Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / fs / splice.c

/*
 * "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@suse.de>
 * Copyright (C) 2005-2006 Linus Torvalds <torvalds@osdl.org>
 * Copyright (C) 2006 Ingo Molnar <mingo@elte.hu>
 *
 */
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/pipe_fs_i.h>
#include <linux/mm_inline.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h>
#include <linux/module.h>
#include <linux/syscalls.h>

/*
 * Passed to the actors
 */
struct splice_desc {
        unsigned int len, total_len;    /* current and remaining length */
        unsigned int flags;             /* splice flags */
        struct file *file;              /* file to read/write */
        loff_t pos;                     /* file position */
};

/*
 * 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 *info,
                                     struct pipe_buffer *buf)
{
        struct page *page = buf->page;
        struct address_space *mapping = page_mapping(page);

        lock_page(page);

        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 (PagePrivate(page))
                try_to_release_page(page, mapping_gfp_mask(mapping));

        if (!remove_mapping(mapping, page)) {
                unlock_page(page);
                return 1;
        }

        buf->flags |= PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU;
        return 0;
}

static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
                                        struct pipe_buffer *buf)
{
        page_cache_release(buf->page);
        buf->page = NULL;
        buf->flags &= ~(PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU);
}

static void *page_cache_pipe_buf_map(struct file *file,
                                     struct pipe_inode_info *info,
                                     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, fall through to mapping.
                 */
                unlock_page(page);
        }

        return kmap(page);
error:
        unlock_page(page);
        return ERR_PTR(err);
}

static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
                                      struct pipe_buffer *buf)
{
        kunmap(buf->page);
}

static void page_cache_pipe_buf_get(struct pipe_inode_info *info,
                                    struct pipe_buffer *buf)
{
        page_cache_get(buf->page);
}

static struct pipe_buf_operations page_cache_pipe_buf_ops = {
        .can_merge = 0,
        .map = page_cache_pipe_buf_map,
        .unmap = page_cache_pipe_buf_unmap,
        .release = page_cache_pipe_buf_release,
        .steal = page_cache_pipe_buf_steal,
        .get = page_cache_pipe_buf_get,
};

/*
 * Pipe output worker. This sets up our pipe format with the page cache
 * pipe buffer operations. Otherwise very similar to the regular pipe_writev().
 */
static ssize_t move_to_pipe(struct pipe_inode_info *pipe, struct page **pages,
                            int nr_pages, unsigned long len,
                            unsigned int offset, unsigned int flags)
{
        int ret, do_wakeup, i;

        ret = 0;
        do_wakeup = 0;
        i = 0;

        if (pipe->inode)
                mutex_lock(&pipe->inode->i_mutex);

        for (;;) {
                if (!pipe->readers) {
                        send_sig(SIGPIPE, current, 0);
                        if (!ret)
                                ret = -EPIPE;
                        break;
                }

                if (pipe->nrbufs < PIPE_BUFFERS) {
                        int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
                        struct pipe_buffer *buf = pipe->bufs + newbuf;
                        struct page *page = pages[i++];
                        unsigned long this_len;

                        this_len = PAGE_CACHE_SIZE - offset;
                        if (this_len > len)
                                this_len = len;

                        buf->page = page;
                        buf->offset = offset;
                        buf->len = this_len;
                        buf->ops = &page_cache_pipe_buf_ops;
                        pipe->nrbufs++;
                        if (pipe->inode)
                                do_wakeup = 1;

                        ret += this_len;
                        len -= this_len;
                        offset = 0;
                        if (!--nr_pages)
                                break;
                        if (!len)
                                break;
                        if (pipe->nrbufs < PIPE_BUFFERS)
                                continue;

                        break;
                }

                if (flags & SPLICE_F_NONBLOCK) {
                        if (!ret)
                                ret = -EAGAIN;
                        break;
                }

                if (signal_pending(current)) {
                        if (!ret)
                                ret = -ERESTARTSYS;
                        break;
                }

                if (do_wakeup) {
                        smp_mb();
                        if (waitqueue_active(&pipe->wait))
                                wake_up_interruptible_sync(&pipe->wait);
                        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                        do_wakeup = 0;
                }

