ClabureDB: Classified Bug-Reports Database

   /*
    *  linux/fs/pipe.c
    *
    *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
    */
   
   #include <linux/mm.h>
   #include <linux/file.h>
   #include <linux/poll.h>
  #include <linux/slab.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/mount.h>
  #include <linux/pipe_fs_i.h>
  #include <linux/uio.h>
  #include <linux/highmem.h>
  #include <linux/pagemap.h>
  #include <linux/audit.h>
  #include <linux/syscalls.h>
  
  #include <asm/uaccess.h>
  #include <asm/ioctls.h>
  
  /*
   * We use a start+len construction, which provides full use of the 
   * allocated memory.
   * -- Florian Coosmann (FGC)
   * 
   * Reads with count = 0 should always return 0.
   * -- Julian Bradfield 1999-06-07.
   *
   * FIFOs and Pipes now generate SIGIO for both readers and writers.
   * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
   *
   * pipe_read & write cleanup
   * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
   */
  
  /* Drop the inode semaphore and wait for a pipe event, atomically */
  void pipe_wait(struct pipe_inode_info *pipe)
  {
          DEFINE_WAIT(wait);
  
          /*
           * Pipes are system-local resources, so sleeping on them
           * is considered a noninteractive wait:
           */
          prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
          if (pipe->inode)
                  mutex_unlock(&pipe->inode->i_mutex);
          schedule();
          finish_wait(&pipe->wait, &wait);
          if (pipe->inode)
                  mutex_lock(&pipe->inode->i_mutex);
  }
  
  static int
  pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len,
                          int atomic)
  {
          unsigned long copy;
  
          while (len > 0) {
                  while (!iov->iov_len)
                          iov++;
                  copy = min_t(unsigned long, len, iov->iov_len);
  
                  if (atomic) {
                          if (__copy_from_user_inatomic(to, iov->iov_base, copy))
                                  return -EFAULT;
                  } else {
                          if (copy_from_user(to, iov->iov_base, copy))
                                  return -EFAULT;
                  }
                  to += copy;
                  len -= copy;
                  iov->iov_base += copy;
                  iov->iov_len -= copy;
          }
          return 0;
  }
  
  static int
  pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len,
                        int atomic)
  {
          unsigned long copy;
  
          while (len > 0) {
                  while (!iov->iov_len)
                          iov++;
                  copy = min_t(unsigned long, len, iov->iov_len);
  
                  if (atomic) {
                          if (__copy_to_user_inatomic(iov->iov_base, from, copy))
                                  return -EFAULT;
                  } else {
                          if (copy_to_user(iov->iov_base, from, copy))
                                 return -EFAULT;
                 }
                 from += copy;
                 len -= copy;
                 iov->iov_base += copy;
                 iov->iov_len -= copy;
         }
         return 0;
 }
 
 /*
  * Attempt to pre-fault in the user memory, so we can use atomic copies.
  * Returns the number of bytes not faulted in.
  */
 static int iov_fault_in_pages_write(struct iovec *iov, unsigned long len)
 {
         while (!iov->iov_len)
                 iov++;
 
         while (len > 0) {
                 unsigned long this_len;
 
                 this_len = min_t(unsigned long, len, iov->iov_len);
                 if (fault_in_pages_writeable(iov->iov_base, this_len))
                         break;
 
                 len -= this_len;
                 iov++;
         }
 
         return len;
 }
 
 /*
  * Pre-fault in the user memory, so we can use atomic copies.
  */
 static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
 {
         while (!iov->iov_len)
                 iov++;
 
         while (len > 0) {
                 unsigned long this_len;
 
                 this_len = min_t(unsigned long, len, iov->iov_len);
                 fault_in_pages_readable(iov->iov_base, this_len);
                 len -= this_len;
                 iov++;
         }
 }
 
 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
                                   struct pipe_buffer *buf)
 {
         struct page *page = buf->page;
 
         /*
          * If nobody else uses this page, and we don't already have a
          * temporary page, let's keep track of it as a one-deep
          * allocation cache. (Otherwise just release our reference to it)
          */
         if (page_count(page) == 1 && !pipe->tmp_page)
                 pipe->tmp_page = page;
         else
                 page_cache_release(page);
 }
 
