Allow users to skip Kernel check for bpf_loop functionality

docs/sources/distributed-traces.md

@@ -127,7 +127,9 @@ have their context propagated. We use this volume path to listen to newly create
 
 #### Kernel version limitations
 
-The network level context propagation incoming headers parsing requires kernel 5.17 or newer.
+The network level context propagation incoming headers parsing generally requires kernel 5.17 or newer for the addition and use of BPF loops.
+
+Some patched kernels, such as RHEL 9.2, may have this functionality ported back. Setting BEYLA_OVERRIDE_BPF_LOOP_ENABLED skips kernel checks in the case your kernel includes the functionality but is lower than 5.17.
 
 ### Go context propagation by instrumenting at library level
 

pkg/config/ebpf_tracer.go

@@ -32,6 +32,10 @@ type EBPFTracer struct {
 	// Enables Linux Traffic Control probes for context propagation
 	ContextPropagationEnabled bool `yaml:"enable_context_propagation" env:"BEYLA_BPF_ENABLE_CONTEXT_PROPAGATION"`
 
+	// Skips checking the kernel version for bpf_loop functionality. Some modified kernels have this
+	// backported prior to version 5.17.
+	OverrideBPFLoopEnabled bool `yaml:"override_bpfloop_enabled" env:"BEYLA_OVERRIDE_BPF_LOOP_ENABLED"`
+
 	// Enables Linux Traffic Control probes for context propagation
 	UseTCForL7CP bool `yaml:"traffic_control_l7_context_propagation" env:"BEYLA_BPF_TC_L7_CP"`
 

pkg/internal/ebpf/common/common.go

@@ -173,7 +173,11 @@ func SupportsContextPropagationWithProbe(log *slog.Logger) bool {
 	return false
 }
 
-func SupportsEBPFLoops() bool {
+func SupportsEBPFLoops(log *slog.Logger, overrideKernelVersion bool) bool {
+	if overrideKernelVersion {
+		log.Debug("Skipping kernel version check for bpf_loop functionality: user supplied confirmation of support")
+		return true
+	}
 	kernelMajor, kernelMinor := KernelVersion()
 	return kernelMajor > 5 || (kernelMajor == 5 && kernelMinor >= 17)
 }

pkg/internal/ebpf/generictracer/generictracer.go

@@ -128,13 +128,14 @@ func (p *Tracer) Load() (*ebpf.CollectionSpec, error) {
 	}
 
 	if p.cfg.EBPF.TrackRequestHeaders || p.cfg.EBPF.UseTCForL7CP || p.cfg.EBPF.ContextPropagationEnabled {
-		if ebpfcommon.SupportsEBPFLoops() {
-			p.log.Info("Found Linux kernel later than 5.17, enabling trace information parsing")
+		if ebpfcommon.SupportsEBPFLoops(p.log, p.cfg.EBPF.OverrideBPFLoopEnabled) {
+			p.log.Info("Found compatible Linux kernel, enabling trace information parsing")
 			loader = loadBpf_tp
 			if p.cfg.EBPF.BpfDebug {
 				loader = loadBpf_tp_debug
 			}
 		}
+		p.log.Info("Found incompatible Linux kernel, disabling trace information parsing")
 	}
 
 	return loader()

pkg/internal/ebpf/httptracer/httptracer.go

@@ -130,8 +130,8 @@ func (p *Tracer) startTC(ctx context.Context) {
 
 	p.log.Info("enabling L7 context-propagation with Linux Traffic Control")
 
-	if !ebpfcommon.SupportsEBPFLoops() {
-		p.log.Error("cannot enable L7 context-propagation, kernel 5.17 or newer required")
+	if !ebpfcommon.SupportsEBPFLoops(p.log, p.cfg.EBPF.OverrideBPFLoopEnabled) {
+		p.log.Error("cannot enable L7 context-propagation, compatible kernel required")
 	}
 
 	p.ifaceManager = tcmanager.NewInterfaceManager()