linux-kpi/drm_shim.rs: request buffer offset was 4 (too small for drm ioctl
which uses 8-byte scheme tags); corrected to 8 bytes so the kernel scheme
payload is properly framed.
redox-drm/scheme.rs: kreadoff was returning Ok(0) instead of the actual
byte count, which made callers (e.g. linux-kpi) think the read returned no
data. Now returns Ok(buf.len()) as documented in the syscall contract.
vasilito
42d0314e60