splice.c 39.6 KB
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/*
 * "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
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 * Jens to support splicing to files, network, direct splicing, etc and
 * fixing lots of bugs.
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 *
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 * Copyright (C) 2005-2006 Jens Axboe <axboe@kernel.dk>
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 * Copyright (C) 2005-2006 Linus Torvalds <torvalds@osdl.org>
 * Copyright (C) 2006 Ingo Molnar <mingo@elte.hu>
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 *
 */
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#include <linux/bvec.h>
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#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
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#include <linux/splice.h>
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#include <linux/memcontrol.h>
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#include <linux/mm_inline.h>
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#include <linux/swap.h>
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#include <linux/writeback.h>
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#include <linux/export.h>
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#include <linux/syscalls.h>
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#include <linux/uio.h>
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#include <linux/security.h>
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#include <linux/gfp.h>
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#include <linux/socket.h>
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#include <linux/compat.h>
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#include <linux/sched/signal.h>

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#include "internal.h"
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/*
 * 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.
 */
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static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
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				     struct pipe_buffer *buf)
{
	struct page *page = buf->page;
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	struct address_space *mapping;
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	lock_page(page);

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	mapping = page_mapping(page);
	if (mapping) {
		WARN_ON(!PageUptodate(page));
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		/*
		 * 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);
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		if (page_has_private(page) &&
		    !try_to_release_page(page, GFP_KERNEL))
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			goto out_unlock;
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		/*
		 * 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;
		}
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	}
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	/*
	 * Raced with truncate or failed to remove page from current
	 * address space, unlock and return failure.
	 */
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out_unlock:
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	unlock_page(page);
	return 1;
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}

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static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
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					struct pipe_buffer *buf)
{
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	put_page(buf->page);
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	buf->flags &= ~PIPE_BUF_FLAG_LRU;
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}

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/*
 * Check whether the contents of buf is OK to access. Since the content
 * is a page cache page, IO may be in flight.
 */
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static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
				       struct pipe_buffer *buf)
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{
	struct page *page = buf->page;
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	int err;
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	if (!PageUptodate(page)) {
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		lock_page(page);

		/*
		 * Page got truncated/unhashed. This will cause a 0-byte
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		 * splice, if this is the first page.
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		 */
		if (!page->mapping) {
			err = -ENODATA;
			goto error;
		}
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		/*
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		 * Uh oh, read-error from disk.
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		 */
		if (!PageUptodate(page)) {
			err = -EIO;
			goto error;
		}

		/*
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		 * Page is ok afterall, we are done.
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		 */
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		unlock_page(page);
	}

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	return 0;
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error:
	unlock_page(page);
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	return err;
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}

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const struct pipe_buf_operations page_cache_pipe_buf_ops = {
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	.can_merge = 0,
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	.confirm = page_cache_pipe_buf_confirm,
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	.release = page_cache_pipe_buf_release,
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	.steal = page_cache_pipe_buf_steal,
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	.get = generic_pipe_buf_get,
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};

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static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
				    struct pipe_buffer *buf)
{
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	if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
		return 1;

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	buf->flags |= PIPE_BUF_FLAG_LRU;
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	return generic_pipe_buf_steal(pipe, buf);
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}

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static const struct pipe_buf_operations user_page_pipe_buf_ops = {
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	.can_merge = 0,
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	.confirm = generic_pipe_buf_confirm,
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	.release = page_cache_pipe_buf_release,
	.steal = user_page_pipe_buf_steal,
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	.get = generic_pipe_buf_get,
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};

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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);
}

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/**
 * splice_to_pipe - fill passed data into a pipe
 * @pipe:	pipe to fill
 * @spd:	data to fill
 *
 * Description:
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 *    @spd contains a map of pages and len/offset tuples, along with
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 *    the struct pipe_buf_operations associated with these pages. This
 *    function will link that data to the pipe.
 *
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 */
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ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
		       struct splice_pipe_desc *spd)
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{
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	unsigned int spd_pages = spd->nr_pages;
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	int ret = 0, page_nr = 0;
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	if (!spd_pages)
		return 0;

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	if (unlikely(!pipe->readers)) {
		send_sig(SIGPIPE, current, 0);
		ret = -EPIPE;
		goto out;
	}
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	while (pipe->nrbufs < pipe->buffers) {
		int newbuf = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
		struct pipe_buffer *buf = pipe->bufs + newbuf;
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		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;
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		buf->flags = 0;
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		pipe->nrbufs++;
		page_nr++;
		ret += buf->len;
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		if (!--spd->nr_pages)
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			break;
	}

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	if (!ret)
		ret = -EAGAIN;
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out:
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	while (page_nr < spd_pages)
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		spd->spd_release(spd, page_nr++);
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	return ret;
}
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EXPORT_SYMBOL_GPL(splice_to_pipe);
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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;
	}
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	pipe_buf_release(pipe, buf);
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	return ret;
}
EXPORT_SYMBOL(add_to_pipe);

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/*
 * Check if we need to grow the arrays holding pages and partial page
 * descriptions.
 */
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int splice_grow_spd(const struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
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{
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	unsigned int buffers = READ_ONCE(pipe->buffers);
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	spd->nr_pages_max = buffers;
	if (buffers <= PIPE_DEF_BUFFERS)
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		return 0;

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	spd->pages = kmalloc_array(buffers, sizeof(struct page *), GFP_KERNEL);
	spd->partial = kmalloc_array(buffers, sizeof(struct partial_page),
				     GFP_KERNEL);
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	if (spd->pages && spd->partial)
		return 0;

	kfree(spd->pages);
	kfree(spd->partial);
	return -ENOMEM;
}

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void splice_shrink_spd(struct splice_pipe_desc *spd)
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{
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	if (spd->nr_pages_max <= PIPE_DEF_BUFFERS)
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		return;

	kfree(spd->pages);
	kfree(spd->partial);
}

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/**
 * generic_file_splice_read - splice data from file to a pipe
 * @in:		file to splice from
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 * @ppos:	position in @in
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 * @pipe:	pipe to splice to
 * @len:	number of bytes to splice
 * @flags:	splice modifier flags
 *
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 * Description:
 *    Will read pages from given file and fill them into a pipe. Can be
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 *    used as long as it has more or less sane ->read_iter().
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 *
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 */
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ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
				 struct pipe_inode_info *pipe, size_t len,
				 unsigned int flags)
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{
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	struct iov_iter to;
	struct kiocb kiocb;
	int idx, ret;
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	iov_iter_pipe(&to, ITER_PIPE | READ, pipe, len);
	idx = to.idx;
	init_sync_kiocb(&kiocb, in);
	kiocb.ki_pos = *ppos;
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	ret = call_read_iter(in, &kiocb, &to);
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	if (ret > 0) {
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		*ppos = kiocb.ki_pos;
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		file_accessed(in);
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	} else if (ret < 0) {
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		to.idx = idx;
		to.iov_offset = 0;
		iov_iter_advance(&to, 0); /* to free what was emitted */
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		/*
		 * callers of ->splice_read() expect -EAGAIN on
		 * "can't put anything in there", rather than -EFAULT.
		 */
		if (ret == -EFAULT)
			ret = -EAGAIN;
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	}
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	return ret;
}
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EXPORT_SYMBOL(generic_file_splice_read);

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const struct pipe_buf_operations default_pipe_buf_ops = {
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	.can_merge = 0,
	.confirm = generic_pipe_buf_confirm,
	.release = generic_pipe_buf_release,
	.steal = generic_pipe_buf_steal,
	.get = generic_pipe_buf_get,
};

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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);

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static ssize_t kernel_readv(struct file *file, const struct kvec *vec,
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			    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() */
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	res = vfs_readv(file, (const struct iovec __user *)vec, vlen, &pos, 0);
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	set_fs(old_fs);

