fuse: support MountOptions.DisableSplice

Change-Id: I929cf60fb5c04920754dd2a2e404d0afebdcd46c

fs/simple_test.go

@@ -61,6 +61,7 @@ type testOptions struct {
 	ro                bool
 	directMount       bool // sets MountOptions.DirectMount
 	directMountStrict bool // sets MountOptions.DirectMountStrict
+	disableSplice     bool // sets MountOptions.DisableSplice
 }
 
 // newTestCase creates the directories `orig` and `mnt` inside a temporary
@@ -111,6 +112,7 @@ func newTestCase(t *testing.T, opts *testOptions) *testCase {
 		DirectMount:       opts.directMount,
 		DirectMountStrict: opts.directMountStrict,
 		EnableLocks:       opts.enableLocks,
+		DisableSplice:     opts.disableSplice,
 	}
 	if !opts.suppressDebug {
 		mOpts.Debug = testutil.VerboseTest()
@@ -390,6 +392,14 @@ func TestPosix(t *testing.T) {
 	}
 }
 
+func TestReadDisableSplice(t *testing.T) {
+	tc := newTestCase(t, &testOptions{
+		disableSplice: true,
+	})
+
+	posixtest.FileBasic(t, tc.mntDir)
+}
+
 func TestOpenDirectIO(t *testing.T) {
 	// Apparently, tmpfs does not allow O_DIRECT, so try to create
 	// a test temp directory in /var/tmp.

fuse/api.go

@@ -329,6 +329,9 @@ 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
+
+	// Disable splicing from files to the FUSE device.
+	DisableSplice bool
 }
 
 // RawFileSystem is an interface close to the FUSE wire protocol.

fuse/server.go

@@ -693,6 +693,11 @@ func (ms *protocolServer) handleRequest(h *operationHandler, req *request) {
 		// This includes osxfuse (a.k.a. macfuse).
 		req.outHeader().Length = uint32(sizeOfOutHeader) + 24
 	}
+	if req.fdData != nil && ms.opts.DisableSplice {
+		req.outPayload, req.status = req.fdData.Bytes(req.outPayload)
+		req.fdData = nil
+	}
+
 	req.serializeHeader(req.outPayloadSize())
 
 	if ms.opts.Debug {

fuse/splice_linux.go

@@ -12,7 +12,7 @@ import (
 )
 
 func (s *Server) setSplice() {
-	s.canSplice = splice.Resizable()
+	s.canSplice = splice.Resizable() && !s.opts.DisableSplice
 }
 
 // trySplice:  Zero-copy read from fdData.Fd into /dev/fuse