add option to enable kernel writeback cache

fuse/api.go

@@ -284,6 +284,13 @@ type MountOptions struct {
 	// directory queries (i.e. 'ls' without '-l') can be faster with
 	// ReadDir, as no per-file stat calls are needed
 	DisableReadDirPlus bool
+
+	// EnableWriteback enables kernel writeback cache.
+	//
+	// See writeback-cache in
+	// https://www.kernel.org/doc/Documentation/filesystems/fuse-io.txt
+	// for more details.
+	EnableWriteback bool
 }
 
 // RawFileSystem is an interface close to the FUSE wire protocol.

fuse/opcode.go

@@ -114,6 +114,9 @@ func doInit(server *Server, req *request) {
 	if server.opts.EnableAcl {
 		kernelFlags |= CAP_POSIX_ACL
 	}
+	if server.opts.EnableWriteback {
+		kernelFlags |= CAP_WRITEBACK_CACHE
+	}
 	if server.opts.SyncRead {
 		// Clear CAP_ASYNC_READ
 		kernelFlags &= ^uint64(CAP_ASYNC_READ)