hardware.firmware = [
      (
       let driverPkg = builtins.fetchurl {
           url = "https://mpow.s3-us-west-1.amazonaws.com/20201202_mpow_BH456A_driver+for+Linux.7z";
           sha256 = "25de05daaecbc698504e3b87f14cf24dd6cec97551ce3f2b720f5e559919d98b";
       };
       in
       pkgs.runCommandNoCC "firmware-rtl8761b" { } ''
       /root/.nix-profile/bin/7z e $driverPkg
       mkdir -p $out/lib/firmware/rtl_bt
       cp rtl8761b_config $out/lib/firmware/rtl_bt/rtl8761b_config.bin
       cp rtl8761b_fw $out/lib/firmware/rtl_bt/rtl8761b_fw.bin
       ''
      )
  ];


[root@nas:/tmp]# nixos-rebuild switch
building Nix...
building the system configuration...
these derivations will be built:
  /nix/store/r3izzizcz6574a5n6wbj8bfmwvkvky6z-firmware-rtl8761b.drv
  /nix/store/r0asxrsz6nlw4y475548b548cvl111mi-firmware.drv
  /nix/store/470hkndb2nmpl7k3b5yw87kw02gcypvx-etc-nixos.conf.drv
  /nix/store/9ysa9601yhd65g75ahxcizglyzqx9g4l-etc.drv
  /nix/store/jh4xaxba32jx65mqhbvcdwgzfs84iv2g-linux-5.10.22-modules-shrunk.drv
  /nix/store/ia4wln4sfswl73lcc5mm5zvlh5l7qmx4-stage-1-init.sh.drv
  /nix/store/a8s6hqj2zsvvn85vjj92bvkxzj1bnas1-initrd-linux-5.10.22.drv
  /nix/store/2g783prx6yh3n1cx5sxfr5m7dvkayqhm-nixos-system-nas-20.09.3454.60b18a066e8.drv
building '/nix/store/r3izzizcz6574a5n6wbj8bfmwvkvky6z-firmware-rtl8761b.drv'...
/build/.attr-0: line 1: /root/.nix-profile/bin/7z: No such file or directory
builder for '/nix/store/r3izzizcz6574a5n6wbj8bfmwvkvky6z-firmware-rtl8761b.drv' failed with exit code 127