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

[Jonah Palmer]

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.
> > -        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
> >       
>