// Copyright 2018 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 linux

import (
	"fmt"
	"strings"

	"gvisor.dev/gvisor/pkg/abi"
	"gvisor.dev/gvisor/pkg/binary"
)

// Constants for open(2).
const (
	O_ACCMODE   = 000000003
	O_RDONLY    = 000000000
	O_WRONLY    = 000000001
	O_RDWR      = 000000002
	O_CREAT     = 000000100
	O_EXCL      = 000000200
	O_NOCTTY    = 000000400
	O_TRUNC     = 000001000
	O_APPEND    = 000002000
	O_NONBLOCK  = 000004000
	O_DSYNC     = 000010000
	O_ASYNC     = 000020000
	O_DIRECT    = 000040000
	O_LARGEFILE = 000100000
	O_DIRECTORY = 000200000
	O_NOFOLLOW  = 000400000
	O_NOATIME   = 001000000
	O_CLOEXEC   = 002000000
	O_SYNC      = 004000000 // __O_SYNC in Linux
	O_PATH      = 010000000
	O_TMPFILE   = 020000000 // __O_TMPFILE in Linux
)

// Constants for fstatat(2).
const (
	AT_SYMLINK_NOFOLLOW = 0x100
)

// Constants for mount(2).
const (
	MS_RDONLY      = 0x1
	MS_NOSUID      = 0x2
	MS_NODEV       = 0x4
	MS_NOEXEC      = 0x8
	MS_SYNCHRONOUS = 0x10
	MS_REMOUNT     = 0x20
	MS_MANDLOCK    = 0x40
	MS_DIRSYNC     = 0x80
	MS_NOATIME     = 0x400
	MS_NODIRATIME  = 0x800
	MS_BIND        = 0x1000
	MS_MOVE        = 0x2000
	MS_REC         = 0x4000

	MS_POSIXACL    = 0x10000
	MS_UNBINDABLE  = 0x20000
	MS_PRIVATE     = 0x40000
	MS_SLAVE       = 0x80000
	MS_SHARED      = 0x100000
	MS_RELATIME    = 0x200000
	MS_KERNMOUNT   = 0x400000
	MS_I_VERSION   = 0x800000
	MS_STRICTATIME = 0x1000000

	MS_MGC_VAL = 0xC0ED0000
	MS_MGC_MSK = 0xffff0000
)

// Constants for umount2(2).
const (
	MNT_FORCE       = 0x1
	MNT_DETACH      = 0x2
	MNT_EXPIRE      = 0x4
	UMOUNT_NOFOLLOW = 0x8
)

// Constants for unlinkat(2).
const (
	AT_REMOVEDIR = 0x200
)

// Constants for linkat(2) and fchownat(2).
const (
	AT_SYMLINK_FOLLOW = 0x400
	AT_EMPTY_PATH     = 0x1000
)

// Constants for all file-related ...at(2) syscalls.
const (
	AT_FDCWD = -100
)

// Special values for the ns field in utimensat(2).
const (
	UTIME_NOW  = ((1 << 30) - 1)
	UTIME_OMIT = ((1 << 30) - 2)
)

// MaxSymlinkTraversals is the maximum number of links that will be followed by
// the kernel to resolve a symlink.
const MaxSymlinkTraversals = 40

// Constants for flock(2).
const (
	LOCK_SH = 1 // shared lock
	LOCK_EX = 2 // exclusive lock
	LOCK_NB = 4 // or'd with one of the above to prevent blocking
	LOCK_UN = 8 // remove lock
)

// Values for mode_t.
const (
	S_IFMT   = 0170000
	S_IFSOCK = 0140000
	S_IFLNK  = 0120000
	S_IFREG  = 0100000
	S_IFBLK  = 060000
	S_IFDIR  = 040000
	S_IFCHR  = 020000
	S_IFIFO  = 010000

	FileTypeMask        = S_IFMT
	ModeSocket          = S_IFSOCK
	ModeSymlink         = S_IFLNK
	ModeRegular         = S_IFREG
	ModeBlockDevice     = S_IFBLK
	ModeDirectory       = S_IFDIR
	ModeCharacterDevice = S_IFCHR
	ModeNamedPipe       = S_IFIFO

	ModeSetUID = 04000
	ModeSetGID = 02000
	ModeSticky = 01000

	ModeUserAll     = 0700
	ModeUserRead    = 0400
	ModeUserWrite   = 0200
	ModeUserExec    = 0100
	ModeGroupAll    = 0070
	ModeGroupRead   = 0040
	ModeGroupWrite  = 0020
	ModeGroupExec   = 0010
	ModeOtherAll    = 0007
	ModeOtherRead   = 0004
	ModeOtherWrite  = 0002
	ModeOtherExec   = 0001
	PermissionsMask = 0777
)

// Values for linux_dirent64.d_type.
const (
	DT_UNKNOWN = 0
	DT_FIFO    = 1
	DT_CHR     = 2
	DT_DIR     = 4
	DT_BLK     = 6
	DT_REG     = 8
	DT_LNK     = 10
	DT_SOCK    = 12
	DT_WHT     = 14
)

