implement load-time log level mask

aya-log-ebpf-macros/src/expand.rs

@@ -151,32 +151,34 @@ pub(crate) fn log(args: LogArgs, level: Option<TokenStream>) -> Result<TokenStre
     let len = Ident::new("len", Span::mixed_site());
     let record = Ident::new("record", Span::mixed_site());
     Ok(quote! {
-        match ::aya_log_ebpf::macro_support::AYA_LOG_BUF.get_ptr_mut(0).and_then(|ptr| unsafe { ptr.as_mut() }) {
-            None => {},
-            Some(::aya_log_ebpf::macro_support::LogBuf { buf: #buf }) => {
-                // Silence unused variable warning; we may need ctx in the future.
-                let _ = #ctx;
-                let _: Option<()> = (|| {
-                    let #size = ::aya_log_ebpf::macro_support::write_record_header(
-                        #buf,
-                        #target,
-                        #level,
-                        module_path!(),
-                        file!(),
-                        line!(),
-                        #num_args,
-                    )?;
-                    let mut #size = #size.get();
-                    #(
-                        {
-                            let #buf = #buf.get_mut(#size..)?;
-                            let #len = ::aya_log_ebpf::macro_support::WriteToBuf::write(#values_iter, #buf)?;
-                            #size += #len.get();
-                        }
-                    )*
-                    let #record = #buf.get(..#size)?;
-                    Result::<_, i64>::ok(::aya_log_ebpf::macro_support::AYA_LOGS.output(#record, 0))
-                })();
+        if ::aya_log_ebpf::macro_support::level_enabled(#level) {
+            match ::aya_log_ebpf::macro_support::AYA_LOG_BUF.get_ptr_mut(0).and_then(|ptr| unsafe { ptr.as_mut() }) {
+                None => {},
+                Some(::aya_log_ebpf::macro_support::LogBuf { buf: #buf }) => {
+                    // Silence unused variable warning; we may need ctx in the future.
+                    let _ = #ctx;
+                    let _: Option<()> = (|| {
+                        let #size = ::aya_log_ebpf::macro_support::write_record_header(
+                            #buf,
+                            #target,
+                            #level,
+                            module_path!(),
+                            file!(),
+                            line!(),
+                            #num_args,
+                        )?;
+                        let mut #size = #size.get();
+                        #(
+                            {
+                                let #buf = #buf.get_mut(#size..)?;
+                                let #len = ::aya_log_ebpf::macro_support::WriteToBuf::write(#values_iter, #buf)?;
+                                #size += #len.get();
+                            }
+                        )*
+                        let #record = #buf.get(..#size)?;
+                        Result::<_, i64>::ok(::aya_log_ebpf::macro_support::AYA_LOGS.output(#record, 0))
+                    })();
+                }
             }
         }
     })

aya-log/CHANGELOG.md

@@ -7,6 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### New Features
+
+- Add eBPF-side log level `AYA_LOG_LEVEL` allowing selective disabling of log
+  levels at load-time. Disabled levels are eliminated by the verifier, reducing
+  instruction count and avoiding program size limits when extensive logging is
+  present.
+
 ### Breaking Changes
 
 - The implementation is now backed by a ring buffer rather than a perf event array. This should

aya-log/README.md

@@ -69,3 +69,33 @@ fn try_xdp_firewall(ctx: XdpContext) -> Result<u32, ()> {
 [aya]: https://github.com/aya-rs/aya
 [log]: https://docs.rs/log
 [env_logger]: https://docs.rs/env_logger
+
+## Disabling log levels at load-time
+
+eBPF instruction budgets are tight. Even if a log statement never executes at
+runtime, the verifier must still evaluate its instructions unless it can prove
+they're unreachable. `aya-log` now exposes a global `AYA_LOG_LEVEL` inside the
+eBPF object allowing you to selectively enable levels before the program is
+loaded.
+
+By default all bits are set (all logging enabled). To disable all logging:
+
+```rust
+let mut bpf = aya::EbpfLoader::new()
+    .set_global(aya_log::LEVEL, &0, false /* must_exist */)
+    .load_file("prog.bpf.o")?;
+# Ok::<(), aya::EbpfError>(())
+```
+
+Enable only Error and Warn:
+
+```rust
+let level = aya_log::Level::Warn as u8;
+let mut bpf = EbpfLoader::new()
+    .set_global(aya_log::LEVEL, &level, false /* must_exist */)
+    .load_file("prog.bpf.o")?;
+```
+
+Because the level is placed in global read-only data, the verifier sees the
+disabled branch as unreachable and prunes the logging instructions, reducing
+overall instruction count and avoiding potential instruction limit issues.

