linux-kernel - [PATCH bpf-next] libbpf: also check /sys/kernel/tracing for tracefs files

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Message-Id: <20220421201125.13907-1-connoro@google.com>
Date:   Thu, 21 Apr 2022 20:11:25 +0000
From:   "Connor O'Brien" <connoro@...gle.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Connor O'Brien" <connoro@...gle.com>
Subject: [PATCH bpf-next] libbpf: also check /sys/kernel/tracing for tracefs files

libbpf looks for tracefs files only under debugfs, but tracefs may be
mounted even if debugfs is not. When /sys/kernel/debug/tracing is
absent, try looking under /sys/kernel/tracing instead.

Signed-off-by: Connor O'Brien <connoro@...gle.com>
---
 tools/lib/bpf/libbpf.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 68cc134d070d..6ef587329eb2 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10140,10 +10140,16 @@ static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
 		 __sync_fetch_and_add(&index, 1));
 }
 
+static bool debugfs_available(void)
+{
+	return !access("/sys/kernel/debug/tracing", F_OK);
+}
+
 static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,
 				   const char *kfunc_name, size_t offset)
 {
-	const char *file = "/sys/kernel/debug/tracing/kprobe_events";
+	const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/kprobe_events" :
+		"/sys/kernel/tracing/kprobe_events";
 
 	return append_to_file(file, "%c:%s/%s %s+0x%zx",
 			      retprobe ? 'r' : 'p',
@@ -10153,7 +10159,8 @@ static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,
 
 static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe)
 {
-	const char *file = "/sys/kernel/debug/tracing/kprobe_events";
+	const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/kprobe_events" :
+		"/sys/kernel/tracing/kprobe_events";
 
 	return append_to_file(file, "-:%s/%s", retprobe ? "kretprobes" : "kprobes", probe_name);
 }
@@ -10163,7 +10170,8 @@ static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retpro
 	char file[256];
 
 	snprintf(file, sizeof(file),
-		 "/sys/kernel/debug/tracing/events/%s/%s/id",
+		 debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" :
+		 "/sys/kernel/tracing/events/%s/%s/id",
 		 retprobe ? "kretprobes" : "kprobes", probe_name);
 
 	return parse_uint_from_file(file, "%d\n");
@@ -10493,7 +10501,8 @@ static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz,
 static inline int add_uprobe_event_legacy(const char *probe_name, bool retprobe,
 					  const char *binary_path, size_t offset)
 {
-	const char *file = "/sys/kernel/debug/tracing/uprobe_events";
+	const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/uprobe_events" :
+		"/sys/kernel/tracing/uprobe_events";
 
 	return append_to_file(file, "%c:%s/%s %s:0x%zx",
 			      retprobe ? 'r' : 'p',
@@ -10503,7 +10512,8 @@ static inline int add_uprobe_event_legacy(const char *probe_name, bool retprobe,
 
 static inline int remove_uprobe_event_legacy(const char *probe_name, bool retprobe)
 {
-	const char *file = "/sys/kernel/debug/tracing/uprobe_events";
+	const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/uprobe_events" :
+		"/sys/kernel/tracing/uprobe_events";
 
 	return append_to_file(file, "-:%s/%s", retprobe ? "uretprobes" : "uprobes", probe_name);
 }
@@ -10513,7 +10523,8 @@ static int determine_uprobe_perf_type_legacy(const char *probe_name, bool retpro
 	char file[512];
 
 	snprintf(file, sizeof(file),
-		 "/sys/kernel/debug/tracing/events/%s/%s/id",
+		 debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" :
+		 "/sys/kernel/tracing/events/%s/%s/id",
 		 retprobe ? "uretprobes" : "uprobes", probe_name);
 
 	return parse_uint_from_file(file, "%d\n");
@@ -11071,7 +11082,8 @@ static int determine_tracepoint_id(const char *tp_category,
 	int ret;
 
 	ret = snprintf(file, sizeof(file),
-		       "/sys/kernel/debug/tracing/events/%s/%s/id",
+		       debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" :
+		       "/sys/kernel/tracing/events/%s/%s/id",
 		       tp_category, tp_name);
 	if (ret < 0)
 		return -errno;
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog