perf sdt: Show proper hint when event not yet in place via 'perf probe'

All events from 'perf list', except SDT events, can be directly recorded
with 'perf record'. But, the flow is little different for SDT events.

Probe points for SDT event needs to be created using 'perf probe' before
recording it using 'perf record'.

Perf shows misleading hint when a user tries to record SDT event without
first creating a probe point. Show proper hint there.

Before patch:

  $ perf record -a -e sdt_glib:idle__add
    event syntax error: 'sdt_glib:idle__add'
                         \___ unknown tracepoint

    Error: File /sys/kernel/debug/tracing/events/sdt_glib/idle__add not found.
    Hint:  Perhaps this kernel misses some CONFIG_ setting to enable this feature?.
    ...

After patch:

  $ perf record -a -e sdt_glib:idle__add
    event syntax error: 'sdt_glib:idle__add'
                         \___ unknown tracepoint

    Error: File /sys/kernel/debug/tracing/events/sdt_glib/idle__add not found.
    Hint:  SDT event cannot be directly recorded on.
           Please first use 'perf probe sdt_glib:idle__add' before recording it.
    ...

  $ perf probe sdt_glib:idle__add
    Added new event:
      sdt_glib:idle__add   (on %idle__add in /usr/lib64/libglib-2.0.so.0.5000.2)

    You can now use it in all perf tools, such as:

        perf record -e sdt_glib:idle__add -aR sleep 1

  $ perf record -a -e sdt_glib:idle__add
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.175 MB perf.data ]
Suggested-and-Acked-by: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexis Berlemont <alexis.berlemont@gmail.com>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170203102642.17258-1-ravi.bangoria@linux.vnet.ibm.com
[ s/Please use/Please first use/ and break the Hint line in two ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/api/fs/tracing_path.c

@@ -86,9 +86,13 @@ void put_tracing_file(char *file)
 	free(file);
 }
 
-static int strerror_open(int err, char *buf, size_t size, const char *filename)
+int tracing_path__strerror_open_tp(int err, char *buf, size_t size,
+				   const char *sys, const char *name)
 {
 	char sbuf[128];
+	char filename[PATH_MAX];
+
+	snprintf(filename, PATH_MAX, "%s/%s", sys, name ?: "*");
 
 	switch (err) {
 	case ENOENT:
@@ -99,10 +103,19 @@ static int strerror_open(int err, char *buf, size_t size, const char *filename)
 		 * - jirka
 		 */
 		if (debugfs__configured() || tracefs__configured()) {
+			/* sdt markers */
+			if (!strncmp(filename, "sdt_", 4)) {
+				snprintf(buf, size,
+					"Error:\tFile %s/%s not found.\n"
+					"Hint:\tSDT event cannot be directly recorded on.\n"
+					"\tPlease first use 'perf probe %s:%s' before recording it.\n",
+					tracing_events_path, filename, sys, name);
+			} else {
 				snprintf(buf, size,
 					 "Error:\tFile %s/%s not found.\n"
 					 "Hint:\tPerhaps this kernel misses some CONFIG_ setting to enable this feature?.\n",
 					 tracing_events_path, filename);
+			}
 			break;
 		}
 		snprintf(buf, size, "%s",
@@ -125,12 +138,3 @@ static int strerror_open(int err, char *buf, size_t size, const char *filename)
 
 	return 0;
 }
-
-int tracing_path__strerror_open_tp(int err, char *buf, size_t size, const char *sys, const char *name)
-{
-	char path[PATH_MAX];
-
-	snprintf(path, PATH_MAX, "%s/%s", sys, name ?: "*");
-
-	return strerror_open(err, buf, size, path);
-}