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

        if (pipe->inode)
                mutex_unlock(&pipe->inode->i_mutex);

        if (do_wakeup) {
                smp_mb();
                if (waitqueue_active(&pipe->wait))
                        wake_up_interruptible(&pipe->wait);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
        }

        while (i < nr_pages)
                page_cache_release(pages[i++]);

        return ret;
}

static int
__generic_file_splice_read(struct file *in, loff_t *ppos,
                           struct pipe_inode_info *pipe, size_t len,
                           unsigned int flags)
{
        struct address_space *mapping = in->f_mapping;
        unsigned int loff, offset, nr_pages;
        struct page *pages[PIPE_BUFFERS];
        struct page *page;
        pgoff_t index, end_index;
        loff_t isize;
        size_t bytes;
        int i, error;

        index = *ppos >> PAGE_CACHE_SHIFT;
        loff = offset = *ppos & ~PAGE_CACHE_MASK;
        nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

        if (nr_pages > PIPE_BUFFERS)
                nr_pages = PIPE_BUFFERS;

        /*
         * Initiate read-ahead on this page range. however, don't call into
         * read-ahead if this is a non-zero offset (we are likely doing small
         * chunk splice and the page is already there) for a single page.
         */
        if (!offset || nr_pages > 1)
                do_page_cache_readahead(mapping, in, index, nr_pages);

        /*
         * Now fill in the holes:
         */
        error = 0;
        bytes = 0;
        for (i = 0; i < nr_pages; i++, index++) {
                unsigned int this_len;

                if (!len)
                        break;

                /*
                 * this_len is the max we'll use from this page
                 */
                this_len = min(len, PAGE_CACHE_SIZE - loff);
find_page:
                /*
                 * lookup the page for this index
                 */
                page = find_get_page(mapping, index);
                if (!page) {
                        /*
                         * page didn't exist, allocate one
                         */
                        page = page_cache_alloc_cold(mapping);
                        if (!page)
                                break;

                        error = add_to_page_cache_lru(page, mapping, index,
                                                mapping_gfp_mask(mapping));
                        if (unlikely(error)) {
                                page_cache_release(page);
                                break;
                        }

                        goto readpage;
                }

                /*
                 * If the page isn't uptodate, we may need to start io on it
                 */
                if (!PageUptodate(page)) {
                        /*
                         * If in nonblock mode then dont block on waiting
                         * for an in-flight io page
                         */
                        if (flags & SPLICE_F_NONBLOCK)
                                break;

                        lock_page(page);

                        /*
                         * page was truncated, stop here. if this isn't the
                         * first page, we'll just complete what we already
                         * added
                         */
                        if (!page->mapping) {
                                unlock_page(page);
                                page_cache_release(page);
                                break;
                        }
                        /*
                         * page was already under io and is now done, great
                         */
                        if (PageUptodate(page)) {
                                unlock_page(page);
                                goto fill_it;
                        }

readpage:
                        /*
                         * need to read in the page
                         */
                        error = mapping->a_ops->readpage(in, page);

                        if (unlikely(error)) {
                                page_cache_release(page);
                                if (error == AOP_TRUNCATED_PAGE)
                                        goto find_page;
                                break;
                        }

                        /*
                         * i_size must be checked after ->readpage().
                         */
                        isize = i_size_read(mapping->host);
                        end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
                        if (unlikely(!isize || index > end_index)) {
                                page_cache_release(page);
                                break;
                        }