 /**
  * generic_pipe_buf_map - virtually map a pipe buffer
  * @pipe:        the pipe that the buffer belongs to
  * @buf:        the buffer that should be mapped
  * @atomic:        whether to use an atomic map
  *
  * Description:
  *        This function returns a kernel virtual address mapping for the
  *        pipe_buffer passed in @buf. If @atomic is set, an atomic map is provided
  *        and the caller has to be careful not to fault before calling
  *        the unmap function.
  *
  *        Note that this function occupies KM_USER0 if @atomic != 0.
  */
 void *generic_pipe_buf_map(struct pipe_inode_info *pipe,
                            struct pipe_buffer *buf, int atomic)
 {
         if (atomic) {
                 buf->flags |= PIPE_BUF_FLAG_ATOMIC;
                 return kmap_atomic(buf->page, KM_USER0);
         }
 
         return kmap(buf->page);
 }
 
 /**
  * generic_pipe_buf_unmap - unmap a previously mapped pipe buffer
  * @pipe:        the pipe that the buffer belongs to
  * @buf:        the buffer that should be unmapped
  * @map_data:        the data that the mapping function returned
  *
  * Description:
  *        This function undoes the mapping that ->map() provided.
  */
 void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
                             struct pipe_buffer *buf, void *map_data)
 {
         if (buf->flags & PIPE_BUF_FLAG_ATOMIC) {
                 buf->flags &= ~PIPE_BUF_FLAG_ATOMIC;
                 kunmap_atomic(map_data, KM_USER0);
         } else
                 kunmap(buf->page);
 }
 
 /**
  * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer
  * @pipe:        the pipe that the buffer belongs to
  * @buf:        the buffer to attempt to steal
  *
  * Description:
  *        This function attempts to steal the &struct page attached to
  *        @buf. If successful, this function returns 0 and returns with
  *        the page locked. The caller may then reuse the page for whatever
  *        he wishes; the typical use is insertion into a different file
  *        page cache.
  */
 int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
                            struct pipe_buffer *buf)
 {
         struct page *page = buf->page;
 
         /*
          * A reference of one is golden, that means that the owner of this
          * page is the only one holding a reference to it. lock the page
          * and return OK.
          */
         if (page_count(page) == 1) {
                 lock_page(page);
                 return 0;
         }
 
         return 1;
 }
 
 /**
  * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
  * @pipe:        the pipe that the buffer belongs to
  * @buf:        the buffer to get a reference to
  *
  * Description:
  *        This function grabs an extra reference to @buf. It's used in
  *        in the tee() system call, when we duplicate the buffers in one
  *        pipe into another.
  */
 void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
 {
         page_cache_get(buf->page);
 }
 
 /**
  * generic_pipe_buf_confirm - verify contents of the pipe buffer
  * @info:        the pipe that the buffer belongs to
  * @buf:        the buffer to confirm
  *
  * Description:
  *        This function does nothing, because the generic pipe code uses
  *        pages that are always good when inserted into the pipe.
  */
 int generic_pipe_buf_confirm(struct pipe_inode_info *info,
                              struct pipe_buffer *buf)
 {
         return 0;
 }
 
 static const struct pipe_buf_operations anon_pipe_buf_ops = {
         .can_merge = 1,
         .map = generic_pipe_buf_map,
         .unmap = generic_pipe_buf_unmap,
         .confirm = generic_pipe_buf_confirm,
         .release = anon_pipe_buf_release,
         .steal = generic_pipe_buf_steal,
         .get = generic_pipe_buf_get,
 };
 
 static ssize_t
 pipe_read(struct kiocb *iocb, const struct iovec *_iov,
            unsigned long nr_segs, loff_t pos)
 {
         struct file *filp = iocb->ki_filp;
         struct inode *inode = filp->f_path.dentry->d_inode;
         struct pipe_inode_info *pipe;
         int do_wakeup;
         ssize_t ret;
         struct iovec *iov = (struct iovec *)_iov;
         size_t total_len;
 
         total_len = iov_length(iov, nr_segs);
         /* Null read succeeds. */
         if (unlikely(total_len == 0))
                 return 0;
 
         do_wakeup = 0;
         ret = 0;
         mutex_lock(&inode->i_mutex);
         pipe = inode->i_pipe;
         for (;;) {
                 int bufs = pipe->nrbufs;
                 if (bufs) {
                         int curbuf = pipe->curbuf;
                         struct pipe_buffer *buf = pipe->bufs + curbuf;
                         const struct pipe_buf_operations *ops = buf->ops;
                         void *addr;
                         size_t chars = buf->len;
                         int error, atomic;
 
