Re: [PATCH v10 3/8] qmp: add QMP command x-query-virtio

[Markus Armbruster <armbru@redhat.com>]

Jonah Palmer <jonah.palmer@oracle.com> writes:

> From: Laurent Vivier <lvivier@redhat.com>
>
> This new command lists all the instances of VirtIODevices with
> their canonical QOM path and name.
>
> Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> ---
>  hw/virtio/meson.build      |  2 ++
>  hw/virtio/virtio-stub.c    | 14 ++++++++++
>  hw/virtio/virtio.c         | 27 ++++++++++++++++++
>  include/hw/virtio/virtio.h |  1 +
>  qapi/meson.build           |  1 +
>  qapi/qapi-schema.json      |  1 +
>  qapi/virtio.json           | 68 ++++++++++++++++++++++++++++++++++++++++++++++
>  tests/qtest/qmp-cmd-test.c |  1 +
>  8 files changed, 115 insertions(+)
>  create mode 100644 hw/virtio/virtio-stub.c
>  create mode 100644 qapi/virtio.json
>
> diff --git a/hw/virtio/meson.build b/hw/virtio/meson.build
> index 521f7d6..d893f5f 100644
> --- a/hw/virtio/meson.build
> +++ b/hw/virtio/meson.build
> @@ -6,8 +6,10 @@ softmmu_virtio_ss.add(when: 'CONFIG_VHOST', if_false: files('vhost-stub.c'))
>  
>  softmmu_ss.add_all(when: 'CONFIG_VIRTIO', if_true: softmmu_virtio_ss)
>  softmmu_ss.add(when: 'CONFIG_VIRTIO', if_false: files('vhost-stub.c'))
> +softmmu_ss.add(when: 'CONFIG_VIRTIO', if_false: files('virtio-stub.c'))
>  
>  softmmu_ss.add(when: 'CONFIG_ALL', if_true: files('vhost-stub.c'))
> +softmmu_ss.add(when: 'CONFIG_ALL', if_true: files('virtio-stub.c'))
>  
>  virtio_ss = ss.source_set()
>  virtio_ss.add(files('virtio.c'))
> diff --git a/hw/virtio/virtio-stub.c b/hw/virtio/virtio-stub.c
> new file mode 100644
> index 0000000..05a81ed
> --- /dev/null
> +++ b/hw/virtio/virtio-stub.c
> @@ -0,0 +1,14 @@
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "qapi/qapi-commands-virtio.h"
> +
> +static void *qmp_virtio_unsupported(Error **errp)
> +{
> +    error_setg(errp, "Virtio is disabled");
> +    return NULL;
> +}
> +
> +VirtioInfoList *qmp_x_query_virtio(Error **errp)
> +{
> +    return qmp_virtio_unsupported(errp);
> +}
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 867834d..76a63a0 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -13,6 +13,8 @@
>  
>  #include "qemu/osdep.h"
>  #include "qapi/error.h"
> +#include "qapi/qapi-commands-virtio.h"
> +#include "qapi/qapi-visit-virtio.h"
>  #include "cpu.h"
>  #include "trace.h"
>  #include "qemu/error-report.h"
> @@ -29,6 +31,9 @@
>  #include "sysemu/runstate.h"
>  #include "standard-headers/linux/virtio_ids.h"
>  
> +/* QAPI list of realized VirtIODevices */
> +static QTAILQ_HEAD(, VirtIODevice) virtio_list;
> +
>  /*
>   * The alignment to use between consumer and producer parts of vring.
>   * x86 pagesize again. This is the default, used by transports like PCI
> @@ -3700,6 +3705,7 @@ 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)
> @@ -3714,6 +3720,7 @@ 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;
>  }
> @@ -3887,6 +3894,8 @@ 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);
>  }

@virtio_list duplicates information that exists in the QOM composition
tree.  It needs to stay in sync.  You could search the composition tree
instead.  I don't particularly care, but a virtio or QOM maintainer
might have a preference.

