Re: [PATCH v7 02/12] accel: Introduce 'query-accels' QMP command

[Markus Armbruster]

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> Introduce the 'query-accels' QMP command which returns a list
> of built-in accelerator names.
>
> - Accelerator is a QAPI enum of all existing accelerators,
>
> - AcceleratorInfo is a QAPI structure providing accelerator
>   specific information. Currently the common structure base
>   provides the name of the accelerator, while the specific
>   part is empty, but each accelerator can expand it.
>
> - 'query-accels' QMP command returns a list of @AcceleratorInfo
>
> For example on a KVM-only build we get:
>
>     { "execute": "query-accels" }
>     {
>         "return": [
>             {
>                 "name": "qtest"
>             },
>             {
>                 "name": "kvm"
>             }
>         ]
>     }
>
> Note that we can't make the enum values or union branches conditional
> because of target-specific poisoning of accelerator definitions.

I second Eduardo's plea to explain this more clearly.  It's important,
because if a properly conditionalized enum is feasible, then query-accel
isn't needed.

> Reviewed-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> Tested-by: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  qapi/machine.json | 47 +++++++++++++++++++++++++++++++++++++++++++++
>  accel/accel-qmp.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
>  accel/meson.build |  2 +-
>  3 files changed, 97 insertions(+), 1 deletion(-)
>  create mode 100644 accel/accel-qmp.c
>
> diff --git a/qapi/machine.json b/qapi/machine.json
> index 6e90d463fc9..6dd3b765248 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1274,3 +1274,50 @@
>  ##
>  { 'event': 'MEM_UNPLUG_ERROR',
>    'data': { 'device': 'str', 'msg': 'str' } }
> +
> +##
> +# @Accelerator:
> +#
> +# An enumeration of accelerator names.
> +#
> +# Since: 6.1
> +##
> +{ 'enum': 'Accelerator',
> +  'data': [ 'hax', 'hvf', 'kvm', 'qtest', 'tcg', 'whpx', 'xen' ] }
> +
> +##
> +# @AcceleratorInfo:
> +#
> +# Accelerator information.
> +#
> +# @name: The accelerator name.
> +#
> +# Since: 6.1
> +##
> +{ 'struct': 'AcceleratorInfo',
> +  'data': { 'name': 'Accelerator' } }
> +
> +##
> +# @query-accels:
> +#
> +# Get a list of AcceleratorInfo for all built-in accelerators.

"built-in" means compiled in.  See accel_builtin_list[] below.

> +#
> +# Returns: a list of @AcceleratorInfo describing each accelerator.
> +#
> +# Since: 6.1
> +#
> +# Example:
> +#
> +# -> { "execute": "query-accels" }
> +# <- { "return": [
> +#        {
> +#            "name": "qtest"
> +#        },
> +#        {
> +#            "name": "kvm"
> +#        }
> +#    ] }
> +#
> +##
> +{ 'command': 'query-accels',
> +  'returns': ['AcceleratorInfo'] }
> diff --git a/accel/accel-qmp.c b/accel/accel-qmp.c
> new file mode 100644
> index 00000000000..426737b3f9a
> --- /dev/null
> +++ b/accel/accel-qmp.c
> @@ -0,0 +1,49 @@
> +/*
> + * QEMU accelerators, QMP commands
> + *
> + * Copyright (c) 2021 Red Hat Inc.
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/qapi-commands-machine.h"
> +
> +static const bool accel_builtin_list[ACCELERATOR__MAX] = {
> +    [ACCELERATOR_QTEST] = true,
> +#ifdef CONFIG_TCG
> +    [ACCELERATOR_TCG] = true,
> +#endif
> +#ifdef CONFIG_KVM
> +    [ACCELERATOR_KVM] = true,
> +#endif
> +#ifdef CONFIG_HAX
> +    [ACCELERATOR_HAX] = true,
> +#endif
> +#ifdef CONFIG_HVF
> +    [ACCELERATOR_HVF] = true,
> +#endif
> +#ifdef CONFIG_WHPX
> +    [ACCELERATOR_WHPX] = true,
> +#endif
> +#ifdef CONFIG_XEN_BACKEND
> +    [ACCELERATOR_XEN] = true,
> +#endif
> +};
> +
> +AcceleratorInfoList *qmp_query_accels(Error **errp)
> +{
> +    AcceleratorInfoList *list = NULL, **tail = &list;
> +
> +    for (Accelerator accel = 0; accel < ACCELERATOR__MAX; accel++) {
> +        if (accel_builtin_list[accel]) {
> +            AcceleratorInfo *info = g_new0(AcceleratorInfo, 1);
> +
> +            info->name = accel;
> +
> +            QAPI_LIST_APPEND(tail, info);
> +        }
> +    }
> +
> +    return list;
> +}

CLI -accel help also lists the available accelerators, but finds them
differently.  Whereas query-accel relies on hard-coded
accel_builtin_list[], that one instead finds the concrete subtypes of
TYPE_ACCEL.

Any particular reason for the difference?

> diff --git a/accel/meson.build b/accel/meson.build
> index b44ba30c864..7a48f6d568d 100644
> --- a/accel/meson.build
> +++ b/accel/meson.build
> @@ -1,4 +1,4 @@
> -specific_ss.add(files('accel-common.c'))
> +specific_ss.add(files('accel-common.c', 'accel-qmp.c'))
>  softmmu_ss.add(files('accel-softmmu.c'))
>  user_ss.add(files('accel-user.c'))