[PATCH bpf-next v3 1/2] bpf: use canonical ftrace path

From: zwisler
Date: Fri Mar 10 2023 - 12:52:31 EST

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From: Ross Zwisler <zwisler@xxxxxxxxxx>

The canonical location for the tracefs filesystem is at /sys/kernel/tracing.

But, from Documentation/trace/ftrace.rst:

Before 4.1, all ftrace tracing control files were within the debugfs
file system, which is typically located at /sys/kernel/debug/tracing.
For backward compatibility, when mounting the debugfs file system,
the tracefs file system will be automatically mounted at:

/sys/kernel/debug/tracing

Many comments and samples in the bpf code still refer to this older
debugfs path, so let's update them to avoid confusion. There are a few
spots where the bpf code explicitly checks both tracefs and debugfs
(tools/bpf/bpftool/tracelog.c and tools/lib/api/fs/fs.c) and I've left
those alone so that the tools can continue to work with both paths.

Signed-off-by: Ross Zwisler <zwisler@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---

v2 was submitted to bpf-next via a pair of pull requests:
https://github.com/kernel-patches/bpf/pull/4672
https://github.com/kernel-patches/bpf/pull/4648

The only change since v2 is that I rebased on the current bpf-next_base.

I've run this through all the BPF selftests on a local machine:
sudo ./test_verifier
sudo make run_tests

and didn't hit any regressions. I've also tested to make sure each
modified selftest runs successfully with each path of tracefs (with and
without debugfs).

---
include/uapi/linux/bpf.h | 8 ++++----
samples/bpf/cpustat_kern.c | 4 ++--
samples/bpf/hbm.c | 4 ++--
samples/bpf/ibumad_kern.c | 4 ++--
samples/bpf/lwt_len_hist.sh | 2 +-
samples/bpf/offwaketime_kern.c | 2 +-
samples/bpf/task_fd_query_user.c | 4 ++--
samples/bpf/test_lwt_bpf.sh | 2 +-
samples/bpf/test_overhead_tp.bpf.c | 4 ++--
tools/include/uapi/linux/bpf.h | 8 ++++----
10 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d8c534e05b0a..13129df937cd 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1647,17 +1647,17 @@ union bpf_attr {
* Description
* This helper is a "printk()-like" facility for debugging. It
* prints a message defined by format *fmt* (of size *fmt_size*)
- * to file *\/sys/kernel/debug/tracing/trace* from DebugFS, if
+ * to file *\/sys/kernel/tracing/trace* from TraceFS, if
* available. It can take up to three additional **u64**
* arguments (as an eBPF helpers, the total number of arguments is
* limited to five).
*
* Each time the helper is called, it appends a line to the trace.
- * Lines are discarded while *\/sys/kernel/debug/tracing/trace* is
- * open, use *\/sys/kernel/debug/tracing/trace_pipe* to avoid this.
+ * Lines are discarded while *\/sys/kernel/tracing/trace* is
+ * open, use *\/sys/kernel/tracing/trace_pipe* to avoid this.
* The format of the trace is customizable, and the exact output
* one will get depends on the options set in
- * *\/sys/kernel/debug/tracing/trace_options* (see also the
+ * *\/sys/kernel/tracing/trace_options* (see also the
* *README* file under the same directory). However, it usually
* defaults to something like:
*
diff --git a/samples/bpf/cpustat_kern.c b/samples/bpf/cpustat_kern.c
index 5aefd19cdfa1..944f13fe164a 100644
--- a/samples/bpf/cpustat_kern.c
+++ b/samples/bpf/cpustat_kern.c
@@ -76,8 +76,8 @@ struct {

/*
* The trace events for cpu_idle and cpu_frequency are taken from:
- * /sys/kernel/debug/tracing/events/power/cpu_idle/format
- * /sys/kernel/debug/tracing/events/power/cpu_frequency/format
+ * /sys/kernel/tracing/events/power/cpu_idle/format
+ * /sys/kernel/tracing/events/power/cpu_frequency/format
*
* These two events have same format, so define one common structure.
*/
diff --git a/samples/bpf/hbm.c b/samples/bpf/hbm.c
index 516fbac28b71..ff58ec43f56a 100644
--- a/samples/bpf/hbm.c
+++ b/samples/bpf/hbm.c
@@ -65,7 +65,7 @@ static void Usage(void);
static void read_trace_pipe2(void);
static void do_error(char *msg, bool errno_flag);

-#define DEBUGFS "/sys/kernel/debug/tracing/"
+#define TRACEFS "/sys/kernel/tracing/"

static struct bpf_program *bpf_prog;
static struct bpf_object *obj;
@@ -77,7 +77,7 @@ static void read_trace_pipe2(void)
FILE *outf;
char *outFname = "hbm_out.log";

- trace_fd = open(DEBUGFS "trace_pipe", O_RDONLY, 0);
+ trace_fd = open(TRACEFS "trace_pipe", O_RDONLY, 0);
if (trace_fd < 0) {
printf("Error opening trace_pipe\n");
return;
diff --git a/samples/bpf/ibumad_kern.c b/samples/bpf/ibumad_kern.c
index 9b193231024a..f07474c72525 100644
--- a/samples/bpf/ibumad_kern.c
+++ b/samples/bpf/ibumad_kern.c
@@ -39,8 +39,8 @@ struct {
/* Taken from the current format defined in
* include/trace/events/ib_umad.h
* and
- * /sys/kernel/debug/tracing/events/ib_umad/ib_umad_read/format
- * /sys/kernel/debug/tracing/events/ib_umad/ib_umad_write/format
+ * /sys/kernel/tracing/events/ib_umad/ib_umad_read/format
+ * /sys/kernel/tracing/events/ib_umad/ib_umad_write/format
*/
struct ib_umad_rw_args {
u64 pad;
diff --git a/samples/bpf/lwt_len_hist.sh b/samples/bpf/lwt_len_hist.sh
index 7078bfcc4f4d..381b2c634784 100755
--- a/samples/bpf/lwt_len_hist.sh
+++ b/samples/bpf/lwt_len_hist.sh
@@ -5,7 +5,7 @@ NS1=lwt_ns1
VETH0=tst_lwt1a
VETH1=tst_lwt1b
BPF_PROG=lwt_len_hist.bpf.o
-TRACE_ROOT=/sys/kernel/debug/tracing
+TRACE_ROOT=/sys/kernel/tracing

