1 files changed, 323 insertions, 0 deletions
diff --git a/pkg/log/log.go b/pkg/log/log.go
new file mode 100644
index 000000000..110e0e196
--- /dev/null
+++ b/pkg/log/log.go
@@ -0,0 +1,323 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package log implements a library for logging.
+//
+// This is separate from the standard logging package because logging may be a
+// high-impact activity, and therefore we wanted to provide as much flexibility
+// as possible in the underlying implementation.
+package log
+
+import (
+	"fmt"
+	"io"
+	stdlog "log"
+	"os"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"syscall"
+	"time"
+
+	"gvisor.googlesource.com/gvisor/pkg/linewriter"
+)
+
+// Level is the log level.
+type Level uint32
+
+// The following levels are fixed, and can never be changed. Since some control
+// RPCs allow for changing the level as an integer, it is only possible to add
+// additional levels, and the existing one cannot be removed.
+const (
+	// Warning indicates that output should always be emitted.
+	Warning Level = iota
+
+	// Info indicates that output should normally be emitted.
+	Info
+
+	// Debug indicates that output should not normally be emitted.
+	Debug
+)
+
+// Emitter is the final destination for logs.
+type Emitter interface {
+	// Emit emits the given log statement. This allows for control over the
+	// timestamp used for logging.
+	Emit(level Level, timestamp time.Time, format string, v ...interface{})
+}
+
+// Writer writes the output to the given writer.
+type Writer struct {
+	// Next is where output is written.
+	Next io.Writer
+
+	// mu protects fields below.
+	mu sync.Mutex
+
+	// errors counts failures to write log messages so it can be reported
+	// when writer start to work again. Needs to be accessed using atomics
+	// to make race detector happy because it's read outside the mutex.
+	errors int32
+}
+
+// Write writes out the given bytes, handling non-blocking sockets.
+func (l *Writer) Write(data []byte) (int, error) {
+	n := 0
+
+	for n < len(data) {
+		w, err := l.Next.Write(data[n:])
+		n += w
+
+		// Is it a non-blocking socket?
+		if pathErr, ok := err.(*os.PathError); ok && pathErr.Err == syscall.EAGAIN {
+			runtime.Gosched()
+			continue
+		}
+
+		// Some other error?
+		if err != nil {
+			l.mu.Lock()
+			atomic.AddInt32(&l.errors, 1)
+			l.mu.Unlock()
+			return n, err
+		}
+	}
+
+	// Do we need to end with a '\n'?
+	if len(data) == 0 || data[len(data)-1] != '\n' {
+		l.Write([]byte{'\n'})
+	}
+
+	// Dirty read in case there were errors (rare).
+	if atomic.LoadInt32(&l.errors) > 0 {
+		l.mu.Lock()
+		defer l.mu.Unlock()
+
+		// Recheck condition under lock.
+		if e := atomic.LoadInt32(&l.errors); e > 0 {
+			msg := fmt.Sprintf("\n*** Dropped %d log messages ***\n", e)
+			if _, err := l.Next.Write([]byte(msg)); err == nil {
+				atomic.StoreInt32(&l.errors, 0)
+			}
+		}
+	}
+
+	return n, nil
+}
+
+// Emit emits the message.
+func (l *Writer) Emit(level Level, timestamp time.Time, format string, args ...interface{}) {
+	fmt.Fprintf(l, format, args...)
+}
+
+// MultiEmitter is an emitter that emits to multiple Emitters.
+type MultiEmitter []Emitter
+
+// Emit emits to all emitters.
+func (m MultiEmitter) Emit(level Level, timestamp time.Time, format string, v ...interface{}) {
+	for _, e := range m {
+		e.Emit(level, timestamp, format, v...)
+	}
+}
+
+// TestLogger is implemented by testing.T and testing.B.
+type TestLogger interface {
+	Logf(format string, v ...interface{})
+}
+
+// TestEmitter may be used for wrapping tests.
+type TestEmitter struct {
+	TestLogger
+}
+
+// Emit emits to the TestLogger.
+func (t TestEmitter) Emit(level Level, timestamp time.Time, format string, v ...interface{}) {
+	t.Logf(format, v...)
+}
+
+// Logger is a high-level logging interface. It is in fact, not used within the
+// log package. Rather it is provided for others to provide contextual loggers
+// that may append some addition information to log statement. BasicLogger
+// satifies this interface, and may be passed around as a Logger.
+type Logger interface {
+	// Debugf logs a debug statement.
+	Debugf(format string, v ...interface{})
+
+	// Infof logs at an info level.
+	Infof(format string, v ...interface{})
+
+	// Warningf logs at a warning level.
+	Warningf(format string, v ...interface{})
+
+	// IsLogging returns true iff this level is being logged. This may be
+	// used to short-circuit expensive operations for debugging calls.
+	IsLogging(level Level) bool
+}
+
+// BasicLogger is the default implementation of Logger.
