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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@kernel.dk>
 * 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/splice.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>
#include <linux/uio.h>
#include <linux/security.h>

/*
 * Attempt to steal a page from a pipe buffer. This should perhaps go into
 * a vm helper function, it's already simplified quite a bit by the
 * addition of remove_mapping(). If success is returned, the caller may
 * attempt to reuse this page for another destination.
 */
static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
                             struct pipe_buffer *buf)
{
      struct page *page = buf->page;
      struct address_space *mapping;

      lock_page(page);

      mapping = page_mapping(page);
      if (mapping) {
            WARN_ON(!PageUptodate(page));

            /*
             * At least for ext2 with nobh option, we need to wait on
             * writeback completing on this page, since we'll remove it
             * from the pagecache.  Otherwise truncate wont wait on the
             * page, allowing the disk blocks to be reused by someone else
             * before we actually wrote our data to them. fs corruption
             * ensues.
             */
            wait_on_page_writeback(page);

            if (PagePrivate(page))
                  try_to_release_page(page, GFP_KERNEL);

            /*
             * If we succeeded in removing the mapping, set LRU flag
             * and return good.
             */
            if (remove_mapping(mapping, page)) {
                  buf->flags |= PIPE_BUF_FLAG_LRU;
                  return 0;
            }
      }

      /*
       * Raced with truncate or failed to remove page from current
       * address space, unlock and return failure.
       */
      unlock_page(page);
      return 1;
}

static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
                              struct pipe_buffer *buf)
{
      page_cache_release(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;
}

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

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

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

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

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

      ret = 0;
      do_wakeup = 0;
      page_nr = 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;

                  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;
                  if (spd->flags & SPLICE_F_GIFT)
                        buf->flags |= PIPE_BUF_FLAG_GIFT;

                  pipe->nrbufs++;
                  page_nr++;
                  ret += buf->len;

                  if (pipe->inode)
                        do_wakeup = 1;

                  if (!--spd->nr_pages)
                        break;
                  if (pipe->nrbufs < PIPE_BUFFERS)
                        continue;

                  break;
            }

            if (spd->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 (page_nr < spd_pages)
            page_cache_release(spd->pages[page_nr++]);

      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, nr_pages, req_pages;
      struct page *pages[PIPE_BUFFERS];
      struct partial_page partial[PIPE_BUFFERS];
      struct page *page;
      pgoff_t index, end_index;
      loff_t isize;
      int error, page_nr;
      struct splice_pipe_desc spd = {
            .pages = pages,
            .partial = partial,
            .flags = flags,
            .ops = &page_cache_pipe_buf_ops,
      };

      index = *ppos >> PAGE_CACHE_SHIFT;
      loff = *ppos & ~PAGE_CACHE_MASK;
      req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
      nr_pages = min(req_pages, (unsigned)PIPE_BUFFERS);

      /*
       * Lookup the (hopefully) full range of pages we need.
       */
      spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
      index += spd.nr_pages;

      /*
       * If find_get_pages_contig() returned fewer pages than we needed,
       * readahead/allocate the rest and fill in the holes.
       */
      if (spd.nr_pages < nr_pages)
            page_cache_sync_readahead(mapping, &in->f_ra, in,
                        index, req_pages - spd.nr_pages);

      error = 0;
      while (spd.nr_pages < nr_pages) {
            /*
             * Page could be there, find_get_pages_contig() breaks on
             * the first hole.
             */
            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,
                                    GFP_KERNEL);
                  if (unlikely(error)) {
                        page_cache_release(page);
                        if (error == -EEXIST)
                              continue;
                        break;
                  }
                  /*
                   * add_to_page_cache() locks the page, unlock it
                   * to avoid convoluting the logic below even more.
                   */
                  unlock_page(page);
            }

            pages[spd.nr_pages++] = page;
            index++;
      }

      /*
       * Now loop over the map and see if we need to start IO on any
       * pages, fill in the partial map, etc.
       */
      index = *ppos >> PAGE_CACHE_SHIFT;
      nr_pages = spd.nr_pages;
      spd.nr_pages = 0;
      for (page_nr = 0; page_nr < nr_pages; page_nr++) {
            unsigned int this_len;

            if (!len)
                  break;