                         if (chars > total_len)
                                 chars = total_len;
 
                         error = ops->confirm(pipe, buf);
                         if (error) {
                                 if (!ret)
                                         error = ret;
                                 break;
                         }
 
                         atomic = !iov_fault_in_pages_write(iov, chars);
 redo:
                         addr = ops->map(pipe, buf, atomic);
                         error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars, atomic);
                         ops->unmap(pipe, buf, addr);
                         if (unlikely(error)) {
                                 /*
                                  * Just retry with the slow path if we failed.
                                  */
                                 if (atomic) {
                                         atomic = 0;
                                         goto redo;
                                 }
                                 if (!ret)
                                         ret = error;
                                 break;
                         }
                         ret += chars;
                         buf->offset += chars;
                         buf->len -= chars;
                         if (!buf->len) {
                                 buf->ops = NULL;
                                 ops->release(pipe, buf);
                                 curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
                                 pipe->curbuf = curbuf;
                                 pipe->nrbufs = --bufs;
                                 do_wakeup = 1;
                         }
                         total_len -= chars;
                         if (!total_len)
                                 break;        /* common path: read succeeded */
                 }
                 if (bufs)        /* More to do? */
                         continue;
                 if (!pipe->writers)
                         break;
                 if (!pipe->waiting_writers) {
                         /* syscall merging: Usually we must not sleep
                          * if O_NONBLOCK is set, or if we got some data.
                          * But if a writer sleeps in kernel space, then
                          * we can wait for that data without violating POSIX.
                          */
                         if (ret)
                                 break;
                         if (filp->f_flags & O_NONBLOCK) {
                                 ret = -EAGAIN;
                                 break;
                         }
                 }
                 if (signal_pending(current)) {
                         if (!ret)
                                 ret = -ERESTARTSYS;
                         break;
                 }
                 if (do_wakeup) {
                         wake_up_interruptible_sync(&pipe->wait);
                          kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
                 }
                 pipe_wait(pipe);
         }
         mutex_unlock(&inode->i_mutex);
 
         /* Signal writers asynchronously that there is more room. */
         if (do_wakeup) {
                 wake_up_interruptible_sync(&pipe->wait);
                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
         }
         if (ret > 0)
                 file_accessed(filp);
         return ret;
 }
 
 static ssize_t
 pipe_write(struct kiocb *iocb, const struct iovec *_iov,
             unsigned long nr_segs, loff_t ppos)
 {
         struct file *filp = iocb->ki_filp;
         struct inode *inode = filp->f_path.dentry->d_inode;
         struct pipe_inode_info *pipe;
         ssize_t ret;
         int do_wakeup;
         struct iovec *iov = (struct iovec *)_iov;
         size_t total_len;
         ssize_t chars;
 
         total_len = iov_length(iov, nr_segs);
         /* Null write succeeds. */
         if (unlikely(total_len == 0))
                 return 0;
 
         do_wakeup = 0;
         ret = 0;
         mutex_lock(&inode->i_mutex);
         pipe = inode->i_pipe;
 
         if (!pipe->readers) {
                 send_sig(SIGPIPE, current, 0);
                 ret = -EPIPE;
                 goto out;
         }
 
         /* We try to merge small writes */
         chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
         if (pipe->nrbufs && chars != 0) {
                 int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &
                                                         (PIPE_BUFFERS-1);
                 struct pipe_buffer *buf = pipe->bufs + lastbuf;
                 const struct pipe_buf_operations *ops = buf->ops;
                 int offset = buf->offset + buf->len;
 
                 if (ops->can_merge && offset + chars <= PAGE_SIZE) {
                         int error, atomic = 1;
                         void *addr;
 
                         error = ops->confirm(pipe, buf);
                         if (error)
                                 goto out;
 
                         iov_fault_in_pages_read(iov, chars);
 redo1:
                         addr = ops->map(pipe, buf, atomic);
                         error = pipe_iov_copy_from_user(offset + addr, iov,
                                                         chars, atomic);
                         ops->unmap(pipe, buf, addr);
                         ret = error;
                         do_wakeup = 1;
                         if (error) {
                                 if (atomic) {
                                         atomic = 0;
                                         goto redo1;
                                 }
                                 goto out;
                         }
                         buf->len += chars;
                         total_len -= chars;
                         ret = chars;
                         if (!total_len)
                                 goto out;
                 }
         }
 
         for (;;) {
                 int bufs;
 
                 if (!pipe->readers) {
                         send_sig(SIGPIPE, current, 0);
                         if (!ret)
                                 ret = -EPIPE;
                         break;
                 }
                 bufs = pipe->nrbufs;
                 if (bufs < PIPE_BUFFERS) {
                         int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS-1);
                         struct pipe_buffer *buf = pipe->bufs + newbuf;
                         struct page *page = pipe->tmp_page;
                         char *src;
                         int error, atomic = 1;
 
