Patch "tracing/events: Add __vstring() and __assign_vstr() helper macros" has been added to the 5.18-stable tree

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This is a note to let you know that I've just added the patch titled

    tracing/events: Add __vstring() and __assign_vstr() helper macros

to the 5.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tracing-events-add-__vstring-and-__assign_vstr-helpe.patch
and it can be found in the queue-5.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3a68f50bc6f54e4ef743e38ffb6064be1ef5e481
Author: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Date:   Tue Jul 5 18:44:54 2022 -0400

    tracing/events: Add __vstring() and __assign_vstr() helper macros
    
    [ Upstream commit 0563231f93c6d1f582b168a47753b345c1e20d81 ]
    
    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@xxxxxxxxxxx
    
    Cc: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxxxxxxxxxxxxx>
    Cc: Ingo Molnar <mingo@xxxxxxxxxx>
    Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Cc: Jason Gunthorpe <jgg@xxxxxxxx>
    Cc: Leon Romanovsky <leon@xxxxxxxxxx>
    Cc: Kalle Valo <kvalo@xxxxxxxxxx>
    Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
    Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
    Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
    Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
    Cc: Arend van Spriel <aspriel@xxxxxxxxx>
    Cc: Franky Lin <franky.lin@xxxxxxxxxxxx>
    Cc: Hante Meuleman <hante.meuleman@xxxxxxxxxxxx>
    Cc: Gregory Greenman <gregory.greenman@xxxxxxxxx>
    Cc: Peter Chen <peter.chen@xxxxxxxxxx>
    Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Cc: Mathias Nyman <mathias.nyman@xxxxxxxxx>
    Cc: Chunfeng Yun <chunfeng.yun@xxxxxxxxxxxx>
    Cc: Bin Liu <b-liu@xxxxxx>
    Cc: Marek Lindner <mareklindner@xxxxxxxxxxxxx>
    Cc: Simon Wunderlich <sw@xxxxxxxxxxxxxxxxxx>
    Cc: Antonio Quartulli <a@xxxxxxxxxxx>
    Cc: Sven Eckelmann <sven@xxxxxxxxxxxxx>
    Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
    Cc: Jim Cromie <jim.cromie@xxxxxxxxx>
    Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index e6e95a9f07a5..b18759a673c6 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 a16783419687..1b7bab60434c 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 42fd1e8813ec..1b7a8f764fdd 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 e80cdc397a43..c3790ec7a453 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 7ee5931300e6..fba4c24ed9e6 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 e1724f73594b..0f51f6b3ab70 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)
 



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