            /*
             * this_len is the max we'll use from this page
             */
            this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
            page = pages[page_nr];

            if (PageReadahead(page))
                  page_cache_async_readahead(mapping, &in->f_ra, in,
                              page, index, req_pages - page_nr);

            /*
             * 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) {
                        if (TestSetPageLocked(page))
                              break;
                  } else
                        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);
                        break;
                  }
                  /*
                   * page was already under io and is now done, great
                   */
                  if (PageUptodate(page)) {
                        unlock_page(page);
                        goto fill_it;
                  }

                  /*
                   * need to read in the page
                   */
                  error = mapping->a_ops->readpage(in, page);
                  if (unlikely(error)) {
                        /*
                         * We really should re-lookup the page here,
                         * but it complicates things a lot. Instead
                         * lets just do what we already stored, and
                         * we'll get it the next time we are called.
                         */
                        if (error == AOP_TRUNCATED_PAGE)
                              error = 0;

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

            /*
             * if this is the last page, see if we need to shrink
             * the length and stop
             */
            if (end_index == index) {
                  unsigned int plen;

                  /*
                   * max good bytes in this page
                   */
                  plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
                  if (plen <= loff)
                        break;

                  /*
                   * force quit after adding this page
                   */
                  this_len = min(this_len, plen - loff);
                  len = this_len;
            }

            partial[page_nr].offset = loff;
            partial[page_nr].len = this_len;
            len -= this_len;
            loff = 0;
            spd.nr_pages++;
            index++;
      }

      /*
       * Release any pages at the end, if we quit early. 'page_nr' is how far
       * we got, 'nr_pages' is how many pages are in the map.
       */
      while (page_nr < nr_pages)
            page_cache_release(pages[page_nr++]);
      in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;

      if (spd.nr_pages)
            return splice_to_pipe(pipe, &spd);

      return error;
}

/**
 * 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 the address_space operations for the source implements
 *    a readpage() hook.
 *
 */
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;
      loff_t isize, left;

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

      left = isize - *ppos;
      if (unlikely(left < len))
            len = left;

      ret = 0;
      spliced = 0;
      while (len && !spliced) {
            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(). 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 ret, more;

      ret = buf->ops->confirm(pipe, buf);
      if (!ret) {
            more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;

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

      return ret;
}

/*
 * 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 *pipe, struct pipe_buffer *buf,
                  struct splice_desc *sd)
{
      struct file *file = sd->u.file;
      struct address_space *mapping = file->f_mapping;
      unsigned int offset, this_len;
      struct page *page;
      void *fsdata;
      int ret;

      /*
       * make sure the data in this buffer is uptodate
       */
      ret = buf->ops->confirm(pipe, buf);
      if (unlikely(ret))
            return ret;

      offset = sd->pos & ~PAGE_CACHE_MASK;

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

      ret = pagecache_write_begin(file, mapping, sd->pos, this_len,
                        AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
      if (unlikely(ret))
            goto out;

      if (buf->page != page) {
            /*
             * Careful, ->map() uses KM_USER0!
             */
            char *src = buf->ops->map(pipe, buf, 1);
            char *dst = kmap_atomic(page, KM_USER1);

            memcpy(dst + offset, src + buf->offset, this_len);
            flush_dcache_page(page);
            kunmap_atomic(dst, KM_USER1);
            buf->ops->unmap(pipe, buf, src);
      }
      ret = pagecache_write_end(file, mapping, sd->pos, this_len, this_len,
                        page, fsdata);
out:
      return ret;
}

