virtio_fs: add sysfs entries for queue information

Introduce sysfs entries to provide visibility to the multiple queues
used by the Virtio FS device. This enhancement allows users to query
information about these queues.

Specifically, add two sysfs entries:
1. Queue name: Provides the name of each queue (e.g. hiprio/requests.8).
2. CPU list: Shows the list of CPUs that can process requests for each
queue.

The CPU list feature is inspired by similar functionality in the block
MQ layer, which provides analogous sysfs entries for block devices.

These new sysfs entries will improve observability and aid in debugging
and performance tuning of Virtio FS devices.
Reviewed-by: Idan Zach <izach@nvidia.com>
Reviewed-by: Shai Malin <smalin@nvidia.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Message-Id: <20240825130716.9506-2-mgurtovoy@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

fs/fuse/virtio_fs.c

@@ -56,12 +56,14 @@ struct virtio_fs_vq {
 	bool connected;
 	long in_flight;
 	struct completion in_flight_zero; /* No inflight requests */
+	struct kobject *kobj;
 	char name[VQ_NAME_LEN];
 } ____cacheline_aligned_in_smp;
 
 /* A virtio-fs device instance */
 struct virtio_fs {
 	struct kobject kobj;
+	struct kobject *mqs_kobj;
 	struct list_head list;    /* on virtio_fs_instances */
 	char *tag;
 	struct virtio_fs_vq *vqs;
@@ -200,6 +202,74 @@ static const struct kobj_type virtio_fs_ktype = {
 	.default_groups = virtio_fs_groups,
 };
 
+static struct virtio_fs_vq *virtio_fs_kobj_to_vq(struct virtio_fs *fs,
+		struct kobject *kobj)
+{
+	int i;
+
+	for (i = 0; i < fs->nvqs; i++) {
+		if (kobj == fs->vqs[i].kobj)
+			return &fs->vqs[i];
+	}
+	return NULL;
+}
+
+static ssize_t name_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct virtio_fs *fs = container_of(kobj->parent->parent, struct virtio_fs, kobj);
+	struct virtio_fs_vq *fsvq = virtio_fs_kobj_to_vq(fs, kobj);
+
+	if (!fsvq)
+		return -EINVAL;
+	return sysfs_emit(buf, "%s\n", fsvq->name);
+}
+
+static struct kobj_attribute virtio_fs_vq_name_attr = __ATTR_RO(name);
+
+static ssize_t cpu_list_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct virtio_fs *fs = container_of(kobj->parent->parent, struct virtio_fs, kobj);
+	struct virtio_fs_vq *fsvq = virtio_fs_kobj_to_vq(fs, kobj);
+	unsigned int cpu, qid;
+	const size_t size = PAGE_SIZE - 1;
+	bool first = true;
+	int ret = 0, pos = 0;
+
+	if (!fsvq)
+		return -EINVAL;
+
+	qid = fsvq->vq->index;
+	for (cpu = 0; cpu < nr_cpu_ids; cpu++) {
+		if (qid < VQ_REQUEST || (fs->mq_map[cpu] == qid - VQ_REQUEST)) {
+			if (first)
+				ret = snprintf(buf + pos, size - pos, "%u", cpu);
+			else
+				ret = snprintf(buf + pos, size - pos, ", %u", cpu);
+
+			if (ret >= size - pos)
+				break;
+			first = false;
+			pos += ret;
+		}
+	}
+	ret = snprintf(buf + pos, size + 1 - pos, "\n");
+	return pos + ret;
+}
+
+static struct kobj_attribute virtio_fs_vq_cpu_list_attr = __ATTR_RO(cpu_list);
+
+static struct attribute *virtio_fs_vq_attrs[] = {
+	&virtio_fs_vq_name_attr.attr,
+	&virtio_fs_vq_cpu_list_attr.attr,
+	NULL
+};
+
+static struct attribute_group virtio_fs_vq_attr_group = {
+	.attrs = virtio_fs_vq_attrs,
+};
+
 /* Make sure virtiofs_mutex is held */
 static void virtio_fs_put_locked(struct virtio_fs *fs)
 {
@@ -280,6 +350,50 @@ static void virtio_fs_start_all_queues(struct virtio_fs *fs)
 	}
 }
 
