Hi. I recently wrote package definition for Linux with Reiser4 patch.

(define (linux-nonfree-urls version)
  "Return a list of URLs for Linux-Nonfree VERSION."
  (list (string-append
         "https://www.kernel.org/pub/linux/kernel/v4.x/"
         "linux-" version ".tar.xz")))


(define-public linux-reiser4
  (let* ((version "4.11.11"))
    (package
      (inherit linux-libre)
      (name "linux-reiser4")
      (version version)
      (source (origin
                (method url-fetch)
                (uri (linux-nonfree-urls version))
                (sha256
                 (base32
                  "1dvs1r3vq15akyv0yxvim6j09pqac5dagqbchvdlsw5yi4fnylc8"))
                (patches (list (computed-file "reiser4-for-4.11.0.patch"
                                              (let ((compressed (origin (method url-fetch)
                                                                        (uri "https://downloads.sourceforge.net/project/reiser4/reiser4-for-linux-4.x/reiser4-for-4.11.0.patch.gz")
                                                                        (sha256 (base32 "1qc421bqassrxv7z5pzsnwsf9d5pz0azm96rykxh02xlrf8ig3hc")))))
                                                #~(system
                                                   (string-append #+(file-append gzip "/bin/gunzip")
                                                                  " < " #$compressed
                                                                  " > " #$output))))))))
      (synopsis "Linux with Reiser4 patch.")
      (description "Linux-Reiser4 is a kernel that supports Reiser4 FS.")
      (license gpl2)
      (home-page "https://reiser4.wiki.kernel.org/index.php/Main_Page"))))