installer: atomically copy directory to specified ESP #1

cole-h · 2021-08-10T20:33:20Z

This copies the files to a temporary directory, then renames them to their
desired destination, and finally removes the temporary directory.

Usable in conjunction with https://github.com/DeterminateSystems/nixpkgs-priv/tree/boot-json and the following module (ripped from my flake; may need modifications):

                ({ pkgs, lib, config, ... }: {
                  boot.loader.manual = {
                    enable = true;
                    installHook =
                      let
                        installer = pkgs.rustPlatform.buildRustPackage rec {
                          pname = "installer";
                          version = "0";
                          src = inputs.experiment;
                          cargoLock.lockFile = src + "/Cargo.lock";
                          buildType = "debug";
                          dontStrip = true;
                        };
                      in
                      pkgs.writeShellScript "install-bootloader" ''
                        set -x
                        cd "$(mktemp -d)" || exit 1

                        ${installer}/bin/generator /nix/var/nix/profiles/system-*-link

                        ${installer}/bin/installer \
                          --toplevel="$1" \
                          --esp="${config.boot.loader.efi.efiSysMountPoint}" \
                          ${lib.optionalString config.boot.loader.efi.canTouchEfiVariables "--touch-efi-vars"} \
                          --console-mode="${config.boot.loader.systemd-boot.consoleMode}" \
                          --timeout="${toString config.boot.loader.timeout}" \
                          --bootctl="${pkgs.systemd}/bin/bootctl" \
                          ${lib.optionalString (config.boot.loader.systemd-boot.configurationLimit != null) ''--configuration-limit="${toString config.boot.loader.systemd-boot.configurationLimit}"''} \
                          --generated-entries="./systemd-boot-entries"
                      '';
                  };
                })

Closes #2.
Closes #4.

grahamc · 2021-08-13T20:06:05Z

    ({ options, lib, ... }: {
      config = lib.mkIf (!(options.boot.loader ? manual)) {
        boot.loader.systemd-boot.enable = true;
        boot.loader.efi.canTouchEfiVariables = true;
      };
    })

cole-h · 2021-08-13T20:16:07Z

installer/src/main.rs

-        console_mode: pico
-            .value_from_str("--console-mode")
-            .unwrap_or_else(|_| String::from("keep")),
+        console_mode: pico.value_from_str("--console-mode")?,
        configuration_limit: pico.value_from_str("--configuration-limit")?,


This should be optional.

corresponding change to your flake example:

${lib.optionalString (config.boot.loader.systemd-boot.configurationLimit != null) ''--configuration-limit="${toString config.boot.loader.systemd-boot.configurationLimit}"''} \

installer/src/main.rs

installer/src/systemd_boot/mod.rs

grahamc · 2021-08-13T20:23:34Z

grahamc@scruffy:~/scruffy/ > sudo nixos-rebuild boot --flake '.#scruffy' -L
building the system configuration...
++ mktemp -d
+ cd /tmp/tmp.VkmzKrKg8O
+ /nix/store/9lbr2291aibmi8bxl2n7v7srw4r944nw-installer-0/bin/generator /nix/var/nix/profiles/system-1-link /nix/var/nix/profiles/system-2-link /nix/var/nix/profiles/system-3-link /nix/var/nix/profiles/system-4-link /nix/var/nix/profiles/system-5-link /nix/var/nix/profiles/system-6-link /nix/var/nix/profiles/system-7-link
+ /nix/store/9lbr2291aibmi8bxl2n7v7srw4r944nw-installer-0/bin/installer --toplevel=/nix/store/zy41vhmfxx6b4657bl1cqs438y3dg2h2-nixos-system-scruffy-21.11.20210810.6f6ade6 --esp=/boot --console-mode=keep --timeout=5 --bootctl=/nix/store/f0dgfrsfwmnvxzlcm2vv5dy1kmknsmpr-systemd-247.6/bin/bootctl --configuration-limit=120 --generated-entries=./systemd-boot-entries
[installer/src/main.rs:80] &args = Args {
    toplevel: "/nix/store/zy41vhmfxx6b4657bl1cqs438y3dg2h2-nixos-system-scruffy-21.11.20210810.6f6ade6",
    dry_run: false,
    generated_entries: "./systemd-boot-entries",
    timeout: Some(
        5,
    ),
    console_mode: "keep",
    configuration_limit: 120,
    editor: true,
    esp: Some(
        "/boot",
    ),
    can_touch_efi_vars: false,
    bootctl: Some(
        "/nix/store/f0dgfrsfwmnvxzlcm2vv5dy1kmknsmpr-systemd-247.6/bin/bootctl",
    ),
}

