perf list: Add tracepoint encoding to detailed output

The tracepoint id holds the config value and is probed in determining
what an event is. Add reading of the id so that we can display the
event encoding as:

$ perf list --details
...
alarmtimer:alarmtimer_cancel [Tracepoint event]
tracepoint/config=0x18c/
...

Signed-off-by: Ian Rogers <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Tested-by: Kan Liang <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Ravi Bangoria <[e-mail]>
Cc: Yang Jihong <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/print-events.c

···
 #include <unistd.h>
 
 #include <api/fs/tracing_path.h>
+#include <api/io.h>
 #include <linux/stddef.h>
 #include <linux/perf_event.h>
 #include <linux/zalloc.h>
···
 
 		evt_items = scandirat(events_fd, sys_dirent->d_name, &evt_namelist, NULL, alphasort);
 		for (int j = 0; j < evt_items; j++) {
+			/*
+			 * Buffer sized at twice the max filename length + 1
+			 * separator + 1 \0 terminator.
+			 */
+			char buf[NAME_MAX * 2 + 2];
+			/* 16 possible hex digits and 22 other characters and \0. */
+			char encoding[16 + 22];
 			struct dirent *evt_dirent = evt_namelist[j];
-			char evt_path[MAXPATHLEN];
-			int evt_fd;
+			struct io id;
+			__u64 config;
 
 			if (evt_dirent->d_type != DT_DIR ||
 			    !strcmp(evt_dirent->d_name, ".") ||
 			    !strcmp(evt_dirent->d_name, ".."))
 				goto next_evt;
 
-			snprintf(evt_path, sizeof(evt_path), "%s/id", evt_dirent->d_name);
-			evt_fd = openat(dir_fd, evt_path, O_RDONLY);
-			if (evt_fd < 0)
-				goto next_evt;
-			close(evt_fd);
+			snprintf(buf, sizeof(buf), "%s/id", evt_dirent->d_name);
+			io__init(&id, openat(dir_fd, buf, O_RDONLY), buf, sizeof(buf));
 
-			snprintf(evt_path, MAXPATHLEN, "%s:%s",
+			if (id.fd < 0)
+				goto next_evt;
+
+			if (io__get_dec(&id, &config) < 0) {
+				close(id.fd);
+				goto next_evt;
+			}
+			close(id.fd);
+
+			snprintf(buf, sizeof(buf), "%s:%s",
 				 sys_dirent->d_name, evt_dirent->d_name);
+			snprintf(encoding, sizeof(encoding), "tracepoint/config=0x%llx/", config);
 			print_cb->print_event(print_state,
 					/*topic=*/NULL,
-					/*pmu_name=*/NULL,
-					evt_path,
+					/*pmu_name=*/NULL, /* really "tracepoint" */
+					/*event_name=*/buf,
 					/*event_alias=*/NULL,
 					/*scale_unit=*/NULL,
 					/*deprecated=*/false,
 					"Tracepoint event",
 					/*desc=*/NULL,
 					/*long_desc=*/NULL,
-					/*encoding_desc=*/NULL);
+					encoding);
 next_evt:
 			free(evt_namelist[j]);
 		}