[PATCH RFC v1 2/4] perf: Add file name and line number to perf extended error reports

[Alexander Shishkin <alexander.shishkin@linux.intel.com>]

If kernel debugging is enabled, include additional information to extended
syscall error reports: file name and line number, to make error hunting even
easier.

And in really desperate times, this allows for such things (a variation on
Hugh Dickins' trick [1]):

	#undef EINVAL
	#define EINVAL perf_err(-22, "")

However, CONFIG_DEBUG_KERNEL might not be the right option for this as I
notice that, for example, debian enables it in its kernels.

[1] http://marc.info/?l=linux-kernel&m=141215166009542

NYet-Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
 include/linux/perf_event.h | 11 +++++++++++
 kernel/events/core.c       |  7 +++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 9e9af962f6..d84a2914f5 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -68,11 +68,21 @@ struct perf_guest_info_callbacks {
 struct perf_err_site {
 	const char		*message;
 	const char		*owner;
+#ifdef CONFIG_DEBUG_KERNEL
+	const char		*file;
+	const int		line;
+#endif
 	const int		code;
 };
 
 #ifdef CONFIG_PERF_EVENTS
 
+#ifdef CONFIG_DEBUG_KERNEL
+#define DEBUG_PERF_ERR	.file = __FILE__, .line = __LINE__,
+#else
+#define DEBUG_PERF_ERR
+#endif
+
 /*
  * Place all occurrences of struct perf_err_site into a special section,
  * so that we can find out their offsets, which we'll use to refer back
@@ -88,6 +98,7 @@ extern const struct perf_err_site __start___perf_err[], __stop___perf_err[];
 		.owner		= PERF_MODNAME,			\
 		.code		= __builtin_constant_p((__c)) ?	\
 		(__c) : 0,					\
+		DEBUG_PERF_ERR					\
 	};							\
 	(__e) = &__err_site;					\
 })
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 85bcf3a5f9..4ff09fdc67 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -75,10 +75,17 @@ static void perf_error_report_site(struct perf_event_attr *attr,
 
 	buffer = kasprintf(GFP_KERNEL,
 			   "{\n"
+#ifdef CONFIG_DEBUG_KERNEL
+			   "\t\"file\": \"%s\",\n"
+			   "\t\"line\": %d,\n"
+#endif
 			   "\t\"code\": %d,\n"
 			   "\t\"module\": \"%s\",\n"
 			   "\t\"message\": \"%s\"\n"
 			   "}\n",
+#ifdef CONFIG_DEBUG_KERNEL
+			   site->file, site->line,
+#endif
 			   site->code, site->owner, site->message
 			   );
 	if (!buffer)
-- 
2.1.4