runtime: Drop QEMU log file support

The QEMU log file is essentially about fine grain tracing of QEMU
internals and mostly useful for developpers, not production. Notably,
the log file isn't limited in size, nor rotated in any way. It means
that a container running in the VM could possibly flood the log file
with a guest triggerable trace. For example, on openshift, the log
file is supposed to reside on a per-VM 14 GiB tmpfs mount. This means
that each pod running with the kata runtime could potentially consume
this amount of host RAM which is not acceptable.

Error messages are best collected from QEMU's stderr as kata is doing
now since PR #5736 was merged. Drop support for the QEMU log file
because it doesn't bring any value but can certainly do harm.

Fixes #6173

Signed-off-by: Greg Kurz <groug@kaod.org>

src/runtime/pkg/govmm/qemu/qemu.go

@@ -2628,9 +2628,6 @@ type Config struct {
 	// PidFile is the -pidfile parameter
 	PidFile string
 
-	// LogFile is the -D parameter
-	LogFile string
-
 	qemuParams []string
 }
 
@@ -2968,13 +2965,6 @@ func (config *Config) appendPidFile() {
 	}
 }
 
-func (config *Config) appendLogFile() {
-	if config.LogFile != "" {
-		config.qemuParams = append(config.qemuParams, "-D")
-		config.qemuParams = append(config.qemuParams, config.LogFile)
-	}
-}
-
 func (config *Config) appendFwCfg(logger QMPLog) {
 	if logger == nil {
 		logger = qmpNullLogger{}
@@ -3013,7 +3003,6 @@ func LaunchQemu(config Config, logger QMPLog) (*exec.Cmd, io.ReadCloser, error)
 	config.appendIOThreads()
 	config.appendIncoming()
 	config.appendPidFile()
-	config.appendLogFile()
 	config.appendFwCfg(logger)
 	config.appendSeccompSandbox()
 

src/runtime/pkg/govmm/qemu/qemu_test.go

@@ -764,8 +764,7 @@ func TestAppendQMPSocketServer(t *testing.T) {
 }
 
 var pidfile = "/run/vc/vm/iamsandboxid/pidfile"
-var logfile = "/run/vc/vm/iamsandboxid/logfile"
-var qemuString = "-name cc-qemu -cpu host -uuid " + agentUUID + " -pidfile " + pidfile + " -D " + logfile
+var qemuString = "-name cc-qemu -cpu host -uuid " + agentUUID + " -pidfile " + pidfile
 
 func TestAppendStrings(t *testing.T) {
 	config := Config{
@@ -774,14 +773,12 @@ func TestAppendStrings(t *testing.T) {
 		UUID:     agentUUID,
 		CPUModel: "host",
 		PidFile:  pidfile,
-		LogFile:  logfile,
 	}
 
 	config.appendName()
 	config.appendCPUModel()
 	config.appendUUID()
 	config.appendPidFile()
-	config.appendLogFile()
 
 	result := strings.Join(config.qemuParams, " ")
 	if result != qemuString {

src/runtime/virtcontainers/qemu.go

@@ -940,10 +940,6 @@ func (q *qemu) StartVM(ctx context.Context, timeout int) error {
 		return err
 	}
 	q.Logger().WithField("vm path", vmPath).Info("created vm path")
-	// append logfile only on debug
-	if q.config.Debug {
-		q.qemuConfig.LogFile = filepath.Join(vmPath, "qemu.log")
-	}
 
 	defer func() {
 		if err != nil {
@@ -1108,19 +1104,6 @@ func (q *qemu) StopVM(ctx context.Context, waitOnly bool) (err error) {
 		}
 	}()
 
-	if q.config.Debug && q.qemuConfig.LogFile != "" {
-		f, err := os.OpenFile(q.qemuConfig.LogFile, os.O_RDONLY, 0)
-		if err == nil {
-			scanner := bufio.NewScanner(f)
-			for scanner.Scan() {
-				q.Logger().WithField("file", q.qemuConfig.LogFile).Debug(scanner.Text())
-			}
-			if err := scanner.Err(); err != nil {
-				q.Logger().WithError(err).Debug("read qemu log failed")
-			}
-		}
-	}
-
 	if err := q.qmpSetup(); err != nil {
 		return err
 	}