+ * 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 nr_pages)
+{
+ struct pipe_buffer *bufs;
+
+ /*
+ * 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 (nr_pages < pipe->nrbufs)
+ return -EBUSY;
+
+ bufs = kcalloc(nr_pages, 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 = nr_pages;
+ return nr_pages * PAGE_SIZE;
+}
+
+/*
+ * Currently we rely on the pipe array holding a power-of-2 number
+ * of pages.
+ */
+static inline unsigned int round_pipe_size(unsigned int size)
+{
+ unsigned long nr_pages;
+
+ nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
+}
+
+/*
+ * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
+ * will return an error.
+ */
+int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
+ size_t *lenp, loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
+ if (ret < 0 || !write)
+ return ret;
+
+ pipe_max_size = round_pipe_size(pipe_max_size);
+ return ret;
+}
+
+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: {
+ unsigned int size, nr_pages;
+
+ size = round_pipe_size(arg);
+ nr_pages = size >> PAGE_SHIFT;
+
+ if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
+ ret = -EPERM;
+ goto out;
+ } else if (nr_pages < PAGE_SIZE) {
+ ret = -EINVAL;
+ goto out;
+ }
+ ret = pipe_set_size(pipe, nr_pages);
+ break;
+ }
+ case F_GETPIPE_SZ:
+ ret = pipe->buffers * PAGE_SIZE;
+ break;
+ default:
+ ret = -EINVAL;
+ break;
+ }
+
+out:
+ mutex_unlock(&pipe->inode->i_mutex);
+ return ret;
+}
+
+/*