BlockdevCacheInfo vs BlockdevCacheOptions in QMP

In [QMP] there's both BlockdevCacheInfo and BlockdevCacheOptions to set caching options.

In https://github.com/canonical/lxd/issues/16348 to fix the QEMU launch and synching the cache modes, I noticed BlockdevCacheOptions is lacking "writeback", whereas BlockdevCacheInfo contains it. To add blockdevices via blockdev-add, BlockdevCacheOptions is used.

Is this a bug or is it an intentional difference?

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