Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1745 insertions, 0 deletions

diff --git a/fs/splice.c b/fs/splice.c
new file mode 100644
index 000000000..d0230cf8e
--- /dev/null
+++ b/fs/splice.c
@@ -0,0 +1,1745 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * "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/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 bool page_cache_pipe_buf_try_steal(struct pipe_inode_info *pipe,
+		struct pipe_buffer *buf)
+{
+	struct folio *folio = page_folio(buf->page);
+	struct address_space *mapping;
+
+	folio_lock(folio);
+
+	mapping = folio_mapping(folio);
+	if (mapping) {
+		WARN_ON(!folio_test_uptodate(folio));
+
+		/*
+		 * At least for ext2 with nobh option, we need to wait on
+		 * writeback completing on this folio, since we'll remove it
+		 * from the pagecache.  Otherwise truncate wont wait on the
+		 * folio, allowing the disk blocks to be reused by someone else
+		 * before we actually wrote our data to them. fs corruption
+		 * ensues.
+		 */
+		folio_wait_writeback(folio);
+
+		if (!filemap_release_folio(folio, GFP_KERNEL))
+			goto out_unlock;
+
+		/*
+		 * If we succeeded in removing the mapping, set LRU flag
+		 * and return good.
+		 */
+		if (remove_mapping(mapping, folio)) {
+			buf->flags |= PIPE_BUF_FLAG_LRU;
+			return true;
+		}
+	}
+
+	/*
+	 * Raced with truncate or failed to remove folio from current
+	 * address space, unlock and return failure.
+	 */
+out_unlock:
+	folio_unlock(folio);
+	return false;
+}
+
+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 = {
+	.confirm	= page_cache_pipe_buf_confirm,
+	.release	= page_cache_pipe_buf_release,
+	.try_steal	= page_cache_pipe_buf_try_steal,
+	.get		= generic_pipe_buf_get,
+};
+
+static bool user_page_pipe_buf_try_steal(struct pipe_inode_info *pipe,
+		struct pipe_buffer *buf)
+{
+	if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
+		return false;
+
+	buf->flags |= PIPE_BUF_FLAG_LRU;
+	return generic_pipe_buf_try_steal(pipe, buf);
+}
+
+static const struct pipe_buf_operations user_page_pipe_buf_ops = {
+	.release	= page_cache_pipe_buf_release,
+	.try_steal	= user_page_pipe_buf_try_steal,
+	.get		= generic_pipe_buf_get,
+};
+
+static void wakeup_pipe_readers(struct pipe_inode_info *pipe)
+{
+	smp_mb();
+	if (waitqueue_active(&pipe->rd_wait))
+		wake_up_interruptible(&pipe->rd_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;
+	unsigned int tail = pipe->tail;
+	unsigned int head = pipe->head;
+	unsigned int mask = pipe->ring_size - 1;
+	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_full(head, tail, pipe->max_usage)) {
+		struct pipe_buffer *buf = &pipe->bufs[head & mask];
+
+		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;
+
+		head++;
+		pipe->head = head;
+		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)
+{
+	unsigned int head = pipe->head;
+	unsigned int tail = pipe->tail;
+	unsigned int mask = pipe->ring_size - 1;
+	int ret;
+
+	if (unlikely(!pipe->readers)) {
+		send_sig(SIGPIPE, current, 0);
+		ret = -EPIPE;
+	} else if (pipe_full(head, tail, pipe->max_usage)) {
+		ret = -EAGAIN;
+	} else {
+		pipe->bufs[head & mask] = *buf;
+		pipe->head = head + 1;
+		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 max_usage = READ_ONCE(pipe->max_usage);
+
+	spd->nr_pages_max = max_usage;
+	if (max_usage <= PIPE_DEF_BUFFERS)
+		return 0;
+
+	spd->pages = kmalloc_array(max_usage, sizeof(struct page *), GFP_KERNEL);
+	spd->partial = kmalloc_array(max_usage, 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 ret;
+
+	iov_iter_pipe(&to, ITER_DEST, pipe, len);
+	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) {
+		/* free what was emitted */
+		pipe_discard_from(pipe, to.start_head);
+		/*
+		 * 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 = {
+	.release	= generic_pipe_buf_release,
+	.try_steal	= generic_pipe_buf_try_steal,
+	.get		= generic_pipe_buf_get,
+};
+
+/* Pipe buffer operations for a socket and similar. */
+const struct pipe_buf_operations nosteal_pipe_buf_ops = {
+	.release	= generic_pipe_buf_release,
+	.get		= generic_pipe_buf_get,
+};
+EXPORT_SYMBOL(nosteal_pipe_buf_ops);
+
+/*
