fastboot - platform/system/core - Git at Google

version             Version of FastBoot protocol supported.
                    It should be "0.4" for this document.

version-bootloader  Version string for the Bootloader.

version-baseband    Version string of the Baseband Software

product             Name of the product

serialno            Product serial number

secure              If the value is "yes", this is a secure
                    bootloader requiring a signature before
                    it will install or boot images.

is-userspace        If the value is "yes", the device is running
                    fastbootd. Otherwise, it is running fastboot
                    in the bootloader.