feat: add log to journald feature

The systemd-journald is used in most major Linux distros that use systemd.
This enables logging using the systemd-journald native protocol, instead
of just writing to stderr.

Cargo.lock

@@ -1250,6 +1250,7 @@ dependencies = [
  "timeago",
  "tokio",
  "tracing",
+ "tracing-journald",
  "tracing-subscriber",
 ]
 
@@ -4514,6 +4515,17 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "tracing-journald"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fc0b4143302cf1022dac868d521e36e8b27691f72c84b3311750d5188ebba657"
+dependencies = [
+ "libc",
+ "tracing-core",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "tracing-log"
 version = "0.2.0"

Cargo.toml

@@ -83,6 +83,7 @@ pretty_env_logger = "0.5"
 structopt = { version = "0.3", default-features = false }
 syslog-tracing = "0.3"
 tracing = "0.1"
+tracing-journald = "0.3.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 
 heed = { version = "0.11", default-features = false, features = ["lmdb"] }

doc/book/reference-manual/configuration.md

@@ -160,6 +160,10 @@ variable, it does not exist in the configuration file:
   Garage daemon send its logs to `syslog` (using the libc `syslog` function)
   instead of printing to stderr.
 
+- `GARAGE_LOG_TO_JOURNALD` (since `v2.0.0`): set this to `1` or `true` to make the
+  Garage daemon send its logs to `journald` (using the native protocol of `systemd-journald`)
+  instead of printing to stderr.
+
 The following environment variables can be used to override the corresponding
 values in the configuration file:
 

nix/compile.nix

@@ -74,6 +74,7 @@ let
       "metrics"
       "telemetry-otlp"
       "syslog"
+      "journald"
     ]));
 
   featuresStr = lib.concatStringsSep "," rootFeatures;

src/garage/Cargo.toml

@@ -57,6 +57,7 @@ opentelemetry.workspace = true
 opentelemetry-prometheus = { workspace = true, optional = true }
 opentelemetry-otlp = { workspace = true, optional = true }
 syslog-tracing = { workspace = true, optional = true }
+tracing-journald = { workspace = true, optional = true }
 
 [dev-dependencies]
 garage_api_common.workspace = true
@@ -101,6 +102,8 @@ metrics = [ "garage_api_admin/metrics", "opentelemetry-prometheus" ]
 telemetry-otlp = [ "opentelemetry-otlp" ]
 # Logging to syslog
 syslog = [ "syslog-tracing" ]
+# Logging to journald
+journald = [ "tracing-journald" ]
 
 # NOTE: bundled-libs and system-libs should be treat as mutually exclusive;
 # exactly one of them should be enabled.

src/garage/main.rs

@@ -208,6 +208,43 @@ fn init_logging(opt: &Opt) {
 		}
 	}
 
+	if std::env::var("GARAGE_LOG_TO_JOURNALD")
+		.map(|x| x == "1" || x == "true")
+		.unwrap_or(false)
+	{
+		#[cfg(feature = "journald")]
+		{
+			use tracing_journald::{Priority, PriorityMappings};
+			use tracing_subscriber::layer::SubscriberExt;
+			use tracing_subscriber::util::SubscriberInitExt;
+
+			let registry = tracing_subscriber::registry()
+				.with(tracing_subscriber::fmt::layer().with_writer(std::io::sink))
+				.with(env_filter);
+			match tracing_journald::layer() {
+				Ok(layer) => {
+					registry
+						.with(layer.with_priority_mappings(PriorityMappings {
+							info: Priority::Informational,
+							debug: Priority::Debug,
+							..PriorityMappings::new()
+						}))
+						.init();
+				}
+				Err(e) => {
+					eprintln!("Couldn't connect to journald: {}.", e);
+					std::process::exit(1);
+				}
+			}
+			return;
+		}
+		#[cfg(not(feature = "journald"))]
+		{
+			eprintln!("Journald support is not enabled in this build.");
+			std::process::exit(1);
+		}
+	}
+
 	tracing_subscriber::fmt()
 		.with_writer(std::io::stderr)
 		.with_env_filter(env_filter)