[PATCH 3/3] perf evsel: Find process with busy PMUs for EBUSY

[Chun-Tse Shao <ctshao@google.com>]

It parses fdinfo with PMU type, comparing with the event which failed to
open, and report the processes causing EBUSY error.

```
Testing cycles and intel_pt//
$ ./perf stat -e cycles &
[1] 55569
$ ./perf stat -e intel_pt// &
[2] 55683
$ ./perf stat -e intel_pt//
Error:
The PMU intel_pt counters are busy and in use by another process.
Possible processes:
55683 ./perf stat -e intel_pt//
```
Only perf with intel_pt was reported.

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
---
 tools/perf/util/evsel.c | 79 +++++++++++++++++++++++++++++------------
 1 file changed, 57 insertions(+), 22 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 9a5b6a6f8d2e5..d2f7c19e023ec 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -3286,7 +3286,8 @@ static bool find_process(const char *name)
 	return ret ? false : true;
 }

-static int dump_perf_event_processes(char *msg, size_t size)
+static int dump_perf_event_processes(const struct perf_event_attr *failed_attr,
+				     char *msg, size_t size)
 {
 	DIR *proc_dir;
 	struct dirent *proc_entry;
@@ -3327,29 +3328,61 @@ static int dump_perf_event_processes(char *msg, size_t size)
 				continue;
 			/* Take care as readlink doesn't null terminate the string. */
 			if (!strncmp(path, "anon_inode:[perf_event]", link_size)) {
-				int cmdline_fd;
-				ssize_t cmdline_size;
-
-				scnprintf(path, sizeof(path), "%s/cmdline", proc_entry->d_name);
-				cmdline_fd = openat(dirfd(proc_dir), path, O_RDONLY);
-				if (cmdline_fd == -1)
-					continue;
-				cmdline_size = read(cmdline_fd, path, sizeof(path) - 1);
-				close(cmdline_fd);
-				if (cmdline_size < 0)
+				int fdinfo_fd;
+				ssize_t fdinfo_size;
+				char *line;
+				u32 perf_event_type = PERF_TYPE_MAX;
+
+				/* Let's check the PMU type reserved by this process */
+				scnprintf(path, sizeof(path), "%s/fdinfo/%s",
+					  proc_entry->d_name, fd_entry->d_name);
+				fdinfo_fd = openat(dirfd(proc_dir), path, O_RDONLY);
+				fdinfo_size = read(fdinfo_fd, path, sizeof(path) - 1);
+				if (fdinfo_size < 0)
 					continue;
-				path[cmdline_size] = '\0';
-				for (ssize_t i = 0; i < cmdline_size; i++) {
-					if (path[i] == '\0')
-						path[i] = ' ';
+				path[fdinfo_size] = '\0';
+
+				line = strtok(path, "\n");
+				while (line != NULL) {
+					if (sscanf(line,
+						   "perf_event-attr.type:\t%u",
+						   &perf_event_type) == 1)
+						break;
+					line = strtok(NULL, "\n");
 				}

-				if (printed == 0)
-					printed += scnprintf(msg, size, "Possible processes:\n");
-
-				printed += scnprintf(msg + printed, size - printed,
-						"%s %s\n", proc_entry->d_name, path);
-				break;
+				/* Report the process which reserves the conflicted PMU. */
+				/* If fdinfo does not contain PMU type, report it too. */
+				if (perf_event_type == failed_attr->type ||
+				    perf_event_type == PERF_TYPE_MAX) {
+					int cmdline_fd;
+					ssize_t cmdline_size;
+
+					scnprintf(path, sizeof(path),
+						  "%s/cmdline",
+						  proc_entry->d_name);
+					cmdline_fd = openat(dirfd(proc_dir), path, O_RDONLY);
+					if (cmdline_fd == -1)
+						continue;
+					cmdline_size = read(cmdline_fd, path, sizeof(path) - 1);
+					close(cmdline_fd);
+					if (cmdline_size < 0)
+						continue;
+					path[cmdline_size] = '\0';
+					for (ssize_t i = 0; i < cmdline_size; i++) {
+						if (path[i] == '\0')
+							path[i] = ' ';
+					}
+
+					if (printed == 0)
+						printed += scnprintf(
+							msg, size,
+							"Possible processes:\n");
+
+					printed += scnprintf(msg + printed, size - printed,
+							"%s %s\n", proc_entry->d_name, path);
+					break;
+				}
 			}
 		}
 		closedir(fd_dir);
@@ -3458,7 +3491,9 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
 			msg, size,
 			"The PMU %s counters are busy and in use by another process.\n",
 			evsel->pmu ? evsel->pmu->name : "");
-		return printed + dump_perf_event_processes(msg + printed, size - printed);
+		return printed + dump_perf_event_processes(&evsel->core.attr,
+							   msg + printed,
+							   size - printed);
 		break;
 	case EINVAL:
 		if (evsel->core.attr.sample_type & PERF_SAMPLE_CODE_PAGE_SIZE && perf_missing_features.code_page_size)
--
2.47.0.163.g1226f6d8fa-goog