                         if (!page) {
                                 page = alloc_page(GFP_HIGHUSER);
                                 if (unlikely(!page)) {
                                         ret = ret ? : -ENOMEM;
                                         break;
                                 }
                                 pipe->tmp_page = page;
                         }
                         /* Always wake up, even if the copy fails. Otherwise
                          * we lock up (O_NONBLOCK-)readers that sleep due to
                          * syscall merging.
                          * FIXME! Is this really true?
                          */
                         do_wakeup = 1;
                         chars = PAGE_SIZE;
                         if (chars > total_len)
                                 chars = total_len;
 
                         iov_fault_in_pages_read(iov, chars);
 redo2:
                         if (atomic)
                                 src = kmap_atomic(page, KM_USER0);
                         else
                                 src = kmap(page);
 
                         error = pipe_iov_copy_from_user(src, iov, chars,
                                                         atomic);
                         if (atomic)
                                 kunmap_atomic(src, KM_USER0);
                         else
                                 kunmap(page);
 
                         if (unlikely(error)) {
                                 if (atomic) {
                                         atomic = 0;
                                         goto redo2;
                                 }
                                 if (!ret)
                                         ret = error;
                                 break;
                         }
                         ret += chars;
 
                         /* Insert it into the buffer array */
                         buf->page = page;
                         buf->ops = &anon_pipe_buf_ops;
                         buf->offset = 0;
                         buf->len = chars;
                         pipe->nrbufs = ++bufs;
                         pipe->tmp_page = NULL;
 
                         total_len -= chars;
                         if (!total_len)
                                 break;
                 }
                 if (bufs < PIPE_BUFFERS)
                         continue;
                 if (filp->f_flags & O_NONBLOCK) {
                         if (!ret)
                                 ret = -EAGAIN;
                         break;
                 }
                 if (signal_pending(current)) {
                         if (!ret)
                                 ret = -ERESTARTSYS;
                         break;
                 }
                 if (do_wakeup) {
                         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--;
         }
 out:
         mutex_unlock(&inode->i_mutex);
         if (do_wakeup) {
                 wake_up_interruptible_sync(&pipe->wait);
                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
         }
         if (ret > 0)
                 file_update_time(filp);
         return ret;
 }
 
 static ssize_t
 bad_pipe_r(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
 {
         return -EBADF;
 }
 
 static ssize_t
 bad_pipe_w(struct file *filp, const char __user *buf, size_t count,
            loff_t *ppos)
 {
         return -EBADF;
 }
 
 static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
         struct inode *inode = filp->f_path.dentry->d_inode;
         struct pipe_inode_info *pipe;
         int count, buf, nrbufs;
 
         switch (cmd) {
                 case FIONREAD:
                         mutex_lock(&inode->i_mutex);
                         pipe = inode->i_pipe;
                         count = 0;
                         buf = pipe->curbuf;
                         nrbufs = pipe->nrbufs;
                         while (--nrbufs >= 0) {
                                 count += pipe->bufs[buf].len;
                                 buf = (buf+1) & (PIPE_BUFFERS-1);
                         }
                         mutex_unlock(&inode->i_mutex);
 
                         return put_user(count, (int __user *)arg);
                 default:
                         return -EINVAL;
         }
 }
 
 /* No kernel lock held - fine */
 static unsigned int
 pipe_poll(struct file *filp, poll_table *wait)
 {
         unsigned int mask;
         struct inode *inode = filp->f_path.dentry->d_inode;
         struct pipe_inode_info *pipe = inode->i_pipe;
         int nrbufs;
 
         poll_wait(filp, &pipe->wait, wait);
 
