Subject: Re: [PATCH bpf-next v3 5/7] samples/bpf: Add a "force" flag to XDP samples

From: Jesper Dangaard Brouer <[email-masked]>
Date: Fri, 25 Jan 2019 09:38:22 +0100

On Thu, 24 Jan 2019 22:47:45 +0100
Maciej Fijalkowski <[email-masked]> wrote:

> diff --git a/samples/bpf/xdp_sample_pkts_user.c b/samples/bpf/xdp_sample_pkts_user.c
> index 5f5828ee0761..362ad35b524d 100644
> --- a/samples/bpf/xdp_sample_pkts_user.c
> +++ b/samples/bpf/xdp_sample_pkts_user.c
> @@ -13,6 +13,8 @@
>  #include <libbpf.h>
>  #include <bpf/bpf.h>
>  #include <sys/resource.h>
> +#include <libgen.h>
> +#include <linux/if_link.h>
>  
>  #include "perf-sys.h"
>  #include "trace_helpers.h"
> @@ -21,12 +23,13 @@
>  static int pmu_fds[MAX_CPUS], if_idx;
>  static struct perf_event_mmap_page *headers[MAX_CPUS];
>  static char *if_name;
> +static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
>  
>  static int do_attach(int idx, int fd, const char *name)
>  {
>  	int err;
>  
> -	err = bpf_set_link_xdp_fd(idx, fd, 0);
> +	err = bpf_set_link_xdp_fd(idx, fd, xdp_flags);
>  	if (err < 0)
>  		printf("ERROR: failed to attach program to %s\n", name);
>  
> @@ -98,21 +101,42 @@ static void sig_handler(int signo)
>  	exit(0);
>  }
>  
> +static void usage(const char *prog)
> +{
> +	fprintf(stderr,
> +		"%s: %s [OPTS] IFINDEX\n\n"
                               ^^^^^^^
The usage help text is wrong, this sample takes the interface name as input.

> +		"OPTS:\n"
> +		"    -F    force loading prog\n",
> +		__func__, prog);
> +}
> +
>  int main(int argc, char **argv)
>  {
>  	struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
>  	struct bpf_prog_load_attr prog_load_attr = {
>  		.prog_type	= BPF_PROG_TYPE_XDP,
>  	};
> +	const char *optstr = "F";
> +	int prog_fd, map_fd, opt;
>  	struct bpf_object *obj;
>  	struct bpf_map *map;
> -	int prog_fd, map_fd;
>  	char filename[256];
>  	int ret, err, i;
>  	int numcpus;
>  
> -	if (argc < 2) {
> -		printf("Usage: %s <ifname>\n", argv[0]);
                                  ^^^^^^^^
Old help text says <ifname>

> +	while ((opt = getopt(argc, argv, optstr)) != -1) {
> +		switch (opt) {
> +		case 'F':
> +			xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;
> +			break;
> +		default:
> +			usage(basename(argv[0]));
> +			return 1;
> +		}
> +	}
> +
> +	if (optind == argc) {
> +		usage(basename(argv[0]));
>  		return 1;
>  	}
>  
> @@ -143,16 +167,16 @@ int main(int argc, char **argv)
>  	}
>  	map_fd = bpf_map__fd(map);
>  
> -	if_idx = if_nametoindex(argv[1]);
> +	if_idx = if_nametoindex(argv[optind]);

The we convert the ifname to ifindex.

>  	if (!if_idx)
> -		if_idx = strtoul(argv[1], NULL, 0);
> +		if_idx = strtoul(argv[optind], NULL, 0);
>  

We do support falling back to using this as an ifindex.

>  	if (!if_idx) {
>  		fprintf(stderr, "Invalid ifname\n");
>  		return 1;
>  	}
> -	if_name = argv[1];
> -	err = do_attach(if_idx, prog_fd, argv[1]);
> +	if_name = argv[optind];
> +	err = do_attach(if_idx, prog_fd, if_name);
>  	if (err)
>  		return err;

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer