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

1 files changed, 25 insertions, 0 deletions

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