Crash recovery for user-space block drivers

If someone wants to post a driver where a significant backend lives in userspace, then there should be a requirement that an open source userspace backend be provided that exercises all of the interfaces. This has been the standard for DRM drivers, but it should be equally true for a userspace filesystem driver or anything else.

GPU drivers are a bit weird, since mesa is a library and programs call into it directly instead of going down through the kernel and up into the userspace portion of the driver, and this systems seems like a place where an even stronger argument could be made. The userspace driver is needed to make the driver interface of the kernel itself work, and therefor definitely an open source reference implementation should be provided.