1 files changed, 98 insertions, 0 deletions
diff --git a/pkg/log/log.go b/pkg/log/log.go
new file mode 100644
index 000000000..d57e8c1ad
--- /dev/null
+++ b/pkg/log/log.go
@@ -0,0 +1,98 @@
+// Copyright 2016 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+// log package provides functionality similar to standard log package with some extensions:
+//  - verbosity levels
+//  - global verbosity setting that can be used by multiple packages
+//  - ability to disable all output
+//  - ability to cache recent output in memory
+package log
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	golog "log"
+	"sync"
+	"time"
+)
+
+var (
+	flagV        = flag.Int("v", 0, "verbosity")
+	mu           sync.Mutex
+	cacheMem     int
+	cacheMaxMem  int
+	cachePos     int
+	cacheEntries []string
+	prependTime  = true // for testing
+)
+
+// EnableCaching enables in memory caching of log output.
+// Caches up to maxLines, but no more than maxMem bytes.
+// Cached output can later be queried with CachedOutput.
+func EnableLogCaching(maxLines, maxMem int) {
+	mu.Lock()
+	defer mu.Unlock()
+	if cacheEntries != nil {
+		Fatalf("log caching is already enabled")
+	}
+	if maxLines < 1 || maxMem < 1 {
+		panic("invalid maxLines/maxMem")
+	}
+	cacheMaxMem = maxMem
+	cacheEntries = make([]string, maxLines)
+}
+
+// Retrieves cached log output.
+func CachedLogOutput() string {
+	mu.Lock()
+	defer mu.Unlock()
+	buf := new(bytes.Buffer)
+	for i := range cacheEntries {
+		pos := (cachePos + i) % len(cacheEntries)
+		if cacheEntries[pos] == "" {
+			continue
+		}
+		buf.WriteString(cacheEntries[pos])
+		buf.Write([]byte{'\n'})
+	}
+	return buf.String()
+}
+
+func Logf(v int, msg string, args ...interface{}) {
+	mu.Lock()
+	doLog := v <= *flagV
+	if cacheEntries != nil && v <= 1 {
+		cacheMem -= len(cacheEntries[cachePos])
+		if cacheMem < 0 {
+			panic("log cache size underflow")
+		}
+		timeStr := ""
+		if prependTime {
+			timeStr = time.Now().Format("2006/01/02 15:04:05 ")
+		}
+		cacheEntries[cachePos] = fmt.Sprintf(timeStr+msg, args...)
+		cacheMem += len(cacheEntries[cachePos])
+		cachePos++
+		if cachePos == len(cacheEntries) {
+			cachePos = 0
+		}
+		for i := 0; i < len(cacheEntries)-1 && cacheMem > cacheMaxMem; i++ {
+			pos := (cachePos + i) % len(cacheEntries)
+			cacheMem -= len(cacheEntries[pos])
+			cacheEntries[pos] = ""
+		}
+		if cacheMem < 0 {
+			panic("log cache size underflow")
+		}
+	}
+	mu.Unlock()
+
+	if doLog {
+		golog.Printf(msg, args...)
+	}
+}
+
+func Fatalf(msg string, args ...interface{}) {
+	golog.Fatalf(msg, args...)
+}