Re: [PATCH v2 1/2] qmp: remove virtio_list, search QOM tree instead

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 26, 2023 at 08:08:28AM -0400, Jonah Palmer wrote:
> 
> On 6/23/23 01:47, Michael S. Tsirkin wrote:
> 
>     On Fri, Jun 09, 2023 at 09:20:39AM -0400, Jonah Palmer wrote:
> 
>         The virtio_list duplicates information about virtio devices that already
>         exist in the QOM composition tree. Instead of creating this list of
>         realized virtio devices, search the QOM composition tree instead.
> 
>         This patch modifies the QMP command qmp_x_query_virtio to instead search
>         the partial paths of '/machine/peripheral/' &
>         '/machine/peripheral-anon/' in the QOM composition tree for virtio
>         devices.
> 
>         A device is found to be a valid virtio device if (1) its canonical path
>         is of 'TYPE_VIRTIO_DEVICE' and (2) the device has been realized.
> 
>         [Jonah: In the previous commit I had written that a device is found to
>          be a valid virtio device if (1) it has a canonical path ending with
>          'virtio-backend'.
> 
>          The code now determines if it's a virtio device by appending
>          'virtio-backend' (if needed) to a given canonical path and then
>          checking that path to see if the device is of type
>         'TYPE_VIRTIO_DEVICE'.
> 
>          The patch also instead now checks to make sure it's a virtio device
>          before attempting to check whether the device is realized or not.]
> 
>         Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> 
> 
>     Could one of QMP maintainers comment on this please?
> 
> 
>         ---
>          hw/virtio/virtio-qmp.c | 128 ++++++++++++++++++++++++++---------------
>          hw/virtio/virtio-qmp.h |   8 +--
>          hw/virtio/virtio.c     |   6 --
>          3 files changed, 82 insertions(+), 60 deletions(-)
> 
>         diff --git a/hw/virtio/virtio-qmp.c b/hw/virtio/virtio-qmp.c
>         index b5e1835299..e936cc8ce5 100644
>         --- a/hw/virtio/virtio-qmp.c
>         +++ b/hw/virtio/virtio-qmp.c
>         @@ -668,67 +668,101 @@ VirtioDeviceFeatures *qmp_decode_features(uint16_t device_id, uint64_t bitmap)
>          VirtioInfoList *qmp_x_query_virtio(Error **errp)
>          {
>              VirtioInfoList *list = NULL;
>         -    VirtioInfo *node;
>         -    VirtIODevice *vdev;
> 
>         -    QTAILQ_FOREACH(vdev, &virtio_list, next) {
>         -        DeviceState *dev = DEVICE(vdev);
>         -        Error *err = NULL;
>         -        QObject *obj = qmp_qom_get(dev->canonical_path, "realized", &err);
>         -
>         -        if (err == NULL) {
>         -            GString *is_realized = qobject_to_json_pretty(obj, true);
>         -            /* virtio device is NOT realized, remove it from list */
>         -            if (!strncmp(is_realized->str, "false", 4)) {
>         -                QTAILQ_REMOVE(&virtio_list, vdev, next);
>         -            } else {
>         -                node = g_new(VirtioInfo, 1);
>         -                node->path = g_strdup(dev->canonical_path);
>         -                node->name = g_strdup(vdev->name);
>         -                QAPI_LIST_PREPEND(list, node);
>         +    /* Query the QOM composition tree for virtio devices */
>         +    qmp_set_virtio_device_list("/machine/peripheral/", &list);
>         +    qmp_set_virtio_device_list("/machine/peripheral-anon/", &list);
> 
>     How sure are we these will forever be the only two places where virtio
>     can live?
> 
> A virtio device will always be considered a peripheral device, right?
> Since peripheral devices are input and/or output devices by definition.
> 
>         +    if (list == NULL) {
>         +        error_setg(errp, "No virtio devices found");
>         +        return NULL;
>         +    }
>         +    return list;
>         +}
>         +
>         +/* qmp_set_virtio_device_list:
>         + * @ppath: An incomplete peripheral path to search from.
