[PATCH v2 2/2] perf tool: Fix ppid for synthesized fork events

[David Ahern]

363b785f38 added synthesized fork events and set a thread's parent id
to itself. Since we are already processing /proc/<pid>/status the ppid
can be determined properly. Make it so.

Signed-off-by: David Ahern <dsahern@xxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Joe Mario <jmario@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
---

v2:
- removed changes to function signature for perf_event__synthesize_comm as
  noted by Jiri

 tools/perf/util/event.c | 92 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 57 insertions(+), 35 deletions(-)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index b49bee8a283d..a31b0fd41c05 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -51,29 +51,32 @@ static struct perf_sample synth_sample = {
 
 /*
  * Assumes that the first 4095 bytes of /proc/pid/stat contains
- * the comm and tgid.
+ * the comm, tgid and ppid.
  */
-static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
+static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len,
+				    pid_t *tgid, pid_t *ppid)
 {
 	char filename[PATH_MAX];
 	char bf[4096];
 	int fd;
 	size_t size = 0, n;
-	pid_t tgid = -1;
-	char *nl, *name, *tgids;
+	char *nl, *name, *tgids, *ppids;
+
+	*tgid = -1;
+	*ppid = -1;
 
 	snprintf(filename, sizeof(filename), "/proc/%d/status", pid);
 
 	fd = open(filename, O_RDONLY);
 	if (fd < 0) {
 		pr_debug("couldn't open %s\n", filename);
-		return 0;
+		return -1;
 	}
 
 	n = read(fd, bf, sizeof(bf) - 1);
 	close(fd);
 	if (n <= 0) {
-		pr_warning("Couldn't get COMM and tgid for pid %d\n",
+		pr_warning("Couldn't get COMM, tigd and ppid for pid %d\n",
 			   pid);
 		return -1;
 	}
@@ -81,6 +84,7 @@ static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
 
 	name = strstr(bf, "Name:");
 	tgids = strstr(bf, "Tgid:");
+	ppids = strstr(bf, "PPid:");
 
 	if (name) {
 		name += 5;  /* strlen("Name:") */
@@ -109,32 +113,51 @@ static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
 		if (nl)
 			*nl = '\0';
 
-		tgid = atoi(tgids);
+		*tgid = atoi(tgids);
 
 	} else
 		pr_debug("Tgid: string not found for pid %d\n", pid);
 
-	return tgid;
+	if (ppids) {
+		ppids += 5;  /* strlen("PPid:") */
+
+		while (*ppids && isspace(*ppids))
+			++ppids;
+
+		nl = strchr(ppids, '\n');
+		if (nl)
+			*nl = '\0';
+
+		*ppid = atoi(ppids);
+	} else
+		pr_debug("PPid: string not found for pid %d\n", pid);
+
+	return 0;
 }
 
-static pid_t perf_event__prepare_comm(union perf_event *event, pid_t pid,
-					 struct machine *machine)
+static int perf_event__prepare_comm(union perf_event *event, pid_t pid,
+				    struct machine *machine,
+				    pid_t *tgid, pid_t *ppid)
 {
 	size_t size;
-	pid_t tgid;
+
+	*ppid = -1;
 
 	memset(&event->comm, 0, sizeof(event->comm));
 
-	if (machine__is_host(machine))
-		tgid = perf_event__get_comm_tgid(pid, event->comm.comm,
-						 sizeof(event->comm.comm));
-	else
-		tgid = machine->pid;
+	if (machine__is_host(machine)) {
+		if (perf_event__get_comm_ids(pid, event->comm.comm,
+					     sizeof(event->comm.comm),
+					     tgid, ppid) != 0) {
+			return -1;
+		}
+	} else
+		*tgid = machine->pid;
 
-	if (tgid < 0)
-		goto out;
+	if (*tgid < 0)
+		return -1;
 
-	event->comm.pid = tgid;
+	event->comm.pid = *tgid;
 	event->comm.header.type = PERF_RECORD_COMM;
 
 	size = strlen(event->comm.comm) + 1;
@@ -144,8 +167,8 @@ static pid_t perf_event__prepare_comm(union perf_event *event, pid_t pid,
 				(sizeof(event->comm.comm) - size) +
 				machine->id_hdr_size);
 	event->comm.tid = pid;
-out:
-	return tgid;
+
+	return 0;
 }
 
 static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
@@ -153,27 +176,27 @@ static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
 					 perf_event__handler_t process,
 					 struct machine *machine)
 {
-	pid_t tgid = perf_event__prepare_comm(event, pid, machine);
+	pid_t tgid, ppid;
 
-	if (tgid == -1)
-		goto out;
+	if (perf_event__prepare_comm(event, pid, machine, &tgid, &ppid) != 0)
+		return -1;
 
 	if (process(tool, event, &synth_sample, machine) != 0)
 		return -1;
 
-out:
 	return tgid;
 }
 
 static int perf_event__synthesize_fork(struct perf_tool *tool,
-				       union perf_event *event, pid_t pid,
-				       pid_t tgid, perf_event__handler_t process,
+				       union perf_event *event,
+				       pid_t pid, pid_t tgid, pid_t ppid,
+				       perf_event__handler_t process,
 				       struct machine *machine)
 {
 	memset(&event->fork, 0, sizeof(event->fork) + machine->id_hdr_size);
 
-	event->fork.ppid = tgid;
-	event->fork.ptid = tgid;
+	event->fork.ppid = ppid;
+	event->fork.ptid = ppid;
 	event->fork.pid  = tgid;
 	event->fork.tid  = pid;
 	event->fork.header.type = PERF_RECORD_FORK;
@@ -365,13 +388,12 @@ static int __event__synthesize_thread(union perf_event *comm_event,
 	char filename[PATH_MAX];
 	DIR *tasks;
 	struct dirent dirent, *next;
-	pid_t tgid;
+	pid_t tgid, ppid;
 
 	/* special case: only send one comm event using passed in pid */
 	if (!full) {
 		tgid = perf_event__synthesize_comm(tool, comm_event, pid,
-						   process, machine);
-
+						process, machine);
 		if (tgid == -1)
 			return -1;
 
@@ -400,12 +422,12 @@ static int __event__synthesize_thread(union perf_event *comm_event,
 		if (*end)
 			continue;
 
-		tgid = perf_event__prepare_comm(comm_event, _pid, machine);
-		if (tgid == -1)
+		if (perf_event__prepare_comm(comm_event, _pid, machine,
+					     &tgid, &ppid) != 0)
 			return -1;
 
 		if (perf_event__synthesize_fork(tool, fork_event, _pid, tgid,
-						process, machine) < 0)
+						ppid, process, machine) < 0)
 			return -1;
 		/*
 		 * Send the prepared comm event
-- 
2.2.1

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