struct file *file, struct iov_iter *iter,
  			     unsigned int flags)
  {
  	struct pipe_inode_info *pipe = get_pipe_info(file);
  	struct splice_desc sd = {
  		.total_len = iov_iter_count(iter),
  		.flags = flags,
  		.u.data = iter
  	};
  	long ret = 0;
  
  	if (!pipe)
  		return -EBADF;
  
  	if (sd.total_len) {
  		pipe_lock(pipe);
  		ret = __splice_from_pipe(pipe, &sd, pipe_to_user);
  		pipe_unlock(pipe);
  	}
  
  	return ret;
  }
  
  /*
   * vmsplice splices a user address range into a pipe. It can be thought of
   * as splice-from-memory, where the regular splice is splice-from-file (or
   * to file). In both cases the output is a pipe, naturally.
   */
  static long vmsplice_to_pipe(struct file *file, struct iov_iter *iter,
  			     unsigned int flags)
  {
  	struct pipe_inode_info *pipe;
  	long ret = 0;
  	unsigned buf_flag = 0;
  
  	if (flags & SPLICE_F_GIFT)
  		buf_flag = PIPE_BUF_FLAG_GIFT;
  
  	pipe = get_pipe_info(file);
  	if (!pipe)
  		return -EBADF;
  
  	pipe_lock(pipe);
  	ret = wait_for_space(pipe, flags);
  	if (!ret)
  		ret = iter_to_pipe(iter, pipe, buf_flag);
  	pipe_unlock(pipe);
  	if (ret > 0)
  		wakeup_pipe_readers(pipe);
  	return ret;
  }
  
  static int vmsplice_type(struct fd f, int *type)
  {
  	if (!f.file)
  		return -EBADF;
  	if (f.file->f_mode & FMODE_WRITE) {
  		*type = WRITE;
  	} else if (f.file->f_mode & FMODE_READ) {
  		*type = READ;
  	} else {
  		fdput(f);
  		return -EBADF;
  	}
  	return 0;
  }
  
  /*
   * Note that vmsplice only really supports true splicing _from_ user memory
   * to a pipe, not the other way around. Splicing from user memory is a simple
   * operation that can be supported without any funky alignment restrictions
   * or nasty vm tricks. We simply map in the user memory and fill them into
   * a pipe. The reverse isn't quite as easy, though. There are two possible
   * solutions for that:
   *
   *	- memcpy() the data internally, at which point we might as well just
   *	  do a regular read() on the buffer anyway.
   *	- Lots of nasty vm tricks, that are neither fast nor flexible (it
   *	  has restriction limitations on both ends of the pipe).
   *
   * Currently we punt and implement it as a normal copy, see pipe_to_user().
   *
   */
  static long do_vmsplice(struct file *f, struct iov_iter *iter, unsigned int flags)
  {
  	if (unlikely(flags & ~SPLICE_F_ALL))
  		return -EINVAL;
  
  	if (!iov_iter_count(iter))
  		return 0;
  
  	if (iov_iter_rw(iter) == WRITE)
  		return vmsplice_to_pipe(f, iter, flags);
  	else
  		return vmsplice_to_user(f, iter, flags);
  }
  
  SYSCALL_DEFINE4(vmsplice, int, fd, const struct iovec __user *, uiov,
  		unsigned long, nr_segs, unsigned int, flags)
  {
  	struct iovec iovstack[UIO_FASTIOV];
  	struct iovec *iov = iovstack;
  	struct iov_iter iter;
  	long error;
  	struct fd f;
  	int type;
  
  	f = fdget(fd);
  	error = vmsplice_type(f, &type);
  	if (error)
  		return error;
  
  	error = import_iovec(type, uiov, nr_segs,
  			     ARRAY_SIZE(iovstack), &iov, &iter);
  	if (!error) {
  		error = do_vmsplice(f.file, &iter, flags);
  		kfree(iov);
  	}
  	fdput(f);
  	return error;
  }
  
  #ifdef CONFIG_COMPAT
  COMPAT_SYSCALL_DEFINE4(vmsplice, int, fd, const struct compat_iovec __user *, iov32,
  		    unsigned int, nr_segs, unsigned int, flags)
  {
  	struct iovec iovstack[UIO_FASTIOV];
  	struct iovec *iov = iovstack;
  	struct iov_iter iter;
  	long error;
  	struct fd f;
  	int type;
  
  	f = fdget(fd);
  	error = vmsplice_type(f, &type);
  	if (error)
  		return error;
  
  	error = compat_import_iovec(type, iov32, nr_segs,
  			     ARRAY_SIZE(iovstack), &iov, &iter);
  	if (!error) {
  		error = do_vmsplice(f.file, &iter, flags);
  		kfree(iov);
  	}
  	fdput(f);
  	return error;
  }
  #endif
  
  SYSCALL_DEFINE6(splice, int, fd_in, loff_t __user *, off_in,
  		int, fd_out, loff_t __user *, off_out,
  		size_t, len, unsigned int, flags)
  {
  	struct fd in, out;
  	long error;
  
  	if (unlikely(!len))
  		return 0;
  
  	if (unlikely(flags & ~SPLICE_F_ALL))
  		return -EINVAL;
  
  	error = -EBADF;
  	in = fdget(fd_in);
  	if (in.file) {
  		if (in.file->f_mode & FMODE_READ) {
  			out = fdget(fd_out);
  			if (out.file) {
  				if (out.file->f_mode & FMODE_WRITE)
  					error = do_splice(in.file, off_in,
  							  out.file, off_out,
  							  len, flags);
  				fdput(out);
  			}
  		}
  		fdput(in);
  	}
  	return error;
  }
  
  /*
   * Make sure there's data to read. Wait for input if we can, otherwise
   * return an appropriate error.
   */
  static int ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
  {
  	int ret;
  
  	/*
  	 * Check ->nrbufs without the inode lock first. This function
  	 * is speculative anyways, so missing one is ok.
  	 */
  	if (pipe->nrbufs)
  		return 0;
  
  	ret = 0;
  	pipe_lock(pipe);
  
  	while (!pipe->nrbufs) {
  		if (signal_pending(current)) {
  			ret = -ERESTARTSYS;
  			break;
  		}
  		if (!pipe->writers)
  			break;
  		if (!pipe->waiting_writers) {
  			if (flags & SPLICE_F_NONBLOCK) {
  				ret = -EAGAIN;
  				break;
  			}
  		}
  		pipe_wait(pipe);
  	}
  
  	pipe_unlock(pipe);
  	return ret;
  }
  
  /*
   * Make sure there's writeable room. Wait for room if we can, otherwise
   * return an appropriate error.
   */
  static int opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
  {
  	int ret;
  
  	/*
  	 * Check ->nrbufs without the inode lock first. This function
  	 * is speculative anyways, so missing one is ok.
  	 */
  	if (pipe->nrbufs < pipe->buffers)
  		return 0;
  
  	ret = 0;
  	pipe_lock(pipe);
  
  	while (pipe->nrbufs >= pipe->buffers) {
  		if (!pipe->readers) {
  			send_sig(SIGPIPE, current, 0);
  			ret = -EPIPE;
  			break;
  		}
  		if (flags & SPLICE_F_NONBLOCK) {
  			ret = -EAGAIN;
  			break;
  		}
  		if (signal_pending(current)) {
  			ret = -ERESTARTSYS;
  			break;
  		}
  		pipe->waiting_writers++;
  		pipe_wait(pipe);
  		pipe->waiting_writers--;
  	}
  
  	pipe_unlock(pipe);
  	return ret;
  }
  
  /*
   * Splice contents of ipipe to opipe.
   */
  static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
  			       struct pipe_inode_info *opipe,
  			       size_t len, unsigned int flags)
  {
  	struct pipe_buffer *ibuf, *obuf;
  	int ret = 0, nbuf;
  	bool input_wakeup = false;
  
  
  retry:
  	ret = ipipe_prep(ipipe, flags);
  	if (ret)
  		return ret;
  
  	ret = opipe_prep(opipe, flags);
  	if (ret)
  		return ret;
  
  	/*
  	 * Potential ABBA deadlock, work around it by ordering lock
  	 * grabbing by pipe info address. Otherwise two different processes
  	 * could deadlock (one doing tee from A -> B, the other from B -> A).
  	 */
  	pipe_double_lock(ipipe, opipe);
  
  	do {
  		if (!opipe->readers) {
  			send_sig(SIGPIPE, current, 0);
  			if (!ret)
  				ret = -EPIPE;
  			break;
  		}
  
  		if (!ipipe->nrbufs && !ipipe->writers)
  			break;
  
  		/*
  		 * Cannot make any progress, because either the input
  		 * pipe is empty or the output pipe is full.
  		 */
  		if (!ipipe->nrbufs || opipe->nrbufs >= opipe->buffers) {
  			/* Already processed some buffers, break */
  			if (ret)
  				break;
  
  			if (flags & SPLICE_F_NONBLOCK) {
  				ret = -EAGAIN;
  				break;
  			}
  
  			/*
  			 * We raced with another reader/writer and haven't
  			 * managed to process any buffers.  A zero return
  			 * value means EOF, so retry instead.
  			 */
  			pipe_unlock(ipipe);
  			pipe_unlock(opipe);
  			goto retry;
  		}
  
  		ibuf = ipipe->bufs + ipipe->curbuf;
  		nbuf = (opipe->curbuf + opipe->nrbufs) & (opipe->buffers - 1);
  		obuf = opipe->bufs + nbuf;
  
  		if (len >= ibuf->len) {
  			/*
  			 * Simply move the whole buffer from ipipe to opipe
  			 */
  			*obuf = *ibuf;
  			ibuf->ops = NULL;
  			opipe->nrbufs++;
  			ipipe->curbuf = (ipipe->curbuf + 1) & (ipipe->buffers - 1);
  			ipipe->nrbufs--;
  			input_wakeup = true;
  		} else {
  			/*
  			 * Get a reference to this pipe buffer,
  			 * so we can copy the contents over.
  			 */
  			pipe_buf_get(ipipe, ibuf);
  			*obuf = *ibuf;
  
  			/*
  			 * Don't inherit the gift flag, we need to
  			 * prevent multiple steals of this page.
  			 */
  			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
  
  			obuf->len = len;
  			opipe->nrbufs++;
  			ibuf->offset += obuf->len;
  			ibuf->len -= obuf->len;
  		}
  		ret += obuf->len;
  		len -= obuf->len;
  	} while (len);
  
  	pipe_unlock(ipipe);
  	pipe_unlock(opipe);
  
  	/*
  	 * If we put data in the output pipe, wakeup any potential readers.
  	 */
  	if (ret > 0)
  		wakeup_pipe_readers(opipe);
  
  	if (input_wakeup)
  		wakeup_pipe_writers(ipipe);
  
  	return ret;
  }
  
  /*
   * Link contents of ipipe to opipe.
   */
  static int link_pipe(struct pipe_inode_info *ipipe,
  		     struct pipe_inode_info *opipe,
  		     size_t len, unsigned int flags)
  {
  	struct pipe_buffer *ibuf, *obuf;
  	int ret = 0, i = 0, nbuf;
  
  	/*
  	 * Potential ABBA deadlock, work around it by ordering lock
  	 * grabbing by pipe info address. Otherwise two different processes
  	 * could deadlock (one doing tee from A -> B, the other from B -> A).
  	 */
  	pipe_double_lock(ipipe, opipe);
  
  	do {
  		if (!opipe->readers) {
  			send_sig(SIGPIPE, current, 0);
  			if (!ret)
  				ret = -EPIPE;
  			break;
  		}
  
  		/*
  		 * If we have iterated all input buffers or ran out of
  		 * output room, break.
  		 */
  		if (i >= ipipe->nrbufs || opipe->nrbufs >= opipe->buffers)
  			break;
  
  		ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (ipipe->buffers-1));
  		nbuf = (opipe->curbuf + opipe->nrbufs) & (opipe->buffers - 1);
  
  		/*
  		 * Get a reference to this pipe buffer,
  		 * so we can copy the contents over.
  		 */
  		pipe_buf_get(ipipe, ibuf);
  
  		obuf = opipe->bufs + nbuf;
  		*obuf = *ibuf;
  
  		/*
  		 * Don't inherit the gift flag, we need to
  		 * prevent multiple steals of this page.
  		 */
  		obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
  
  		if (obuf->len > len)
  			obuf->len = len;
  
  		opipe->nrbufs++;
  		ret += obuf->len;
  		len -= obuf->len;
  		i++;
  	} while (len);
  
  	/*
  	 * return EAGAIN if we have the potential of some data in the
  	 * future, otherwise just return 0
  	 */
  	if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
  		ret = -EAGAIN;
  
  	pipe_unlock(ipipe);
  	pipe_unlock(opipe);
  
  	/*
  	 * If we put data in the output pipe, wakeup any potential readers.
  	 */
  	if (ret > 0)
  		wakeup_pipe_readers(opipe);
  
  	return ret;
  }
  
  /*
   * This is a tee(1) implementation that works on pipes. It doesn't copy
   * any data, it simply references the 'in' pages on the 'out' pipe.
   * The 'flags' used are the SPLICE_F_* variants, currently the only
   * applicable one is SPLICE_F_NONBLOCK.
   */
  static long do_tee(struct file *in, struct file *out, size_t len,
  		   unsigned int flags)
  {
  	struct pipe_inode_info *ipipe = get_pipe_info(in);
  	struct pipe_inode_info *opipe = get_pipe_info(out);
  	int ret = -EINVAL;
  
  	/*
  	 * Duplicate the contents of ipipe to opipe without actually
  	 * copying the data.
  	 */
  	if (ipipe && opipe && ipipe != opipe) {
  		/*
  		 * Keep going, unless we encounter an error. The ipipe/opipe
  		 * ordering doesn't really matter.
  		 */
  		ret = ipipe_prep(ipipe, flags);
  		if (!ret) {
  			ret = opipe_prep(opipe, flags);
  			if (!ret)
  				ret = link_pipe(ipipe, opipe, len, flags);
  		}
  	}
  
  	return ret;
  }
  
  SYSCALL_DEFINE4(tee, int, fdin, int, fdout, size_t, len, unsigned int, flags)
  {
  	struct fd in;
  	int error;
  
  	if (unlikely(flags & ~SPLICE_F_ALL))
  		return -EINVAL;
  
  	if (unlikely(!len))
  		return 0;
  
  	error = -EBADF;
  	in = fdget(fdin);
  	if (in.file) {
  		if (in.file->f_mode & FMODE_READ) {
  			struct fd out = fdget(fdout);
  			if (out.file) {
  				if (out.file->f_mode & FMODE_WRITE)
  					error = do_tee(in.file, out.file,
  							len, flags);
  				fdput(out);
  			}
  		}
   		fdput(in);
   	}
  
  	return error;
  }
  