                        /*
                         * if this is the last page, see if we need to shrink
                         * the length and stop
                         */
                        if (end_index == index) {
                                loff = PAGE_CACHE_SIZE - (isize & ~PAGE_CACHE_MASK);
                                if (bytes + loff > isize) {
                                        page_cache_release(page);
                                        break;
                                }
                                /*
                                 * force quit after adding this page
                                 */
                                nr_pages = i;
                                this_len = min(this_len, loff);
                        }
                }
fill_it:
                pages[i] = page;
                bytes += this_len;
                len -= this_len;
                loff = 0;
        }

        if (i)
                return move_to_pipe(pipe, pages, i, bytes, offset, flags);

        return error;
}

/**
 * generic_file_splice_read - splice data from file to a pipe
 * @in:         file to splice from
 * @pipe:       pipe to splice to
 * @len:        number of bytes to splice
 * @flags:      splice modifier flags
 *
 * Will read pages from given file and fill them into a pipe.
 */
ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
                                 struct pipe_inode_info *pipe, size_t len,
                                 unsigned int flags)
{
        ssize_t spliced;
        int ret;

        ret = 0;
        spliced = 0;

        while (len) {
                ret = __generic_file_splice_read(in, ppos, pipe, len, flags);

                if (ret < 0)
                        break;
                else if (!ret) {
                        if (spliced)
                                break;
                        if (flags & SPLICE_F_NONBLOCK) {
                                ret = -EAGAIN;
                                break;
                        }
                }

                *ppos += ret;
                len -= ret;
                spliced += ret;
        }

        if (spliced)
                return spliced;

        return ret;
}

EXPORT_SYMBOL(generic_file_splice_read);

/*
 * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
 * using sendpage().
 */
static int pipe_to_sendpage(struct pipe_inode_info *info,
                            struct pipe_buffer *buf, struct splice_desc *sd)
{
        struct file *file = sd->file;
        loff_t pos = sd->pos;
        unsigned int offset;
        ssize_t ret;
        void *ptr;
        int more;

        /*
         * Sub-optimal, but we are limited by the pipe ->map. We don't
         * need a kmap'ed buffer here, we just want to make sure we
         * have the page pinned if the pipe page originates from the
         * page cache.
         */
        ptr = buf->ops->map(file, info, buf);
        if (IS_ERR(ptr))
                return PTR_ERR(ptr);

        offset = pos & ~PAGE_CACHE_MASK;
        more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;

        ret = file->f_op->sendpage(file, buf->page, offset, sd->len, &pos,more);

        buf->ops->unmap(info, buf);
        if (ret == sd->len)
                return 0;

        return -EIO;
}

/*
 * This is a little more tricky than the file -> pipe splicing. There are
 * basically three cases:
 *
 *      - Destination page already exists in the address space and there
 *        are users of it. For that case we have no other option that
 *        copying the data. Tough luck.
 *      - Destination page already exists in the address space, but there
 *        are no users of it. Make sure it's uptodate, then drop it. Fall
 *        through to last case.
 *      - Destination page does not exist, we can add the pipe page to
 *        the page cache and avoid the copy.
 *
 * If asked to move pages to the output file (SPLICE_F_MOVE is set in
 * sd->flags), we attempt to migrate pages from the pipe to the output
 * file address space page cache. This is possible if no one else has
 * the pipe page referenced outside of the pipe and page cache. If
 * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
 * a new page in the output file page cache and fill/dirty that.
 */
static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
                        struct splice_desc *sd)
{
        struct file *file = sd->file;
        struct address_space *mapping = file->f_mapping;
        gfp_t gfp_mask = mapping_gfp_mask(mapping);
        unsigned int offset;
        struct page *page;
        pgoff_t index;
        char *src;
        int ret;

        /*
         * make sure the data in this buffer is uptodate
         */
        src = buf->ops->map(file, info, buf);
        if (IS_ERR(src))
                return PTR_ERR(src);

        index = sd->pos >> PAGE_CACHE_SHIFT;
        offset = sd->pos & ~PAGE_CACHE_MASK;

