logger_cb: remove default callbacks (#294)

The logic related to filtering by callbacks must be a decision of the
library consumers, as it is not possible to know which is the best
strategy for each case.

This also adds to the related selftest other example that shows how to
filter using callbacks.

Be warned that if filters are not defined via callbacks, all output is
passed to logFallback() which outputs to stderr.

logger_cb.go

@@ -8,7 +8,6 @@ import "C"
 import (
 	"fmt"
 	"os"
-	"regexp"
 	"strings"
 )
 
@@ -47,102 +46,30 @@ const (
 
 // Callbacks stores the callbacks to be used by libbpfgo
 type Callbacks struct {
-	Log        func(level int, msg string, keyValues ...interface{})
+	Log        func(level int, msg string)
 	LogFilters []func(libLevel int, msg string) bool
 }
 
 // callbacks is initialized with default callbacks, but can be changed by SetLoggerCbs
 var callbacks = Callbacks{
-	Log: logFallback,
-	LogFilters: []func(libLevel int, msg string) bool{
-		LogFilterLevel,
-		LogFilterOutput,
-	},
+	Log:        logFallback,
+	LogFilters: []func(libLevel int, msg string) bool{},
 }
 
 // SetLoggerCbs receives Callbacks type to be used to log libbpf outputs and to filter out those outputs
 func SetLoggerCbs(cbs Callbacks) {
-	if cbs.Log == nil {
+	if cbs.Log == nil { // guarantee that there is always an outputter
 		cbs.Log = logFallback
 	}
 
 	callbacks = cbs
 }
 
-// logFallback:
-// - level is ignored in this stage
-// - type coercion only takes care of string types
-// - keyValues is not required to contain pairs
-// - outputs all to stderr
-func logFallback(level int, msg string, keyValues ...interface{}) {
-	var (
-		args   = make([]string, 0)
-		outMsg = msg
-	)
-
-	for _, v := range keyValues {
-		if s, ok := v.(string); ok {
-			outMsg += " [%s]"
-			args = append(args, s)
-		}
-	}
-
-	outMsg += "\n"
-	if len(keyValues) > 0 {
-		fmt.Fprintf(os.Stderr, outMsg, args)
-	} else {
-		fmt.Fprint(os.Stderr, outMsg)
-	}
-}
-
-// LogFilterLevel filters by checking its print level
-// In case the consumer defines its own filters functions via SetLoggerCbs, this can also be passed
-func LogFilterLevel(libbpfPrintLevel int, output string) bool {
-	return libbpfPrintLevel != LibbpfWarnLevel
-}
-
-var (
-	// triggered by: libbpf/src/nlattr.c->libbpf_nla_dump_errormsg()
-	// "libbpf: Kernel error message: %s\n"
-	// 1. %s = "Exclusivity flag on"
-	regexKernelExclusivityFlagOn = regexp.MustCompile(`libbpf:.*Kernel error message:.*Exclusivity flag on`)
-
-	// triggered by: libbpf/src/libbpf.c->bpf_program__attach_kprobe_opts()
-	// "libbpf: prog '%s': failed to create %s '%s+0x%zx' perf event: %s\n"
-	// 1. %s = trace_check_map_func_compatibility
-	// 2. %s = kretprobe or kprobe
-	// 3. %s = check_map_func_compatibility (function name)
-	// 4. %x = offset (ignored in this check)
-	// 5. %s = No such file or directory
-	regexKprobePerfEvent = regexp.MustCompile(`libbpf:.*prog 'trace_check_map_func_compatibility'.*failed to create kprobe.*perf event: No such file or directory`)
-
-	// triggered by: libbpf/src/libbpf.c->bpf_program__attach_fd()
-	// "libbpf: prog '%s': failed to attach to %s: %s\n"
-	// 1. %s = cgroup_skb_ingress or cgroup_skb_egress
-	// 2. %s = cgroup
-	// 3. %s = Invalid argument
-	regexAttachCgroup = regexp.MustCompile(`libbpf:.*prog 'cgroup_skb_ingress|cgroup_skb_egress'.*failed to attach to cgroup.*Invalid argument`)
-)
-
-// LogFilterOutput filters out some errors by using regex
-// In case the consumer defines its own filters functions via SetLoggerCbs, this can also be passed
-func LogFilterOutput(libbpfPrintLevel int, output string) bool {
-	// BUG: https:/github.com/aquasecurity/tracee/issues/1676
-	if regexKernelExclusivityFlagOn.MatchString(output) {
-		return true
-	}
-
-	// BUG: https://github.com/aquasecurity/tracee/issues/2446
-	if regexKprobePerfEvent.MatchString(output) {
-		return true
-	}
-
-	// AttachCgroupLegacy() will first try AttachCgroup() and it might fail. This
-	// is not an error and is the best way of probing for eBPF cgroup attachment
-	// link existence.
-	if regexAttachCgroup.MatchString(output) {
-		return true
-	}
+// logFallback is the default logger callback
+// - level is ignored
+// - output, suffixed with a newline, is printed to stderr
+func logFallback(level int, msg string) {
+	var outMsg = msg + "\n"
 
