Re: [Qemu-ppc] [PATCH v2 13/18] hw/nvram/fw_cfg: Add QMP 'info fw_cfg' command

[Eric Blake]

On 3/7/19 7:32 PM, Philippe Mathieu-Daudé wrote:
> When debugging a paravirtualized guest firmware, it results very
> useful to dump the fw_cfg table.
> Add a QMP command which returns the most useful fields.
> Since the QMP protocol is not designed for passing stream data,
> we don't display a fw_cfg item data, only it's size:
> 
> { "execute": "query-fw_cfg-items" }
> {
>     "return": [
>         {
>             "architecture_specific": false,
>             "key": 0,
>             "writeable": false,
>             "size": 4,
>             "keyname": "signature"

You could return a base64-encoded representation of the field (we do
that in other interfaces where raw binary can't be passed reliably over
JSON).  For 4 bytes, that makes sense,


>         {
>             "architecture_specific": true,
>             "key": 3,
>             "writeable": false,
>             "size": 324,
>             "keyname": "e820_tables"

for 324 bytes, it gets a bit long. Still, may be worth it for the added
debug visibility.


> +++ b/qapi/misc.json
> @@ -3051,3 +3051,47 @@
>    'data': 'NumaOptions',
>    'allow-preconfig': true
>  }
> +
> +##
> +# @FirmwareConfigurationItem:
> +#
> +# Firmware Configuration (fw_cfg) item.
> +#
> +# @key: The uint16 selector key.
> +# @keyname: The stringified name if the selector refers to a well-known
> +#           numerically defined item.
> +# @architecture_specific: Indicates whether the configuration setting is

Prefer '-' over '_' in new interfaces.

> +#                         architecture specific.
> +#                  false: The item is a generic configuration item.
> +#                  true:  The item is specific to a particular architecture.
> +# @writeable: Indicates whether the configuration setting is writeable by
> +#             the guest.

writable

> +# @size: The length of @data associated with the item.
> +# @data: A string representating the firmware configuration data.

representing

> +#        Note: This field is currently not used.

Either drop the field until it has a use, or let it be the base64
encoding and use it now.

> +# @path: If the key is a 'file', the named file path.
> +# @order: If the key is a 'file', the named file order.
> +#
> +# Since 4.0
> +##
> +{ 'struct': 'FirmwareConfigurationItem',
> +  'data': { 'key': 'uint16',
> +            '*keyname': 'str',
> +            'architecture_specific': 'bool',
> +            'writeable': 'bool',
> +            '*data': 'str',
> +            'size': 'int',
> +            '*path': 'str',
> +            '*order': 'int' } }

Is it worth making 'keyname' an enum type, and turning this into a flat
union where 'path' and 'order' appear on the branch associated with
'file', and where all other well-known keynames have smaller branches?


> +
> +
> +##
> +# @query-fw_cfg-items:

That looks weird to mix - and _. Any reason we can't just go with
query-firmware-config?

> +#
> +# Returns the list of Firmware Configuration items.
> +#
> +# Returns: A list of @FirmwareConfigurationItem for each entry.
> +#
> +# Since 4.0
> +##
> +{ 'command': 'query-fw_cfg-items', 'returns': ['FirmwareConfigurationItem']}
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org