modules/nix: Add nix wrapper, that checks nix store size before working

2 files changed, 58 insertions, 1 deletions

diff --git a/modules/by-name/ni/nix/module.nix b/modules/by-name/ni/nix/module.nix
index b7e64989..e46d6e85 100644
--- a/modules/by-name/ni/nix/module.nix
+++ b/modules/by-name/ni/nix/module.nix
@@ -21,6 +21,38 @@
 }: let
   inherit (sources) nixpkgs;
 
+  lix =
+    pkgs.lixPackageSets.latest.lix;
+
+  nixWrapperBase = pkgs.writeShellApplication {
+    inherit (lix) name;
+
+    text = builtins.readFile ./nix_wrapper.sh;
+    inheritPath = false;
+    runtimeInputs = [
+      pkgs.lixPackageSets.latest.lix
+      pkgs.libnotify
+      pkgs.btrfs-progs
+      pkgs.coreutils
+      pkgs.gnused
+      pkgs.gnugrep
+      pkgs.bc
+    ];
+
+    derivationArgs = {
+      inherit (lix) meta pname version;
+    };
+  };
+
+  nixWrapper = pkgs.symlinkJoin {
+    inherit (lix) name;
+    paths = [
+      nixWrapperBase
+      pkgs.lixPackageSets.latest.lix
+    ];
+    inherit (lix) meta pname version;
+  };
+
   cfg = config.soispha.nix;
 in {
   options.soispha.nix = {
@@ -29,7 +61,7 @@ in {
 
   config = lib.mkIf cfg.enable {
     nix = {
-      package = pkgs.lixPackageSets.latest.lix;
+      package = nixWrapper;
 
       # Disable nix channels  (this is a remnant of old days)
       channel.enable = false;
diff --git a/modules/by-name/ni/nix/nix_wrapper.sh b/modules/by-name/ni/nix/nix_wrapper.sh
new file mode 100755
index 00000000..55b12dc9
--- /dev/null
+++ b/modules/by-name/ni/nix/nix_wrapper.sh
@@ -0,0 +1,25 @@
+#! /usr/bin/env sh
+
+set -eu
+
+notify-send "Running nix via the wrapper."
+
+if [ "$_NIX_WRAPPER_FALLBACK" = "true" ]; then
+    # Allow skipping the size check.
+    nix "$@"
+else
+    usage="$(btrfs filesystem usage /nix --raw 2>/dev/null)"
+    avail="$(echo "$usage" | grep 'Device size:' | cut -f 3 | sed 's/ //g')"
+    used="$(echo "$usage" | grep 'Used:' | cut -f 4 | head -n 1 | sed 's/ //g')"
+    perc="$(printf "scale=3\n%d / %d\n" "$used" "$avail" | bc)"
+    perc="$(printf "%d * 100\n" "$perc" | bc)"
+
+    if test -gt "$perc" "0.2"; then
+        nix "$@"
+    else
+        echo "Not enough space free, in nix store: Only, $perc is still free."
+        exit 3
+    fi
+fi
+
+# vim: ft=sh