raise max file descriptors allowed to infinity

Author: usamasaqib

lading/src/bin/lading.rs

@@ -67,6 +67,8 @@ enum Error {
     MissingTelemetry,
     #[error(transparent)]
     Registration(#[from] lading_signal::RegisterError),
+    #[error("Failed to raise RLIMIT_NOFILE to infinity (requires CAP_SYS_RESOURCE): {0}")]
+    RaiseFileLimit(#[source] std::io::Error),
 }
 
 fn default_config_path() -> String {
@@ -729,6 +731,25 @@ fn init_tracing(json_output: bool) {
     }
 }
 
+/// Raise the open file descriptor limit (`RLIMIT_NOFILE`) to infinity.
+///
+/// Sets both the soft and hard limits to `RLIM_INFINITY`. Raising the hard
+/// limit requires the `CAP_SYS_RESOURCE` capability.
+fn raise_open_file_limit() -> io::Result<()> {
+    let limit = libc::rlimit {
+        rlim_cur: libc::RLIM_INFINITY,
+        rlim_max: libc::RLIM_INFINITY,
+    };
+    // SAFETY: `limit` is a fully-initialized `rlimit`; `setrlimit` only reads
+    // from the pointer for the duration of the call.
+    let ret = unsafe { libc::setrlimit(libc::RLIMIT_NOFILE, &raw const limit) };
+    if ret == 0 {
+        Ok(())
+    } else {
+        Err(io::Error::last_os_error())
+    }
+}
+
 fn main() -> Result<(), Error> {
     // Two-parser fallback logic until CliFlatLegacy is removed
     let (json_output, args) = match CliWithSubcommands::try_parse() {
@@ -763,7 +784,12 @@ fn main() -> Result<(), Error> {
         limit = memory_limit.to_string()
     );
 
-    let config = get_config(&args, None);
+    let config = get_config(&args, None)?;
+
+    if config.maximize_open_file_limit {
+        raise_open_file_limit().map_err(Error::RaiseFileLimit)?;
+        info!("Raised RLIMIT_NOFILE to infinity.");
+    }
 
     let experiment_duration = if args.experiment_duration_infinite {
         Duration::MAX
@@ -785,7 +811,7 @@ fn main() -> Result<(), Error> {
         experiment_duration,
         warmup_duration,
         disable_inspector,
-        config?,
+        config,
     ));
     // The splunk_hec generator spawns long running tasks that are not plugged
     // into the shutdown mechanism we have here. This is a bug and needs to be

lading/src/config.rs

@@ -118,6 +118,11 @@ pub struct Config {
     pub target_metrics: Option<Vec<target_metrics::Config>>,
     /// The target inspector sub-program
     pub inspector: Option<inspector::Config>,
+    /// When true, raise the open file descriptor limit (`RLIMIT_NOFILE`) to
+    /// infinity on startup. Raising the hard limit requires `CAP_SYS_RESOURCE`.
+    /// Default is false.
+    #[serde(default)]
+    pub maximize_open_file_limit: bool,
 }
 
 /// Partial configuration used for merging multiple config files
@@ -147,6 +152,8 @@ pub struct PartialConfig {
     pub target_metrics: Option<Vec<target_metrics::Config>>,
     /// The target inspector sub-program.
     pub inspector: Option<inspector::Config>,
+    /// When true, raise `RLIMIT_NOFILE` to infinity on startup.
+    pub maximize_open_file_limit: Option<bool>,
 }
 
 /// Default value for [`Telemetry::Log`] expiration
@@ -280,6 +287,7 @@ impl Config {
             blackhole: partial.blackhole,
             target_metrics: partial.target_metrics,
             inspector: partial.inspector,
+            maximize_open_file_limit: partial.maximize_open_file_limit.unwrap_or(false),
         })
     }
 
@@ -334,6 +342,11 @@ impl Config {
             base.observer = overlay.observer;
         }
 
+        // Last writer wins for the file-descriptor limit toggle.
+        if overlay.maximize_open_file_limit.is_some() {
+            base.maximize_open_file_limit = overlay.maximize_open_file_limit;
+        }
+
         // Merge generators
         base.generator.extend(overlay.generator);
         check_duplicate_generator_ids(&base.generator)?;
@@ -546,6 +559,7 @@ mod tests {
             blackhole: vec![],
             target_metrics: None,
             inspector: None,
+            maximize_open_file_limit: None,
         }
     }
 
@@ -559,6 +573,7 @@ mod tests {
             blackhole: blackholes,
             target_metrics: None,
             inspector: None,
+            maximize_open_file_limit: None,
         }
     }
 
@@ -572,6 +587,7 @@ mod tests {
             blackhole: vec![],
             target_metrics: Some(metrics),
             inspector: None,
+            maximize_open_file_limit: None,
         }
     }
 
@@ -660,6 +676,7 @@ blackhole:
                 inspector: Option::default(),
                 target_metrics: Option::default(),
                 sample_period_milliseconds: 1_000,
+                maximize_open_file_limit: false,
             },
         );
         Ok(())