Implement FUSE_RELEASE/RELEASEDIR

Fixes #3314

pkg/abi/linux/fuse.go

@@ -395,3 +395,21 @@ type FUSEOpenOut struct {
 
 	_ uint32
 }
+
+// FUSEReleaseIn is the request sent by the kernel to the daemon
+// when there is no more reference to a file.
+//
+// +marshal
+type FUSEReleaseIn struct {
+	// Fh is the file handler for the file to be released.
+	Fh uint64
+
+	// Flags of the file.
+	Flags uint32
+
+	// ReleaseFlags of this release request.
+	ReleaseFlags uint32
+
+	// LockOwner is the id of the lock owner if there is one.
+	LockOwner uint64
+}

pkg/sentry/fsimpl/fuse/dev.go

@@ -168,6 +168,9 @@ func (fd *DeviceFD) readLocked(ctx context.Context, dst usermem.IOSequence, opts
 
 			// We're done with this request.
 			fd.queue.Remove(req)
+			if req.hdr.Opcode == linux.FUSE_RELEASE {
+				fd.numActiveRequests -= 1
+			}
 
 			// Restart the read as this request was invalid.
 			log.Warningf("fuse.DeviceFD.Read: request found was too large. Restarting read.")
@@ -184,6 +187,9 @@ func (fd *DeviceFD) readLocked(ctx context.Context, dst usermem.IOSequence, opts
 		if readCursor >= req.hdr.Len {
 			// Fully done with this req, remove it from the queue.
 			fd.queue.Remove(req)
+			if req.hdr.Opcode == linux.FUSE_RELEASE {
+				fd.numActiveRequests -= 1
+			}
 			break
 		}
 	}

pkg/sentry/fsimpl/fuse/file.go

@@ -18,6 +18,8 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
@@ -54,8 +56,34 @@ func (fd *fileDescription) filesystem() *vfs.Filesystem {
 	return fd.vfsfd.VirtualDentry().Mount().Filesystem()
 }
 
+func (fd *fileDescription) statusFlags() uint32 {
+	return fd.vfsfd.StatusFlags()
+}
+
 // Release implements vfs.FileDescriptionImpl.Release.
-func (fd *fileDescription) Release(ctx context.Context) {}
+func (fd *fileDescription) Release(ctx context.Context) {
+	// no need to release if FUSE server doesn't implement Open.
+	conn := fd.inode().fs.conn
+	if conn.noOpen {
+		return
+	}
+
+	in := linux.FUSEReleaseIn{
+		Fh:    fd.Fh,
+		Flags: fd.statusFlags(),
+	}
+	// TODO(gvisor.dev/issue/3245): add logic when we support file lock owner.
+	var opcode linux.FUSEOpcode
+	if fd.inode().Mode().IsDir() {
+		opcode = linux.FUSE_RELEASEDIR
+	} else {
+		opcode = linux.FUSE_RELEASE
+	}
+	kernelTask := kernel.TaskFromContext(ctx)
+	// ignoring errors and FUSE server reply is analogous to Linux's behavior.
+	req, _ := conn.NewRequest(auth.CredentialsFromContext(ctx), uint32(kernelTask.ThreadID()), fd.inode().NodeID, opcode, &in)
+	conn.CallAsync(kernelTask, req)
+}
 
 // PRead implements vfs.FileDescriptionImpl.PRead.
 func (fd *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
@@ -82,7 +110,6 @@ func (fd *fileDescription) Seek(ctx context.Context, offset int64, whence int32)
 	return 0, nil
 }
 
-// Stat implements FileDescriptionImpl.Stat.
 // Stat implements vfs.FileDescriptionImpl.Stat.
 func (fd *fileDescription) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
 	fs := fd.filesystem()

test/fuse/BUILD

@@ -11,3 +11,8 @@ syscall_test(
     fuse = "True",
     test = "//test/fuse/linux:open_test",
 )
+
+syscall_test(
+    fuse = "True",
+    test = "//test/fuse/linux:release_test",
+)

test/fuse/linux/BUILD

@@ -31,6 +31,19 @@ cc_binary(
     ],
 )
 