	return res;
}

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static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
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				 struct pipe_inode_info *pipe, size_t len,
				 unsigned int flags)
{
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	struct kvec *vec, __vec[PIPE_DEF_BUFFERS];
	struct iov_iter to;
	struct page **pages;
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	unsigned int nr_pages;
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	size_t offset, base, copied = 0;
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	ssize_t res;
	int i;
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	if (pipe->nrbufs == pipe->buffers)
		return -EAGAIN;
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	/*
	 * Try to keep page boundaries matching to source pagecache ones -
	 * it probably won't be much help, but...
	 */
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	offset = *ppos & ~PAGE_MASK;
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	iov_iter_pipe(&to, ITER_PIPE | READ, pipe, len + offset);
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	res = iov_iter_get_pages_alloc(&to, &pages, len + offset, &base);
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	if (res <= 0)
		return -ENOMEM;
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	nr_pages = DIV_ROUND_UP(res + base, PAGE_SIZE);
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	vec = __vec;
	if (nr_pages > PIPE_DEF_BUFFERS) {
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		vec = kmalloc_array(nr_pages, sizeof(struct kvec), GFP_KERNEL);
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		if (unlikely(!vec)) {
			res = -ENOMEM;
			goto out;
		}
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	}
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	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;
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	}

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	res = kernel_readv(in, vec, nr_pages, *ppos);
	if (res > 0) {
		copied = res;
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		*ppos += res;
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	}
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	if (vec != __vec)
		kfree(vec);
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out:
	for (i = 0; i < nr_pages; i++)
		put_page(pages[i]);
	kvfree(pages);
	iov_iter_advance(&to, copied);	/* truncates and discards */
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	return res;
}

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/*
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 * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
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 * using sendpage(). Return the number of bytes sent.
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 */
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static int pipe_to_sendpage(struct pipe_inode_info *pipe,
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			    struct pipe_buffer *buf, struct splice_desc *sd)
{
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	struct file *file = sd->u.file;
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	loff_t pos = sd->pos;
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	int more;
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	if (!likely(file->f_op->sendpage))
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		return -EINVAL;

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	more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
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	if (sd->len < sd->total_len && pipe->nrbufs > 1)
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		more |= MSG_SENDPAGE_NOTLAST;
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	return file->f_op->sendpage(file, buf->page, buf->offset,
				    sd->len, &pos, more);
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}

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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);
}

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/**
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 * splice_from_pipe_feed - feed available data from a pipe to a file
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 * @pipe:	pipe to splice from
 * @sd:		information to @actor
 * @actor:	handler that splices the data
 *
 * Description:
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 *    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.
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 *
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 *    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.
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 */
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static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_desc *sd,
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			  splice_actor *actor)
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{
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	int ret;
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	while (pipe->nrbufs) {
		struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
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		sd->len = buf->len;
		if (sd->len > sd->total_len)
			sd->len = sd->total_len;
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		ret = pipe_buf_confirm(pipe, buf);
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		if (unlikely(ret)) {
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			if (ret == -ENODATA)
				ret = 0;
			return ret;
		}
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		ret = actor(pipe, buf, sd);
		if (ret <= 0)
			return ret;

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

		sd->num_spliced += ret;
		sd->len -= ret;
		sd->pos += ret;
		sd->total_len -= ret;

		if (!buf->len) {
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			pipe_buf_release(pipe, buf);
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			pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
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			pipe->nrbufs--;
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			if (pipe->files)
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				sd->need_wakeup = true;
		}
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		if (!sd->total_len)
			return 0;
	}
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	return 1;
}
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/**
 * 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.
 */
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static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
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{
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	/*
	 * Check for signal early to make process killable when there are
	 * always buffers available
	 */
	if (signal_pending(current))
		return -ERESTARTSYS;

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	while (!pipe->nrbufs) {
		if (!pipe->writers)
			return 0;
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		if (!pipe->waiting_writers && sd->num_spliced)
			return 0;
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		if (sd->flags & SPLICE_F_NONBLOCK)
			return -EAGAIN;
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		if (signal_pending(current))
			return -ERESTARTSYS;
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		if (sd->need_wakeup) {
			wakeup_pipe_writers(pipe);
			sd->need_wakeup = false;
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		}

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		pipe_wait(pipe);
	}
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	return 1;
}
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/**
 * splice_from_pipe_begin - start splicing from pipe
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 * @sd:		information about the splice operation
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 *
 * 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.
 */
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static void splice_from_pipe_begin(struct splice_desc *sd)
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{
	sd->num_spliced = 0;
	sd->need_wakeup = false;
}
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/**
 * 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().
 */
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static void splice_from_pipe_end(struct pipe_inode_info *pipe, struct splice_desc *sd)
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{
	if (sd->need_wakeup)
		wakeup_pipe_writers(pipe);
}
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/**
 * __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;
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	splice_from_pipe_begin(sd);
	do {
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		cond_resched();
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		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;
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}
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EXPORT_SYMBOL(__splice_from_pipe);
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/**
 * 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:
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 *    See __splice_from_pipe. This function locks the pipe inode,
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 *    otherwise it's identical to __splice_from_pipe().
 *
 */
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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;
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	struct splice_desc sd = {
		.total_len = len,
		.flags = flags,
		.pos = *ppos,
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		.u.file = out,
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	};
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	pipe_lock(pipe);
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	ret = __splice_from_pipe(pipe, &sd, actor);
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	pipe_unlock(pipe);
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	return ret;
}

