feat: EnvFilter

Add the ` EnvFilter` layer to support additional filtering at
compile-time.

Signed-off-by: Jonathan Woollett-Light <jcawl@amazon.co.uk>

Author: Jonathan Woollett-Light

Cargo.lock

@@ -30,7 +30,7 @@ vm-allocator = "0.1.0"
 vm-fdt = "0.2.0"
 vm-superio = "0.7.0"
 tracing = { git = "https://github.com/tokio-rs/tracing", rev = "27f688efb72316a26f3ec1f952c82626692c08ff", features = ["attributes"] }
-tracing-subscriber = { git = "https://github.com/tokio-rs/tracing", rev = "27f688efb72316a26f3ec1f952c82626692c08ff" }
+tracing-subscriber = { git = "https://github.com/tokio-rs/tracing", rev = "27f688efb72316a26f3ec1f952c82626692c08ff", features = ["env-filter"] }
 log = { version = "0.4.17", features = ["serde"] }
 
 dumbo = { path = "../dumbo" }

src/vmm/Cargo.toml

@@ -16,7 +16,7 @@ use libc::O_NONBLOCK;
 use rate_limiter::{BucketUpdate, RateLimiter, TokenBucket};
 use serde::{Deserialize, Serialize};
 use tracing::{Collect, Event};
-use tracing_subscriber::filter::LevelFilter;
+use tracing_subscriber::filter::{EnvFilter, LevelFilter};
 use tracing_subscriber::fmt::format::{self, FormatEvent, FormatFields};
 use tracing_subscriber::fmt::writer::BoxMakeWriter;
 use tracing_subscriber::fmt::FmtContext;
@@ -312,7 +312,8 @@ pub enum UpdateLoggerError {
     Filter(ReloadError),
 }
 
-type FmtInner = Layered<tracing_subscriber::reload::Subscriber<LevelFilter>, Registry>;
+type ReloadSubscriber<S> = tracing_subscriber::reload::Subscriber<S>;
+type FmtInner = Layered<ReloadSubscriber<LevelFilter>, Layered<EnvFilter, Registry>>;
 type FmtType = FmtSubscriber<FmtInner, format::DefaultFields, LoggerFormatter, BoxMakeWriter>;
 
 /// Handles that allow re-configuring the logger.
@@ -331,7 +332,7 @@ impl LoggerConfig {
         let (filter, filter_handle) = {
             let level = tracing::Level::from(self.level.unwrap_or_default());
             let filter_subscriber = LevelFilter::from_level(level);
-            tracing_subscriber::reload::Subscriber::new(filter_subscriber)
+            ReloadSubscriber::new(filter_subscriber)
         };
 
         // Setup fmt layer
@@ -363,10 +364,16 @@ impl LoggerConfig {
                     self.show_log_origin.unwrap_or_default(),
                 ))
                 .with_writer(fmt_writer);
-            tracing_subscriber::reload::Subscriber::new(fmt_subscriber)
+            ReloadSubscriber::new(fmt_subscriber)
         };
 
+        // Setup the env layer
+        let env = EnvFilter::builder()
+            .with_default_directive(LevelFilter::TRACE.into())
+            .from_env_lossy();
+
         Registry::default()
+            .with(env)
             .with(filter)
             .with(fmt)
             .try_init()