/**
 * __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, do_wakeup, err;

      ret = 0;
      do_wakeup = 0;

      for (;;) {
            if (pipe->nrbufs) {
                  struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
                  const 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 <= 0) {
                        if (!ret && err != -ENODATA)
                              ret = err;

                        break;
                  }

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

                  sd->len -= err;
                  sd->pos += err;
                  sd->total_len -= err;
                  if (sd->len)
                        continue;

                  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;
                  }

                  if (!sd->total_len)
                        break;
            }

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

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

      return 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 input and output inodes,
 *    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 inode *inode = out->f_mapping->host;
      struct splice_desc sd = {
            .total_len = len,
            .flags = flags,
            .pos = *ppos,
            .u.file = out,
      };

      /*
       * The actor worker might be calling ->prepare_write and
       * ->commit_write. Most of the time, these expect i_mutex to
       * be held. Since this may result in an ABBA deadlock with
       * pipe->inode, we have to order lock acquiry here.
       */
      inode_double_lock(inode, pipe->inode);
      ret = __splice_from_pipe(pipe, &sd, actor);
      inode_double_unlock(inode, pipe->inode);

      return ret;
}

/**
 * generic_file_splice_write_nolock - generic_file_splice_write without mutexes
 * @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. The caller is responsible
 *    for acquiring i_mutex on both inodes.
 *
 */
ssize_t
generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out,
                         loff_t *ppos, size_t len, unsigned int flags)
{
      struct address_space *mapping = out->f_mapping;
      struct inode *inode = mapping->host;
      struct splice_desc sd = {
            .total_len = len,
            .flags = flags,
            .pos = *ppos,
            .u.file = out,
      };
      ssize_t ret;
      int err;

      err = remove_suid(out->f_path.dentry);
      if (unlikely(err))
            return err;

      ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
      if (ret > 0) {
            unsigned long nr_pages;

            *ppos += ret;
            nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

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

                  if (err)
                        ret = err;
            }
            balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
      }

      return ret;
}

EXPORT_SYMBOL(generic_file_splice_write_nolock);

/**
 * generic_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.
 *
 */
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;
      struct inode *inode = mapping->host;
      int killsuid, killpriv;
      ssize_t ret;
      int err = 0;

      killpriv = security_inode_need_killpriv(out->f_path.dentry);
      killsuid = should_remove_suid(out->f_path.dentry);
      if (unlikely(killsuid || killpriv)) {
            mutex_lock(&inode->i_mutex);
            if (killpriv)
                  err = security_inode_killpriv(out->f_path.dentry);
            if (!err && killsuid)
                  err = __remove_suid(out->f_path.dentry, killsuid);
            mutex_unlock(&inode->i_mutex);
            if (err)
                  return err;
      }

      ret = splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
      if (ret > 0) {
            unsigned long nr_pages;

            *ppos += ret;
            nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

            /*
             * If file or inode is SYNC and we actually wrote some data,
             * sync it.
             */
            if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
                  mutex_lock(&inode->i_mutex);
                  err = generic_osync_inode(inode, mapping,
                                      OSYNC_METADATA|OSYNC_DATA);
                  mutex_unlock(&inode->i_mutex);

                  if (err)
                        ret = err;
            }
            balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
      }

      return ret;
}

EXPORT_SYMBOL(generic_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);

/*
 * 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;

      ret = security_file_permission(out, MAY_WRITE);
      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)
{
      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;

      ret = security_file_permission(in, MAY_READ);
      if (unlikely(ret < 0))
            return ret;

      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;
      umode_t i_mode;
      size_t len;
      int i, flags;

      /*
       * 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_path.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 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;

      while (len) {
            size_t read_len;
            loff_t pos = sd->pos;

            ret = do_splice_to(in, &pos, pipe, len, flags);
            if (unlikely(ret <= 0))
                  goto out_release;

            read_len = ret;
            sd->total_len = read_len;

