ClabureDB: Classified Bug-Reports Database

   /*
    * "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))
                          goto out_unlock;
  
                  /*
                   * If we succeeded in removing the mapping, set LRU flag
                   * and return good.
                   */
                  if (remove_mapping(mapping, page)) {
                          buf->flags |= PIPE_BUF_FLAG_LRU;
                          return 0;
                  }
          }
  
          /*
           * Raced with truncate or failed to remove page from current
           * address space, unlock and return failure.
           */
  out_unlock:
          unlock_page(page);
          return 1;
  }
  
  static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
                                          struct pipe_buffer *buf)
  {
          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)
                 spd->spd_release(spd, page_nr++);
 
         return ret;
 }
 
 static void spd_release_page(struct splice_pipe_desc *spd, unsigned int i)
 {
         page_cache_release(spd->pages[i]);
 }
 
 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,
                 .spd_release = spd_release_page,
         };
 
         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,
                                                 mapping_gfp_mask(mapping));
                         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 (!trylock_page(page)) {
                                         error = -EAGAIN;
                                         break;
                                 }
                         } else
                                 lock_page(page);
 
                         /*
                          * Page was truncated, or invalidated by the
                          * filesystem.  Redo the find/create, but this time the
                          * page is kept locked, so there's no chance of another
                          * race with truncate/invalidate.
                          */
                         if (!page->mapping) {
                                 unlock_page(page);
                                 page = find_or_create_page(mapping, index,
                                                 mapping_gfp_mask(mapping));
 
                                 if (!page) {
                                         error = -ENOMEM;
                                         break;
                                 }
                                 page_cache_release(pages[page_nr]);
                                 pages[page_nr] = page;
                         }
                         /*
                          * 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)
 {
         loff_t isize, left;
         int ret;
 
         isize = i_size_read(in->f_mapping->host);
         if (unlikely(*ppos >= isize))
                 return 0;
 
         left = isize - *ppos;
         if (unlikely(left < len))
                 len = left;
 
         ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
         if (ret > 0)
                 *ppos += ret;
 
         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 ->write_begin and
          * ->write_end. 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 = file_remove_suid(out);
         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;
         struct splice_desc sd = {
                 .total_len = len,
                 .flags = flags,
                 .pos = *ppos,
                 .u.file = out,
         };
         ssize_t ret;
 
         inode_double_lock(inode, pipe->inode);
         ret = file_remove_suid(out);
         if (likely(!ret))
                 ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
         inode_double_unlock(inode, pipe->inode);
         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))) {
                         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;
                 }
                 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;
 
         if (unlikely(out->f_flags & O_APPEND))
                 return -EINVAL;
 
         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)
 {
         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;
 
         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, prev_pos = pos;

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

                read_len = ret;
                sd->total_len = read_len;

                /*
                 * NOTE: nonblocking mode only applies to the input. We
                 * must not do the output in nonblocking mode as then we
                 * could get stuck data in the internal pipe:
                 */
                ret = actor(pipe, sd);
                if (unlikely(ret <= 0)) {
                        sd->pos = prev_pos;
                        goto out_release;
                }

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

                if (ret < read_len) {
                        sd->pos = prev_pos + ret;
                        goto out_release;
                }
        }

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

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

                if (buf->ops) {
                        buf->ops->release(pipe, buf);
                        buf->ops = NULL;
                }
        }

        if (!bytes)
                bytes = ret;

        goto done;
}
EXPORT_SYMBOL(splice_direct_to_actor);

static int direct_splice_actor(struct pipe_inode_info *pipe,
                               struct splice_desc *sd)
{
        struct file *file = sd->u.file;

        return do_splice_from(pipe, file, &sd->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 = sd.pos;

        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;
}

/*
 * 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;

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

                error = -EFAULT;
                if (copy_from_user(&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_fast((unsigned long)base, npages,
                                        0, &pages[buffers]);

                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++;
        }

        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,
                .spd_release = spd_release_page,
        };

        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);

        /*
         * return EAGAIN if we have the potential of some data in the
         * future, otherwise just return 0
         */
        if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
                ret = -EAGAIN;

        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);
                }
        }

        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;
}