-	return false
+	fmt.Fprint(os.Stderr, outMsg)
 }

logger_cb_test.go

@@ -1,43 +1,52 @@
 package libbpfgo
 
-import "testing"
+import (
+	"bytes"
+	"io"
+	"os"
+	"testing"
 
-func TestLogFilterOutput(t *testing.T) {
-	tests := []struct {
-		libbpfPrintLevel int
-		output           string
-		expectedResult   bool
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLogFallback(t *testing.T) {
+	tt := []struct {
+		message string
 	}{
 		{
-			output:         "libbpf: prog 'trace_check_map_func_compatibility': failed to create kprobe 'check_map_func_compatibility+0x0' perf event: No such file or directory\n",
-			expectedResult: true,
-		},
-		{
-			output:         "libbpf: Kernel error message: Exclusivity flag on\n",
-			expectedResult: true,
-		},
-		{
-			output:         "libbpf: prog 'cgroup_skb_ingress': failed to attach to cgroup 'cgroup': Invalid argument\n",
-			expectedResult: true,
-		},
-		{
-			output:         "libbpf: prog 'cgroup_skb_egress': failed to attach to cgroup 'cgroup': Invalid argument\n",
-			expectedResult: true,
+			message: "This is a warning message",
 		},
 		{
-			output:         "This is not a log message that should be filtered\n",
-			expectedResult: false,
+			message: "This is a information message",
 		},
 		{
-			output:         "libbpf: This is not a log message that should be filtered\n",
-			expectedResult: false,
+			message: "This is a debug message",
 		},
 	}
 
-	for _, test := range tests {
-		result := LogFilterOutput(test.libbpfPrintLevel, test.output)
-		if result != test.expectedResult {
-			t.Errorf("For input '%s', expected %v but got %v", test.output, test.expectedResult, result)
-		}
+	for _, tc := range tt {
+		var buf bytes.Buffer
+
+		r, w, err := os.Pipe()
+		require.NoError(t, err, "failed to create pipe")
+
+		writeEnd := os.NewFile(uintptr(w.Fd()), "pipe")
+
+		oldStderr := os.Stderr
+		os.Stderr = writeEnd
+
+		// level is ignored
+		logFallback(LibbpfInfoLevel, tc.message)
+
+		os.Stderr = oldStderr
+
+		err = writeEnd.Close()
+		require.NoError(t, err, "failed to close writeEnd")
+		_, err = io.Copy(&buf, r)
+		require.NoError(t, err, "failed to copy from read end to buffer")
+
+		// The message should be printed to stderr with a newline
+		assert.Equal(t, tc.message+"\n", buf.String())
 	}
 }

selftest/log-callbacks/main.go

@@ -13,17 +13,20 @@ import (
 
 var logOutput []string
 
-func log(level int, msg string, keyValues ...interface{}) {
+// log is a handler to save the log output
+func log(level int, msg string) {
 	logOutput = append(logOutput, msg)
 }
 
 func main() {
+	//
+	// Filter example 1: filter out all outputs but containing "found program 'kprobe__sys_mmap'"
+	//
 	filterMatch := "found program 'kprobe__sys_mmap'"
 	bpf.SetLoggerCbs(bpf.Callbacks{
-		Log: log, // use log() as a handler for libbpf outputs that are not excluded by LogFilters
+		Log: log,
 		LogFilters: []func(libLevel int, msg string) bool{
 			func(libLevel int, msg string) bool {
-				// filter all output but containing "found program 'kprobe__sys_mmap'"
 				return !strings.Contains(msg, filterMatch)
 			},
 		},
@@ -34,11 +37,39 @@ func main() {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(-1)
 	}
-	defer bpfModule.Close()
+	bpfModule.Close()
 
 	if len(logOutput) != 1 {
 		fmt.Fprintln(os.Stderr, fmt.Sprintf("Log output should contain only one output matching the string: %s", filterMatch))
 		fmt.Fprintln(os.Stderr, fmt.Sprintf("Log output: %v", logOutput))
 		os.Exit(-1)
 	}
+
+	// clean logOutput
+	logOutput = []string{}
+
+	//
+	// Filter example 2: filter out all outputs which level is LibbpfDebugLevel
+	//
+	bpf.SetLoggerCbs(bpf.Callbacks{
+		Log: log,
+		LogFilters: []func(libLevel int, msg string) bool{
+			func(libLevel int, msg string) bool {
+				return libLevel == bpf.LibbpfDebugLevel
+			},
+		},
+	})
+
+	bpfModule, err = bpf.NewModuleFromFile("main.bpf.o")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	bpfModule.Close()
+
+	if len(logOutput) != 0 {
+		fmt.Fprintln(os.Stderr, "Log output should be empty")
+		fmt.Fprintln(os.Stderr, fmt.Sprintf("Log output: %v", logOutput))
+		os.Exit(-1)
+	}
 }