trace-cmd: Have the pid to vcpu mappings know about sparse maps

If the kvm vcpuX files do not map directly to the guest's CPUs, then the
tmaps will not match and the host will not have a mapping to the guest.

That is, if the hypervisor has:

 # ls -d /sys/kernel/debug/kvm/[0-9]*/vcpu*
/sys/kernel/debug/kvm/408-7/vcpu0   /sys/kernel/debug/kvm/408-7/vcpu24
/sys/kernel/debug/kvm/408-7/vcpu1   /sys/kernel/debug/kvm/408-7/vcpu26
/sys/kernel/debug/kvm/408-7/vcpu16  /sys/kernel/debug/kvm/408-7/vcpu28
/sys/kernel/debug/kvm/408-7/vcpu18  /sys/kernel/debug/kvm/408-7/vcpu30
/sys/kernel/debug/kvm/408-7/vcpu20  /sys/kernel/debug/kvm/408-7/vcpu8
/sys/kernel/debug/kvm/408-7/vcpu22  /sys/kernel/debug/kvm/408-7/vcpu9

But the guest sees CPUs 0-11, the kvm exit/enter events will also show the
above numbers (vcpu 8 for guest CPU 3).

Have the mapping logic look at these files and sort them, and then map the
threads to CPU via them.

Link: https://lore.kernel.org/linux-trace-devel/20220708014244.677826-3-rostedt@goodmis.org
Link: https://lore.kernel.org/all/20220504010242.1388192-1-vineethrp@google.com/

Reported-by: Vineeth Pillai <vineethrp@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 99 insertions, 1 deletions

diff --git a/tracecmd/trace-tsync.c b/tracecmd/trace-tsync.c
index a96b4e43..57baff39 100644
--- a/tracecmd/trace-tsync.c
+++ b/tracecmd/trace-tsync.c
@@ -16,14 +16,105 @@ struct trace_mapping {
 	struct tep_format_field		*common_pid;
 	int				*pids;
 	int				*map;
+	int				*vcpu;
 	int				max_cpus;
 };
 
+static int cmp_tmap_vcpu(const void *A, const void *B)
+{
+	const int *a = A;
+	const int *b = B;
+
+	if (*a < *b)
+		return -1;
+	return *a > *b;
+}
+
+static int map_kvm_vcpus(int guest_pid, struct trace_mapping *tmap)
+{
+	struct dirent *entry;
+	const char *debugfs;
+	char *vm_dir_str = NULL;
+	char *pid_file = NULL;
+	char *kvm_dir;
+	int pid_file_len;
+	bool found = false;
+	DIR *dir;
+	int ret = -1;
+	int i;
+
+	tmap->vcpu = malloc(sizeof(*tmap->vcpu) * tmap->max_cpus);
+	if (!tmap->vcpu)
+		return -1;
+
+	memset(tmap->vcpu, -1, sizeof(*tmap->vcpu) * tmap->max_cpus);
+
+	debugfs = tracefs_debug_dir();
+	if (!debugfs)
+		return -1;
+
+	if (asprintf(&kvm_dir, "%s/kvm", debugfs) < 0)
+		return -1;
+
+	dir = opendir(kvm_dir);
+	if (!dir)
+		goto out;
+
+	if (asprintf(&pid_file, "%d-", guest_pid) <= 0)
+		goto out;
+
+	pid_file_len = strlen(pid_file);
+
+	while ((entry = readdir(dir))) {
+		if (entry->d_type != DT_DIR ||
+		    strncmp(entry->d_name, pid_file, pid_file_len) != 0)
+			continue;
+		if (asprintf(&vm_dir_str, "%s/%s", kvm_dir, entry->d_name) < 0)
+			goto out;
+		found = true;
+		break;
+	}
+	if (!found)
+		goto out;
+
+	closedir(dir);
+	dir = opendir(vm_dir_str);
+	if (!dir)
+		goto out;
+	i = 0;
+	while ((entry = readdir(dir))) {
+		if (entry->d_type != DT_DIR ||
+		    strncmp(entry->d_name, "vcpu", 4))
+			continue;
+		if (i == tmap->max_cpus)
+			goto out;
+		tmap->vcpu[i] = strtol(entry->d_name + 4, NULL, 10);
+		i++;
+	}
+
+	if (i < tmap->max_cpus)
+		goto out;
+
+	qsort(tmap->vcpu, tmap->max_cpus, sizeof(*tmap->vcpu), cmp_tmap_vcpu);
+
+	ret = 0;
+
+ out:
+	if (dir)
+		closedir(dir);
+	free(vm_dir_str);
+	free(pid_file);
+	free(kvm_dir);
+
+	return ret;
+}
+
 static int map_vcpus(struct tep_event *event, struct tep_record *record,
 		     int cpu, void *context)
 {
 	struct trace_mapping *tmap = context;
 	unsigned long long val;
+	int *vcpu;
 	int type;
 	int pid;
 	int ret;
@@ -53,10 +144,13 @@ static int map_vcpus(struct tep_event *event, struct tep_record *record,
 
 	cpu = (int)val;
 
+	vcpu = bsearch(&cpu, tmap->vcpu, tmap->max_cpus, sizeof(cpu), cmp_tmap_vcpu);
 	/* Sanity check, warn? */
-	if (cpu >= tmap->max_cpus)
+	if (!vcpu)
 		return 0;
 
+	cpu = vcpu - tmap->vcpu;
+
 	/* Already have this one? Should we check if it is the same? */
 	if (tmap->map[cpu] >= 0)
 		return 0;
@@ -123,6 +217,10 @@ static void stop_mapping_vcpus(int cpu_count, struct trace_guest *guest)
 	if (!tmap.map)
 		return;
 
+	/* Check if the kvm vcpu mappings are the same */
+	if (map_kvm_vcpus(guest->pid, &tmap) < 0)
+		goto out;
+
 	for (i = 0; i < tmap.max_cpus; i++)
 		tmap.map[i] = -1;