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/**
 * 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;

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			ret = pipe_buf_confirm(pipe, buf);
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			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;
		}

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		iov_iter_bvec(&from, ITER_BVEC | WRITE, array, n,
			      sd.total_len - left);
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		ret = vfs_iter_write(out, &from, &sd.pos, 0);
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		if (ret <= 0)
			break;

		sd.num_spliced += ret;
		sd.total_len -= ret;
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		*ppos = sd.pos;
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		/* 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;
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				pipe_buf_release(pipe, buf);
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				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);

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static int write_pipe_buf(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
			  struct splice_desc *sd)
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{
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	int ret;
	void *data;
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	loff_t tmp = sd->pos;
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	data = kmap(buf->page);
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	ret = __kernel_write(sd->u.file, data + buf->offset, sd->len, &tmp);
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	kunmap(buf->page);
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	return ret;
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}

static ssize_t default_file_splice_write(struct pipe_inode_info *pipe,
					 struct file *out, loff_t *ppos,
					 size_t len, unsigned int flags)
{
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	ssize_t ret;
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	ret = splice_from_pipe(pipe, out, ppos, len, flags, write_pipe_buf);
	if (ret > 0)
		*ppos += ret;
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	return ret;
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}

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/**
 * generic_splice_sendpage - splice data from a pipe to a socket
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 * @pipe:	pipe to splice from
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 * @out:	socket to write to
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 * @ppos:	position in @out
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 * @len:	number of bytes to splice
 * @flags:	splice modifier flags
 *
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 * Description:
 *    Will send @len bytes from the pipe to a network socket. No data copying
 *    is involved.
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 *
 */
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ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
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				loff_t *ppos, size_t len, unsigned int flags)
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{
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	return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
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}

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EXPORT_SYMBOL(generic_splice_sendpage);
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/*
 * Attempt to initiate a splice from pipe to file.
 */
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static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
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			   loff_t *ppos, size_t len, unsigned int flags)
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{
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	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *,
				loff_t *, size_t, unsigned int);
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	if (out->f_op->splice_write)
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		splice_write = out->f_op->splice_write;
	else
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		splice_write = default_file_splice_write;

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	return splice_write(pipe, out, ppos, len, flags);
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}

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/*
 * Attempt to initiate a splice from a file to a pipe.
 */
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static long do_splice_to(struct file *in, loff_t *ppos,
			 struct pipe_inode_info *pipe, size_t len,
			 unsigned int flags)
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{
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	ssize_t (*splice_read)(struct file *, loff_t *,
			       struct pipe_inode_info *, size_t, unsigned int);
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	int ret;

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	if (unlikely(!(in->f_mode & FMODE_READ)))
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		return -EBADF;

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	ret = rw_verify_area(READ, in, ppos, len);
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	if (unlikely(ret < 0))
		return ret;

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	if (unlikely(len > MAX_RW_COUNT))
		len = MAX_RW_COUNT;

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	if (in->f_op->splice_read)
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		splice_read = in->f_op->splice_read;
	else
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		splice_read = default_file_splice_read;

	return splice_read(in, ppos, pipe, len, flags);
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}

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/**
 * 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
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 *    pipe is cached in the process, and reused during the lifetime of
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 *    that process.
 *
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 */
ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
			       splice_direct_actor *actor)
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{
	struct pipe_inode_info *pipe;
	long ret, bytes;
	umode_t i_mode;
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	size_t len;
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	int i, flags, more;
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	/*
	 * 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!
	 */
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	i_mode = file_inode(in)->i_mode;
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	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;
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	if (unlikely(!pipe)) {
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		pipe = alloc_pipe_info();
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		if (!pipe)
			return -ENOMEM;

		/*
		 * We don't have an immediate reader, but we'll read the stuff
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		 * out of the pipe right after the splice_to_pipe(). So set
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		 * PIPE_READERS appropriately.
		 */
		pipe->readers = 1;

		current->splice_pipe = pipe;
	}

	/*
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	 * Do the splice.
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	 */
	ret = 0;
	bytes = 0;
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	len = sd->total_len;
	flags = sd->flags;

	/*
	 * Don't block on output, we have to drain the direct pipe.
	 */
	sd->flags &= ~SPLICE_F_NONBLOCK;
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	more = sd->flags & SPLICE_F_MORE;
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	while (len) {
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		size_t read_len;
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		loff_t pos = sd->pos, prev_pos = pos;
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		ret = do_splice_to(in, &pos, pipe, len, flags);
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		if (unlikely(ret <= 0))
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			goto out_release;

		read_len = ret;
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		sd->total_len = read_len;
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		/*
		 * 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;
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		/*
		 * 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:
		 */
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		ret = actor(pipe, sd);
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		if (unlikely(ret <= 0)) {
			sd->pos = prev_pos;
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			goto out_release;
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		}
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		bytes += ret;
		len -= ret;
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		sd->pos = pos;
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		if (ret < read_len) {
			sd->pos = prev_pos + ret;
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			goto out_release;
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		}
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	}

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done:
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	pipe->nrbufs = pipe->curbuf = 0;
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	file_accessed(in);
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	return bytes;

out_release:
	/*
	 * If we did an incomplete transfer we must release
	 * the pipe buffers in question:
	 */
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	for (i = 0; i < pipe->buffers; i++) {
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		struct pipe_buffer *buf = pipe->bufs + i;

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		if (buf->ops)
			pipe_buf_release(pipe, buf);
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	}

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	if (!bytes)
		bytes = ret;
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	goto done;
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}
EXPORT_SYMBOL(splice_direct_to_actor);

static int direct_splice_actor(struct pipe_inode_info *pipe,
			       struct splice_desc *sd)
{
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	struct file *file = sd->u.file;
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	return do_splice_from(pipe, file, sd->opos, sd->total_len,
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			      sd->flags);
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}

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/**
 * do_splice_direct - splices data directly between two files
 * @in:		file to splice from
 * @ppos:	input file offset
 * @out:	file to splice to
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 * @opos:	output file offset
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 * @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.
 *
 */
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long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
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		      loff_t *opos, size_t len, unsigned int flags)
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{
	struct splice_desc sd = {
		.len		= len,
		.total_len	= len,
		.flags		= flags,
		.pos		= *ppos,
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		.u.file		= out,
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		.opos		= opos,
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	};
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	long ret;
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	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;

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	ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
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	if (ret > 0)
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		*ppos = sd.pos;
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	return ret;
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}
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EXPORT_SYMBOL(do_splice_direct);
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static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
{
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	for (;;) {
		if (unlikely(!pipe->readers)) {
			send_sig(SIGPIPE, current, 0);
			return -EPIPE;
		}
		if (pipe->nrbufs != pipe->buffers)
			return 0;
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		if (flags & SPLICE_F_NONBLOCK)
			return -EAGAIN;
		if (signal_pending(current))
			return -ERESTARTSYS;
		pipe->waiting_writers++;
		pipe_wait(pipe);
		pipe->waiting_writers--;
	}
}

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static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
			       struct pipe_inode_info *opipe,
			       size_t len, unsigned int flags);
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/*
 * Determine where to splice to/from.
 */
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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)
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{
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	struct pipe_inode_info *ipipe;
	struct pipe_inode_info *opipe;
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	loff_t offset;
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	long ret;
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	ipipe = get_pipe_info(in);
	opipe = get_pipe_info(out);
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	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) {
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		if (off_in)
			return -ESPIPE;
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		if (off_out) {
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			if (!(out->f_mode & FMODE_PWRITE))
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				return -EINVAL;
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			if (copy_from_user(&offset, off_out, sizeof(loff_t)))
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				return -EFAULT;
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		} else {
			offset = out->f_pos;
		}
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		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;

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		file_start_write(out);
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		ret = do_splice_from(ipipe, out, &offset, len, flags);
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		file_end_write(out);