Make systemd watchdog backend only build for linux

This patch ensures that the systemd watchdog backend is only used when
building for linux.

Right now, there is no other watchdog implementation. Thus, there is a
"dummy_watchdog" module introduced that does nothing. This might be
removed and replaced by something specific, if we ever build
thin-edge.io for other targets, such as Apple, FreeBSD or others.

Suggested-by: Albin Suresh <albin.suresh@softwareag.com>
Signed-off-by: Matthias Beyer <matthias.beyer@ifm.com>

3 files changed, 19 insertions, 1 deletions

diff --git a/crates/core/tedge_watchdog/src/dummy_watchdog.rs b/crates/core/tedge_watchdog/src/dummy_watchdog.rs
new file mode 100644
index 00000000..f701ffbe
--- /dev/null
+++ b/crates/core/tedge_watchdog/src/dummy_watchdog.rs
@@ -0,0 +1,3 @@
+pub async fn start_watchdog(_config_dir: PathBuf) -> Result<(), anyhow::Error> {
+    anyhow::Error::from(crate::error::WatchdogError::WatchdogNotAvailable)
+}
diff --git a/crates/core/tedge_watchdog/src/error.rs b/crates/core/tedge_watchdog/src/error.rs
index f9763798..27a9a1ed 100644
--- a/crates/core/tedge_watchdog/src/error.rs
+++ b/crates/core/tedge_watchdog/src/error.rs
@@ -4,6 +4,10 @@ use tedge_config::{ConfigSettingError, TEdgeConfigError};
 
 #[derive(Debug, thiserror::Error)]
 pub enum WatchdogError {
+    #[cfg(not(target_os = "linux"))]
+    #[error("The watchdog is not available on this platform")]
+    WatchdogNotAvailable,
+
     #[error("Fail to run `{cmd}`: {from}")]
     CommandExecError { cmd: String, from: std::io::Error },
 
diff --git a/crates/core/tedge_watchdog/src/main.rs b/crates/core/tedge_watchdog/src/main.rs
index e4478b2f..8f0c2b4b 100644
--- a/crates/core/tedge_watchdog/src/main.rs
+++ b/crates/core/tedge_watchdog/src/main.rs
@@ -3,7 +3,18 @@ use std::path::PathBuf;
 use tedge_config::DEFAULT_TEDGE_CONFIG_PATH;
 
 mod error;
+
+// on linux, we use systemd
+#[cfg(target_os = "linux")]
 mod systemd_watchdog;
+#[cfg(target_os = "linux")]
+use systemd_watchdog as watchdog;
+
+// on non-linux, we do nothing for now
+#[cfg(not(target_os = "linux"))]
+mod dummy_watchdog;
+#[cfg(not(target_os = "linux"))]
+use dummy_watchdog as watchdog;
 
 #[derive(Debug, clap::Parser)]
 #[clap(
@@ -31,5 +42,5 @@ async fn main() -> Result<(), anyhow::Error> {
     let watchdog_opt = WatchdogOpt::parse();
     tedge_utils::logging::initialise_tracing_subscriber(watchdog_opt.debug);
 
-    systemd_watchdog::start_watchdog(watchdog_opt.config_dir).await
+    watchdog::start_watchdog(watchdog_opt.config_dir).await
 }