netdev - Re: [PATCH v2 bpf-next 10/12] bpftool: add C output format option to btf dump subcommand

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Date:   Fri, 24 May 2019 10:13:59 +0100
From:   Quentin Monnet <quentin.monnet@...ronome.com>
To:     Andrii Nakryiko <andriin@...com>, andrii.nakryiko@...il.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...com,
        daniel@...earbox.net, kernel-team@...com
Subject: Re: [PATCH v2 bpf-next 10/12] bpftool: add C output format option to
 btf dump subcommand

Hi Andrii,

Some nits inline, nothing blocking though.

2019-05-23 13:42 UTC-0700 ~ Andrii Nakryiko <andriin@...com>
> Utilize new libbpf's btf_dump API to emit BTF as a C definitions.
> 
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>  tools/bpf/bpftool/btf.c | 74 +++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 72 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index a22ef6587ebe..1cdbfad42b38 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -340,11 +340,48 @@ static int dump_btf_raw(const struct btf *btf,
>  	return 0;
>  }
>  
> +static void btf_dump_printf(void *ctx, const char *fmt, va_list args)

Nit: This function could have a printf attribute ("__printf(2, 0)").

> +{
> +	vfprintf(stdout, fmt, args);
> +}
> +
> +static int dump_btf_c(const struct btf *btf,
> +		      __u32 *root_type_ids, int root_type_cnt)
> +{
> +	struct btf_dump *d;
> +	int err = 0, i;
> +
> +	d = btf_dump__new(btf, NULL, NULL, btf_dump_printf);
> +	if (IS_ERR(d))
> +		return PTR_ERR(d);
> +
> +	if (root_type_cnt) {
> +		for (i = 0; i < root_type_cnt; i++) {
> +			err = btf_dump__dump_type(d, root_type_ids[i]);
> +			if (err)
> +				goto done;
> +		}
> +	} else {
> +		int cnt = btf__get_nr_types(btf);
> +
> +		for (i = 1; i <= cnt; i++) {
> +			err = btf_dump__dump_type(d, i);
> +			if (err)
> +				goto done;
> +		}
> +	}
> +
> +done:
> +	btf_dump__free(d);
> +	return err;
> +}
> +
>  static int do_dump(int argc, char **argv)
>  {
>  	struct btf *btf = NULL;
>  	__u32 root_type_ids[2];
>  	int root_type_cnt = 0;
> +	bool dump_c = false;
>  	__u32 btf_id = -1;
>  	const char *src;
>  	int fd = -1;
> @@ -431,6 +468,29 @@ static int do_dump(int argc, char **argv)
>  		goto done;
>  	}
>  
> +	while (argc) {
> +		if (is_prefix(*argv, "format")) {
> +			NEXT_ARG();
> +			if (argc < 1) {
> +				p_err("expecting value for 'format' option\n");
> +				goto done;
> +			}
> +			if (strcmp(*argv, "c") == 0) {
> +				dump_c = true;
> +			} else if (strcmp(*argv, "raw") == 0) {

Do you think we could use is_prefix() instead of strcmp() here?

> +				dump_c = false;
> +			} else {
> +				p_err("unrecognized format specifier: '%s'",
> +				      *argv);

Would it be worth reminding the user about the valid specifiers in that
message? (But then we already have it in do_help(), so maybe not.)

> +				goto done;
> +			}
> +			NEXT_ARG();
> +		} else {
> +			p_err("unrecognized option: '%s'", *argv);
> +			goto done;
> +		}
> +	}
> +
>  	if (!btf) {
>  		err = btf__get_from_id(btf_id, &btf);
>  		if (err) {
> @@ -444,7 +504,16 @@ static int do_dump(int argc, char **argv)
>  		}
>  	}
>  
> -	dump_btf_raw(btf, root_type_ids, root_type_cnt);
> +	if (dump_c) {
> +		if (json_output) {
> +			p_err("JSON output for C-syntax dump is not supported");
> +			err = -ENOTSUP;
> +			goto done;
> +		}
> +		err = dump_btf_c(btf, root_type_ids, root_type_cnt);
> +	} else {
> +		err = dump_btf_raw(btf, root_type_ids, root_type_cnt);
> +	}
>  
>  done:
>  	close(fd);
> @@ -460,10 +529,11 @@ static int do_help(int argc, char **argv)
>  	}
>  
>  	fprintf(stderr,
> -		"Usage: %s btf dump BTF_SRC\n"
> +		"Usage: %s btf dump BTF_SRC [format FORMAT]\n"
>  		"       %s btf help\n"
>  		"\n"
>  		"       BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | file FILE }\n"
> +		"       FORMAT  := { raw | c }\n"
>  		"       " HELP_SPEC_MAP "\n"
>  		"       " HELP_SPEC_PROGRAM "\n"
>  		"       " HELP_SPEC_OPTIONS "\n"
>