linux: make sure all config options have the same value

Currently, kernel config options whose value is "yes" always override
options whose value is "no".

This is not always desired.

Generally speaking, if someone defines an option to have the value
"no", presumably they are disabling the option for a reason, so it's
not always OK to silently enable it due to another, probably unrelated
reason.

For example, a user may want to reduce the kernel attack surface and
therefore may want to disable features that are being enabled in
common-config.nix.

In fact, common-config.nix was already silently enabling options that
were intended to be disabled in hardened/config.nix for security
reasons, such as INET_DIAG.

By eliminating the custom merge function, these config options will
now use the default module option merge functions which make sure
that all options with the highest priority have the same value.

A user that wishes to override an option defined in common-config.nix
can currently use mkForce or mkOverride to do so, e.g.:

BINFMT_MISC = mkForce (option no);

That said, this is not going to be necessary in the future, because
the plan is for kernel config options defined in nixpkgs to use a
lower priority by default, like it currently happens for other module
options.

1 files changed, 1 insertions, 21 deletions

diff --git a/nixos/modules/system/boot/kernel_config.nix b/nixos/modules/system/boot/kernel_config.nix
index 783685c9dfe4..5d9534024b06 100644
--- a/nixos/modules/system/boot/kernel_config.nix
+++ b/nixos/modules/system/boot/kernel_config.nix
@@ -2,24 +2,6 @@
 
 with lib;
 let
-  findWinner = candidates: winner:
-    any (x: x == winner) candidates;
-
-  # winners is an ordered list where first item wins over 2nd etc
-  mergeAnswer = winners: locs: defs:
-    let
-      values = map (x: x.value) defs;
-      inter = intersectLists values winners;
-      winner = head winners;
-    in
-    if defs == [] then abort "This case should never happen."
-    else if winner == [] then abort "Give a valid list of winner"
-    else if inter == [] then mergeOneOption locs defs
-    else if findWinner values winner then
-      winner
-    else
-      mergeAnswer (tail winners) locs defs;
-
   mergeFalseByDefault = locs: defs:
     if defs == [] then abort "This case should never happen."
     else if any (x: x == false) (getValues defs) then false
@@ -28,9 +10,7 @@ let
   kernelItem = types.submodule {
     options = {
       tristate = mkOption {
-        type = types.enum [ "y" "m" "n" null ] // {
-          merge = mergeAnswer [ "y" "m" "n" ];
-        };
+        type = types.enum [ "y" "m" "n" null ];
         default = null;
         internal = true;
         visible = true;