Merge pull request #9158 from mvo5/debug-via-kernelenv

logger: add support for setting snapd.debug=1 on kernel cmdline

logger/export_test.go

@@ -27,10 +27,18 @@ func GetLogger() Logger {
 }
 
 func GetLoggerFlags() int {
-	log, ok := GetLogger().(Log)
+	log, ok := GetLogger().(*Log)
 	if !ok {
 		return -1
 	}
 
 	return log.log.Flags()
 }
+
+func MockProcCmdline(new string) (restore func()) {
+	old := procCmdline
+	procCmdline = new
+	return func() {
+		procCmdline = old
+	}
+}

logger/logger.go

@@ -23,11 +23,14 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"log"
 	"os"
+	"strings"
 	"sync"
 
 	"github.com/snapcore/snapd/osutil"
+	"github.com/snapcore/snapd/strutil"
 )
 
 // A Logger is a fairly minimal logging tool.
@@ -121,23 +124,29 @@ func SetLogger(l Logger) {
 
 type Log struct {
 	log *log.Logger
+
+	debug bool
 }
 
 // Debug only prints if SNAPD_DEBUG is set
-func (l Log) Debug(msg string) {
-	if osutil.GetenvBool("SNAPD_DEBUG") {
+func (l *Log) Debug(msg string) {
+	if l.debug || osutil.GetenvBool("SNAPD_DEBUG") {
 		l.log.Output(3, "DEBUG: "+msg)
 	}
 }
 
 // Notice alerts the user about something, as well as putting it syslog
-func (l Log) Notice(msg string) {
+func (l *Log) Notice(msg string) {
 	l.log.Output(3, msg)
 }
 
 // New creates a log.Logger using the given io.Writer and flag.
 func New(w io.Writer, flag int) (Logger, error) {
-	return Log{log: log.New(w, "", flag)}, nil
+	logger := &Log{
+		log:   log.New(w, "", flag),
+		debug: debugEnabledOnKernelCmdline(),
+	}
+	return logger, nil
 }
 
 // SimpleSetup creates the default (console) logger
@@ -153,3 +162,16 @@ func SimpleSetup() error {
 	}
 	return err
 }
+
+var procCmdline = "/proc/cmdline"
+
+// TODO: consider generalizing this to snapdenv and having it used by
+// other places that consider SNAPD_DEBUG
+func debugEnabledOnKernelCmdline() bool {
+	buf, err := ioutil.ReadFile(procCmdline)
+	if err != nil {
+		return false
+	}
+	l := strings.Split(string(buf), " ")
+	return strutil.ListContains(l, "snapd.debug=1")
+}

logger/logger_test.go

@@ -21,8 +21,10 @@ package logger_test
 
 import (
 	"bytes"
+	"io/ioutil"
 	"log"
 	"os"
+	"path/filepath"
 	"runtime"
 	"testing"
 
@@ -122,3 +124,17 @@ func (s *LogSuite) TestWithLoggerLock(c *C) {
 	})
 	c.Check(called, Equals, true)
 }
+
+func (s *LogSuite) TestIntegrationDebugFromKernelCmdline(c *C) {
+	mockProcCmdline := filepath.Join(c.MkDir(), "proc-cmdline")
+	err := ioutil.WriteFile(mockProcCmdline, []byte("console=tty panic=-1 snapd.debug=1"), 0644)
+	c.Assert(err, IsNil)
+	restore := logger.MockProcCmdline(mockProcCmdline)
+	defer restore()
+
+	var buf bytes.Buffer
+	l, err := logger.New(&buf, logger.DefaultFlags)
+	c.Assert(err, IsNil)
+	l.Debug("xyzzy")
+	c.Check(buf.String(), testutil.Contains, `DEBUG: xyzzy`)
+}