>         + * @list: A list of realized virtio devices.
>         + * Searches a given incomplete peripheral path (e.g. '/machine/peripheral/'
>         + * or '/machine/peripheral-anon/') for realized virtio devices and adds them
>         + * to a given list of virtio devices.
>         + */
>         +void qmp_set_virtio_device_list(const char *ppath, VirtioInfoList **list)
>         +{
>         +    ObjectPropertyInfoList *plist;
>         +    VirtioInfoList *node;
>         +    Error *err = NULL;
>         +
>         +    /* Search an incomplete path for virtio devices */
>         +    plist = qmp_qom_list(ppath, &err);
>         +    if (err == NULL) {
>         +        ObjectPropertyInfoList *start = plist;
>         +        while (plist != NULL) {
>         +            ObjectPropertyInfo *value = plist->value;
>         +            GString *path = g_string_new(ppath);
>         +            g_string_append(path, value->name);
>         +            g_string_append(path, "/virtio-backend");
>         +
>         +            /* Determine if full path is a realized virtio device */
>         +            VirtIODevice *vdev = qmp_find_virtio_device(path->str);
>         +            if (vdev != NULL) {
>         +                node = g_new0(VirtioInfoList, 1);
>         +                node->value = g_new(VirtioInfo, 1);
>         +                node->value->path = g_strdup(path->str);
>         +                node->value->name = g_strdup(vdev->name);
>         +                QAPI_LIST_PREPEND(*list, node->value);
>                      }
>         -           g_string_free(is_realized, true);
>         +            g_string_free(path, true);
>         +            plist = plist->next;
>                  }
>         -        qobject_unref(obj);
>         +        qapi_free_ObjectPropertyInfoList(start);
>              }
>         -
>         -    return list;
>          }
> 
>          VirtIODevice *qmp_find_virtio_device(const char *path)
>          {
>         -    VirtIODevice *vdev;
>         -
>         -    QTAILQ_FOREACH(vdev, &virtio_list, next) {
>         -        DeviceState *dev = DEVICE(vdev);
>         -
>         -        if (strcmp(dev->canonical_path, path) != 0) {
>         -            continue;
>         +    Error *err = NULL;
>         +    char *basename;
>         +
>         +    /* Append 'virtio-backend' to path if needed */
>         +    basename = g_path_get_basename(path);
>         +    if (strcmp(basename, "virtio-backend")) {
>         +        GString *temp = g_string_new(path);
>         +        char *last = strrchr(path, '/');
>         +        if (g_strcmp0(last, "/")) {
>         +            g_string_append(temp, "/virtio-backend");
>         +        } else {
>         +            g_string_append(temp, "virtio-backend");
>                  }
>         +        path = g_strdup(temp->str);
>         +        g_string_free(temp, true);
>         +    }
> 
>     I don't much like the string operations. We should be able to
>     check object types instead.
> 
> 
> I don't either but in order for us to check if the object is a
> virtio device type, we need to use the device's path ending
> with '/virtio-backend'.
> 
> If there's a better method to checking this though, or perhaps
> checking a different type, that doesn't involve string
> manipulation, then I'm all for it.

TYPE_VIRTIO_DEVICE ?


