linux/common-config: EFI_VARS_PSTORE=y

This enables the kernel to save crash logs much earlier, rather than
losing any log from before the efi_pstore module is loaded in stage 2.

nixos/tests/systemd-pstore.nix

@@ -1,14 +1,39 @@
 {
   name = "systemd-pstore";
 
-  nodes.machine = { };
+  nodes.machine = {
+    virtualisation.useEFIBoot = true;
+    boot.initrd.systemd.enable = true;
+    testing.initrdBackdoor = true;
+  };
 
   testScript = ''
+    machine.switch_root()
     with subtest("pstore API fs is mounted"):
       machine.succeed("stat /sys/fs/pstore")
 
     with subtest("systemd-pstore.service doesn't run because nothing crashed"):
       output = machine.execute("systemctl status systemd-pstore.service", check_return=False)[1]
       t.assertIn("condition unmet", output)
+      machine.fail("stat /var/lib/systemd/pstore/*/*/dmesg.txt")
+
+    with subtest("systemd-pstore.service saves dmesg.txt files"):
+      machine.execute("echo c > /proc/sysrq-trigger", check_return=False, check_output=False)
+      machine.wait_for_shutdown()
+      machine.switch_root()
+      machine.wait_for_unit("systemd-pstore.service")
+      machine.succeed("stat /var/lib/systemd/pstore/*/*/dmesg.txt")
+
+    with subtest("crashes in initrd can be recovered too"):
+      machine.succeed(
+        "rm -r /var/lib/systemd/pstore/*",
+        "sync",
+      )
+      machine.shutdown()
+      machine.execute("echo c > /proc/sysrq-trigger", check_return=False, check_output=False)
+      machine.wait_for_shutdown()
+      machine.switch_root()
+      machine.wait_for_unit("systemd-pstore.service")
+      machine.succeed("stat /var/lib/systemd/pstore/*/*/dmesg.txt")
   '';
 }

pkgs/os-specific/linux/kernel/common-config.nix

@@ -1224,6 +1224,7 @@ let
         EFI = lib.mkIf stdenv.hostPlatform.isEfi yes;
         EFI_STUB = yes; # EFI bootloader in the bzImage itself
         EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER = whenOlder "6.2" yes; # initrd kernel parameter for EFI
+        EFI_VARS_PSTORE = yes;
 
         # Generic compression support for EFI payloads
         # Add new platforms only after they have been verified to build and boot.

pkgs/os-specific/linux/systemd/default.nix

@@ -930,6 +930,7 @@ stdenv.mkDerivation (finalAttrs: {
             systemd-nspawn-configfile
             systemd-oomd
             systemd-portabled
+            systemd-pstore
             systemd-resolved
             systemd-shutdown
             systemd-sysupdate