Write generation state into a state file and restructure the services.json file produced by nix.

nix/lib.nix

@@ -18,16 +18,14 @@ in
       };
 
       services =
-        map
+        lib.listToAttrs
+          (map
             (name:
               let
                 serviceName = "${name}.service";
               in
-            {
-              name = serviceName;
-              service = ''${nixosConfig.config.systemd.units."${serviceName}".unit}/${serviceName}'';
-            })
-          nixosConfig.config.service-manager.services;
+              lib.nameValuePair serviceName { storePath = ''${nixosConfig.config.systemd.units."${serviceName}".unit}/${serviceName}''; })
+            nixosConfig.config.service-manager.services);
 
       servicesPath = pkgs.writeTextFile {
         name = "services";

nix/modules/default.nix

@@ -4,9 +4,10 @@
 }:
 let
   services =
-    lib.listToAttrs (lib.flip lib.genList 30 (ix: {
-      name = "service-${toString ix}";
-      value = {
+    lib.listToAttrs
+      (lib.flip lib.genList 10 (ix:
+        lib.nameValuePair "service-${toString ix}"
+          {
             enable = true;
             description = "service-${toString ix}";
             wants = [ "network-online.target" ];
@@ -25,10 +26,10 @@ let
             };
             wantedBy = [ "multi-user.target" ];
             script = ''
-          sleep ${if ix > 20 then "3" else "1"}
+              sleep ${if ix > 5 then "3" else "1"}
             '';
-      };
-    }));
+          })
+      );
 in
 {
   options = {

src/activate.rs

@@ -1,73 +1,135 @@
 use anyhow::Result;
 use serde::{Deserialize, Serialize};
-use std::collections::HashSet;
+use std::collections::{HashMap, HashSet};
+use std::fs::DirBuilder;
 use std::path::Path;
 use std::time::Duration;
-use std::{fs, io, iter, str};
+use std::{fs, io, str};
 
-use super::{create_store_link, systemd, StorePath};
+use super::{create_store_link, systemd, StorePath, SERVICE_MANAGER_STATE_DIR, SYSTEMD_UNIT_DIR};
 
-#[derive(Debug, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct ServiceConfig {
-    name: String,
-    service: String,
+    #[serde(flatten)]
+    store_path: StorePath,
 }
 
-impl ServiceConfig {
-    fn store_path(&self) -> StorePath {
-        StorePath::from(self.service.to_owned())
-    }
+type Services = HashMap<String, ServiceConfig>;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct LinkedServiceConfig {
+    #[serde(flatten)]
+    service_config: ServiceConfig,
+    linked_path: String,
 }
 
+type LinkedServices = HashMap<String, LinkedServiceConfig>;
+
 pub fn activate(store_path: StorePath) -> Result<()> {
     log::info!("Activating service-manager profile: {}", store_path);
 
-    let file = fs::File::open(store_path.path + "/services/services.json")?;
+    log::debug!("{:?}", read_linked_services()?);
+
+    log::info!("Reading service definitions...");
+    let file = fs::File::open(store_path.store_path + "/services/services.json")?;
     let reader = io::BufReader::new(file);
+    let services: Services = serde_json::from_reader(reader)?;
 
-    let services: Vec<ServiceConfig> = serde_json::from_reader(reader)?;
-
-    services.iter().try_for_each(|service| {
-        create_store_link(
-            &service.store_path(),
-            Path::new(&format!("/run/systemd/system/{}", service.name)),
-        )
-    })?;
+    let linked_services = link_services(services);
+    serialise_linked_services(&linked_services)?;
 
     let service_manager = systemd::ServiceManager::new_session()?;
-    start_services(&service_manager, &services, &Some(Duration::from_secs(30)))?;
-
+    start_services(
+        &service_manager,
+        linked_services,
+        &Some(Duration::from_secs(30)),
+    )?;
     Ok(())
 }
 
+fn link_services(services: Services) -> LinkedServices {
+    services.iter().fold(
+        HashMap::with_capacity(services.len()),
+        |mut linked_services, (name, service_config)| {
+            let linked_path = format!("{}/{}", SYSTEMD_UNIT_DIR, name);
+            match create_store_link(&service_config.store_path, Path::new(&linked_path)) {
+                Ok(_) => {
+                    linked_services.insert(
+                        name.to_owned(),
+                        LinkedServiceConfig {
+                            service_config: service_config.to_owned(),
+                            linked_path,
+                        },
+                    );
+                    linked_services
+                }
+                e @ Err(_) => {
+                    log::error!("Error linking service {}, skipping.", name);
+                    log::error!("{:?}", e);
+                    linked_services
+                }
+            }
+        },
+    )
+}
+
+// FIXME: we should probably lock this file to avoid concurrent writes
+fn serialise_linked_services(linked_services: &LinkedServices) -> Result<()> {
+    let state_file = format!("{}/services.json", SERVICE_MANAGER_STATE_DIR);
+    DirBuilder::new()
+        .recursive(true)
+        .create(SERVICE_MANAGER_STATE_DIR)?;
+
+    log::info!("Writing state info into file: {}", state_file);
+    let writer = io::BufWriter::new(fs::File::create(state_file)?);
+    serde_json::to_writer(writer, linked_services)?;
+    Ok(())
+}
+
+fn read_linked_services() -> Result<LinkedServices> {
+    let state_file = format!("{}/services.json", SERVICE_MANAGER_STATE_DIR);
+    DirBuilder::new()
+        .recursive(true)
+        .create(SERVICE_MANAGER_STATE_DIR)?;
+
+    if Path::new(&state_file).is_file() {
+        log::info!("Reading state info from {}", state_file);
+        let reader = io::BufReader::new(fs::File::open(state_file)?);
+        let linked_services = serde_json::from_reader(reader)?;
+        return Ok(linked_services);
+    }
+    Ok(HashMap::default())
+}
+
 fn start_services(
     service_manager: &systemd::ServiceManager,
-    services: &[ServiceConfig],
+    services: LinkedServices,
     timeout: &Option<Duration>,
 ) -> Result<()> {
     service_manager.daemon_reload()?;
 
     let job_monitor = service_manager.monitor_jobs_init()?;
 
