On Wed, 12 May 2021 16:52:05 +0000
Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote:
> The underlying need is to support non-NUL-terminated C strings.
>
> I assumed that since the commentary around 9a6944fee68e claims
> the proper way to trace C strings is to use __string and friends,
> and those do not support non-NUL-terminated strings, that such
> strings are really not first-class citizens. Thus I concluded
> that my use of '%.*s' was incorrect.
>
> Having some __string-style helpers that can deal with such
> strings would be valuable.
I guess the best I can do is a strncpy version, that will add the '\0' in
the ring buffer. That way we don't need to save the length as well (length
would need to be at least 4 bytes, where as '\0' is one).
Something like this?
I added "__string_len()" and "__assign_str_len()". You use them just like
__string() and __assign_str() but add a max length that you want to use
(although, it will always allocate "len" regardless if the string is
smaller). Then use __get_str() just like you use __string().
Would something like that work?
-- Steve
diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
index 8268bf747d6f..7ab23535a0c8 100644
--- a/include/trace/trace_events.h
+++ b/include/trace/trace_events.h
@@ -102,6 +102,9 @@ TRACE_MAKE_SYSTEM_STR();
#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)
+#undef __string_len
+#define __string_len(item, src, len) __dynamic_array(char, item, -1)
+
#undef __bitmask
#define __bitmask(item, nr_bits) __dynamic_array(char, item, -1)
@@ -197,6 +200,9 @@ TRACE_MAKE_SYSTEM_STR();
#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)
+#undef __string_len
+#define __string_len(item, src, len) __dynamic_array(char, item, -1)
+
#undef __bitmask
#define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1)
@@ -444,6 +450,9 @@ static struct trace_event_functions trace_event_type_funcs_##call = { \
#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)
+#undef __string_len
+#define __string_len(item, src, len) __dynamic_array(char, item, -1)
+
#undef __bitmask
#define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1)
@@ -492,6 +501,9 @@ static struct trace_event_fields trace_event_fields_##call[] = { \
#define __string(item, src) __dynamic_array(char, item, \
strlen((src) ? (const char *)(src) : "(null)") + 1)
+#undef __string_len
+#define __string_len(item, src, len) __dynamic_array(char, item, (len) + 1)
+
/*
* __bitmask_size_in_bytes_raw is the number of bytes needed to hold
* num_possible_cpus().
@@ -655,10 +667,18 @@ static inline notrace int trace_event_get_offsets_##call( \
#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)
+#undef __string_len
+#define __string_len(item, src, len) __dynamic_array(char, item, -1)
+
#undef __assign_str
#define __assign_str(dst, src) \
strcpy(__get_str(dst), (src) ? (const char *)(src) : "(null)");
+#undef __assign_str_len
+#define __assign_str_len(dst, src, len) \
+ strncpy(__get_str(dst), (src) ? (const char *)(src) : "(null)", len); \
+ __get_str(dst)[len] = '\0';
+
#undef __bitmask
#define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1)
