Pay attention to DisableWritebackCaching.

connection.go

@@ -57,6 +57,7 @@ const maxReadahead = 1 << 20
 
 // A connection to the fuse kernel process.
 type Connection struct {
+	cfg         MountConfig
 	debugLogger *log.Logger
 	errorLogger *log.Logger
 
@@ -65,9 +66,6 @@ type Connection struct {
 	dev      *os.File
 	protocol fusekernel.Protocol
 
-	// The context from which all op contexts inherit.
-	parentCtx context.Context
-
 	mu sync.Mutex
 
 	// A map from fuse "unique" request ID (*not* the op ID for logging used
@@ -94,15 +92,15 @@ type opState struct {
 //
 // The loggers may be nil.
 func newConnection(
-	parentCtx context.Context,
+	cfg MountConfig,
 	debugLogger *log.Logger,
 	errorLogger *log.Logger,
 	dev *os.File) (c *Connection, err error) {
 	c = &Connection{
+		cfg:         cfg,
 		debugLogger: debugLogger,
 		errorLogger: errorLogger,
 		dev:         dev,
-		parentCtx:   parentCtx,
 		cancelFuncs: make(map[uint64]func()),
 	}
 
@@ -165,12 +163,10 @@ func (c *Connection) Init() (err error) {
 	// Tell the kernel not to use pitifully small 4 KiB writes.
 	initOp.Flags |= fusekernel.InitBigWrites
 
-	// TODO(jacobsa): Make this opt out and discuss benefits and caveats:
-	//  *  Write performance may be better (cf. http://thread.gmane.org/gmane.comp.file-systems.fuse.devel/13923)
-	//  *  (Discuss what writeback caching even means)
-	//  *  File systems need to implement setattr for dealing with kernel's stored time (find code reference)
-	//  *  File systems no longer "own" mtime; kernel will cache it even if no writes (cf. http://thread.gmane.org/gmane.comp.file-systems.fuse.devel/14808)
-	initOp.Flags |= fusekernel.InitWritebackCache
+	// Enable writeback caching if the user hasn't asked us not to.
+	if !c.cfg.DisableWritebackCaching {
+		initOp.Flags |= fusekernel.InitWritebackCache
+	}
 
 	c.Reply(ctx, nil)
 	return
@@ -234,7 +230,7 @@ func (c *Connection) beginOp(
 	opCode uint32,
 	fuseID uint64) (ctx context.Context) {
 	// Start with the parent context.
-	ctx = c.parentCtx
+	ctx = c.cfg.OpContext
 
 	// Set up a cancellation function.
 	//

mount.go

@@ -67,14 +67,14 @@ func Mount(
 	}
 
 	// Choose a parent context for ops.
-	opContext := config.OpContext
-	if opContext == nil {
-		opContext = context.Background()
+	cfgCopy := *config
+	if cfgCopy.OpContext == nil {
+		cfgCopy.OpContext = context.Background()
 	}
 
 	// Create a Connection object wrapping the device.
 	connection, err := newConnection(
-		opContext,
+		cfgCopy,
 		config.DebugLogger,
 		config.ErrorLogger,
 		dev)