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Date:   Mon, 23 May 2022 21:28:08 +0000
Message-Id: <20220523212808.603526-1-connoro@google.com>
Mime-Version: 1.0
Subject: [PATCH bpf-next v2] libbpf: also check /sys/kernel/tracing for
 tracefs files
From:   "Connor O'Brien" <connoro@google.com>
To:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>
Cc:     Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
        Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Connor O'Brien" <connoro@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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@google.com>
---
v1->v2: cache result of debugfs check.

 src/libbpf.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/src/libbpf.c b/src/libbpf.c
index 2262bcd..cc47c52 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -9945,10 +9945,22 @@ static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
 		 __sync_fetch_and_add(&index, 1));
 }
 
+static bool debugfs_available(void)
+{
+	static bool initialized = false, available;
+
+	if (!initialized) {
+		available = !access("/sys/kernel/debug/tracing", F_OK);
+		initialized = true;
+	}
+	return available;
+}
+
 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',
@@ -9958,7 +9970,8 @@ 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);
 }
@@ -9968,7 +9981,8 @@ 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");
@@ -10144,7 +10158,8 @@ 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',
@@ -10154,7 +10169,8 @@ 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);
 }
@@ -10164,7 +10180,8 @@ 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");
@@ -10295,7 +10312,8 @@ 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;
-- 
2.36.1.124.g0e6072fb45-goog