[PATCH v7 6/9] trace-cmd: Find and store pids of tasks, which run virtual CPUs of given VM

[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 |  1 +
 tracecmd/trace-record.c        | 56 ++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/tracecmd/include/trace-local.h b/tracecmd/include/trace-local.h
index 8413054..62f5e47 100644
--- a/tracecmd/include/trace-local.h
+++ b/tracecmd/include/trace-local.h
@@ -245,6 +245,7 @@ int tracecmd_local_cpu_count(void);
 void tracecmd_set_clock(struct buffer_instance *instance);
 void tracecmd_remove_instance(struct buffer_instance *instance);
 
+int get_guest_vcpu_pid(unsigned int guest_cid, unsigned int guest_vcpu);
 /* No longer in event-utils.h */
 void __noreturn die(const char *fmt, ...); /* Can be overriden */
 void *malloc_or_die(unsigned int size); /* Can be overridden */
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 3950242..8c8e46f 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -2746,10 +2746,12 @@ static bool is_digits(const char *s)
 	return true;
 }
 
+#define VCPUS_MAX 256
 struct guest {
 	char *name;
 	int cid;
 	int pid;
+	int cpu_pid[VCPUS_MAX];
 };
 
 static struct guest *guests;
@@ -2767,6 +2769,45 @@ 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_t;
+	char path[PATH_MAX];
+	unsigned int vcpu;
+	char *buf = NULL;
+	DIR *dir;
+	FILE *ft;
+	size_t n;
+
+	snprintf(path, sizeof(path), "/proc/%s/task", guest_task);
+	dir = opendir(path);
+	if (!dir)
+		return;
+
+	for (entry_t = readdir(dir); entry_t; entry_t = readdir(dir)) {
+		if (!(entry_t->d_type == DT_DIR && is_digits(entry_t->d_name)))
+			continue;
+
+		snprintf(path, sizeof(path), "/proc/%s/task/%s/comm",
+			 guest_task, entry_t->d_name);
+		ft = fopen(path, "r");
+		if (!ft)
+			continue;
+		if (getline(&buf, &n, ft) < 0)
+			goto next;
+		if (strncmp(buf, "CPU ", 4) != 0)
+			goto next;
+
+		vcpu = atoi(buf+4);
+		if (!(vcpu >= 0 && vcpu < VCPUS_MAX))
+			goto next;
+		guest->cpu_pid[vcpu] = atoi(entry_t->d_name);
+
+next:
+		fclose(ft);
+	}
+}
+
 static void read_qemu_guests(void)
 {
 	static bool initialized;
@@ -2828,6 +2869,8 @@ 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");
@@ -2873,6 +2916,19 @@ 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 || guest_vcpu >= VCPUS_MAX)
+		return -1;
+
+	for (i = 0; i < guests_len; i++)
+		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;
-- 
2.20.1