[CRIU] [PATCH 5/9] Handle vmsplice failure for read mode pre-dump

[Andrei Vagin]

On Sun, Sep 22, 2019 at 09:54:54AM +0530, Abhishek Dubey wrote:
> vmsplice fails to completely splice 2^k pages
> from user-buffer to ppb pipes. Sometimes last
> page is partially spliced.
> To overcome this, page count for splicing is
> kept 1 less than the size of pipe.
> 
> Signed-off-by: Abhishek Dubey <dubeyabhishek777 at gmail.com>
> ---
>  criu/page-pipe.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/criu/page-pipe.c b/criu/page-pipe.c
> index a821696..e60dd85 100644
> --- a/criu/page-pipe.c
> +++ b/criu/page-pipe.c
> @@ -40,6 +40,22 @@ static int __ppb_resize_pipe(struct page_pipe_buf *ppb, unsigned long new_size)
>  	ret /= PAGE_SIZE;
>  	BUG_ON(ret < ppb->pipe_size);
>  
> +	/*
> +	 * TODO: Investigate and handle
> +	 * Sometimes vmsplice fails to splice N pages(where N=2^k)
> +	 * from user buffer to pipe, so restricting page-pipe
> +	 * capacity to accommodate N-1 pages.
> +	 * e.g. Pipe size can be 512 pages, but it's filled till
> +	 * 511 pages.
> +	 *
> +	 * Steps to reproduce issue:
> +	 * 1. Comment-out next two lines following this comment
> +	 * 2. Run maps007/maps004 from transitive tests with
> +	 *    --pre-dump-mode=read option
> +	 */
> +	if (opts.pre_dump_mode == PRE_DUMP_READ)
> +		ret -= 1;

This doesn't look nice...

> +
>  	pr_debug("Grow pipe %x -> %x\n", ppb->pipe_size, ret);
>  	ppb->pipe_size = ret;
>  
> -- 
> 2.7.4
>