            /*
             * 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))
                  goto out_release;

            bytes += ret;
            len -= ret;
            sd->pos = pos;

            if (ret < read_len)
                  goto out_release;
      }

      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(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->pos, sd->total_len, sd->flags);
}

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

      ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
      if (ret > 0)
            *ppos += ret;

      return ret;
}

/*
 * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
 * location, so checking ->i_pipe is not enough to verify that this is a
 * pipe.
 */
static inline struct pipe_inode_info *pipe_info(struct inode *inode)
{
      if (S_ISFIFO(inode->i_mode))
            return inode->i_pipe;

      return NULL;
}

/*
 * 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 = pipe_info(in->f_path.dentry->d_inode);
      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 = pipe_info(out->f_path.dentry->d_inode);
      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;
}

/*
 * Do a copy-from-user while holding the mmap_semaphore for reading, in a
 * manner safe from deadlocking with simultaneous mmap() (grabbing mmap_sem
 * for writing) and page faulting on the user memory pointed to by src.
 * This assumes that we will very rarely hit the partial != 0 path, or this
 * will not be a win.
 */
static int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)
{
      int partial;

      if (!access_ok(VERIFY_READ, src, n))
            return -EFAULT;

      pagefault_disable();
      partial = __copy_from_user_inatomic(dst, src, n);
      pagefault_enable();

      /*
       * Didn't copy everything, drop the mmap_sem and do a faulting copy
       */
      if (unlikely(partial)) {
            up_read(&current->mm->mmap_sem);
            partial = copy_from_user(dst, src, n);
            down_read(&current->mm->mmap_sem);
      }

      return partial;
}

/*
 * Map an iov into an array of pages and offset/length tupples. With the
 * partial_page structure, we can map several non-contiguous ranges into
 * our ones pages[] map instead of splitting that operation into pieces.
 * Could easily be exported as a generic helper for other users, in which
 * case one would probably want to add a 'max_nr_pages' parameter as well.
 */
static int get_iovec_page_array(const struct iovec __user *iov,
                        unsigned int nr_vecs, struct page **pages,
                        struct partial_page *partial, int aligned)
{
      int buffers = 0, error = 0;

      down_read(&current->mm->mmap_sem);

      while (nr_vecs) {
            unsigned long off, npages;
            struct iovec entry;
            void __user *base;
            size_t len;
            int i;

            error = -EFAULT;
            if (copy_from_user_mmap_sem(&entry, iov, sizeof(entry)))
                  break;

            base = entry.iov_base;
            len = entry.iov_len;

            /*
             * Sanity check this iovec. 0 read succeeds.
             */
            error = 0;
            if (unlikely(!len))
                  break;
            error = -EFAULT;
            if (!access_ok(VERIFY_READ, base, len))
                  break;

            /*
             * Get this base offset and number of pages, then map
             * in the user pages.
             */
            off = (unsigned long) base & ~PAGE_MASK;

            /*
             * If asked for alignment, the offset must be zero and the
             * length a multiple of the PAGE_SIZE.
             */
            error = -EINVAL;
            if (aligned && (off || len & ~PAGE_MASK))
                  break;

            npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
            if (npages > PIPE_BUFFERS - buffers)
                  npages = PIPE_BUFFERS - buffers;

            error = get_user_pages(current, current->mm,
                               (unsigned long) base, npages, 0, 0,
                               &pages[buffers], NULL);

            if (unlikely(error <= 0))
                  break;

            /*
             * Fill this contiguous range into the partial page map.
             */
            for (i = 0; i < error; i++) {
                  const int plen = min_t(size_t, len, PAGE_SIZE - off);

                  partial[buffers].offset = off;
                  partial[buffers].len = plen;

                  off = 0;
                  len -= plen;
                  buffers++;
            }

            /*
             * We didn't complete this iov, stop here since it probably
             * means we have to move some of this into a pipe to
             * be able to continue.
             */
            if (len)
                  break;