+cc_binary(
+    name = "release_test",
+    testonly = 1,
+    srcs = ["release_test.cc"],
+    deps = [
+        gtest,
+        ":fuse_base",
+        "//test/util:fuse_util",
+        "//test/util:test_main",
+        "//test/util:test_util",
+    ],
+)
+
 cc_library(
     name = "fuse_base",
     testonly = 1,

test/fuse/linux/fuse_base.cc

@@ -387,7 +387,8 @@ void FuseTest::ServerProcessFuseRequest() {
 
   requests_.AddMemBlock(in_header->opcode, buf.data(), len);
 
-  if (in_header->opcode == FUSE_RELEASE) return;
+  if (in_header->opcode == FUSE_RELEASE || in_header->opcode == FUSE_RELEASEDIR)
+    return;
   // Check if there is a corresponding response.
   if (responses_.End()) {
     GTEST_NONFATAL_FAILURE_("No more FUSE response is expected");

test/fuse/linux/fuse_base.h

@@ -166,13 +166,13 @@ class FuseTest : public ::testing::Test {
  protected:
   TempPath mount_point_;
 
+  // Unmounts the mountpoint of the FUSE server.
+  void UnmountFuse();
+
  private:
   // Opens /dev/fuse and inherit the file descriptor for the FUSE server.
   void MountFuse();
 
-  // Unmounts the mountpoint of the FUSE server.
-  void UnmountFuse();
-
   // Creates a socketpair for communication and forks FUSE server.
   void SetUpFuseServer();
 

test/fuse/linux/open_test.cc

@@ -33,6 +33,10 @@ namespace testing {
 namespace {
 
 class OpenTest : public FuseTest {
+  // OpenTest doesn't care the release request when close a fd,
+  // so doesn't check leftover requests when tearing down.
+  void TearDown() { UnmountFuse(); }
+
  protected:
   const std::string test_file_ = "test_file";
   const mode_t regular_file_ = S_IFREG | S_IRWXU | S_IRWXG | S_IRWXO;

test/fuse/linux/release_test.cc

@@ -0,0 +1,74 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/fuse.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/statfs.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <string>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "test/fuse/linux/fuse_base.h"
+#include "test/util/fuse_util.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+class ReleaseTest : public FuseTest {
+ protected:
+  const std::string test_file_ = "test_file";
+};
+
+TEST_F(ReleaseTest, RegularFile) {
+  const std::string test_file_path =
+      JoinPath(mount_point_.path().c_str(), test_file_);
+  SetServerInodeLookup(test_file_, S_IFREG | S_IRWXU | S_IRWXG | S_IRWXO);
+
+  struct fuse_out_header out_header = {
+      .len = sizeof(struct fuse_out_header) + sizeof(struct fuse_open_out),
+  };
+  struct fuse_open_out out_payload = {
+      .fh = 1,
+      .open_flags = O_RDWR,
+  };
+  auto iov_out = FuseGenerateIovecs(out_header, out_payload);
+  SetServerResponse(FUSE_OPEN, iov_out);
+  FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(Open(test_file_path, O_RDWR));
+  SkipServerActualRequest();
+  ASSERT_THAT(close(fd.release()), SyscallSucceeds());
+
+  struct fuse_in_header in_header;
+  struct fuse_release_in in_payload;
+  auto iov_in = FuseGenerateIovecs(in_header, in_payload);
+  GetServerActualRequest(iov_in);
+
+  EXPECT_EQ(in_header.len, sizeof(in_header) + sizeof(in_payload));
+  EXPECT_EQ(in_header.opcode, FUSE_RELEASE);
+  EXPECT_EQ(in_payload.flags, O_RDWR);
+  EXPECT_EQ(in_payload.fh, 1);
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor