fs/splice.c - kernel/common - Git at Google

 /*
  * "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 = ACCESS_ONCE(pipe->buffers);

 	spd->nr_pages_max = buffers;
 	if (buffers <= PIPE_DEF_BUFFERS)
 		return 0;

 	spd->pages = kmalloc(buffers * sizeof(struct page *), GFP_KERNEL);
 	spd->partial = kmalloc(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, ITER_PIPE | 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,
 };

 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, ITER_PIPE | 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(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, ITER_BVEC | 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, const struct iovec __user *uiov,
 			     unsigned long nr_segs, unsigned int flags)
 {
 	struct pipe_inode_info *pipe;
 	struct splice_desc sd;
 	long ret;
 	struct iovec iovstack[UIO_FASTIOV];
 	struct iovec *iov = iovstack;
 	struct iov_iter iter;

 	pipe = get_pipe_info(file);
 	if (!pipe)
 		return -EBADF;

 	ret = import_iovec(READ, uiov, nr_segs,
 			   ARRAY_SIZE(iovstack), &iov, &iter);
 	if (ret < 0)
 		return ret;

 	sd.total_len = iov_iter_count(&iter);
 	sd.len = 0;
 	sd.flags = flags;
 	sd.u.data = &iter;
 	sd.pos = 0;

 	if (sd.total_len) {
 		pipe_lock(pipe);
 		ret = __splice_from_pipe(pipe, &sd, pipe_to_user);
 		pipe_unlock(pipe);
 	}

 	kfree(iov);
 	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, const struct iovec __user *uiov,
 			     unsigned long nr_segs, unsigned int flags)
 {
 	struct pipe_inode_info *pipe;
 	struct iovec iovstack[UIO_FASTIOV];
 	struct iovec *iov = iovstack;
 	struct iov_iter from;
 	long ret;
 	unsigned buf_flag = 0;

 	if (flags & SPLICE_F_GIFT)
 		buf_flag = PIPE_BUF_FLAG_GIFT;

 	pipe = get_pipe_info(file);
 	if (!pipe)
 		return -EBADF;

 	ret = import_iovec(WRITE, uiov, nr_segs,
 			   ARRAY_SIZE(iovstack), &iov, &from);
 	if (ret < 0)
 		return ret;

 	pipe_lock(pipe);
 	ret = wait_for_space(pipe, flags);
 	if (!ret)
 		ret = iter_to_pipe(&from, pipe, buf_flag);
 	pipe_unlock(pipe);
 	if (ret > 0)
 		wakeup_pipe_readers(pipe);
 	kfree(iov);
 	return ret;
 }

 /*
  * 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().
  *
  */
 SYSCALL_DEFINE4(vmsplice, int, fd, const struct iovec __user *, iov,
 		unsigned long, nr_segs, unsigned int, flags)
 {
 	struct fd f;
 	long error;

 	if (unlikely(flags & ~SPLICE_F_ALL))
 		return -EINVAL;
 	if (unlikely(nr_segs > UIO_MAXIOV))
 		return -EINVAL;
 	else if (unlikely(!nr_segs))
 		return 0;

 	error = -EBADF;
 	f = fdget(fd);
 	if (f.file) {
 		if (f.file->f_mode & FMODE_WRITE)
 			error = vmsplice_to_pipe(f.file, iov, nr_segs, flags);
 		else if (f.file->f_mode & FMODE_READ)
 			error = vmsplice_to_user(f.file, iov, nr_segs, flags);

 		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)
 {
 	unsigned i;
 	struct iovec __user *iov;
 	if (nr_segs > UIO_MAXIOV)
 		return -EINVAL;
 	iov = compat_alloc_user_space(nr_segs * sizeof(struct iovec));
 	for (i = 0; i < nr_segs; i++) {
 		struct compat_iovec v;
 		if (get_user(v.iov_base, &iov32[i].iov_base) ||
 		    get_user(v.iov_len, &iov32[i].iov_len) ||
 		    put_user(compat_ptr(v.iov_base), &iov[i].iov_base) ||
 		    put_user(v.iov_len, &iov[i].iov_len))
 			return -EFAULT;
 	}
 	return sys_vmsplice(fd, iov, nr_segs, flags);
 }
 #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.
 			 */
 			if (!pipe_buf_get(ipipe, ibuf)) {
 				if (ret == 0)
 					ret = -EFAULT;
 				break;
 			}
 			*obuf = *ibuf;

 			/*
 			 * Don't inherit the gift flag, we need to
 			 * prevent multiple steals of this page.
 			 */
 			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;

 			pipe_buf_mark_unmergeable(obuf);

 			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.
 		 */
 		if (!pipe_buf_get(ipipe, ibuf)) {
 			if (ret == 0)
 				ret = -EFAULT;
 			break;
 		}

 		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;

 		pipe_buf_mark_unmergeable(obuf);

 		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;
 }