            /*
             * Don't continue if we mapped fewer pages than we asked for,
             * or if we mapped the max number of pages that we have
             * room for.
             */
            if (error < npages || buffers == PIPE_BUFFERS)
                  break;

            nr_vecs--;
            iov++;
      }

      up_read(&current->mm->mmap_sem);

      if (buffers)
            return buffers;

      return error;
}

static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
                  struct splice_desc *sd)
{
      char *src;
      int ret;

      ret = buf->ops->confirm(pipe, buf);
      if (unlikely(ret))
            return ret;

      /*
       * See if we can use the atomic maps, by prefaulting in the
       * pages and doing an atomic copy
       */
      if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
            src = buf->ops->map(pipe, buf, 1);
            ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
                                          sd->len);
            buf->ops->unmap(pipe, buf, src);
            if (!ret) {
                  ret = sd->len;
                  goto out;
            }
      }

      /*
       * No dice, use slow non-atomic map and copy
       */
      src = buf->ops->map(pipe, buf, 0);

      ret = sd->len;
      if (copy_to_user(sd->u.userptr, src + buf->offset, sd->len))
            ret = -EFAULT;

      buf->ops->unmap(pipe, buf, src);
out:
      if (ret > 0)
            sd->u.userptr += ret;
      return ret;
}

/*
 * For lack of a better implementation, implement vmsplice() to userspace
 * as a simple copy of the pipes pages to the user iov.
 */
static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
                       unsigned long nr_segs, unsigned int flags)
{
      struct pipe_inode_info *pipe;
      struct splice_desc sd;
      ssize_t size;
      int error;
      long ret;

      pipe = pipe_info(file->f_path.dentry->d_inode);
      if (!pipe)
            return -EBADF;

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

      error = ret = 0;
      while (nr_segs) {
            void __user *base;
            size_t len;

            /*
             * Get user address base and length for this iovec.
             */
            error = get_user(base, &iov->iov_base);
            if (unlikely(error))
                  break;
            error = get_user(len, &iov->iov_len);
            if (unlikely(error))
                  break;

            /*
             * Sanity check this iovec. 0 read succeeds.
             */
            if (unlikely(!len))
                  break;
            if (unlikely(!base)) {
                  error = -EFAULT;
                  break;
            }

            if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
                  error = -EFAULT;
                  break;
            }

            sd.len = 0;
            sd.total_len = len;
            sd.flags = flags;
            sd.u.userptr = base;
            sd.pos = 0;

            size = __splice_from_pipe(pipe, &sd, pipe_to_user);
            if (size < 0) {
                  if (!ret)
                        ret = size;

                  break;
            }

            ret += size;

            if (size < len)
                  break;

            nr_segs--;
            iov++;
      }

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

      if (!ret)
            ret = error;

      return ret;
}

/*
 * vmsplice splices a user address range into a pipe. It can be thought of
 * as splice-from-memory, where the regular splice is splice-from-file (or
 * to file). In both cases the output is a pipe, naturally.
 */
static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
                       unsigned long nr_segs, unsigned int flags)
{
      struct pipe_inode_info *pipe;
      struct page *pages[PIPE_BUFFERS];
      struct partial_page partial[PIPE_BUFFERS];
      struct splice_pipe_desc spd = {
            .pages = pages,
            .partial = partial,
            .flags = flags,
            .ops = &user_page_pipe_buf_ops,
      };

      pipe = pipe_info(file->f_path.dentry->d_inode);
      if (!pipe)
            return -EBADF;

      spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
                                  flags & SPLICE_F_GIFT);
      if (spd.nr_pages <= 0)
            return spd.nr_pages;

      return splice_to_pipe(pipe, &spd);
}

/*
 * 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().
 *
 */
asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
                       unsigned long nr_segs, unsigned int flags)
{
      struct file *file;
      long error;
      int fput;

      if (unlikely(nr_segs > UIO_MAXIOV))
            return -EINVAL;
      else if (unlikely(!nr_segs))
            return 0;

