bpf: Clarify a bpf_bprintf_prepare macro

The per-cpu buffers contain bprintf data rather than printf arguments.
The macro name and comment were a bit confusing, this rewords them in a
clearer way.

Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/bpf/20210517092830.1026418-1-revest@chromium.org

kernel/bpf/helpers.c

@@ -692,13 +692,14 @@ static int bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
 	return -EINVAL;
 }
 
-/* Per-cpu temp buffers which can be used by printf-like helpers for %s or %p
+/* Per-cpu temp buffers used by printf-like helpers to store the bprintf binary
+ * arguments representation.
  */
-#define MAX_PRINTF_BUF_LEN	512
+#define MAX_BPRINTF_BUF_LEN	512
 
 /* Support executing three nested bprintf helper calls on a given CPU */
 struct bpf_bprintf_buffers {
-	char tmp_bufs[3][MAX_PRINTF_BUF_LEN];
+	char tmp_bufs[3][MAX_BPRINTF_BUF_LEN];
 };
 static DEFINE_PER_CPU(struct bpf_bprintf_buffers, bpf_bprintf_bufs);
 static DEFINE_PER_CPU(int, bpf_bprintf_nest_level);
@@ -761,7 +762,7 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
 		if (num_args && try_get_fmt_tmp_buf(&tmp_buf))
 			return -EBUSY;
 
-		tmp_buf_end = tmp_buf + MAX_PRINTF_BUF_LEN;
+		tmp_buf_end = tmp_buf + MAX_BPRINTF_BUF_LEN;
 		*bin_args = (u32 *)tmp_buf;
 	}