Re: [PATCH v4 2/2] qapi: add '@fdset' feature for BlockdevOptionsVirtioBlkVhostVdpa

[Markus Armbruster]

Stefano Garzarella <sgarzare@redhat.com> writes:

> The virtio-blk-vhost-vdpa driver in libblkio 1.3.0 supports the fd
> passing through the new 'fd' property.
>
> Since now we are using qemu_open() on '@path' if the virtio-blk driver
> supports the fd passing, let's announce it.
> In this way, the management layer can pass the file descriptor of an
> already opened vhost-vdpa character device. This is useful especially
> when the device can only be accessed with certain privileges.
>
> Add the '@fdset' feature only when the virtio-blk-vhost-vdpa driver
> in libblkio supports it.
>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>
> Notes:
>     v4:
>     - added this patch to allow libvirt to discover we support fdset [Markus]
>
>  meson.build          | 4 ++++
>  qapi/block-core.json | 8 +++++++-
>  2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/meson.build b/meson.build
> index 78890f0155..8ea911f7b4 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2108,6 +2108,10 @@ config_host_data.set('CONFIG_LZO', lzo.found())
>  config_host_data.set('CONFIG_MPATH', mpathpersist.found())
>  config_host_data.set('CONFIG_MPATH_NEW_API', mpathpersist_new_api)
>  config_host_data.set('CONFIG_BLKIO', blkio.found())
> +if blkio.found()
> +  config_host_data.set('CONFIG_BLKIO_VHOST_VDPA_FD',
> +                       blkio.version().version_compare('>=1.3.0'))
> +endif
>  config_host_data.set('CONFIG_CURL', curl.found())
>  config_host_data.set('CONFIG_CURSES', curses.found())
>  config_host_data.set('CONFIG_GBM', gbm.found())
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 98d9116dae..1538d84ef4 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -3955,10 +3955,16 @@
>  #
>  # @path: path to the vhost-vdpa character device.
>  #
> +# Features:
> +# @fdset: Member @path supports the special "/dev/fdset/N" path (since 8.1)

Slightly long line, break it like this:

   # @fdset: Member @path supports the special "/dev/fdset/N" path
   #     since 8.1)

> +#
>  # Since: 7.2
>  ##
>  { 'struct': 'BlockdevOptionsVirtioBlkVhostVdpa',
> -  'data': { 'path': 'str' },
> +  'data': { 'path': { 'type': 'str',
> +                      'features': [ { 'name' :'fdset',
> +                                      'if': 'CONFIG_BLKIO_VHOST_VDPA_FD' } ]
> +            } },
>    'if': 'CONFIG_BLKIO' }
>  
>  ##

Tacking the feature to the member works.

For what it's worth, the existing features serving similar purposes are
all tacked to the command or type.

Do libvirt developers have a preference?