        /*
         * Reuse buf page, if SPLICE_F_MOVE is set.
         */
        if (sd->flags & SPLICE_F_MOVE) {
                /*
                 * If steal succeeds, buf->page is now pruned from the vm
                 * side (LRU and page cache) and we can reuse it. The page
                 * will also be looked on successful return.
                 */
                if (buf->ops->steal(info, buf))
                        goto find_page;

                page = buf->page;
                if (add_to_page_cache(page, mapping, index, gfp_mask))
                        goto find_page;

                if (!(buf->flags & PIPE_BUF_FLAG_LRU))
                        lru_cache_add(page);
        } else {
find_page:
                page = find_lock_page(mapping, index);
                if (!page) {
                        ret = -ENOMEM;
                        page = page_cache_alloc_cold(mapping);
                        if (unlikely(!page))
                                goto out_nomem;

                        /*
                         * This will also lock the page
                         */
                        ret = add_to_page_cache_lru(page, mapping, index,
                                                    gfp_mask);
                        if (unlikely(ret))
                                goto out;
                }

                /*
                 * We get here with the page locked. If the page is also
                 * uptodate, we don't need to do more. If it isn't, we
                 * may need to bring it in if we are not going to overwrite
                 * the full page.
                 */
                if (!PageUptodate(page)) {
                        if (sd->len < PAGE_CACHE_SIZE) {
                                ret = mapping->a_ops->readpage(file, page);
                                if (unlikely(ret))
                                        goto out;

                                lock_page(page);

                                if (!PageUptodate(page)) {
                                        /*
                                         * Page got invalidated, repeat.
                                         */
                                        if (!page->mapping) {
                                                unlock_page(page);
                                                page_cache_release(page);
                                                goto find_page;
                                        }
                                        ret = -EIO;
                                        goto out;
                                }
                        } else
                                SetPageUptodate(page);
                }
        }

        ret = mapping->a_ops->prepare_write(file, page, 0, sd->len);
        if (ret == AOP_TRUNCATED_PAGE) {
                page_cache_release(page);
                goto find_page;
        } else if (ret)
                goto out;

        if (!(buf->flags & PIPE_BUF_FLAG_STOLEN)) {
                char *dst = kmap_atomic(page, KM_USER0);

                memcpy(dst + offset, src + buf->offset, sd->len);
                flush_dcache_page(page);
                kunmap_atomic(dst, KM_USER0);
        }

        ret = mapping->a_ops->commit_write(file, page, 0, sd->len);
        if (ret == AOP_TRUNCATED_PAGE) {
                page_cache_release(page);
                goto find_page;
        } else if (ret)
                goto out;

        mark_page_accessed(page);
        balance_dirty_pages_ratelimited(mapping);
out:
        if (!(buf->flags & PIPE_BUF_FLAG_STOLEN))
                page_cache_release(page);

        unlock_page(page);
out_nomem:
        buf->ops->unmap(info, buf);
        return ret;
}

typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
                           struct splice_desc *);

/*
 * Pipe input worker. Most of this logic works like a regular pipe, the
 * key here is the 'actor' worker passed in that actually moves the data
 * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
 */
static ssize_t move_from_pipe(struct pipe_inode_info *pipe, struct file *out,
                              loff_t *ppos, size_t len, unsigned int flags,
                              splice_actor *actor)
{
        int ret, do_wakeup, err;
        struct splice_desc sd;

        ret = 0;
        do_wakeup = 0;

        sd.total_len = len;
        sd.flags = flags;
        sd.file = out;
        sd.pos = *ppos;

        if (pipe->inode)
                mutex_lock(&pipe->inode->i_mutex);

        for (;;) {
                if (pipe->nrbufs) {
                        struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
                        struct pipe_buf_operations *ops = buf->ops;

                        sd.len = buf->len;
                        if (sd.len > sd.total_len)
                                sd.len = sd.total_len;

                        err = actor(pipe, buf, &sd);
                        if (err) {
                                if (!ret && err != -ENODATA)
                                        ret = err;

