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 mask `AYA_LOG_LEVEL_MASK` and loader API `EbpfLoader::set_log_level_mask()`
+  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 +69,37 @@ 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 bitmask `AYA_LOG_LEVEL_MASK`
+inside the eBPF object allowing you to selectively enable levels before the
+program is loaded.
+
+Bits (least-significant first) map to levels: Error=bit0, Warn=bit1, Info=bit2,
+Debug=bit3, Trace=bit4.
+
+By default all bits are set (all logging enabled). To disable all logging:
+
+```rust
+use aya::EbpfLoader;
+
+let mut bpf = EbpfLoader::new()
+    .set_log_level_mask(0) // disable all levels
+    .load_file("prog.bpf.o")?;
+# Ok::<(), aya::EbpfError>(())
+```
+
+Enable only Error and Warn:
+
+```rust
+let mut bpf = EbpfLoader::new()
+    .set_log_level_mask(0b11)
+    .load_file("prog.bpf.o")?;
+```
+
+Because the mask 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/src/bpf.rs

@@ -341,6 +341,21 @@ impl<'a> EbpfLoader<'a> {
         self
     }
 
+    /// Sets the aya-log eBPF log level mask before loading programs.
+    ///
+    /// This is a convenience wrapper around [`EbpfLoader::set_global`] that patches the
+    /// `AYA_LOG_LEVEL_MASK` symbol exposed by `aya-log-ebpf`.
+    ///
+    /// Each bit enables a level where bit0=Error, bit1=Warn, bit2=Info, bit3=Debug, bit4=Trace.
+    /// For example to enable only Error and Warn pass `0b0000_0011` (3). To disable all logging
+    /// pass 0.
+    ///
+    /// If the symbol does not exist in the object (e.g., logging not linked) no error is raised.
+    pub fn set_log_level_mask(&mut self, mask: u32) -> &mut Self {
+        // Best-effort: don't require symbol to exist.
+        self.set_global("AYA_LOG_LEVEL_MASK", &mask, false)
+    }
+
     /// Loads eBPF bytecode from a file.
     ///
     /// # Examples

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

@@ -9,6 +9,8 @@ pub mod macro_support {
     use aya_ebpf::macros::map;
     use aya_ebpf::maps::{PerCpuArray, RingBuf};
     use aya_log_common::LogValueLength;
+    #[cfg(target_arch = "bpf")]
+    use core::ptr::read_volatile;
     pub use aya_log_common::{
         DefaultFormatter, DisplayHint, IpFormatter, Level, LowerHexFormatter, LowerMacFormatter,
         UpperHexFormatter, UpperMacFormatter, WriteToBuf, write_record_header,
@@ -34,4 +36,21 @@ 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 mask controlling which log statements are active.
+    /// Bits correspond to variants of `Level` (1-based discriminant) shifted into a mask.
+    /// By default all bits set (enable all levels). Userspace may patch this symbol before load
+    /// via `EbpfLoader::set_log_level_mask` (to be implemented) using global data patching.
+    /// When a bit is unset, verifier will see the guarded block as unreachable and prune it.
+    #[no_mangle]
+    pub static mut AYA_LOG_LEVEL_MASK: u32 = 0xFFFF_FFFF;
+
+    /// Returns `true` if the provided level is enabled according to `AYA_LOG_LEVEL_MASK`.
+    #[inline(always)]
+    pub fn level_enabled(lvl: Level) -> bool {
+        // SAFETY: Mask lives in .rodata for BPF (declared mutable for patching), we only read it.
+        let mask = unsafe { read_volatile(&AYA_LOG_LEVEL_MASK) };
+        let bit: u32 = 1u32 << (lvl as u32 - 1);
+        (mask & bit) != 0
+    }
 }

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 +174,48 @@ fn log() {
 
     assert_eq!(records.next(), None);
 }
+
+#[test_log::test]
+fn log_level_mask_only_error_warn() {
+    // Enable only Error (bit0) and Warn (bit1)
+    let mut bpf = EbpfLoader::new()
+        .set_log_level_mask(0b11)
+        .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();
+
+    // We expect only the Error and Warn records to be present, in program order.
+    let expected: Vec<CapturedLog<'_>> = vec![
+        CapturedLog {
+            body: "69, 420, wao, 77616f".into(),
+            level: Level::Error,
+            target: "log".into(),
+        },
+        CapturedLog {
+            body: "hex lc: 2f, hex uc: 2F".into(),
+            level: Level::Warn,
+            target: "log".into(),
+        },
+    ];
+
+    assert_eq!(captured_logs, expected, "unexpected log records when mask filters levels");
+}