[PATCH v20 03/15] trace-cmd: Find and store pids of tasks, which run virtual CPUs of given VM

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>]

From: Tzvetomir Stoyanov <tstoyanov@vmware.com>

In order to match host and guest events, a mapping between guest VCPU
and the host task, running this VCPU is needed. Extended existing
struct guest to hold such mapping and added logic in read_qemu_guests()
function to initialize it. Implemented a new internal API,
get_guest_vcpu_pid(), to retrieve VCPU-task mapping for given VM.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
---
 tracecmd/include/trace-local.h |  2 +
 tracecmd/trace-record.c        | 77 ++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)

diff --git a/tracecmd/include/trace-local.h b/tracecmd/include/trace-local.h
index 29f27793..a5cf0640 100644
--- a/tracecmd/include/trace-local.h
+++ b/tracecmd/include/trace-local.h
@@ -247,6 +247,8 @@ void update_first_instance(struct buffer_instance *instance, int topt);
 
 void show_instance_file(struct buffer_instance *instance, const char *name);
 
+int get_guest_vcpu_pid(unsigned int guest_cid, unsigned int guest_vcpu);
+
 /* moved from trace-cmd.h */
 void tracecmd_create_top_instance(char *name);
 void tracecmd_remove_instances(void);
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 28fe31b7..4370c964 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -3035,11 +3035,30 @@ struct guest {
 	char *name;
 	int cid;
 	int pid;
+	int cpu_max;
+	int *cpu_pid;
 };
 
 static struct guest *guests;
 static size_t guests_len;
 
+static int set_vcpu_pid_mapping(struct guest *guest, int cpu, int pid)
+{
+	int *cpu_pid;
+
+	if (cpu < 0 || pid < 0)
+		return -1;
+	if (cpu >= guest->cpu_max) {
+		cpu_pid = realloc(guest->cpu_pid, (cpu + 1) * sizeof(int));
+		if (!cpu_pid)
+			return -1;
+		guest->cpu_max = cpu + 1;
+		guest->cpu_pid = cpu_pid;
+	}
+	guest->cpu_pid[cpu] = pid;
+	return 0;
+}
+
 static char *get_qemu_guest_name(char *arg)
 {
 	char *tok, *end = arg;
@@ -3052,6 +3071,46 @@ static char *get_qemu_guest_name(char *arg)
 	return arg;
 }
 
+static void read_qemu_guests_pids(char *guest_task, struct guest *guest)
+{
+	struct dirent *entry;
+	char path[PATH_MAX];
+	char *buf = NULL;
+	size_t n = 0;
+	long int vcpu;
+	long int pid;
+	DIR *dir;
+	FILE *f;
+
+	snprintf(path, sizeof(path), "/proc/%s/task", guest_task);
+	dir = opendir(path);
+	if (!dir)
+		return;
+
+	while ((entry = readdir(dir))) {
+		if (!(entry->d_type == DT_DIR && is_digits(entry->d_name)))
+			continue;
+
+		snprintf(path, sizeof(path), "/proc/%s/task/%s/comm",
+			 guest_task, entry->d_name);
+		f = fopen(path, "r");
+		if (!f)
+			continue;
+
+		if (getline(&buf, &n, f) >= 0 &&
+		    strncmp(buf, "CPU ", 4) == 0) {
+			vcpu = strtol(buf + 4, NULL, 10);
+			pid = strtol(entry->d_name, NULL, 10);
+			if (vcpu < INT_MAX && pid < INT_MAX &&
+			    vcpu >= 0 && pid >= 0)
+				set_vcpu_pid_mapping(guest, vcpu, pid);
+		}
+
+		fclose(f);
+	}
+	free(buf);
+}
+
 static void read_qemu_guests(void)
 {
 	static bool initialized;
@@ -3115,6 +3174,8 @@ static void read_qemu_guests(void)
 		if (!is_qemu)
 			goto next;
 
+		read_qemu_guests_pids(entry->d_name, &guest);
+
 		guests = realloc(guests, (guests_len + 1) * sizeof(*guests));
 		if (!guests)
 			die("Can not allocate guest buffer");
@@ -3160,6 +3221,22 @@ static char *parse_guest_name(char *guest, int *cid, int *port)
 	return guest;
 }
 
+int get_guest_vcpu_pid(unsigned int guest_cid, unsigned int guest_vcpu)
+{
+	int i;
+
+	if (!guests)
+		return -1;
+
+	for (i = 0; i < guests_len; i++) {
+		if (!guests[i].cpu_pid || guest_vcpu >= guests[i].cpu_max)
+			continue;
+		if (guest_cid == guests[i].cid)
+			return guests[i].cpu_pid[guest_vcpu];
+	}
+	return -1;
+}
+
 static void set_prio(int prio)
 {
 	struct sched_param sp;
-- 
2.24.1