Re: [libvirt PATCH] docs: document external swtpm

+ ``external`` + For this backend, libvirt expects the TPM emulator to be started externally. + The path to the unix socket where the emulator is listening is passed + via the ``source`` element. Other ``backend`` sub-elements do not apply + in these case, since they are controlled by the emulator command line.

``source`` - The ``source`` element specifies the location of the TPM state storage . This - element only works with the ``emulator`` backend. + For the ``emulator`` backend, the ``source`` element specifies the location + of the TPM state storage. :since:`Since v10.10.0` + + For the ``external`` backend, it specifies the socket of the externally + run TPM emulator. :since:`Since v9.0.0`