         /* Reading only -- no need for acquiring the semaphore.  */
         nrbufs = pipe->nrbufs;
         mask = 0;
         if (filp->f_mode & FMODE_READ) {
                 mask = (nrbufs > 0) ? POLLIN | POLLRDNORM : 0;
                 if (!pipe->writers && filp->f_version != pipe->w_counter)
                         mask |= POLLHUP;
         }
 
         if (filp->f_mode & FMODE_WRITE) {
                 mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
                 /*
                  * Most Unices do not set POLLERR for FIFOs but on Linux they
                  * behave exactly like pipes for poll().
                  */
                 if (!pipe->readers)
                         mask |= POLLERR;
         }
 
         return mask;
 }
 
 static int
 pipe_release(struct inode *inode, int decr, int decw)
 {
         struct pipe_inode_info *pipe;
 
         mutex_lock(&inode->i_mutex);
         pipe = inode->i_pipe;
         pipe->readers -= decr;
         pipe->writers -= decw;
 
         if (!pipe->readers && !pipe->writers) {
                 free_pipe_info(inode);
         } else {
                 wake_up_interruptible_sync(&pipe->wait);
                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
         }
         mutex_unlock(&inode->i_mutex);
 
         return 0;
 }
 
 static int
 pipe_read_fasync(int fd, struct file *filp, int on)
 {
         struct inode *inode = filp->f_path.dentry->d_inode;
         int retval;
 
         mutex_lock(&inode->i_mutex);
         retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_readers);
         mutex_unlock(&inode->i_mutex);
 
         if (retval < 0)
                 return retval;
 
         return 0;
 }
 
 
 static int
 pipe_write_fasync(int fd, struct file *filp, int on)
 {
         struct inode *inode = filp->f_path.dentry->d_inode;
         int retval;
 
         mutex_lock(&inode->i_mutex);
         retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_writers);
         mutex_unlock(&inode->i_mutex);
 
         if (retval < 0)
                 return retval;
 
         return 0;
 }
 
 
 static int
 pipe_rdwr_fasync(int fd, struct file *filp, int on)
 {
         struct inode *inode = filp->f_path.dentry->d_inode;
         struct pipe_inode_info *pipe = inode->i_pipe;
         int retval;
 
         mutex_lock(&inode->i_mutex);
 
         retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
 
         if (retval >= 0)
                 retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
 
         mutex_unlock(&inode->i_mutex);
 
         if (retval < 0)
                 return retval;
 
         return 0;
 }
 
 
 static int
 pipe_read_release(struct inode *inode, struct file *filp)
 {
         return pipe_release(inode, 1, 0);
 }
 
 static int
 pipe_write_release(struct inode *inode, struct file *filp)
 {
         return pipe_release(inode, 0, 1);
 }
 
 static int
 pipe_rdwr_release(struct inode *inode, struct file *filp)
 {
         int decr, decw;
 
         decr = (filp->f_mode & FMODE_READ) != 0;
         decw = (filp->f_mode & FMODE_WRITE) != 0;
         return pipe_release(inode, decr, decw);
 }
 
 static int
 pipe_read_open(struct inode *inode, struct file *filp)
 {
         /* We could have perhaps used atomic_t, but this and friends
            below are the only places.  So it doesn't seem worthwhile.  */
         mutex_lock(&inode->i_mutex);
         inode->i_pipe->readers++;
         mutex_unlock(&inode->i_mutex);
 
         return 0;
 }
 
 static int
 pipe_write_open(struct inode *inode, struct file *filp)
 {
         mutex_lock(&inode->i_mutex);
         inode->i_pipe->writers++;
         mutex_unlock(&inode->i_mutex);
 
         return 0;
 }
 
 static int
 pipe_rdwr_open(struct inode *inode, struct file *filp)
 {
         mutex_lock(&inode->i_mutex);
         if (filp->f_mode & FMODE_READ)
                 inode->i_pipe->readers++;
         if (filp->f_mode & FMODE_WRITE)
                 inode->i_pipe->writers++;
         mutex_unlock(&inode->i_mutex);
 
         return 0;
 }
 
 /*
  * The file_operations structs are not static because they
  * are also used in linux/fs/fifo.c to do operations on FIFOs.
  *
  * Pipes reuse fifos' file_operations structs.
  */
 const struct file_operations read_pipefifo_fops = {
         .llseek                = no_llseek,
         .read                = do_sync_read,
         .aio_read        = pipe_read,
         .write                = bad_pipe_w,
         .poll                = pipe_poll,
         .unlocked_ioctl        = pipe_ioctl,
         .open                = pipe_read_open,
         .release        = pipe_read_release,
         .fasync                = pipe_read_fasync,
 };
 