aya-log/src/lib.rs

@@ -67,12 +67,15 @@ use std::{
 
 const MAP_NAME: &str = "AYA_LOGS";
 
+pub const LEVEL: &str = "AYA_LOG_LEVEL";
+pub use aya_log_common::Level;
+
 use aya::{
     Ebpf, Pod,
     maps::{Map, MapData, MapError, MapInfo, RingBuf},
     programs::{ProgramError, loaded_programs},
 };
-use aya_log_common::{Argument, DisplayHint, LOG_FIELDS, Level, LogValueLength, RecordField};
+use aya_log_common::{Argument, DisplayHint, LOG_FIELDS, LogValueLength, RecordField};
 use log::{Log, Record, error};
 use thiserror::Error;
 

ebpf/aya-log-ebpf/src/lib.rs

@@ -34,4 +34,18 @@ pub mod macro_support {
     // test/integration-test/Cargo.toml.
     #[cfg_attr(target_arch = "bpf", map)]
     pub static AYA_LOGS: RingBuf = RingBuf::with_byte_size((LOG_BUF_CAPACITY as u32) << 4, 0);
+
+    /// Global log level controlling which log statements are active.
+    ///
+    /// Userspace may patch this symbol before load via `EbpfLoader::set_global`.
+    #[unsafe(no_mangle)]
+    pub static mut AYA_LOG_LEVEL: u8 = 0xff;
+
+    /// Returns `true` if the provided level is enabled according to [`AYA_LOG_LEVEL`].
+    #[inline(always)]
+    pub fn level_enabled(level: Level) -> bool {
+        #[expect(static_mut_refs)]
+        let current_level = unsafe { core::ptr::read_volatile(&AYA_LOG_LEVEL) };
+        level as u8 <= current_level
+    }
 }

test/integration-test/src/tests/log.rs

@@ -2,6 +2,7 @@ use std::{borrow::Cow, sync::Mutex};
 
 use aya::{Ebpf, programs::UProbe};
 use aya_log::EbpfLogger;
+use aya::EbpfLoader;
 use log::{Level, Log, Record};
 
 #[unsafe(no_mangle)]
@@ -173,3 +174,54 @@ fn log() {
 
     assert_eq!(records.next(), None);
 }
+
+#[test_log::test]
+fn log_level_only_error_warn() {
+    let level = aya_log::Level::Warn as u8;
+    let mut bpf = EbpfLoader::new()
+        .set_global(aya_log::LEVEL, &level, true /* must_exist */)
+        .load(crate::LOG)
+        .unwrap();
+
+    let mut captured_logs = Vec::new();
+    let logger = TestingLogger {
+        log: Mutex::new(|record: &Record| {
+            captured_logs.push(CapturedLog {
+                body: format!("{}", record.args()).into(),
+                level: record.level(),
+                target: record.target().to_string().into(),
+            });
+        }),
+    };
+    let mut logger = EbpfLogger::init_with_logger(&mut bpf, &logger).unwrap();
+
+    let prog: &mut UProbe = bpf.program_mut("test_log").unwrap().try_into().unwrap();
+    prog.load().unwrap();
+    prog.attach("trigger_ebpf_program", "/proc/self/exe", None, None)
+        .unwrap();
+
+    trigger_ebpf_program();
+    logger.flush();
+
+    let mut records = captured_logs.iter();
+
+    assert_eq!(
+        records.next(),
+        Some(&CapturedLog {
+            body: "69, 420, wao, 77616f".into(),
+            level: Level::Error,
+            target: "log".into(),
+        })
+    );
+
+    assert_eq!(
+        records.next(),
+        Some(&CapturedLog {
+            body: "hex lc: 2f, hex uc: 2F".into(),
+            level: Level::Warn,
+            target: "log".into(),
+        })
+    );
+
+    assert_eq!(records.next(), None);
+}

xtask/public-api/aya-log.txt

@@ -1,4 +1,5 @@
 pub mod aya_log
+pub use aya_log::Level
 pub enum aya_log::Error
 pub aya_log::Error::MapError(aya::maps::MapError)
 pub aya_log::Error::MapNotFound
@@ -297,6 +298,7 @@ impl<T> core::borrow::BorrowMut<T> for aya_log::UpperMacFormatter where T: ?core
 pub fn aya_log::UpperMacFormatter::borrow_mut(&mut self) -> &mut T
 impl<T> core::convert::From<T> for aya_log::UpperMacFormatter
 pub fn aya_log::UpperMacFormatter::from(t: T) -> T
+pub const aya_log::LEVEL: &str
 pub trait aya_log::Formatter<T>
 pub fn aya_log::Formatter::format(v: T) -> alloc::string::String
 impl aya_log::Formatter<&[u8]> for aya_log::LowerHexBytesFormatter