netdev - Re: [PATCHv2 bpf-next] libbpf: making bpf_prog_load() ignore name if kernel doesn't support

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Date:   Mon, 15 Aug 2022 16:36:01 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        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>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org
Subject: Re: [PATCHv2 bpf-next] libbpf: making bpf_prog_load() ignore name if
 kernel doesn't support

On 13/08/2022 01:09, Hangbin Liu wrote:
> Similar with commit 10b62d6a38f7 ("libbpf: Add names for auxiliary maps"),
> let's make bpf_prog_load() also ignore name if kernel doesn't support
> program name.
> 
> To achieve this, we need to call sys_bpf_prog_load() directly in
> probe_kern_prog_name() to avoid circular dependency. sys_bpf_prog_load()
> also need to be exported in the libbpf_internal.h file.
> 
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
> v2: move sys_bpf_prog_load definition to libbpf_internal.h. memset attr
>     to 0 specifically to aviod padding.
> ---
>  tools/lib/bpf/bpf.c             |  6 ++----
>  tools/lib/bpf/libbpf.c          | 12 ++++++++++--
>  tools/lib/bpf/libbpf_internal.h |  3 +++
>  3 files changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 6a96e665dc5d..575867d69496 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -84,9 +84,7 @@ static inline int sys_bpf_fd(enum bpf_cmd cmd, union bpf_attr *attr,
>  	return ensure_good_fd(fd);
>  }
>  
> -#define PROG_LOAD_ATTEMPTS 5
> -
> -static inline int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int attempts)
> +int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int attempts)
>  {
>  	int fd;
>  
> @@ -263,7 +261,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type,
>  	attr.prog_ifindex = OPTS_GET(opts, prog_ifindex, 0);
>  	attr.kern_version = OPTS_GET(opts, kern_version, 0);
>  
> -	if (prog_name)
> +	if (prog_name && kernel_supports(NULL, FEAT_PROG_NAME))
>  		libbpf_strlcpy(attr.prog_name, prog_name, sizeof(attr.prog_name));
>  	attr.license = ptr_to_u64(license);
>  
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 3f01f5cd8a4c..4a351897bdcc 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4419,10 +4419,18 @@ static int probe_kern_prog_name(void)
>  		BPF_MOV64_IMM(BPF_REG_0, 0),
>  		BPF_EXIT_INSN(),
>  	};
> -	int ret, insn_cnt = ARRAY_SIZE(insns);
> +	union bpf_attr attr;
> +	int ret;
> +
> +	memset(&attr, 0, sizeof(attr));
> +	attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
> +	attr.license = ptr_to_u64("GPL");
> +	attr.insns = ptr_to_u64(insns);
> +	attr.insn_cnt = (__u32)ARRAY_SIZE(insns);
> +	libbpf_strlcpy(attr.prog_name, "test", sizeof(attr.prog_name));
>  
>  	/* make sure loading with name works */
> -	ret = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "test", "GPL", insns, insn_cnt, NULL);
> +	ret = sys_bpf_prog_load(&attr, sizeof(attr), PROG_LOAD_ATTEMPTS);
>  	return probe_fd(ret);
>  }
>  
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index 4135ae0a2bc3..377642ff51fc 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -573,4 +573,7 @@ static inline bool is_pow_of_2(size_t x)
>  	return x && (x & (x - 1)) == 0;
>  }
>  
> +#define PROG_LOAD_ATTEMPTS 5
> +int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int attempts);
> +
>  #endif /* __LIBBPF_LIBBPF_INTERNAL_H */

Looks good to me, thanks!

Acked-by: Quentin Monnet <quentin@...valent.com>