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

            fput_light(file, fput);
      }

      return error;
}

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;
}

/*
 * Make sure there's data to read. Wait for input if we can, otherwise
 * return an appropriate error.
 */
static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
{
      int ret;

      /*
       * Check ->nrbufs without the inode lock first. This function
       * is speculative anyways, so missing one is ok.
       */
      if (pipe->nrbufs)
            return 0;

      ret = 0;
      mutex_lock(&pipe->inode->i_mutex);

      while (!pipe->nrbufs) {
            if (signal_pending(current)) {
                  ret = -ERESTARTSYS;
                  break;
            }
            if (!pipe->writers)
                  break;
            if (!pipe->waiting_writers) {
                  if (flags & SPLICE_F_NONBLOCK) {
                        ret = -EAGAIN;
                        break;
                  }
            }
            pipe_wait(pipe);
      }

      mutex_unlock(&pipe->inode->i_mutex);
      return ret;
}

/*
 * Make sure there's writeable room. Wait for room if we can, otherwise
 * return an appropriate error.
 */
static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
{
      int ret;

      /*
       * Check ->nrbufs without the inode lock first. This function
       * is speculative anyways, so missing one is ok.
       */
      if (pipe->nrbufs < PIPE_BUFFERS)
            return 0;

      ret = 0;
      mutex_lock(&pipe->inode->i_mutex);

      while (pipe->nrbufs >= PIPE_BUFFERS) {
            if (!pipe->readers) {
                  send_sig(SIGPIPE, current, 0);
                  ret = -EPIPE;
                  break;
            }
            if (flags & SPLICE_F_NONBLOCK) {
                  ret = -EAGAIN;
                  break;
            }
            if (signal_pending(current)) {
                  ret = -ERESTARTSYS;
                  break;
            }
            pipe->waiting_writers++;
            pipe_wait(pipe);
            pipe->waiting_writers--;
      }

      mutex_unlock(&pipe->inode->i_mutex);
      return ret;
}

/*
 * Link contents of ipipe to opipe.
 */
static int link_pipe(struct pipe_inode_info *ipipe,
                 struct pipe_inode_info *opipe,
                 size_t len, unsigned int flags)
{
      struct pipe_buffer *ibuf, *obuf;
      int ret = 0, i = 0, nbuf;

      /*
       * Potential ABBA deadlock, work around it by ordering lock
       * grabbing by inode address. Otherwise two different processes
       * could deadlock (one doing tee from A -> B, the other from B -> A).
       */
      inode_double_lock(ipipe->inode, opipe->inode);

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

            /*
             * If we have iterated all input buffers or ran out of
             * output room, break.
             */
            if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
                  break;

            ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
            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;

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

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

            opipe->nrbufs++;
            ret += obuf->len;
            len -= obuf->len;
            i++;
      } while (len);

      inode_double_unlock(ipipe->inode, opipe->inode);

      /*
       * If we put data in the output pipe, wakeup any potential readers.
       */
      if (ret > 0) {
            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 = pipe_info(in->f_path.dentry->d_inode);
      struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
      int ret = -EINVAL;

      /*
       * Duplicate the contents of ipipe to opipe without actually
       * copying the data.
       */
      if (ipipe && opipe && ipipe != opipe) {
            /*
             * Keep going, unless we encounter an error. The ipipe/opipe
             * ordering doesn't really matter.
             */
            ret = link_ipipe_prep(ipipe, flags);
            if (!ret) {
                  ret = link_opipe_prep(opipe, flags);
                  if (!ret) {
                        ret = link_pipe(ipipe, opipe, len, flags);
                        if (!ret && (flags & SPLICE_F_NONBLOCK))
                              ret = -EAGAIN;
                  }
            }
      }

      return ret;
}

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;
}

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