installer/src/systemd_boot/mod.rs

grahamc · 2021-08-13T20:25:39Z

Opa! I'm switched!

cole-h · 2021-08-13T20:29:10Z

Also, there should probably be some better error handling -- would be nice if there was some way to differentiate between fatal and not-so-fatal errors.

This copies the files to a temporary directory, then renames them to their desired destination, and finally removes the temporary directory.

Also implements the configuration_limit and editor flags.

We don't need to error if the directory we're trying to clean doesn't exist (it will be created). We do need to error if `nix-env` returns empty output -- `nix- env` requires root to list the generations of a profile (for whatever reason...).

It's a bit annoying having to run this as root even for a dry run (because `nix- env` needs root to create a lockfile to list generations... for some reason). So, we just do the work ourselves.

This function isn't only run against the ESP, so we don't want to give that impression in the function signature.

grahamc · 2021-08-17T20:51:41Z

installer/src/systemd_boot/mod.rs

+pub(crate) fn bootloader_is_old(
+    bootloader_version: Option<usize>,
+    systemd_version: usize,
+) -> Result<bool> {
+    if let Some(bootloader_version) = bootloader_version {
+        let old = systemd_version > bootloader_version;
+        Ok(old)
    } else {
-        String::from("/nix/var/nix/profiles/system")
+        warn!("could not find any previously installed systemd-boot");
+        Ok(false)
+    }
+}
+
+pub(crate) fn get_bootloader_version(bootctl: &Path, esp: &Path) -> Result<Option<usize>> {
+    trace!("checking bootloader version");
+
+    debug!("running `bootctl status`");
+    let output = Command::new(&bootctl)
+        .args(&[&format!("--path={}", &esp.display()), "status"])
+        .output()?
+        .stdout;
+
+    let version = self::parse_bootloader_version(&output)?;
+
+    Ok(version)
+}
+
+pub(crate) fn parse_bootloader_version(output: &[u8]) -> Result<Option<usize>> {
+    let output = str::from_utf8(output)?;
+
+    // pat in its own str so that `cargo fmt` doesn't choke...
+    let pat = "^\\W+File:.*/EFI/(BOOT|systemd)/.*\\.efi \\(systemd-boot (?P<version>\\d+)\\)$";
+
+    // See enumerate_binaries() in systemd bootctl.c for code which generates this:
+    // https://github.com/systemd/systemd/blob/788733428d019791ab9d780b4778a472794b3748/src/boot/bootctl.c#L221-L224
+    let re = RegexBuilder::new(pat)
+        .multi_line(true)
+        .case_insensitive(true)
+        .build()?;
+    let caps = re.captures(output);
+
+    let version = if let Some(caps) = caps {
+        caps.name("version")
+            .and_then(|cap| cap.as_str().parse::<usize>().ok())
+    } else {
+        None
    };


Consider making more things. For example, we're not just comparing usizes we're comparing installed SystemdBoot versions.

What if there was a struct of SystemdBootVersion with a version field, and you could construct it by calling SystemdBootVersion::detect_version() which executes the command and calls SystemdBootVersion::from_status_output(string) which calls SystemdBootVersion::new(version number)? Then we've got a little library, and a struct we could hang some helper functions on, like Ord for comparing.

All this could go in to a nice, small file with some tests just for it, in an easy to consume nibble of code. Compare that to here: 50 lines of self-contained-ish code burried 200 lines deep in a nearly 500 line long file.