 const struct file_operations write_pipefifo_fops = {
         .llseek                = no_llseek,
         .read                = bad_pipe_r,
         .write                = do_sync_write,
         .aio_write        = pipe_write,
         .poll                = pipe_poll,
         .unlocked_ioctl        = pipe_ioctl,
         .open                = pipe_write_open,
         .release        = pipe_write_release,
         .fasync                = pipe_write_fasync,
 };
 
 const struct file_operations rdwr_pipefifo_fops = {
         .llseek                = no_llseek,
         .read                = do_sync_read,
         .aio_read        = pipe_read,
         .write                = do_sync_write,
         .aio_write        = pipe_write,
         .poll                = pipe_poll,
         .unlocked_ioctl        = pipe_ioctl,
         .open                = pipe_rdwr_open,
         .release        = pipe_rdwr_release,
         .fasync                = pipe_rdwr_fasync,
 };
 
 struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
 {
         struct pipe_inode_info *pipe;
 
         pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
         if (pipe) {
                 init_waitqueue_head(&pipe->wait);
                 pipe->r_counter = pipe->w_counter = 1;
                 pipe->inode = inode;
         }
 
         return pipe;
 }
 
 void __free_pipe_info(struct pipe_inode_info *pipe)
 {
         int i;
 
         for (i = 0; i < PIPE_BUFFERS; i++) {
                 struct pipe_buffer *buf = pipe->bufs + i;
                 if (buf->ops)
                         buf->ops->release(pipe, buf);
         }
         if (pipe->tmp_page)
                 __free_page(pipe->tmp_page);
         kfree(pipe);
 }
 
 void free_pipe_info(struct inode *inode)
 {
         __free_pipe_info(inode->i_pipe);
         inode->i_pipe = NULL;
 }
 
 static struct vfsmount *pipe_mnt __read_mostly;
 static int pipefs_delete_dentry(struct dentry *dentry)
 {
         /*
          * At creation time, we pretended this dentry was hashed
          * (by clearing DCACHE_UNHASHED bit in d_flags)
          * At delete time, we restore the truth : not hashed.
          * (so that dput() can proceed correctly)
          */
         dentry->d_flags |= DCACHE_UNHASHED;
         return 0;
 }
 
 /*
  * pipefs_dname() is called from d_path().
  */
 static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
 {
         return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
                                 dentry->d_inode->i_ino);
 }
 
 static struct dentry_operations pipefs_dentry_operations = {
         .d_delete        = pipefs_delete_dentry,
         .d_dname        = pipefs_dname,
 };
 
 static struct inode * get_pipe_inode(void)
 {
         struct inode *inode = new_inode(pipe_mnt->mnt_sb);
         struct pipe_inode_info *pipe;
 
         if (!inode)
                 goto fail_inode;
 
         pipe = alloc_pipe_info(inode);
         if (!pipe)
                 goto fail_iput;
         inode->i_pipe = pipe;
 
         pipe->readers = pipe->writers = 1;
         inode->i_fop = &rdwr_pipefifo_fops;
 
         /*
          * Mark the inode dirty from the very beginning,
          * that way it will never be moved to the dirty
          * list because "mark_inode_dirty()" will think
          * that it already _is_ on the dirty list.
          */
         inode->i_state = I_DIRTY;
         inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
         inode->i_uid = current->fsuid;
         inode->i_gid = current->fsgid;
         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 
         return inode;
 
 fail_iput:
         iput(inode);
 
 fail_inode:
         return NULL;
 }
 
 struct file *create_write_pipe(int flags)
 {
         int err;
         struct inode *inode;
         struct file *f;
         struct dentry *dentry;
         struct qstr name = { .name = "" };
 
         err = -ENFILE;
         inode = get_pipe_inode();
         if (!inode)
                 goto err;
 
         err = -ENOMEM;
         dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);
         if (!dentry)
                 goto err_inode;
 
         dentry->d_op = &pipefs_dentry_operations;
         /*
          * We dont want to publish this dentry into global dentry hash table.
          * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
          * This permits a working /proc/$pid/fd/XXX on pipes
          */
         dentry->d_flags &= ~DCACHE_UNHASHED;
         d_instantiate(dentry, inode);
 
         err = -ENFILE;
         f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipefifo_fops);
         if (!f)
                 goto err_dentry;
         f->f_mapping = inode->i_mapping;
 
         f->f_flags = O_WRONLY | (flags & O_NONBLOCK);
         f->f_version = 0;
 
         return f;
 
  err_dentry:
         free_pipe_info(inode);
         dput(dentry);
         return ERR_PTR(err);
 
  err_inode:
         free_pipe_info(inode);
         iput(inode);
  err:
         return ERR_PTR(err);
 }
 
 void free_write_pipe(struct file *f)
 {
         free_pipe_info(f->f_dentry->d_inode);
         path_put(&f->f_path);
         put_filp(f);
 }
 
 struct file *create_read_pipe(struct file *wrf, int flags)
 {
         struct file *f = get_empty_filp();
         if (!f)
                 return ERR_PTR(-ENFILE);
 