>  
>  bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev)
> @@ -3897,6 +3906,24 @@ bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev)
>      return virtio_bus_ioeventfd_enabled(vbus);
>  }
>  
> +VirtioInfoList *qmp_x_query_virtio(Error **errp)
> +{
> +    VirtioInfoList *list = NULL;
> +    VirtioInfoList *node;
> +    VirtIODevice *vdev;
> +
> +    QTAILQ_FOREACH(vdev, &virtio_list, next) {
> +        DeviceState *dev = DEVICE(vdev);
> +        node = g_new0(VirtioInfoList, 1);
> +        node->value = g_new(VirtioInfo, 1);
> +        node->value->path = g_strdup(dev->canonical_path);
> +        node->value->name = g_strdup(vdev->name);
> +        QAPI_LIST_PREPEND(list, node->value);
> +    }
> +
> +    return list;
> +}
> +
>  static const TypeInfo virtio_device_info = {
>      .name = TYPE_VIRTIO_DEVICE,
>      .parent = TYPE_DEVICE,
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 0a12bd5..3b4eb85 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -110,6 +110,7 @@ struct VirtIODevice
>      bool use_guest_notifier_mask;
>      AddressSpace *dma_as;
>      QLIST_HEAD(, VirtQueue) *vector_queues;
> +    QTAILQ_ENTRY(VirtIODevice) next;
>  };
>  
>  struct VirtioDeviceClass {
> diff --git a/qapi/meson.build b/qapi/meson.build
> index c0c49c1..e332f28 100644
> --- a/qapi/meson.build
> +++ b/qapi/meson.build
> @@ -48,6 +48,7 @@ qapi_all_modules = [
>    'sockets',
>    'trace',
>    'transaction',
> +  'virtio',
>    'yank',
>  ]
>  if have_system
> diff --git a/qapi/qapi-schema.json b/qapi/qapi-schema.json
> index 4912b97..1512ada 100644
> --- a/qapi/qapi-schema.json
> +++ b/qapi/qapi-schema.json
> @@ -93,3 +93,4 @@
>  { 'include': 'audio.json' }
>  { 'include': 'acpi.json' }
>  { 'include': 'pci.json' }
> +{ 'include': 'virtio.json' }
> diff --git a/qapi/virtio.json b/qapi/virtio.json
> new file mode 100644
> index 0000000..5372cde
> --- /dev/null
> +++ b/qapi/virtio.json
> @@ -0,0 +1,68 @@
> +# -*- Mode: Python -*-
> +# vim: filetype=python
> +#
> +
> +##
> +# = Virtio devices
> +##
> +
> +##
> +# @VirtioInfo:
> +#
> +# Basic information about a given VirtIODevice
> +#
> +# @path: The VirtIODevice's canonical QOM path
> +#
> +# @name: Name of the VirtIODevice
> +#
> +# Since: 7.0
> +#
> +##
> +{ 'struct': 'VirtioInfo',
> +  'data': { 'path': 'str',
> +            'name': 'str' } }
> +
> +##
> +# @x-query-virtio:
> +#
> +# Returns a list of all realized VirtIODevices
> +#
> +# Features:
> +# @unstable: This command is meant for debugging

End with a period for consistency with existing docs.

> +#
> +# Returns: List of gathered VirtIODevices
> +#
> +# Since: 7.0
> +#
> +# Example:
> +#
> +# -> { "execute": "x-query-virtio" }
> +# <- { "return": [
> +#        {
> +#            "path": "/machine/peripheral-anon/device[4]/virtio-backend",
> +#            "name": "virtio-input"
> +#        },
> +#        {
> +#            "path": "/machine/peripheral/crypto0/virtio-backend",
> +#            "name": "virtio-crypto"
> +#        },
> +#        {
> +#            "path": "/machine/peripheral-anon/device[2]/virtio-backend",
> +#            "name": "virtio-scsi"
> +#        },
> +#        {
> +#            "path": "/machine/peripheral-anon/device[1]/virtio-backend",
> +#            "name": "virtio-net"
> +#        },
> +#        {
> +#            "path": "/machine/peripheral-anon/device[0]/virtio-backend",
> +#            "name": "virtio-serial"
> +#        }
> +#      ]
> +#    }
> +#
> +##
> +
> +{ 'command': 'x-query-virtio',
> +  'returns': [ 'VirtioInfo' ],
> +  'features': [ 'unstable' ] }

This command is actually redundant: qom-list and qom-get suffice to
search /machine/ for virtio devices whose property realized is true.

To recognize virtio devices without relying on a naming convention, you
can use

    {"execute": "qom-list-types",
     "arguments": {"implements": "virtio-device"}}

Perhaps we want the command anyway, for convenience.  That's for to the
virtio maintainer to decide, I guess.  In case of "wanted":

QAPI schema
Reviewed-by: Markus Armbruster <armbru@redhat.com>

But please point out the redundancy in the commit message and/or a
comment.

[...]