[CRIU] [PATCH] criu: uffd runtime detection

[Mike Rapoport]

On Wed, May 04, 2016 at 08:22:25AM +0000, Adrian Reber wrote:
> From: Adrian Reber <areber at redhat.com>
> 
> Now that userfaultfd/lazy-pages support is enable all the time, this
> adds runtime detection of userfaultfd. On a system without the
> userfaultfd syscall following is printed:
> 
> uffd daemon:
> 
> (00.000004) Error (uffd.c:176): lazy-pages: Runtime detection of userfaultfd failed on this system.
> (00.000024) Error (uffd.c:177): lazy-pages: Processes cannot be lazy-restored on this system.
> 
> or criu restore
> 
> (00.457047)   6858: Error (uffd.c:176): lazy-pages: Runtime detection of userfaultfd failed on this system.
> (00.457049)   6858: Error (uffd.c:177): lazy-pages: Processes cannot be lazy-restored on this system.
> 
> Signed-off-by: Adrian Reber <areber at redhat.com>
> ---
>  criu/uffd.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)

Acked-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
 
> diff --git a/criu/uffd.c b/criu/uffd.c
> index c17f003..fb0cab1 100644
> --- a/criu/uffd.c
> +++ b/criu/uffd.c
> @@ -160,10 +160,33 @@ out:
>  	return ret;
>  }
> 
> +/* Runtime detection if userfaultfd can be used */
> +
> +static int check_for_uffd()
> +{
> +	int uffd;
> +
> +	uffd = syscall(SYS_userfaultfd, 0);
> +	/*
> +	 * uffd == -1 is probably enough to not use lazy-restore
> +	 * on this system. Additionally checking for ENOSYS
> +	 * makes sure it is actually not implemented.
> +	 */
> +	if ((uffd == -1) && (errno == ENOSYS)) {
> +		pr_err("Runtime detection of userfaultfd failed on this system.\n");
> +		pr_err("Processes cannot be lazy-restored on this system.\n");
> +		return -1;
> +	}
> +	close(uffd);
> +	return 0;
> +}
> +
>  /* This function is used by 'criu restore --lazy-pages' */
>  int setup_uffd(struct task_restore_args *task_args, int pid)
>  {
>  	struct uffdio_api uffdio_api;
> +	if (check_for_uffd())
> +		return -1;
>  	/*
>  	 * Open userfaulfd FD which is passed to the restorer blob and
>  	 * to a second process handling the userfaultfd page faults.
> @@ -810,6 +833,9 @@ int cr_lazy_pages()
>  	int epollfd;
>  	int ret;
> 
> +	if (check_for_uffd())
> +		return -1;
> +
>  	if (!opts.addr) {
>  		pr_info("Please specify a file name for the unix domain socket\n");
>  		pr_info("used to communicate between the lazy-pages server\n");
> -- 
> 1.8.3.1
> 
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