Similar feedback applies to the systemd version stuff.

grahamc

Looking MUCH better with these improvements. This review is just one one specific commit, though. Maybe toss in a couple tests for cmp and eq?

installer/src/systemd_boot/version/mod.rs

installer/src/systemd_boot/version/systemd.rs

grahamc · 2021-08-18T17:36:12Z

installer/src/systemd_boot/version/systemd_boot.rs

+        Ok(version)
+    }
+
+    pub fn detect_version(bootctl: &Path, esp: &Path) -> Result<Option<Self>> {


This return type is a bit weird. It might be worth looking out for ways to improve this, like an enum of DetectionResult { ExecError, ParseError, Ok } -- but not sure, and definitely not asking you to do it now.

installer/src/systemd_boot/version/systemd_boot.rs

grahamc

Looking pretty good!

grahamc · 2021-08-19T15:52:08Z

installer/src/systemd_boot/mod.rs

+                    .status()?;
+            }
+        } else {
+            warn!("could not find any previously installed systemd-boot");


Note this is not warning-grade error if this is a new installation, what is the difference between installing and upgrading? Maybe we should automatically install if that fails?

I just felt like there should be the "least magic" happening as possible -- if a user wants to install systemd-boot, they should use the --install flag. Otherwise, they want to upgrade their bootloader. If systemd-boot isn't present, then that's fine; we'll just copy the kernels and boot entries to the specified ESP and let them install it either manually (via bootctl) or via this tool.

Does that make sense? This is more a warning that "we'll copy everything you want, but it won't boot yet, because there's no installed bootloader (systemd-boot)".

installer/src/systemd_boot/mod.rs

installer/src/systemd_boot/version/mod.rs

Also test most of those split-out functions.

cole-h force-pushed the atomic_copy branch from 48a115c to b0a49af Compare August 12, 2021 20:20

cole-h commented Aug 13, 2021

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grahamc reviewed Aug 13, 2021

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cole-h commented Aug 13, 2021

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cole-h added 7 commits August 16, 2021 11:22

installer: atomically copy directory to specified ESP

46bb29d

This copies the files to a temporary directory, then renames them to their desired destination, and finally removes the temporary directory.

installer: remove old files (kernels, initrds, entries)

9155cb3

Also implements the configuration_limit and editor flags.

installer: configuration_limit is optional

027d8eb

installer: don't try to read nonexistent directories

cc78fef

installer: add logging

c7a3813

installer: use flag for first install

f758a6f

cole-h force-pushed the atomic_copy branch from b0a49af to f758a6f Compare August 16, 2021 18:24

This was referenced Aug 17, 2021

No more unwraps or expects #5

Open

installer: move to a vaguely plan-based workflow #6

Merged

cole-h added 2 commits August 17, 2021 12:48

installer: list profile generations ourselves

46d8983

It's a bit annoying having to run this as root even for a dry run (because `nix- env` needs root to create a lockfile to list generations... for some reason). So, we just do the work ourselves.

installer: rename arg

108a6d4

This function isn't only run against the ESP, so we don't want to give that impression in the function signature.

cole-h force-pushed the atomic_copy branch 2 times, most recently from 4995743 to 3b4b29a Compare August 17, 2021 20:42

grahamc reviewed Aug 17, 2021

View reviewed changes

cole-h force-pushed the atomic_copy branch 2 times, most recently from fb3f953 to 0fcb3ba Compare August 18, 2021 17:03

grahamc reviewed Aug 18, 2021

View reviewed changes

grahamc approved these changes Aug 19, 2021

View reviewed changes

cole-h added 2 commits August 19, 2021 09:24

installer: split some logic into functions

43b2552

Also test most of those split-out functions.

installer: remove "guidance" comments

4577271

installer: split version logic into a module

ff657ed

cole-h force-pushed the atomic_copy branch from b752db5 to ff657ed Compare August 19, 2021 16:26

cole-h merged commit 39f506a into main Aug 19, 2021

cole-h deleted the atomic_copy branch August 19, 2021 16:32

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installer: atomically copy directory to specified ESP #1

installer: atomically copy directory to specified ESP #1

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installer: atomically copy directory to specified ESP #1

installer: atomically copy directory to specified ESP #1

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