static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node)
{
	const gfp_t flags = GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL |
			    __GFP_NOWARN | __GFP_ZERO;
	int nr_meta_pages = RINGBUF_PGOFF + RINGBUF_POS_PAGES;
	int nr_data_pages = data_sz >> PAGE_SHIFT;
	int nr_pages = nr_meta_pages + nr_data_pages;
	struct page **pages, *page;
	struct bpf_ringbuf *rb;
	size_t array_size;
	int i;

	/* Each data page is mapped twice to allow "virtual"
	 * continuous read of samples wrapping around the end of ring
	 * buffer area:
	 * ------------------------------------------------------
	 * | meta pages |  real data pages  |  same data pages  |
	 * ------------------------------------------------------
	 * |            | 1 2 3 4 5 6 7 8 9 | 1 2 3 4 5 6 7 8 9 |
	 * ------------------------------------------------------
	 * |            | TA             DA | TA             DA |
	 * ------------------------------------------------------
	 *                               ^^^^^^^
	 *                                  |
	 * Here, no need to worry about special handling of wrapped-around
	 * data due to double-mapped data pages. This works both in kernel and
	 * when mmap()'ed in user-space, simplifying both kernel and
	 * user-space implementations significantly.
	 */
	array_size = (nr_meta_pages + 2 * nr_data_pages) * sizeof(*pages);
	pages = bpf_map_area_alloc(array_size, numa_node);
	if (!pages)
		return NULL;

	for (i = 0; i < nr_pages; i++) {
		page = alloc_pages_node(numa_node, flags, 0);
		if (!page) {
			nr_pages = i;
			goto err_free_pages;
		}
		pages[i] = page;
		if (i >= nr_meta_pages)
			pages[nr_data_pages + i] = page;
	}

	rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages,
		  VM_ALLOC | VM_USERMAP, PAGE_KERNEL);
	if (rb) {
		rb->pages = pages;
		rb->nr_pages = nr_pages;
		return rb;
	}

err_free_pages:
	for (i = 0; i < nr_pages; i++)
		__free_page(pages[i]);
	kvfree(pages);
	return NULL;
}
static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node)
{
	const gfp_t flags = GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL |
			    __GFP_NOWARN | __GFP_ZERO;
	int nr_meta_pages = RINGBUF_PGOFF + RINGBUF_POS_PAGES;
	int nr_data_pages = data_sz >> PAGE_SHIFT;
	int nr_pages = nr_meta_pages + nr_data_pages;
	struct page **pages, *page;
	struct bpf_ringbuf *rb;
	size_t array_size;
	int i;

	 
	array_size = (nr_meta_pages + 2 * nr_data_pages) * sizeof(*pages);
	pages = bpf_map_area_alloc(array_size, numa_node);
	if (!pages)
		return NULL;

	for (i = 0; i < nr_pages; i++) {
		page = alloc_pages_node(numa_node, flags, 0);
		if (!page) {
			nr_pages = i;
			goto err_free_pages;
		}
		pages[i] = page;
		if (i >= nr_meta_pages)
			pages[nr_data_pages + i] = page;
	}

	rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages,
		  VM_ALLOC | VM_USERMAP, PAGE_KERNEL);
	if (rb) {
		rb->pages = pages;
		rb->nr_pages = nr_pages;
		return rb;
	}

err_free_pages:
	for (i = 0; i < nr_pages; i++)
		__free_page(pages[i]);
	kvfree(pages);
	return NULL;
}