         /* Grab pipe from the writer */
         f->f_path = wrf->f_path;
         path_get(&wrf->f_path);
         f->f_mapping = wrf->f_path.dentry->d_inode->i_mapping;
 
         f->f_pos = 0;
         f->f_flags = O_RDONLY | (flags & O_NONBLOCK);
         f->f_op = &read_pipefifo_fops;
         f->f_mode = FMODE_READ;
         f->f_version = 0;
 
         return f;
 }
 
 int do_pipe_flags(int *fd, int flags)
 {
         struct file *fw, *fr;
         int error;
         int fdw, fdr;
 
         if (flags & ~(O_CLOEXEC | O_NONBLOCK))
                 return -EINVAL;

        fw = create_write_pipe(flags);
        if (IS_ERR(fw))
                return PTR_ERR(fw);
        fr = create_read_pipe(fw, flags);
        error = PTR_ERR(fr);
        if (IS_ERR(fr))
                goto err_write_pipe;

        error = get_unused_fd_flags(flags);
        if (error < 0)
                goto err_read_pipe;
        fdr = error;

        error = get_unused_fd_flags(flags);
        if (error < 0)
                goto err_fdr;
        fdw = error;

        error = audit_fd_pair(fdr, fdw);
        if (error < 0)
                goto err_fdw;

        fd_install(fdr, fr);
        fd_install(fdw, fw);
        fd[0] = fdr;
        fd[1] = fdw;

        return 0;

 err_fdw:
        put_unused_fd(fdw);
 err_fdr:
        put_unused_fd(fdr);
 err_read_pipe:
        path_put(&fr->f_path);
        put_filp(fr);
 err_write_pipe:
        free_write_pipe(fw);
        return error;
}

int do_pipe(int *fd)
{
        return do_pipe_flags(fd, 0);
}

/*
 * sys_pipe() is the normal C calling standard for creating
 * a pipe. It's not the way Unix traditionally does this, though.
 */
asmlinkage long __weak sys_pipe2(int __user *fildes, int flags)
{
        int fd[2];
        int error;

        error = do_pipe_flags(fd, flags);
        if (!error) {
                if (copy_to_user(fildes, fd, sizeof(fd))) {
                        sys_close(fd[0]);
                        sys_close(fd[1]);
                        error = -EFAULT;
                }
        }
        return error;
}

asmlinkage long __weak sys_pipe(int __user *fildes)
{
        return sys_pipe2(fildes, 0);
}

/*
 * pipefs should _never_ be mounted by userland - too much of security hassle,
 * no real gain from having the whole whorehouse mounted. So we don't need
 * any operations on the root directory. However, we need a non-trivial
 * d_name - pipe: will go nicely and kill the special-casing in procfs.
 */
static int pipefs_get_sb(struct file_system_type *fs_type,
                         int flags, const char *dev_name, void *data,
                         struct vfsmount *mnt)
{
        return get_sb_pseudo(fs_type, "pipe:", NULL, PIPEFS_MAGIC, mnt);
}

static struct file_system_type pipe_fs_type = {
        .name                = "pipefs",
        .get_sb                = pipefs_get_sb,
        .kill_sb        = kill_anon_super,
};

static int __init init_pipe_fs(void)
{
        int err = register_filesystem(&pipe_fs_type);

        if (!err) {
                pipe_mnt = kern_mount(&pipe_fs_type);
                if (IS_ERR(pipe_mnt)) {
                        err = PTR_ERR(pipe_mnt);
                        unregister_filesystem(&pipe_fs_type);
                }
        }
        return err;
}

static void __exit exit_pipe_fs(void)
{
        unregister_filesystem(&pipe_fs_type);
        mntput(pipe_mnt);
}

fs_initcall(init_pipe_fs);
module_exit(exit_pipe_fs);