>         -        Error *err = NULL;
>         -        QObject *obj = qmp_qom_get(dev->canonical_path, "realized", &err);
>         -        if (err == NULL) {
>         -            GString *is_realized = qobject_to_json_pretty(obj, true);
>         -            /* virtio device is NOT realized, remove it from list */
>         -            if (!strncmp(is_realized->str, "false", 4)) {
>         -                g_string_free(is_realized, true);
>         -                qobject_unref(obj);
>         -                QTAILQ_REMOVE(&virtio_list, vdev, next);
>         -                return NULL;
>         -            }
>         +    /* Verify the canonical path is a virtio device */
>         +    Object *obj = object_resolve_path(path, NULL);
>         +    if (!obj || !object_dynamic_cast(obj, TYPE_VIRTIO_DEVICE)) {
>         +        object_unref(obj);
>         +        return NULL;
>         +    }
>         +
>         +    /* Verify the virtio device is realized */
>         +    QObject *qobj = qmp_qom_get(path, "realized", &err);
>         +    if (err == NULL) {
>         +        GString *is_realized = qobject_to_json_pretty(qobj, true);
>         +        if (!strncmp(is_realized->str, "false", 4)) {
>                      g_string_free(is_realized, true);
>         -        } else {
>         -            /* virtio device doesn't exist in QOM tree */
>         -            QTAILQ_REMOVE(&virtio_list, vdev, next);
>         -            qobject_unref(obj);
>         +            qobject_unref(qobj);
>                      return NULL;
>                  }
>         -        /* device exists in QOM tree & is realized */
>         -        qobject_unref(obj);
>         -        return vdev;
>         +        g_string_free(is_realized, true);
>         +    } else {
>         +        qobject_unref(qobj);
>         +        return NULL;
>              }
>         -    return NULL;
>         +    qobject_unref(qobj);
>         +
>         +    /* Get VirtIODevice object */
>         +    VirtIODevice *vdev = VIRTIO_DEVICE(obj);
>         +    return vdev;
>          }
> 
>          VirtioStatus *qmp_x_query_virtio_status(const char *path, Error **errp)
>         diff --git a/hw/virtio/virtio-qmp.h b/hw/virtio/virtio-qmp.h
>         index 8af5f5e65a..4b2b7875b4 100644
>         --- a/hw/virtio/virtio-qmp.h
>         +++ b/hw/virtio/virtio-qmp.h
>         @@ -15,13 +15,7 @@
>          #include "hw/virtio/virtio.h"
>          #include "hw/virtio/vhost.h"
> 
>         -#include "qemu/queue.h"
>         -
>         -typedef QTAILQ_HEAD(QmpVirtIODeviceList, VirtIODevice) QmpVirtIODeviceList;
>         -
>         -/* QAPI list of realized VirtIODevices */
>         -extern QmpVirtIODeviceList virtio_list;
>         -
>         +void qmp_set_virtio_device_list(const char *ppath, VirtioInfoList **list);
>          VirtIODevice *qmp_find_virtio_device(const char *path);
>          VirtioDeviceStatus *qmp_decode_status(uint8_t bitmap);
>          VhostDeviceProtocols *qmp_decode_protocols(uint64_t bitmap);
>         diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>         index 295a603e58..83c5db3d26 100644
>         --- a/hw/virtio/virtio.c
>         +++ b/hw/virtio/virtio.c
>         @@ -45,8 +45,6 @@
>          #include "standard-headers/linux/virtio_mem.h"
>          #include "standard-headers/linux/virtio_vsock.h"
> 
>         -QmpVirtIODeviceList virtio_list;
>         -
>          /*
>           * Maximum size of virtio device config space
>           */
>         @@ -3616,7 +3614,6 @@ static void virtio_device_realize(DeviceState *dev, Error **errp)
>              vdev->listener.commit = virtio_memory_listener_commit;
>              vdev->listener.name = "virtio";
>              memory_listener_register(&vdev->listener, vdev->dma_as);
>         -    QTAILQ_INSERT_TAIL(&virtio_list, vdev, next);
>          }
> 
>          static void virtio_device_unrealize(DeviceState *dev)
>         @@ -3631,7 +3628,6 @@ static void virtio_device_unrealize(DeviceState *dev)
>                  vdc->unrealize(dev);
>              }
> 
>         -    QTAILQ_REMOVE(&virtio_list, vdev, next);
>              g_free(vdev->bus_name);
>              vdev->bus_name = NULL;
>          }
>         @@ -3805,8 +3801,6 @@ static void virtio_device_class_init(ObjectClass *klass, void *data)
>              vdc->stop_ioeventfd = virtio_device_stop_ioeventfd_impl;
> 
>              vdc->legacy_features |= VIRTIO_LEGACY_FEATURES;
>         -
>         -    QTAILQ_INIT(&virtio_list);
>          }
> 
>          bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev)
>         --
>         2.39.3
>