// 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 ttydev implements a vfs.Device for /dev/tty.
package ttydev

import (
	"gvisor.dev/gvisor/pkg/abi/linux"
	"gvisor.dev/gvisor/pkg/context"
	"gvisor.dev/gvisor/pkg/errors/linuxerr"
	"gvisor.dev/gvisor/pkg/sentry/kernel"
	"gvisor.dev/gvisor/pkg/sentry/vfs"
)

const (
	// See drivers/tty/tty_io.c:tty_init().
	ttyDevMinor     = 0
	consoleDevMinor = 1
)

// ttyDevice implements vfs.Device for /dev/tty.
//
// +stateify savable
type ttyDevice struct{}

// Open implements vfs.Device.Open.
func (ttyDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
	t := kernel.TaskFromContext(ctx)
	if t == nil {
		return nil, linuxerr.ENXIO
	}
	tty := t.ThreadGroup().TTY()
	if tty == nil {
		return nil, linuxerr.ENXIO
	}
	// Opening /dev/tty does not set the controlling terminal. See Linux
	// tty_open().
	opts.Flags |= linux.O_NOCTTY
	return tty.Open(ctx, mnt, vfsd, opts)
}

// Register registers all devices implemented by this package in vfsObj.
func Register(vfsObj *vfs.VirtualFilesystem) error {
	return vfsObj.RegisterDevice(vfs.CharDevice, linux.TTYAUX_MAJOR, ttyDevMinor, ttyDevice{}, &vfs.RegisterDeviceOptions{
		GroupName: "tty",
		Pathname:  "tty",
		FilePerms: 0666,
	})
}