From 0563231f93c6d1f582b168a47753b345c1e20d81 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Google)" Date: Tue, 5 Jul 2022 18:44:54 -0400 Subject: [PATCH] tracing/events: Add __vstring() and __assign_vstr() helper macros There's several places that open code the following logic: TP_STRUCT__entry(__dynamic_array(char, msg, MSG_MAX)), TP_fast_assign(vsnprintf(__get_str(msg), MSG_MAX, vaf->fmt, *vaf->va);) To load a string created by variable array va_list. The main issue with this approach is that "MSG_MAX" usage in the __dynamic_array() portion. That actually just reserves the MSG_MAX in the event, and even wastes space because there's dynamic meta data also saved in the event to denote the offset and size of the dynamic array. It would have been better to just use a static __array() field. Instead, create __vstring() and __assign_vstr() that work like __string and __assign_str() but instead of taking a destination string to copy, take a format string and a va_list pointer and fill in the values. It uses the helper: #define __trace_event_vstr_len(fmt, va) \ ({ \ va_list __ap; \ int __ret; \ \ va_copy(__ap, *(va)); \ __ret = vsnprintf(NULL, 0, fmt, __ap) + 1; \ va_end(__ap); \ \ min(__ret, TRACE_EVENT_STR_MAX); \ }) To figure out the length to store the string. It may be slightly slower as it needs to run the vsnprintf() twice, but it now saves space on the ring buffer. Link: https://lkml.kernel.org/r/20220705224749.053570613@goodmis.org Cc: Dennis Dalessandro Cc: Ingo Molnar Cc: Andrew Morton Cc: Jason Gunthorpe Cc: Leon Romanovsky Cc: Kalle Valo Cc: "David S. Miller" Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Arend van Spriel Cc: Franky Lin Cc: Hante Meuleman Cc: Gregory Greenman Cc: Peter Chen Cc: Greg Kroah-Hartman Cc: Mathias Nyman Cc: Chunfeng Yun Cc: Bin Liu Cc: Marek Lindner Cc: Simon Wunderlich Cc: Antonio Quartulli Cc: Sven Eckelmann Cc: Johannes Berg Cc: Jim Cromie Signed-off-by: Steven Rostedt (Google) --- include/linux/trace_events.h | 18 ++++++++++++++++++ include/trace/stages/stage1_struct_define.h | 3 +++ include/trace/stages/stage2_data_offsets.h | 3 +++ include/trace/stages/stage4_event_fields.h | 3 +++ include/trace/stages/stage5_get_offsets.h | 4 ++++ include/trace/stages/stage6_event_callback.h | 7 +++++++ 6 files changed, 38 insertions(+) diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index e6e95a9..b18759a 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -916,6 +916,24 @@ perf_trace_buf_submit(void *raw_data, int size, int rctx, u16 type, #endif +#define TRACE_EVENT_STR_MAX 512 + +/* + * gcc warns that you can not use a va_list in an inlined + * function. But lets me make it into a macro :-/ + */ +#define __trace_event_vstr_len(fmt, va) \ +({ \ + va_list __ap; \ + int __ret; \ + \ + va_copy(__ap, *(va)); \ + __ret = vsnprintf(NULL, 0, fmt, __ap) + 1; \ + va_end(__ap); \ + \ + min(__ret, TRACE_EVENT_STR_MAX); \ +}) + #endif /* _LINUX_TRACE_EVENT_H */ /* diff --git a/include/trace/stages/stage1_struct_define.h b/include/trace/stages/stage1_struct_define.h index a167834..1b7bab60 100644 --- a/include/trace/stages/stage1_struct_define.h +++ b/include/trace/stages/stage1_struct_define.h @@ -26,6 +26,9 @@ #undef __string_len #define __string_len(item, src, len) __dynamic_array(char, item, -1) +#undef __vstring +#define __vstring(item, fmt, ap) __dynamic_array(char, item, -1) + #undef __bitmask #define __bitmask(item, nr_bits) __dynamic_array(char, item, -1) diff --git a/include/trace/stages/stage2_data_offsets.h b/include/trace/stages/stage2_data_offsets.h index 42fd1e8..1b7a8f7 100644 --- a/include/trace/stages/stage2_data_offsets.h +++ b/include/trace/stages/stage2_data_offsets.h @@ -32,6 +32,9 @@ #undef __string_len #define __string_len(item, src, len) __dynamic_array(char, item, -1) +#undef __vstring +#define __vstring(item, fmt, ap) __dynamic_array(char, item, -1) + #undef __bitmask #define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1) diff --git a/include/trace/stages/stage4_event_fields.h b/include/trace/stages/stage4_event_fields.h index e80cdc3..c3790ec 100644 --- a/include/trace/stages/stage4_event_fields.h +++ b/include/trace/stages/stage4_event_fields.h @@ -38,6 +38,9 @@ #undef __string_len #define __string_len(item, src, len) __dynamic_array(char, item, -1) +#undef __vstring +#define __vstring(item, fmt, ap) __dynamic_array(char, item, -1) + #undef __bitmask #define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1) diff --git a/include/trace/stages/stage5_get_offsets.h b/include/trace/stages/stage5_get_offsets.h index 7ee5931..fba4c24 100644 --- a/include/trace/stages/stage5_get_offsets.h +++ b/include/trace/stages/stage5_get_offsets.h @@ -39,6 +39,10 @@ #undef __string_len #define __string_len(item, src, len) __dynamic_array(char, item, (len) + 1) +#undef __vstring +#define __vstring(item, fmt, ap) __dynamic_array(char, item, \ + __trace_event_vstr_len(fmt, ap)) + #undef __rel_dynamic_array #define __rel_dynamic_array(type, item, len) \ __item_length = (len) * sizeof(type); \ diff --git a/include/trace/stages/stage6_event_callback.h b/include/trace/stages/stage6_event_callback.h index e1724f7..0f51f6b 100644 --- a/include/trace/stages/stage6_event_callback.h +++ b/include/trace/stages/stage6_event_callback.h @@ -24,6 +24,9 @@ #undef __string_len #define __string_len(item, src, len) __dynamic_array(char, item, -1) +#undef __vstring +#define __vstring(item, fmt, ap) __dynamic_array(char, item, -1) + #undef __assign_str #define __assign_str(dst, src) \ strcpy(__get_str(dst), (src) ? (const char *)(src) : "(null)"); @@ -35,6 +38,10 @@ __get_str(dst)[len] = '\0'; \ } while(0) +#undef __assign_vstr +#define __assign_vstr(dst, fmt, va) \ + vsnprintf(__get_str(dst), TRACE_EVENT_STR_MAX, fmt, *(va)) + #undef __bitmask #define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1) -- 2.7.4