62b6d36335
Add an "--extra" option that can be used to specify an extra (non-boot) filename that must exist within the booted filesystem. Note that only files within the FAT-formatted bootable partition will be visible to this filter. Files within the operating system's root disk (e.g. "/etc/redhat-release") are not generally accessible to the firmware and so cannot be used as the existence check filter filename. Signed-off-by: Michael Brown <mcb30@ipxe.org>