netdev - Re: [PATCH bpf-next v7 2/5] libbpf: add function to setup XDP

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Date:   Sat, 27 Jan 2018 02:23:36 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Eric Leblond <eric@...it.org>
Cc:     alexei.starovoitov@...il.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v7 2/5] libbpf: add function to setup XDP

On 01/25/2018 01:05 AM, Eric Leblond wrote:
> Most of the code is taken from set_link_xdp_fd() in bpf_load.c and
> slightly modified to be library compliant.
> 
> Signed-off-by: Eric Leblond <eric@...it.org>
> Acked-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  tools/lib/bpf/bpf.c    | 127 +++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/lib/bpf/libbpf.c |   2 +
>  tools/lib/bpf/libbpf.h |   4 ++
>  3 files changed, 133 insertions(+)
> 
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 5128677e4117..749a447ec9ed 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -25,6 +25,17 @@
>  #include <asm/unistd.h>
>  #include <linux/bpf.h>
>  #include "bpf.h"
> +#include "libbpf.h"
> +#include "nlattr.h"
> +#include <uapi/linux/rtnetlink.h>

Doesn't libbpf pull in already -I$(srctree)/tools/include/uapi? Seems the
other headers don't need 'uapi/' path prefix.

> +#include <sys/socket.h>
> +#include <errno.h>
> +
> +#ifndef IFLA_XDP_MAX
> +#define IFLA_XDP	43
> +#define IFLA_XDP_FD	1
> +#define IFLA_XDP_FLAGS	3
> +#endif

Hm, given we pull in tools/include/uapi/linux/netlink.h, shouldn't we also
get include/uapi/linux/if_link.h dependency in here, so above ifdef workaround
can be avoided?

>  /*
>   * When building perf, unistd.h is overridden. __NR_bpf is
> @@ -46,7 +57,9 @@
>  # endif
>  #endif
>  
> +#ifndef min
>  #define min(x, y) ((x) < (y) ? (x) : (y))
> +#endif
>  
>  static inline __u64 ptr_to_u64(const void *ptr)
>  {
> @@ -413,3 +426,117 @@ int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
>  
>  	return err;
>  }
> +
> +int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
> +{
> +	struct sockaddr_nl sa;
> +	int sock, seq = 0, len, ret = -1;
> +	char buf[4096];
> +	struct nlattr *nla, *nla_xdp;
> +	struct {
[...]