                                break;
                        }

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

                        if (!buf->len) {
                                buf->ops = NULL;
                                ops->release(pipe, buf);
                                pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
                                pipe->nrbufs--;
                                if (pipe->inode)
                                        do_wakeup = 1;
                        }

                        sd.pos += sd.len;
                        sd.total_len -= sd.len;
                        if (!sd.total_len)
                                break;
                }

                if (pipe->nrbufs)
                        continue;
                if (!pipe->writers)
                        break;
                if (!pipe->waiting_writers) {
                        if (ret)
                                break;
                }

                if (flags & SPLICE_F_NONBLOCK) {
                        if (!ret)
                                ret = -EAGAIN;
                        break;
                }

                if (signal_pending(current)) {
                        if (!ret)
                                ret = -ERESTARTSYS;
                        break;
                }

                if (do_wakeup) {
                        smp_mb();
                        if (waitqueue_active(&pipe->wait))
                                wake_up_interruptible_sync(&pipe->wait);
                        kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
                        do_wakeup = 0;
                }

                pipe_wait(pipe);
        }

        if (pipe->inode)
                mutex_unlock(&pipe->inode->i_mutex);

        if (do_wakeup) {
                smp_mb();
                if (waitqueue_active(&pipe->wait))
                        wake_up_interruptible(&pipe->wait);
                kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
        }

        return ret;
}

/**
 * generic_file_splice_write - splice data from a pipe to a file
 * @pipe:       pipe info
 * @out:        file to write to
 * @len:        number of bytes to splice
 * @flags:      splice modifier flags
 *
 * Will either move or copy pages (determined by @flags options) from
 * the given pipe inode to the given file.
 *
 */
ssize_t
generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
                          loff_t *ppos, size_t len, unsigned int flags)
{
        struct address_space *mapping = out->f_mapping;
        ssize_t ret;

        ret = move_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
        if (ret > 0) {
                struct inode *inode = mapping->host;

                *ppos += ret;

                /*
                 * If file or inode is SYNC and we actually wrote some data,
                 * sync it.
                 */
                if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
                        int err;

                        mutex_lock(&inode->i_mutex);
                        err = generic_osync_inode(inode, mapping,
                                                  OSYNC_METADATA|OSYNC_DATA);
                        mutex_unlock(&inode->i_mutex);

                        if (err)
                                ret = err;
                }
        }

        return ret;
}

EXPORT_SYMBOL(generic_file_splice_write);

/**
 * generic_splice_sendpage - splice data from a pipe to a socket
 * @inode:      pipe inode
 * @out:        socket to write to
 * @len:        number of bytes to splice
 * @flags:      splice modifier flags
 *
 * 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 move_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)
{
        int ret;

        if (unlikely(!out->f_op || !out->f_op->splice_write))
                return -EINVAL;

        if (unlikely(!(out->f_mode & FMODE_WRITE)))
                return -EBADF;

        ret = rw_verify_area(WRITE, out, ppos, len);
        if (unlikely(ret < 0))
                return ret;

        return out->f_op->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)
{
        loff_t isize, left;
        int ret;

        if (unlikely(!in->f_op || !in->f_op->splice_read))
                return -EINVAL;

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

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

        isize = i_size_read(in->f_mapping->host);
        if (unlikely(*ppos >= isize))
                return 0;
        
        left = isize - *ppos;
        if (unlikely(left < len))
                len = left;

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

long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
                      size_t len, unsigned int flags)
{
        struct pipe_inode_info *pipe;
        long ret, bytes;
        loff_t out_off;
        umode_t i_mode;
        int i;

        /*
         * 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 = in->f_dentry->d_inode->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(NULL);
                if (!pipe)
                        return -ENOMEM;

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

                current->splice_pipe = pipe;
        }

        /*
         * Do the splice.
         */
        ret = 0;
        bytes = 0;
        out_off = 0;

        while (len) {
                size_t read_len, max_read_len;

                /*
                 * Do at most PIPE_BUFFERS pages worth of transfer:
                 */
                max_read_len = min(len, (size_t)(PIPE_BUFFERS*PAGE_SIZE));

                ret = do_splice_to(in, ppos, pipe, max_read_len, flags);
                if (unlikely(ret < 0))
                        goto out_release;

                read_len = ret;

                /*
                 * 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 = do_splice_from(pipe, out, &out_off, read_len,
                                     flags & ~SPLICE_F_NONBLOCK);
                if (unlikely(ret < 0))
                        goto out_release;

                bytes += ret;
                len -= ret;

                /*
                 * In nonblocking mode, if we got back a short read then
                 * that was due to either an IO error or due to the
                 * pagecache entry not being there. In the IO error case
                 * the _next_ splice attempt will produce a clean IO error
                 * return value (not a short read), so in both cases it's
                 * correct to break out of the loop here:
                 */
                if ((flags & SPLICE_F_NONBLOCK) && (read_len < max_read_len))
                        break;
        }

        pipe->nrbufs = pipe->curbuf = 0;

        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) {
                        buf->ops->release(pipe, buf);
                        buf->ops = NULL;
                }
        }
        pipe->nrbufs = pipe->curbuf = 0;

        /*
         * If we transferred some data, return the number of bytes:
         */
        if (bytes > 0)
                return bytes;

        return ret;
}

EXPORT_SYMBOL(do_splice_direct);

/*
 * 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 *pipe;
        loff_t offset, *off;
        long ret;

        pipe = in->f_dentry->d_inode->i_pipe;
        if (pipe) {
                if (off_in)
                        return -ESPIPE;
                if (off_out) {
                        if (out->f_op->llseek == no_llseek)
                                return -EINVAL;
                        if (copy_from_user(&offset, off_out, sizeof(loff_t)))
                                return -EFAULT;
                        off = &offset;
                } else
                        off = &out->f_pos;

                ret = do_splice_from(pipe, out, off, len, flags);

                if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
                        ret = -EFAULT;

                return ret;
        }

        pipe = out->f_dentry->d_inode->i_pipe;
        if (pipe) {
                if (off_out)
                        return -ESPIPE;
                if (off_in) {
                        if (in->f_op->llseek == no_llseek)
                                return -EINVAL;
                        if (copy_from_user(&offset, off_in, sizeof(loff_t)))
                                return -EFAULT;
                        off = &offset;
                } else
                        off = &in->f_pos;

                ret = do_splice_to(in, off, pipe, len, flags);

                if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
                        ret = -EFAULT;

                return ret;
        }

        return -EINVAL;
}

asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
                           int fd_out, loff_t __user *off_out,
                           size_t len, unsigned int flags)
{
        long error;
        struct file *in, *out;
        int fput_in, fput_out;

        if (unlikely(!len))
                return 0;

        error = -EBADF;
        in = fget_light(fd_in, &fput_in);
        if (in) {
                if (in->f_mode & FMODE_READ) {
                        out = fget_light(fd_out, &fput_out);
                        if (out) {
                                if (out->f_mode & FMODE_WRITE)
                                        error = do_splice(in, off_in,
                                                          out, off_out,
                                                          len, flags);
                                fput_light(out, fput_out);
                        }
                }

                fput_light(in, fput_in);
        }

        return error;
}

/*
 * 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, do_wakeup, i, ipipe_first;

        ret = do_wakeup = ipipe_first = 0;

        /*
         * Potential ABBA deadlock, work around it by ordering lock
         * grabbing by inode address. Otherwise two different processes
         * could deadlock (one doing tee from A -> B, the other from B -> A).
         */
        if (ipipe->inode < opipe->inode) {
                ipipe_first = 1;
                mutex_lock(&ipipe->inode->i_mutex);
                mutex_lock(&opipe->inode->i_mutex);
        } else {
                mutex_lock(&opipe->inode->i_mutex);
                mutex_lock(&ipipe->inode->i_mutex);
        }

        for (i = 0;; i++) {
                if (!opipe->readers) {
                        send_sig(SIGPIPE, current, 0);
                        if (!ret)
                                ret = -EPIPE;
                        break;
                }
                if (ipipe->nrbufs - i) {
                        ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));

