Enable Configurable Maximum Buffer Size for FUSE Messages

connection.go

@@ -80,6 +80,8 @@ type Connection struct {
 	// Freelists, serviced by freelists.go.
 	inMessages  freelist.Freelist // GUARDED_BY(mu)
 	outMessages freelist.Freelist // GUARDED_BY(mu)
+
+	inMessageSize int
 }
 
 // State that is maintained for each in-flight op. This is stuffed into the
@@ -121,6 +123,12 @@ func newConnection(
 		cancelFuncs: make(map[uint64]func()),
 	}
 
+	maxPayload := max(buffer.MaxReadSize, buffer.MaxWriteSize)
+	if cfg.MaxMessageSize > 0 {
+		maxPayload = max(maxPayload, int(cfg.MaxMessageSize))
+	}
+	c.inMessageSize = maxPayload + buffer.GetPageSize()
+
 	// Initialize.
 	if err := c.Init(); err != nil {
 		c.close()
@@ -172,7 +180,9 @@ func (c *Connection) Init() error {
 	// Respond to the init op.
 	initOp.Library = c.protocol
 	initOp.MaxReadahead = maxReadahead
-	initOp.MaxWrite = buffer.MaxWriteSize
+
+	maxPayload := c.inMessageSize - buffer.GetPageSize()
+	initOp.MaxWrite = uint32(maxPayload)
 
 	initOp.Flags = 0
 
@@ -190,7 +200,6 @@ func (c *Connection) Init() error {
 	// payload. It applies to both requests and replies, and does not include
 	// the extra 1 page for the FUSE header and the "args" struct. We set it to
 	// the max of our message in/out payload sizes.
-	maxPayload := max(buffer.MaxReadSize, buffer.MaxWriteSize)
 	initOp.MaxPages = uint16(maxPayload / buffer.GetPageSize())
 
 	// Enable writeback caching if the user hasn't asked us not to.

freelists.go

@@ -31,7 +31,7 @@ func (c *Connection) getInMessage() *buffer.InMessage {
 	c.mu.Unlock()
 
 	if x == nil {
-		x = buffer.NewInMessage()
+		x = buffer.NewInMessage(c.inMessageSize)
 	}
 
 	return x

internal/buffer/in_message.go

@@ -28,13 +28,8 @@ import (
 // this.
 var pageSize int
 
-// We size the buffer to have enough room for a fuse request plus data
-// associated with a write request.
-var bufSize int
-
 func init() {
 	pageSize = syscall.Getpagesize()
-	bufSize = pageSize + MaxWriteSize
 }
 
 // Return the hardware page size. Note that this is not always 4KiB! Notably
@@ -53,9 +48,9 @@ type InMessage struct {
 }
 
 // NewInMessage creates a new InMessage with its storage initialized.
-func NewInMessage() *InMessage {
+func NewInMessage(size int) *InMessage {
 	return &InMessage{
-		storage: make([]byte, bufSize),
+		storage: make([]byte, size),
 	}
 }
 

mount_config.go

@@ -241,6 +241,10 @@ type MountConfig struct {
 	// to always provide ReadFileOp.Dst. If the file system populates ReadFileOp.Data,
 	// that data will be used for a vectored read, irrespective of this flag's value.
 	UseVectoredRead bool
+
+	// The maximum size of a FUSE message (in bytes) that the daemon is
+	// prepared to read or write. If not set, defaults to 1 MiB.
+	MaxMessageSize uint32
 }
 
 type FUSEImpl uint8