Building BCacheFS module with Rust support via DKMS package

[Martin Steigerwald <martin@lichtvoll.de>]

Greetings.

I am building my own kernel with:

time eatmydata make LLVM=1 -j16 bindeb-pkg LOCALVERSION=-t14g5

I do have rustc and rust-src as of 1.95.0+dfsg1-2, bindgen as of 
0.72.1-1+b2 on Devuan Ceres which is based on Debian Unstable aka Sid.

I am quite confident my kernel is build with rust support:

% grep _RUST /boot/config-7.1.6-t14g5
CONFIG_RUSTC_VERSION=109500
CONFIG_RUST_IS_AVAILABLE=y
CONFIG_RUSTC_LLVM_VERSION=210108
CONFIG_RUSTC_LLVM_MAJOR_VERSION=21
CONFIG_RUSTC_CLANG_LLVM_COMPATIBLE=y
CONFIG_RUSTC_HAS_SPAN_FILE=y
CONFIG_RUSTC_HAS_UNNECESSARY_TRANSMUTES=y
CONFIG_RUSTC_HAS_FILE_WITH_NUL=y
CONFIG_RUSTC_HAS_FILE_AS_C_STR=y
CONFIG_RUST=y
CONFIG_RUSTC_VERSION_TEXT=
  "rustc 1.95.0 (59807616e 2026-04-14) (built from a source tarball)"
CONFIG_HAVE_RUST=y
CONFIG_HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC=y
# CONFIG_RUST_FW_LOADER_ABSTRACTIONS is not set
# CONFIG_BLK_DEV_RUST_NULL is not set
# CONFIG_ANDROID_BINDER_IPC_RUST is not set
# CONFIG_RUST_BITMAP_HARDENED is not set
# CONFIG_FIND_BIT_BENCHMARK_RUST is not set
# CONFIG_RUST_DEBUG_ASSERTIONS is not set
CONFIG_RUST_OVERFLOW_CHECKS=y
# CONFIG_RUST_BUILD_ASSERT_ALLOW is not set
CONFIG_RUST_INLINE_HELPERS=y

I install linux-image and linux-header packages.

Yet with bcachefs-kernel-dkms up to 1:1.39.0 I see:

built without Rust support; this will be required in the near future - 
ensure a compatible Rust toolchain (rustc + bindgen + rust-src) is 
available at module build time

Would bcachefs-kernel-dkms use LLVM automatically? AFAIR I did not manage 
to have a kernel with Rust support using GCC which I used previously.

Best
-- 
Martin