Add FUSE character device

This change adds a FUSE character device backed by devtmpfs. This
device will be used to establish a connection between the FUSE
server daemon and fusefs. The FileDescriptionImpl methods will
be implemented as we flesh out fusefs some more. The tests assert
that the device can be opened and used.

1 files changed, 54 insertions, 0 deletions

diff --git a/pkg/sentry/devices/miscdev/miscdev.go b/pkg/sentry/devices/miscdev/miscdev.go
new file mode 100644
index 000000000..500d92ed9
--- /dev/null
+++ b/pkg/sentry/devices/miscdev/miscdev.go
@@ -0,0 +1,54 @@
+// 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.
+
+// Package miscdev implements "misc" character devices, as implemented in Linux
+// by drivers/char/misc.c and fs/fuse/dev.c.
+package miscdev
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/devtmpfs"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+)
+
+// miscDevMajor is the major device number for devices defined in this package.
+const miscDevMajor = linux.MISC_MAJOR
+
+// Register registers all devices implemented by this package in vfsObj.
+func Register(vfsObj *vfs.VirtualFilesystem) error {
+	for minor, dev := range map[uint32]vfs.Device{
+		fuseDevMinor: fuseDevice{},
+	} {
+		if err := vfsObj.RegisterDevice(vfs.CharDevice, miscDevMajor, minor, dev, &vfs.RegisterDeviceOptions{
+			GroupName: "misc",
+		}); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// CreateDevtmpfsFiles creates device special files in dev representing all
+// devices implemented by this package.
+func CreateDevtmpfsFiles(ctx context.Context, dev *devtmpfs.Accessor) error {
+	for minor, name := range map[uint32]string{
+		fuseDevMinor: "fuse",
+	} {
+		if err := dev.CreateDeviceFile(ctx, name, vfs.CharDevice, miscDevMajor, minor, 0666 /* mode */); err != nil {
+			return err
+		}
+	}
+	return nil
+}