Re: [PATCH RESEND] libtraceevent: Pretty print function parameters of enum-type

[Steven Rostedt <rostedt@goodmis.org>]

On Fri,  6 Feb 2026 17:15:12 +0800
Donglin Peng <dolinux.peng@gmail.com> wrote:

> From: Donglin Peng <pengdonglin@xiaomi.com>

Hi Donglin,

> 
> The tep_btf_print_args() function currently prints values of
> enum parameters in decimal format, which reduces readability.
> 
> Utilize the BTF information to resolve enum type parameters
> and print their symbolic names where possible. This enhances
> the trace log readability by displaying meaningful identifiers
> instead of raw numbers.
> 
> Before:
> mod_memcg_lruvec_state(lruvec=0xffff88800c18a540, idx=5, val=320)
> 
> After:
> mod_memcg_lruvec_state(lruvec=0xffff88800c18a540, idx=5 [NR_SLAB_RECLAIMABLE_B], val=320)
> 
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Signed-off-by: Donglin Peng <pengdonglin@xiaomi.com>
> ---
>  src/trace-btf.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/src/trace-btf.c b/src/trace-btf.c
> index 859b0860ce2a..85f5fefb4d3b 100644
> --- a/src/trace-btf.c
> +++ b/src/trace-btf.c
> @@ -32,6 +32,16 @@ struct tep_btf {
>  #define REALLOC_SIZE (1 << 10)
>  #define REALLOC_MASK (REALLOC_SIZE - 1)
>  
> +#define for_each_enum(i, enum_type, member)			\
> +	for (i = 0, member = btf_enum(enum_type);		\
> +	     i < BTF_INFO_VLEN(enum_type->info);		\
> +	     i++, member++)


You can make the above into:

 #define for_each_enum(enum_type, member)			\
	for (int __i = 0, member = btf_enum(enum_type);		\
	     __i < BTF_INFO_VLEN((enum_type)->info);		\
	     __i++, member++)

Then you don't need to pass in the counter "i".

(also it's good to put parenthesis around "enum_type").

> +
> +static inline struct btf_enum *btf_enum(const struct btf_type *t)
> +{
> +	return (struct btf_enum *)(t + 1);
> +}
> +
>  static const char *btf_name(struct tep_btf *btf, int off)
>  {
>  	if (off < btf->hdr->str_len)
> @@ -546,10 +556,11 @@ int tep_btf_print_args(struct tep_handle *tep, struct trace_seq *s, void *args,
>  	struct tep_btf *btf = tep->btf;
>  	struct btf_type *type = tep_btf_find_func(btf, func);
>  	struct btf_param *param;
> +	struct btf_enum *enump;
>  	unsigned long long arg;
>  	unsigned int encode;
>  	const char *param_name;
> -	int a, p, x, nr;
> +	int a, p, x, nr, i;

And the above doesn't need to be changed.

Thanks,

-- Steve

>  
>  	if (!func)
>  		return -1;
> @@ -628,6 +639,13 @@ int tep_btf_print_args(struct tep_handle *tep, struct trace_seq *s, void *args,
>  			break;
>  		case BTF_KIND_ENUM:
>  			trace_seq_printf(s, "%lld", arg);
> +			for_each_enum(i, t, enump) {
> +				if (arg == enump->val) {
> +					trace_seq_printf(s, " [%s]",
> +						btf_name(btf, enump->name_off));
> +					break;
> +				}
> +			}
>  			break;
>  		default:
>  			/* This does not handle complex arguments */