linux-kernel - Re: [PATCH bpf-next] bpftool: specify XDP Hints ifname when loading program

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Date:   Fri, 12 May 2023 11:23:00 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Larysa Zaremba <larysa.zaremba@...el.com>
Cc:     Stanislav Fomichev <sdf@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Niklas Söderlund <niklas.soderlund@...igine.com>
Subject: Re: [PATCH bpf-next] bpftool: specify XDP Hints ifname when loading
 program

2023-05-11 17:13 UTC+0200 ~ Larysa Zaremba <larysa.zaremba@...el.com>
> Add ability to specify a network interface used to resolve
> XDP Hints kfuncs when loading program through bpftool.
> 
> Usage:
> bpftool prog load <bpf_obj_path> <pin_path> dev xdpmeta <ifname>

Thanks for this patch!

Regarding the command-line syntax, I'm not a big fan of the optional
sub-keyword for the device for XDP hints. I must admit I had not
anticipated other another use for the "dev" keyword. Instead, have you
considered one of the following:

1) Adding a different keyword ("xdpmeta_dev"?) and making it
incompatible with "dev"

2) Another alternative would be adding a sub-keyword for offload too:

    bpftool p l [...] dev <[offload <ifname> | xdpmeta <ifname>]>

If the ifname is provided with no sub-keyword, we would consider it for
offload for legacy support, possibly warn that the syntax is deprecated.

What do you think?

> 
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---
>  tools/bpf/bpftool/prog.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index 91b6075b2db3..a9cb96d99277 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -1517,12 +1517,13 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  	struct bpf_program *prog = NULL, *pos;
>  	unsigned int old_map_fds = 0;
>  	const char *pinmaps = NULL;
> +	__u32 offload_ifindex = 0;
>  	bool auto_attach = false;
> +	__u32 meta_ifindex = 0;
>  	struct bpf_object *obj;
>  	struct bpf_map *map;
>  	const char *pinfile;
>  	unsigned int i, j;
> -	__u32 ifindex = 0;
>  	const char *file;
>  	int idx, err;
>  
> @@ -1614,17 +1615,25 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  			map_replace[old_map_fds].fd = fd;
>  			old_map_fds++;
>  		} else if (is_prefix(*argv, "dev")) {
> +			__u32 *cur_ifindex;
> +
>  			NEXT_ARG();
>  
> -			if (ifindex) {
> -				p_err("offload device already specified");
> +			if (offload_ifindex || meta_ifindex) {
> +				p_err("device already specified");

I'd add a note to tell somehow that offload and XDP hints are mutually
exclusive. I suspect not all users understand these well.

>  				goto err_free_reuse_maps;
>  			}
> +			if (is_prefix(*argv, "xdpmeta")) {
> +				cur_ifindex = &meta_ifindex;
> +				NEXT_ARG();
> +			} else {
> +				cur_ifindex = &offload_ifindex;
> +			}
>  			if (!REQ_ARGS(1))
>  				goto err_free_reuse_maps;
>  
> -			ifindex = if_nametoindex(*argv);
> -			if (!ifindex) {
> +			*cur_ifindex = if_nametoindex(*argv);
> +			if (!(*cur_ifindex)) {
>  				p_err("unrecognized netdevice '%s': %s",
>  				      *argv, strerror(errno));
>  				goto err_free_reuse_maps;
> @@ -1671,7 +1680,12 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  				goto err_close_obj;
>  		}
>  
> -		bpf_program__set_ifindex(pos, ifindex);
> +		if (prog_type == BPF_PROG_TYPE_XDP && meta_ifindex) {
> +			bpf_program__set_flags(pos, BPF_F_XDP_DEV_BOUND_ONLY);
> +			bpf_program__set_ifindex(pos, meta_ifindex);
> +		} else {
> +			bpf_program__set_ifindex(pos, offload_ifindex);
> +		}
>  		if (bpf_program__type(pos) != prog_type)
>  			bpf_program__set_type(pos, prog_type);
>  		bpf_program__set_expected_attach_type(pos, expected_attach_type);
> @@ -1709,7 +1723,7 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  	idx = 0;
>  	bpf_object__for_each_map(map, obj) {
>  		if (bpf_map__type(map) != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
> -			bpf_map__set_ifindex(map, ifindex);
> +			bpf_map__set_ifindex(map, offload_ifindex);
>  
>  		if (j < old_map_fds && idx == map_replace[j].idx) {
>  			err = bpf_map__reuse_fd(map, map_replace[j++].fd);

Could you please also update the following items:

- The usage message for "bpftool prog load" near the end of prog.c

- The related doc in Documentation/bpftool-prog.rst (command summary
near the top, and detailed description later in the doc)

- Bash completion (for keyword "dev", look for "_sysfs_get_netdevs" in
bash-completion/bpftool). I'm happy to help with this one if necessary.

Thanks,
Quentin