+static void virtio_fs_delete_queues_sysfs(struct virtio_fs *fs)
+{
+	struct virtio_fs_vq *fsvq;
+	int i;
+
+	for (i = 0; i < fs->nvqs; i++) {
+		fsvq = &fs->vqs[i];
+		kobject_put(fsvq->kobj);
+	}
+}
+
+static int virtio_fs_add_queues_sysfs(struct virtio_fs *fs)
+{
+	struct virtio_fs_vq *fsvq;
+	char buff[12];
+	int i, j, ret;
+
+	for (i = 0; i < fs->nvqs; i++) {
+		fsvq = &fs->vqs[i];
+
+		sprintf(buff, "%d", i);
+		fsvq->kobj = kobject_create_and_add(buff, fs->mqs_kobj);
+		if (!fs->mqs_kobj) {
+			ret = -ENOMEM;
+			goto out_del;
+		}
+
+		ret = sysfs_create_group(fsvq->kobj, &virtio_fs_vq_attr_group);
+		if (ret) {
+			kobject_put(fsvq->kobj);
+			goto out_del;
+		}
+	}
+
+	return 0;
+
+out_del:
+	for (j = 0; j < i; j++) {
+		fsvq = &fs->vqs[j];
+		kobject_put(fsvq->kobj);
+	}
+	return ret;
+}
+
 /* Add a new instance to the list or return -EEXIST if tag name exists*/
 static int virtio_fs_add_instance(struct virtio_device *vdev,
 				  struct virtio_fs *fs)
@@ -303,17 +417,22 @@ static int virtio_fs_add_instance(struct virtio_device *vdev,
 	 */
 	fs->kobj.kset = virtio_fs_kset;
 	ret = kobject_add(&fs->kobj, NULL, "%d", vdev->index);
-	if (ret < 0) {
-		mutex_unlock(&virtio_fs_mutex);
-		return ret;
+	if (ret < 0)
+		goto out_unlock;
+
+	fs->mqs_kobj = kobject_create_and_add("mqs", &fs->kobj);
+	if (!fs->mqs_kobj) {
+		ret = -ENOMEM;
+		goto out_del;
 	}
 
 	ret = sysfs_create_link(&fs->kobj, &vdev->dev.kobj, "device");
-	if (ret < 0) {
-		kobject_del(&fs->kobj);
-		mutex_unlock(&virtio_fs_mutex);
-		return ret;
-	}
+	if (ret < 0)
+		goto out_put;
+
+	ret = virtio_fs_add_queues_sysfs(fs);
+	if (ret)
+		goto out_remove;
 
 	list_add_tail(&fs->list, &virtio_fs_instances);
 
@@ -322,6 +441,16 @@ static int virtio_fs_add_instance(struct virtio_device *vdev,
 	kobject_uevent(&fs->kobj, KOBJ_ADD);
 
 	return 0;
+
+out_remove:
+	sysfs_remove_link(&fs->kobj, "device");
+out_put:
+	kobject_put(fs->mqs_kobj);
+out_del:
+	kobject_del(&fs->kobj);
+out_unlock:
+	mutex_unlock(&virtio_fs_mutex);
+	return ret;
 }
 
 /* Return the virtio_fs with a given tag, or NULL */
@@ -1050,7 +1179,9 @@ static void virtio_fs_remove(struct virtio_device *vdev)
 	mutex_lock(&virtio_fs_mutex);
 	/* This device is going away. No one should get new reference */
 	list_del_init(&fs->list);
+	virtio_fs_delete_queues_sysfs(fs);
 	sysfs_remove_link(&fs->kobj, "device");
+	kobject_put(fs->mqs_kobj);
 	kobject_del(&fs->kobj);
 	virtio_fs_stop_all_queues(fs);
 	virtio_fs_drain_all_queues_locked(fs);