+type BasicLogger struct {
+	Level
+	Emitter
+}
+
+// Debugf implements logger.Debugf.
+func (l *BasicLogger) Debugf(format string, v ...interface{}) {
+	if l.IsLogging(Debug) {
+		l.Emit(Debug, time.Now(), format, v...)
+	}
+}
+
+// Infof implements logger.Infof.
+func (l *BasicLogger) Infof(format string, v ...interface{}) {
+	if l.IsLogging(Info) {
+		l.Emit(Info, time.Now(), format, v...)
+	}
+}
+
+// Warningf implements logger.Warningf.
+func (l *BasicLogger) Warningf(format string, v ...interface{}) {
+	if l.IsLogging(Warning) {
+		l.Emit(Warning, time.Now(), format, v...)
+	}
+}
+
+// IsLogging implements logger.IsLogging.
+func (l *BasicLogger) IsLogging(level Level) bool {
+	return atomic.LoadUint32((*uint32)(&l.Level)) >= uint32(level)
+}
+
+// SetLevel sets the logging level.
+func (l *BasicLogger) SetLevel(level Level) {
+	atomic.StoreUint32((*uint32)(&l.Level), uint32(level))
+}
+
+// logMu protects Log below. We use atomic operations to read the value, but
+// updates require logMu to ensure consistency.
+var logMu sync.Mutex
+
+// log is the default logger.
+var log atomic.Value
+
+// Log retieves the global logger.
+func Log() *BasicLogger {
+	return log.Load().(*BasicLogger)
+}
+
+// SetTarget sets the log target.
+//
+// This is not thread safe and shouldn't be called concurrently with any
+// logging calls.
+func SetTarget(target Emitter) {
+	logMu.Lock()
+	defer logMu.Unlock()
+	oldLog := Log()
+	log.Store(&BasicLogger{Level: oldLog.Level, Emitter: target})
+}
+
+// SetLevel sets the log level.
+func SetLevel(newLevel Level) {
+	Log().SetLevel(newLevel)
+}
+
+// Debugf logs to the global logger.
+func Debugf(format string, v ...interface{}) {
+	Log().Debugf(format, v...)
+}
+
+// Infof logs to the global logger.
+func Infof(format string, v ...interface{}) {
+	Log().Infof(format, v...)
+}
+
+// Warningf logs to the global logger.
+func Warningf(format string, v ...interface{}) {
+	Log().Warningf(format, v...)
+}
+
+// defaultStackSize is the default buffer size to allocate for stack traces.
+const defaultStackSize = 1 << 16 // 64KB
+
+// maxStackSize is the maximum buffer size to allocate for stack traces.
+const maxStackSize = 1 << 26 // 64MB
+
+// stacks returns goroutine stacks, like panic.
+func stacks(all bool) []byte {
+	var trace []byte
+	for s := defaultStackSize; s <= maxStackSize; s *= 4 {
+		trace = make([]byte, s)
+		nbytes := runtime.Stack(trace, all)
+		if nbytes == s {
+			continue
+		}
+		return trace[:nbytes]
+	}
+	trace = append(trace, []byte("\n\n...<too large, truncated>")...)
+	return trace
+}
+
+// Traceback logs the given message and dumps a stacktrace of the current
+// goroutine.
+//
+// This will be print a traceback, tb, as Warningf(format+":\n%s", v..., tb).
+func Traceback(format string, v ...interface{}) {
+	v = append(v, stacks(false))
+	Warningf(format+":\n%s", v...)
+}
+
+// TracebackAll logs the given message and dumps a stacktrace of all goroutines.
+//
+// This will be print a traceback, tb, as Warningf(format+":\n%s", v..., tb).
+func TracebackAll(format string, v ...interface{}) {
+	v = append(v, stacks(true))
+	Warningf(format+":\n%s", v...)
+}
+
+// IsLogging returns whether the global logger is logging.
+func IsLogging(level Level) bool {
+	return Log().IsLogging(level)
+}
+
+// CopyStandardLogTo redirects the stdlib log package global output to the global
+// logger for the specified level.
+func CopyStandardLogTo(l Level) error {
+	var f func(string, ...interface{})
+
+	switch l {
+	case Debug:
+		f = Debugf
+	case Info:
+		f = Infof
+	case Warning:
+		f = Warningf
+	default:
+		return fmt.Errorf("Unknown log level %v", l)
+	}
+
+	stdlog.SetOutput(linewriter.NewWriter(func(p []byte) {
+		// We must not retain p, but log formatting is not required to
+		// be synchronous (though the in-package implementations are),
+		// so we must make a copy.
+		b := make([]byte, len(p))
+		copy(b, p)
+
+		f("%s", b)
+	}))
+
+	return nil
+}
+
+func init() {
+	// Store the initial value for the log.
+	log.Store(&BasicLogger{Level: Info, Emitter: GoogleEmitter{&Writer{Next: os.Stderr}}})
+}