+ * 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_occupancy(pipe->head, pipe->tail) > 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->wr_wait))
+		wake_up_interruptible(&pipe->wr_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)
+{
+	unsigned int head = pipe->head;
+	unsigned int tail = pipe->tail;
+	unsigned int mask = pipe->ring_size - 1;
+	int ret;
+
+	while (!pipe_empty(head, tail)) {
+		struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+
+		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);
+			tail++;
+			pipe->tail = tail;
+			if (pipe->files)
+				sd->need_wakeup = true;
+		}
+
+		if (!sd->total_len)
+			return 0;
+	}
+
+	return 1;
+}
+
+/* We know we have a pipe buffer, but maybe it's empty? */
+static inline bool eat_empty_buffer(struct pipe_inode_info *pipe)
+{
+	unsigned int tail = pipe->tail;
+	unsigned int mask = pipe->ring_size - 1;
+	struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+
+	if (unlikely(!buf->len)) {
+		pipe_buf_release(pipe, buf);
+		pipe->tail = tail+1;
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * 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;
+
+repeat:
+	while (pipe_empty(pipe->head, pipe->tail)) {
+		if (!pipe->writers)
+			return 0;
+
+		if (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_readable(pipe);
+	}
+
+	if (eat_empty_buffer(pipe))
+		goto repeat;
+
+	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->max_usage;
+	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;
+		unsigned int head, tail, mask;
+		size_t left;
+		int n;
+
+		ret = splice_from_pipe_next(pipe, &sd);
+		if (ret <= 0)
+			break;
+
+		if (unlikely(nbufs < pipe->max_usage)) {
+			kfree(array);
+			nbufs = pipe->max_usage;
+			array = kcalloc(nbufs, sizeof(struct bio_vec),
+					GFP_KERNEL);
+			if (!array) {
+				ret = -ENOMEM;
+				break;
+			}
+		}
+
+		head = pipe->head;
+		tail = pipe->tail;
+		mask = pipe->ring_size - 1;
+
+		/* build the vector */
+		left = sd.total_len;
+		for (n = 0; !pipe_empty(head, tail) && left && n < nbufs; tail++) {
+			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+			size_t this_len = buf->len;
+
+			/* zero-length bvecs are not supported, skip them */
+			if (!this_len)
+				continue;
+			this_len = min(this_len, left);
+
+			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;
+			n++;
+		}
+
+		iov_iter_bvec(&from, ITER_SOURCE, 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 */
+		tail = pipe->tail;
+		while (ret) {
+			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+			if (ret >= buf->len) {
+				ret -= buf->len;
+				buf->len = 0;
+				pipe_buf_release(pipe, buf);
+				tail++;
+				pipe->tail = tail;
+				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);
+
+/**
+ * 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);
+
+static int warn_unsupported(struct file *file, const char *op)
+{
+	pr_debug_ratelimited(
+		"splice %s not supported for file %pD4 (pid: %d comm: %.20s)\n",
+		op, file, current->pid, current->comm);
+	return -EINVAL;
+}
+
+/*
+ * 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)
+{
+	if (unlikely(!out->f_op->splice_write))
+		return warn_unsupported(out, "write");
+	return out->f_op->splice_write(pipe, out, ppos, len, flags);
+}
+
+/*
+ * Indicate to the caller that there was a premature EOF when reading from the
+ * source and the caller didn't indicate they would be sending more data after
+ * this.
+ */
+static void do_splice_eof(struct splice_desc *sd)
+{
+	if (sd->splice_eof)
+		sd->splice_eof(sd);
+}
+
+/*
+ * 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)
+{
+	unsigned int p_space;
+	int ret;
+
+	if (unlikely(!(in->f_mode & FMODE_READ)))
+		return -EBADF;
+
+	/* Don't try to read more the pipe has space for. */
+	p_space = pipe->max_usage - pipe_occupancy(pipe->head, pipe->tail);
+	len = min_t(size_t, len, p_space << PAGE_SHIFT);
+
+	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 (unlikely(!in->f_op->splice_read))
+		return warn_unsupported(in, "read");
+	return in->f_op->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;
+	size_t len;
+	int i, flags, more;
+
+	/*
+	 * We require the input to be seekable, as we don't want to randomly
+	 * drop data for eg socket -> socket splicing. Use the piped splicing
+	 * for that!
