bpf: use canonical ftrace path

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 <[e-mail]>
Acked-by: Michael S. Tsirkin <[e-mail]>
Reviewed-by: Steven Rostedt (Google) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

include/uapi/linux/bpf.h

···
  * 	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:
  *

samples/bpf/cpustat_kern.c

···
 
 /*
  * 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.
  */

samples/bpf/hbm.c

···
 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;
···
 	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;

samples/bpf/ibumad_kern.c

···
 /* 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;

samples/bpf/lwt_len_hist.sh

···
 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

samples/bpf/offwaketime_kern.c

···
 }
 
 #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];

samples/bpf/task_fd_query_user.c

···
 	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);
···
 	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);

samples/bpf/test_lwt_bpf.sh

···
 
 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()

samples/bpf/test_overhead_tp.bpf.c

···
 #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;
···
 	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;

tools/include/uapi/linux/bpf.h

···
  * 	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:
  *