netdev - Re: [PATCH bpf-next 2/3] bpftool: match programs by name

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Date:   Tue, 10 Dec 2019 13:04:13 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Paul Chaignon <paul.chaignon@...nge.com>
Cc:     bpf@...r.kernel.org, Quentin Monnet <quentin.monnet@...ronome.com>,
        paul.chaignon@...il.com, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf-next 2/3] bpftool: match programs by name

On Tue, 10 Dec 2019 17:06:42 +0100, Paul Chaignon wrote:
> When working with frequently modified BPF programs, both the ID and the
> tag may change.  bpftool currently doesn't provide a "stable" way to match
> such programs.
> 
> This patch implements lookup by name for programs.  The show and dump
> commands will return all programs with the given name, whereas other
> commands will error out if several programs have the same name.
> 
> Signed-off-by: Paul Chaignon <paul.chaignon@...nge.com>

> @@ -164,7 +165,7 @@ prog_parse_fds(int *argc, char ***argv, int *fds)
>  		}
>  		return 1;
>  	} else if (is_prefix(**argv, "tag")) {
> -		unsigned char tag[BPF_TAG_SIZE];
> +		char tag[BPF_TAG_SIZE];

Perhaps better to change the argument to prog_fd_by_nametag() to void *?

>  
>  		NEXT_ARGP();
>  
> @@ -176,7 +177,20 @@ prog_parse_fds(int *argc, char ***argv, int *fds)
>  		}
>  		NEXT_ARGP();
>  
> -		return prog_fd_by_tag(tag, fds);
> +		return prog_fd_by_nametag(tag, fds, true);
> +	} else if (is_prefix(**argv, "name")) {
> +		char *name;
> +
> +		NEXT_ARGP();
> +
> +		name = **argv;
> +		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {

Is this needed? strncmp will simply never match, is it preferred to
hard error?

> +			p_err("can't parse name");
> +			return -1;
> +		}
> +		NEXT_ARGP();
> +
> +		return prog_fd_by_nametag(name, fds, false);
>  	} else if (is_prefix(**argv, "pinned")) {
>  		char *path;
>  
> @@ -191,7 +205,7 @@ prog_parse_fds(int *argc, char ***argv, int *fds)
>  		return 1;
>  	}
>  
> -	p_err("expected 'id', 'tag' or 'pinned', got: '%s'?", **argv);
> +	p_err("expected 'id', 'tag', 'name' or 'pinned', got: '%s'?", **argv);
>  	return -1;
>  }
>