Re: [PATCH v4 2/2] trace: acquire buffer from temparary trace sequence

[Steven Rostedt]

On Fri, 16 Dec 2022 17:03:05 +0800
Linyu Yuan <quic_linyyuan@xxxxxxxxxxx> wrote:

> diff --git a/include/trace/stages/stage3_trace_output.h b/include/trace/stages/stage3_trace_output.h
> index 66374df..f60c453 100644
> --- a/include/trace/stages/stage3_trace_output.h
> +++ b/include/trace/stages/stage3_trace_output.h
> @@ -139,3 +139,11 @@
>  		u64 ____val = (u64)(value);		\
>  		(u32) do_div(____val, NSEC_PER_SEC);	\
>  	})
> +
> +/* Macros with flow control statements should be avoided */
> +#undef __get_buf
> +#define __get_buf(len)							\
> +	({								\
> +		WARN_ON_ONCE(seq_buf_buffer_left(&p->seq) < (len));	\

The WARN_ON_ONCE() should be part of the trace_seq_acquire().

> +		trace_seq_acquire(p, (len));				\
> +	})
> diff --git a/include/trace/stages/stage7_class_define.h b/include/trace/stages/stage7_class_define.h
> index 8795429..bcb960d 100644
> --- a/include/trace/stages/stage7_class_define.h
> +++ b/include/trace/stages/stage7_class_define.h
> @@ -23,6 +23,7 @@
>  #undef __get_rel_sockaddr
>  #undef __print_array
>  #undef __print_hex_dump
> +#undef __get_buf
>  
>  /*
>   * The below is not executed in the kernel. It is only what is
> diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
> index 9c90b3a..c900b7c 100644
> --- a/kernel/trace/trace_seq.c
> +++ b/kernel/trace/trace_seq.c
> @@ -403,3 +403,25 @@ int trace_seq_hex_dump(struct trace_seq *s, const char *prefix_str,
>  	return 1;
>  }
>  EXPORT_SYMBOL(trace_seq_hex_dump);
> +
> +/**
> + * trace_seq_acquire - acquire seq buffer with size len
> + * @s: trace sequence descriptor
> + * @len: size of buffer to be acquired
> + *
> + * acquire buffer with size of @len from trace_seq for output usage,
> + * user can fill string into that buffer.
> + *
> + * Returns start address of acquired buffer.
> + *
> + * it allow multiple usage in one trace output function call.
> + */
> +char *trace_seq_acquire(struct trace_seq *s, size_t len)
> +{
> +	char *ret = trace_seq_buffer_ptr(s);

	if (!WARN_ON_ONCE(seq_buf_buffer_left(&p->seq) < (len)))
> +
> +		seq_buf_commit(&s->seq, len);

As seq_buf_commit() should never be called without enough length.

-- Steve

> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(trace_seq_acquire);
> --