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

[Laszlo Ersek]

Hi Markus,

On 03/09/19 16:04, Markus Armbruster wrote:
> The subject "Add QMP 'info fw_cfg' command" misspells query-fw_cfg-items
> :)
> 
> Eric Blake <address@hidden> writes:
> 
>> On 3/7/19 7:32 PM, Philippe Mathieu-Daudé wrote:

>>> +##
>>> +# @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.
> 
> Ignorant questions, I'm afraid...
> 
> What determines the possible values of @key?

the text file "docs/specs/fw_cfg.txt" explains this somewhat.

- In section "Selector (Control) Register", it lays out the structure of
the key space.

> What's the difference between a "well-known" and a "not well-known"
> value?  Examples?

- In section "Firmware Configuration Items", it explains the selectors
FW_CFG_SIGNATURE, FW_CFG_ID, FW_CFG_FILE_DIR.

- Then it "implies" readers should consult
"include/standard-headers/linux/qemu_fw_cfg.h". :)

All in all, a selector is "well known" if the QEMU source code defines
-- perhaps through incorporating a kernel include file -- a macro
directly for the numeric value of the selector key. Such a selector is
"well known" because guest firmware is allowed / required to refer
directly to the numeric value, rather than to look it up in the fw_cfg
file directory, by name (such as "etc/table-loader", "bootorder", ...).

Thanks!
Laszlo