+	 */
+	if (unlikely(!(in->f_mode & FMODE_LSEEK)))
+		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;
+
+	WARN_ON_ONCE(!pipe_empty(pipe->head, pipe->tail));
+
+	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 read_failure;
+
+		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->tail = pipe->head = 0;
+	file_accessed(in);
+	return bytes;
+
+read_failure:
+	/*
+	 * If the user did *not* set SPLICE_F_MORE *and* we didn't hit that
+	 * "use all of len" case that cleared SPLICE_F_MORE, *and* we did a
+	 * "->splice_in()" that returned EOF (ie zero) *and* we have sent at
+	 * least 1 byte *then* we will also do the ->splice_eof() call.
+	 */
+	if (ret == 0 && !more && len > 0 && bytes)
+		do_splice_eof(sd);
+out_release:
+	/*
+	 * If we did an incomplete transfer we must release
+	 * the pipe buffers in question:
+	 */
+	for (i = 0; i < pipe->ring_size; 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);
+}
+
+static void direct_file_splice_eof(struct splice_desc *sd)
+{
+	struct file *file = sd->u.file;
+
+	if (file->f_op->splice_eof)
+		file->f_op->splice_eof(file);
+}
+
+/**
+ * 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,
+		.splice_eof	= direct_file_splice_eof,
+		.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_full(pipe->head, pipe->tail, pipe->max_usage))
+			return 0;
+		if (flags & SPLICE_F_NONBLOCK)
+			return -EAGAIN;
+		if (signal_pending(current))
+			return -ERESTARTSYS;
+		pipe_wait_writable(pipe);
+	}
+}
+
+static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
+			       struct pipe_inode_info *opipe,
+			       size_t len, unsigned int flags);
+
+long splice_file_to_pipe(struct file *in,
+			 struct pipe_inode_info *opipe,
+			 loff_t *offset,
+			 size_t len, unsigned int flags)
+{
+	long ret;
+
+	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);
+	return ret;
+}
+
+/*
+ * Determine where to splice to/from.
+ */
+long do_splice(struct file *in, loff_t *off_in, struct file *out,
+	       loff_t *off_out, size_t len, unsigned int flags)
+{
+	struct pipe_inode_info *ipipe;
+	struct pipe_inode_info *opipe;
+	loff_t offset;
+	long ret;
+
+	if (unlikely(!(in->f_mode & FMODE_READ) ||
+		     !(out->f_mode & FMODE_WRITE)))
+		return -EBADF;
+
+	ipipe = get_pipe_info(in, true);
+	opipe = get_pipe_info(out, true);
+
+	if (ipipe && opipe) {
+		if (off_in || off_out)
+			return -ESPIPE;
+
+		/* Splicing to self would be fun, but... */
+		if (ipipe == opipe)
+			return -EINVAL;
+
+		if ((in->f_flags | out->f_flags) & O_NONBLOCK)
+			flags |= SPLICE_F_NONBLOCK;
+
+		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;
+			offset = *off_out;
+		} else {
+			offset = out->f_pos;
+		}
+
+		if (unlikely(out->f_flags & O_APPEND))
+			return -EINVAL;
+
+		ret = rw_verify_area(WRITE, out, &offset, len);
+		if (unlikely(ret < 0))
+			return ret;
+
+		if (in->f_flags & O_NONBLOCK)
+			flags |= SPLICE_F_NONBLOCK;
+
+		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
+			*off_out = offset;
+
+		return ret;
+	}
+
+	if (opipe) {
+		if (off_out)
+			return -ESPIPE;
+		if (off_in) {
+			if (!(in->f_mode & FMODE_PREAD))
+				return -EINVAL;
+			offset = *off_in;
+		} else {
+			offset = in->f_pos;
+		}
+
+		if (out->f_flags & O_NONBLOCK)
+			flags |= SPLICE_F_NONBLOCK;
+
+		ret = splice_file_to_pipe(in, opipe, &offset, len, flags);