                        /*
                         * If we have room, fill this buffer
                         */
                        if (opipe->nrbufs < PIPE_BUFFERS) {
                                int nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);

                                /*
                                 * Get a reference to this pipe buffer,
                                 * so we can copy the contents over.
                                 */
                                ibuf->ops->get(ipipe, ibuf);

                                obuf = opipe->bufs + nbuf;
                                *obuf = *ibuf;

                                if (obuf->len > len)
                                        obuf->len = len;

                                opipe->nrbufs++;
                                do_wakeup = 1;
                                ret += obuf->len;
                                len -= obuf->len;

                                if (!len)
                                        break;
                                if (opipe->nrbufs < PIPE_BUFFERS)
                                        continue;
                        }

                        /*
                         * We have input available, but no output room.
                         * If we already copied data, return that. If we
                         * need to drop the opipe lock, it must be ordered
                         * last to avoid deadlocks.
                         */
                        if ((flags & SPLICE_F_NONBLOCK) || !ipipe_first) {
                                if (!ret)
                                        ret = -EAGAIN;
                                break;
                        }
                        if (signal_pending(current)) {
                                if (!ret)
                                        ret = -ERESTARTSYS;
                                break;
                        }
                        if (do_wakeup) {
                                smp_mb();
                                if (waitqueue_active(&opipe->wait))
                                        wake_up_interruptible(&opipe->wait);
                                kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
                                do_wakeup = 0;
                        }

                        opipe->waiting_writers++;
                        pipe_wait(opipe);
                        opipe->waiting_writers--;
                        continue;
                }

                /*
                 * No input buffers, do the usual checks for available
                 * writers and blocking and wait if necessary
                 */
                if (!ipipe->writers)
                        break;
                if (!ipipe->waiting_writers) {
                        if (ret)
                                break;
                }
                /*
                 * pipe_wait() drops the ipipe mutex. To avoid deadlocks
                 * with another process, we can only safely do that if
                 * the ipipe lock is ordered last.
                 */
                if ((flags & SPLICE_F_NONBLOCK) || ipipe_first) {
                        if (!ret)
                                ret = -EAGAIN;
                        break;
                }
                if (signal_pending(current)) {
                        if (!ret)
                                ret = -ERESTARTSYS;
                        break;
                }

                if (waitqueue_active(&ipipe->wait))
                        wake_up_interruptible_sync(&ipipe->wait);
                kill_fasync(&ipipe->fasync_writers, SIGIO, POLL_OUT);

                pipe_wait(ipipe);
        }

        mutex_unlock(&ipipe->inode->i_mutex);
        mutex_unlock(&opipe->inode->i_mutex);

        if (do_wakeup) {
                smp_mb();
                if (waitqueue_active(&opipe->wait))
                        wake_up_interruptible(&opipe->wait);
                kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
        }

        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 = in->f_dentry->d_inode->i_pipe;
        struct pipe_inode_info *opipe = out->f_dentry->d_inode->i_pipe;

        /*
         * Link ipipe to the two output pipes, consuming as we go along.
         */
        if (ipipe && opipe)
                return link_pipe(ipipe, opipe, len, flags);

        return -EINVAL;
}

asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
{
        struct file *in;
        int error, fput_in;

        if (unlikely(!len))
                return 0;

        error = -EBADF;
        in = fget_light(fdin, &fput_in);
        if (in) {
                if (in->f_mode & FMODE_READ) {
                        int fput_out;
                        struct file *out = fget_light(fdout, &fput_out);

                        if (out) {
                                if (out->f_mode & FMODE_WRITE)
                                        error = do_tee(in, out, len, flags);
                                fput_light(out, fput_out);
                        }
                }
                fput_light(in, fput_in);
        }

        return error;
}