-    let successful_services = services.iter().fold(HashSet::new(), |set, service| {
-        match service_manager.restart_unit(&service.name) {
+    let successful_services = services.keys().fold(
+        HashSet::with_capacity(services.len()),
+        |mut set, service| match service_manager.restart_unit(service) {
             Ok(_) => {
-                log::info!("Restarting service {}...", service.name);
-                set.into_iter()
-                    .chain(iter::once(Box::new(service.name.to_owned())))
-                    .collect()
+                log::info!("Restarting service {}...", service);
+                set.insert(Box::new(service.to_owned()));
+                set
             }
             Err(e) => {
                 log::error!(
                     "Error restarting unit, please consult the logs: {}",
-                    service.name
+                    service
                 );
                 log::error!("{}", e);
                 set
             }
-        }
-    });
+        },
+    );
 
     if !service_manager.monitor_jobs_finish(job_monitor, timeout, successful_services)? {
         anyhow::bail!("Timeout waiting for systemd jobs");

src/generate.rs

@@ -4,7 +4,7 @@ use std::collections::HashMap;
 use std::path::Path;
 use std::{fs, process, str};
 
-use super::{create_store_link, StorePath, FLAKE_ATTR, PROFILE_NAME};
+use super::{create_store_link, StorePath, FLAKE_ATTR, GCROOT_PATH, PROFILE_PATH};
 
 #[derive(Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
@@ -14,9 +14,6 @@ struct NixBuildOutput {
 }
 
 pub fn generate(flake_uri: &str) -> Result<()> {
-    let profile_path = format!("/nix/var/nix/profiles/{}", PROFILE_NAME);
-    let gcroot_path = format!("/nix/var/nix/gcroots/{}-current", PROFILE_NAME);
-
     // FIXME: we should not hard-code the system here
     let flake_attr = format!("{}.x86_64-linux", FLAKE_ATTR);
 
@@ -24,10 +21,10 @@ pub fn generate(flake_uri: &str) -> Result<()> {
     let store_path = run_nix_build(flake_uri, &flake_attr).and_then(get_store_path)?;
 
     log::info!("Generating new generation from {}", store_path);
-    install_nix_profile(&store_path, &profile_path).map(print_out_and_err)?;
+    install_nix_profile(&store_path, PROFILE_PATH).map(print_out_and_err)?;
 
     log::info!("Registering GC root...");
-    create_gcroot(&gcroot_path, &profile_path)?;
+    create_gcroot(GCROOT_PATH, PROFILE_PATH)?;
     Ok(())
 }
 
@@ -36,7 +33,7 @@ fn install_nix_profile(store_path: &StorePath, profile_path: &str) -> Result<pro
         .arg("--profile")
         .arg(profile_path)
         .arg("--set")
-        .arg(&store_path.path)
+        .arg(&store_path.store_path)
         .output()
         .map_err(anyhow::Error::from)
 }

src/lib.rs

@@ -3,29 +3,34 @@ pub mod generate;
 mod systemd;
 
 use anyhow::Result;
+use serde::{Deserialize, Serialize};
 use std::os::unix;
 use std::path::Path;
 use std::{fs, str};
 
 const FLAKE_ATTR: &str = "serviceConfig";
-const PROFILE_NAME: &str = "service-manager";
+const PROFILE_PATH: &str = "/nix/var/nix/profiles/service-manager";
+const GCROOT_PATH: &str = "/nix/var/nix/gcroots/service-manager-current";
+const SYSTEMD_UNIT_DIR: &str = "/run/systemd/system";
+const SERVICE_MANAGER_STATE_DIR: &str = "/var/lib/service-manager/state";
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
 pub struct StorePath {
-    pub path: String,
+    pub store_path: String,
 }
 
 impl From<String> for StorePath {
     fn from(path: String) -> Self {
         StorePath {
-            path: path.trim().into(),
+            store_path: path.trim().into(),
         }
     }
 }
 
 impl std::fmt::Display for StorePath {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.path)
+        write!(f, "{}", self.store_path)
     }
 }
 
@@ -34,7 +39,7 @@ fn create_store_link(store_path: &StorePath, from: &Path) -> Result<()> {
     if from.is_symlink() {
         fs::remove_file(from)?;
     }
-    unix::fs::symlink(&store_path.path, from).map_err(anyhow::Error::from)
+    unix::fs::symlink(&store_path.store_path, from).map_err(anyhow::Error::from)
 }
 
 pub fn compose<A, B, C, G, F>(f: F, g: G) -> impl Fn(A) -> C

src/main.rs

@@ -28,7 +28,7 @@ fn main() -> ExitCode {
     let args = Args::parse();
 
     // FIXME: set default level to info
-    env_logger::Builder::from_env(env_logger::Env::default().default_filter_or("info")).init();
+    env_logger::Builder::from_env(env_logger::Env::default().default_filter_or("debug")).init();
     handle_toplevel_error(go(args.action))
 }