+/*
+ * Allocate a new array of pipe buffers and copy the info over. Returns the
+ * pipe size if successful, or return -ERROR on error.
+ */
+static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
+{
+ struct pipe_buffer *bufs;
+
+ /*
+ * Must be a power-of-2 currently
+ */
+ if (!is_power_of_2(arg))
+ return -EINVAL;
+
+ /*
+ * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
+ * expect a lot of shrink+grow operations, just free and allocate
+ * again like we would do for growing. If the pipe currently
+ * contains more buffers than arg, then return busy.
+ */
+ if (arg < pipe->nrbufs)
+ return -EBUSY;
+
+ bufs = kcalloc(arg, sizeof(struct pipe_buffer), GFP_KERNEL);
+ if (unlikely(!bufs))
+ return -ENOMEM;
+
+ /*
+ * The pipe array wraps around, so just start the new one at zero
+ * and adjust the indexes.
+ */
+ if (pipe->nrbufs) {
+ const unsigned int tail = pipe->nrbufs & (pipe->buffers - 1);
+ const unsigned int head = pipe->nrbufs - tail;
+
+ if (head)
+ memcpy(bufs, pipe->bufs + pipe->curbuf, head * sizeof(struct pipe_buffer));
+ if (tail)
+ memcpy(bufs + head, pipe->bufs + pipe->curbuf, tail * sizeof(struct pipe_buffer));
+ }
+
+ pipe->curbuf = 0;
+ kfree(pipe->bufs);
+ pipe->bufs = bufs;
+ pipe->buffers = arg;
+ return arg;
+}
+
+long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+ struct pipe_inode_info *pipe;
+ long ret;
+
+ pipe = file->f_path.dentry->d_inode->i_pipe;
+ if (!pipe)
+ return -EBADF;
+
+ mutex_lock(&pipe->inode->i_mutex);
+
+ switch (cmd) {
+ case F_SETPIPE_SZ:
+ if (!capable(CAP_SYS_ADMIN) && arg > pipe_max_pages) {
+ ret = -EINVAL;
+ goto out;
+ }
+ /*
+ * The pipe needs to be at least 2 pages large to
+ * guarantee POSIX behaviour.
+ */
+ if (arg < 2) {
+ ret = -EINVAL;
+ goto out;
+ }
+ ret = pipe_set_size(pipe, arg);
+ break;
+ case F_GETPIPE_SZ:
+ ret = pipe->buffers;
+ break;
+ default:
+ ret = -EINVAL;
+ break;
+ }
+
+out:
+ mutex_unlock(&pipe->inode->i_mutex);
+ return ret;
+}
+