function cleanup {
# To reset saved histogram, remove pinned map
diff --git a/samples/bpf/offwaketime_kern.c b/samples/bpf/offwaketime_kern.c
index eb4d94742e6b..23f12b47e9e5 100644
--- a/samples/bpf/offwaketime_kern.c
+++ b/samples/bpf/offwaketime_kern.c
@@ -110,7 +110,7 @@ static inline int update_counts(void *ctx, u32 pid, u64 delta)
}

#if 1
-/* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
+/* taken from /sys/kernel/tracing/events/sched/sched_switch/format */
struct sched_switch_args {
unsigned long long pad;
char prev_comm[TASK_COMM_LEN];
diff --git a/samples/bpf/task_fd_query_user.c b/samples/bpf/task_fd_query_user.c
index a33d74bd3a4b..1e61f2180470 100644
--- a/samples/bpf/task_fd_query_user.c
+++ b/samples/bpf/task_fd_query_user.c
@@ -235,7 +235,7 @@ static int test_debug_fs_uprobe(char *binary_path, long offset, bool is_return)
struct bpf_link *link;
ssize_t bytes;

- snprintf(buf, sizeof(buf), "/sys/kernel/debug/tracing/%s_events",
+ snprintf(buf, sizeof(buf), "/sys/kernel/tracing/%s_events",
event_type);
kfd = open(buf, O_WRONLY | O_TRUNC, 0);
CHECK_PERROR_RET(kfd < 0);
@@ -252,7 +252,7 @@ static int test_debug_fs_uprobe(char *binary_path, long offset, bool is_return)
close(kfd);
kfd = -1;

- snprintf(buf, sizeof(buf), "/sys/kernel/debug/tracing/events/%ss/%s/id",
+ snprintf(buf, sizeof(buf), "/sys/kernel/tracing/events/%ss/%s/id",
event_type, event_alias);
efd = open(buf, O_RDONLY, 0);
CHECK_PERROR_RET(efd < 0);
diff --git a/samples/bpf/test_lwt_bpf.sh b/samples/bpf/test_lwt_bpf.sh
index 2e9f5126963b..0bf2d0f6bf4b 100755
--- a/samples/bpf/test_lwt_bpf.sh
+++ b/samples/bpf/test_lwt_bpf.sh
@@ -21,7 +21,7 @@ IP_LOCAL="192.168.99.1"

PROG_SRC="test_lwt_bpf.c"
BPF_PROG="test_lwt_bpf.o"
-TRACE_ROOT=/sys/kernel/debug/tracing
+TRACE_ROOT=/sys/kernel/tracing
CONTEXT_INFO=$(cat ${TRACE_ROOT}/trace_options | grep context)

function lookup_mac()
diff --git a/samples/bpf/test_overhead_tp.bpf.c b/samples/bpf/test_overhead_tp.bpf.c
index 67cab3881969..8b498328e961 100644
--- a/samples/bpf/test_overhead_tp.bpf.c
+++ b/samples/bpf/test_overhead_tp.bpf.c
@@ -7,7 +7,7 @@
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>

-/* from /sys/kernel/debug/tracing/events/task/task_rename/format */
+/* from /sys/kernel/tracing/events/task/task_rename/format */
struct task_rename {
__u64 pad;
__u32 pid;
@@ -21,7 +21,7 @@ int prog(struct task_rename *ctx)
return 0;
}

-/* from /sys/kernel/debug/tracing/events/fib/fib_table_lookup/format */
+/* from /sys/kernel/tracing/events/fib/fib_table_lookup/format */
struct fib_table_lookup {
__u64 pad;
__u32 tb_id;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d8c534e05b0a..13129df937cd 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1647,17 +1647,17 @@ union bpf_attr {
* Description
* This helper is a "printk()-like" facility for debugging. It
* prints a message defined by format *fmt* (of size *fmt_size*)
- * to file *\/sys/kernel/debug/tracing/trace* from DebugFS, if
+ * to file *\/sys/kernel/tracing/trace* from TraceFS, if
* available. It can take up to three additional **u64**
* arguments (as an eBPF helpers, the total number of arguments is
* limited to five).
*
* Each time the helper is called, it appends a line to the trace.
- * Lines are discarded while *\/sys/kernel/debug/tracing/trace* is
- * open, use *\/sys/kernel/debug/tracing/trace_pipe* to avoid this.
+ * Lines are discarded while *\/sys/kernel/tracing/trace* is
+ * open, use *\/sys/kernel/tracing/trace_pipe* to avoid this.
* The format of the trace is customizable, and the exact output
* one will get depends on the options set in
- * *\/sys/kernel/debug/tracing/trace_options* (see also the
+ * *\/sys/kernel/tracing/trace_options* (see also the
* *README* file under the same directory). However, it usually
* defaults to something like:
*

base-commit: d1d51a62d060d02f99ee407959e24ad10a40e053
prerequisite-patch-id: 9d1a70f239e7476600fe4018125df58a368dc725
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prerequisite-patch-id: 5001694a51d83ed8ca428855b92b3ead261a469d
--
2.40.0.rc1.284.g88254d51c5-goog

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