+		if (!off_in)
+			in->f_pos = offset;
+		else
+			*off_in = offset;
+
+		return ret;
+	}
+
+	return -EINVAL;
+}
+
+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, *__off_in = NULL, *__off_out = NULL;
+	long ret;
+
+	ipipe = get_pipe_info(in, true);
+	opipe = get_pipe_info(out, true);
+
+	if (ipipe && off_in)
+		return -ESPIPE;
+	if (opipe && off_out)
+		return -ESPIPE;
+
+	if (off_out) {
+		if (copy_from_user(&offset, off_out, sizeof(loff_t)))
+			return -EFAULT;
+		__off_out = &offset;
+	}
+	if (off_in) {
+		if (copy_from_user(&offset, off_in, sizeof(loff_t)))
+			return -EFAULT;
+		__off_in = &offset;
+	}
+
+	ret = do_splice(in, __off_in, out, __off_out, len, flags);
+	if (ret < 0)
+		return ret;
+
+	if (__off_out && copy_to_user(off_out, __off_out, sizeof(loff_t)))
+		return -EFAULT;
+	if (__off_in && copy_to_user(off_in, __off_in, sizeof(loff_t)))
+		return -EFAULT;
+
+	return ret;
+}
+
+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;
+
+	while (iov_iter_count(from)) {
+		struct page *pages[16];
+		ssize_t left;
+		size_t start;
+		int i, n;
+
+		left = iov_iter_get_pages2(from, pages, ~0UL, 16, &start);
+		if (left <= 0) {
+			ret = left;
+			break;
+		}
+
+		n = DIV_ROUND_UP(left + start, PAGE_SIZE);
+		for (i = 0; i < n; i++) {
+			int size = min_t(int, left, PAGE_SIZE - start);
+
+			buf.page = pages[i];
+			buf.offset = start;
+			buf.len = size;
+			ret = add_to_pipe(pipe, &buf);
+			if (unlikely(ret < 0)) {
+				iov_iter_revert(from, left);
+				// this one got dropped by add_to_pipe()
+				while (++i < n)
+					put_page(pages[i]);
+				goto out;
+			}
+			total += ret;
+			left -= size;
+			start = 0;
+		}
+	}
+out:
+	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, true);
+	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, true);
+	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 = ITER_SOURCE;
+	} else if (f.file->f_mode & FMODE_READ) {
+		*type = ITER_DEST;
+	} 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().
+ *
+ */
+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;
+	ssize_t error;
+	struct fd f;
+	int type;
+
+	if (unlikely(flags & ~SPLICE_F_ALL))
+		return -EINVAL;
+
+	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 < 0)
+		goto out_fdput;
+
+	if (!iov_iter_count(&iter))
+		error = 0;
+	else if (type == ITER_SOURCE)
+		error = vmsplice_to_pipe(f.file, &iter, flags);
+	else
+		error = vmsplice_to_user(f.file, &iter, flags);
+
+	kfree(iov);
+out_fdput:
+	fdput(f);
+	return error;
+}
+
+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) {
+		out = fdget(fd_out);
+		if (out.file) {
+			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 the pipe occupancy without the inode lock first. This function
+	 * is speculative anyways, so missing one is ok.
+	 */
+	if (!pipe_empty(pipe->head, pipe->tail))
+		return 0;
+
+	ret = 0;
+	pipe_lock(pipe);
+
+	while (pipe_empty(pipe->head, pipe->tail)) {
+		if (signal_pending(current)) {
+			ret = -ERESTARTSYS;
+			break;
+		}
+		if (!pipe->writers)
+			break;
+		if (flags & SPLICE_F_NONBLOCK) {
+			ret = -EAGAIN;
+			break;
+		}
+		pipe_wait_readable(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 pipe occupancy without the inode lock first. This function
+	 * is speculative anyways, so missing one is ok.
+	 */
+	if (!pipe_full(pipe->head, pipe->tail, pipe->max_usage))
+		return 0;
+
+	ret = 0;
+	pipe_lock(pipe);
+
+	while (pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
+		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_wait_writable(pipe);
+	}
+
+	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;
+	unsigned int i_head, o_head;
+	unsigned int i_tail, o_tail;
+	unsigned int i_mask, o_mask;
+	int ret = 0;
+	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);
+
+	i_tail = ipipe->tail;
+	i_mask = ipipe->ring_size - 1;
+	o_head = opipe->head;
+	o_mask = opipe->ring_size - 1;
+
+	do {
+		size_t o_len;
+
+		if (!opipe->readers) {
+			send_sig(SIGPIPE, current, 0);
+			if (!ret)
+				ret = -EPIPE;
+			break;
+		}
+
+		i_head = ipipe->head;
+		o_tail = opipe->tail;
+
+		if (pipe_empty(i_head, i_tail) && !ipipe->writers)
+			break;
+
+		/*
+		 * Cannot make any progress, because either the input
+		 * pipe is empty or the output pipe is full.
+		 */
+		if (pipe_empty(i_head, i_tail) ||
+		    pipe_full(o_head, o_tail, opipe->max_usage)) {
+			/* 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[i_tail & i_mask];
+		obuf = &opipe->bufs[o_head & o_mask];
+
+		if (len >= ibuf->len) {
+			/*
+			 * Simply move the whole buffer from ipipe to opipe
+			 */
+			*obuf = *ibuf;
+			ibuf->ops = NULL;
+			i_tail++;
+			ipipe->tail = i_tail;
+			input_wakeup = true;
+			o_len = obuf->len;
+			o_head++;
+			opipe->head = o_head;
+		} 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 and merge flags, we need to
+			 * prevent multiple steals of this page.
+			 */
+			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
+			obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;
+
+			obuf->len = len;
+			ibuf->offset += len;
+			ibuf->len -= len;
+			o_len = len;
+			o_head++;
+			opipe->head = o_head;
+		}
+		ret += o_len;
+		len -= o_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;
+	unsigned int i_head, o_head;
+	unsigned int i_tail, o_tail;
+	unsigned int i_mask, o_mask;
+	int ret = 0;
+
+	/*
+	 * 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);
+
+	i_tail = ipipe->tail;
+	i_mask = ipipe->ring_size - 1;
+	o_head = opipe->head;
+	o_mask = opipe->ring_size - 1;
+
+	do {
+		if (!opipe->readers) {
+			send_sig(SIGPIPE, current, 0);
+			if (!ret)
+				ret = -EPIPE;
+			break;
+		}
+
+		i_head = ipipe->head;
+		o_tail = opipe->tail;
+
+		/*
+		 * If we have iterated all input buffers or run out of
+		 * output room, break.
+		 */
+		if (pipe_empty(i_head, i_tail) ||
+		    pipe_full(o_head, o_tail, opipe->max_usage))
+			break;
+
+		ibuf = &ipipe->bufs[i_tail & i_mask];
+		obuf = &opipe->bufs[o_head & o_mask];
+
+		/*
+		 * 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 and merge flag, we need to prevent
+		 * multiple steals of this page.
+		 */
+		obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
+		obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;
+
+		if (obuf->len > len)
+			obuf->len = len;
+		ret += obuf->len;
+		len -= obuf->len;
+
+		o_head++;
+		opipe->head = o_head;
+		i_tail++;
+	} 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);
+
+	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.
+ */
+long do_tee(struct file *in, struct file *out, size_t len, unsigned int flags)
+{
+	struct pipe_inode_info *ipipe = get_pipe_info(in, true);
+	struct pipe_inode_info *opipe = get_pipe_info(out, true);
+	int ret = -EINVAL;
+
+	if (unlikely(!(in->f_mode & FMODE_READ) ||
+		     !(out->f_mode & FMODE_WRITE)))
+		return -EBADF;
+
+	/*
+	 * Duplicate the contents of ipipe to opipe without actually
+	 * copying the data.
+	 */
+	if (ipipe && opipe && ipipe != opipe) {
+		if ((in->f_flags | out->f_flags) & O_NONBLOCK)
+			flags |= SPLICE_F_NONBLOCK;
+
+		/*
+		 * 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, out;
+	int error;
+
+	if (unlikely(flags & ~SPLICE_F_ALL))
+		return -EINVAL;
+
+	if (unlikely(!len))
+		return 0;
+
+	error = -EBADF;
+	in = fdget(fdin);
+	if (in.file) {
+		out = fdget(fdout);
+		if (out.file) {
+			error = do_tee(in.file, out.file, len, flags);
+			fdput(out);
+		}
+ 		fdput(in);
+ 	}
+
+	return error;
+}