// Values for preadv2/pwritev2.
const (
	RWF_HIPRI = 0x00000001
	RWF_DSYNC = 0x00000002
	RWF_SYNC  = 0x00000004
	RWF_VALID = RWF_HIPRI | RWF_DSYNC | RWF_SYNC
)

// Stat represents struct stat.
type Stat struct {
	Dev     uint64
	Ino     uint64
	Nlink   uint64
	Mode    uint32
	UID     uint32
	GID     uint32
	_       int32
	Rdev    uint64
	Size    int64
	Blksize int64
	Blocks  int64
	ATime   Timespec
	MTime   Timespec
	CTime   Timespec
	_       [3]int64
}

// SizeOfStat is the size of a Stat struct.
var SizeOfStat = binary.Size(Stat{})

// Flags for statx.
const (
	AT_STATX_SYNC_TYPE    = 0x6000
	AT_STATX_SYNC_AS_STAT = 0x0000
	AT_STATX_FORCE_SYNC   = 0x2000
	AT_STATX_DONT_SYNC    = 0x4000
)

// Mask values for statx.
const (
	STATX_TYPE        = 0x00000001
	STATX_MODE        = 0x00000002
	STATX_NLINK       = 0x00000004
	STATX_UID         = 0x00000008
	STATX_GID         = 0x00000010
	STATX_ATIME       = 0x00000020
	STATX_MTIME       = 0x00000040
	STATX_CTIME       = 0x00000080
	STATX_INO         = 0x00000100
	STATX_SIZE        = 0x00000200
	STATX_BLOCKS      = 0x00000400
	STATX_BASIC_STATS = 0x000007ff
	STATX_BTIME       = 0x00000800
	STATX_ALL         = 0x00000fff
	STATX__RESERVED   = 0x80000000
)

// Bitmasks for Statx.Attributes and Statx.AttributesMask, from
// include/uapi/linux/stat.h.
const (
	STATX_ATTR_COMPRESSED = 0x00000004
	STATX_ATTR_IMMUTABLE  = 0x00000010
	STATX_ATTR_APPEND     = 0x00000020
	STATX_ATTR_NODUMP     = 0x00000040
	STATX_ATTR_ENCRYPTED  = 0x00000800
	STATX_ATTR_AUTOMOUNT  = 0x00001000
)

// Statx represents struct statx.
type Statx struct {
	Mask           uint32
	Blksize        uint32
	Attributes     uint64
	Nlink          uint32
	UID            uint32
	GID            uint32
	Mode           uint16
	Ino            uint64
	Size           uint64
	Blocks         uint64
	AttributesMask uint64
	Atime          StatxTimestamp
	Btime          StatxTimestamp
	Ctime          StatxTimestamp
	Mtime          StatxTimestamp
	RdevMajor      uint32
	RdevMinor      uint32
	DevMajor       uint32
	DevMinor       uint32
}

// FileMode represents a mode_t.
type FileMode uint

// Permissions returns just the permission bits.
func (m FileMode) Permissions() FileMode {
	return m & PermissionsMask
}

// FileType returns just the file type bits.
func (m FileMode) FileType() FileMode {
	return m & FileTypeMask
}

// ExtraBits returns everything but the file type and permission bits.
func (m FileMode) ExtraBits() FileMode {
	return m &^ (PermissionsMask | FileTypeMask)
}

// String returns a string representation of m.
func (m FileMode) String() string {
	var s []string
	if ft := m.FileType(); ft != 0 {
		s = append(s, fileType.Parse(uint64(ft)))
	}
	if eb := m.ExtraBits(); eb != 0 {
		s = append(s, modeExtraBits.Parse(uint64(eb)))
	}
	s = append(s, fmt.Sprintf("0o%o", m.Permissions()))
	return strings.Join(s, "|")
}

var modeExtraBits = abi.FlagSet{
	{
		Flag: ModeSetUID,
		Name: "S_ISUID",
	},
	{
		Flag: ModeSetGID,
		Name: "S_ISGID",
	},
	{
		Flag: ModeSticky,
		Name: "S_ISVTX",
	},
}

var fileType = abi.ValueSet{
	ModeSocket:          "S_IFSOCK",
	ModeSymlink:         "S_IFLINK",
	ModeRegular:         "S_IFREG",
	ModeBlockDevice:     "S_IFBLK",
	ModeDirectory:       "S_IFDIR",
	ModeCharacterDevice: "S_IFCHR",
	ModeNamedPipe:       "S_IFIFO",
}

// Constants for memfd_create(2). Source: include/uapi/linux/memfd.h
const (
	MFD_CLOEXEC       = 0x0001
	MFD_ALLOW_SEALING = 0x0002
)

// Constants related to file seals. Source: include/uapi/{asm-generic,linux}/fcntl.h
const (
	F_LINUX_SPECIFIC_BASE = 1024
	F_ADD_SEALS           = F_LINUX_SPECIFIC_BASE + 9
	F_GET_SEALS           = F_LINUX_SPECIFIC_BASE + 10

	F_SEAL_SEAL   = 0x0001 // Prevent further seals from being set.
	F_SEAL_SHRINK = 0x0002 // Prevent file from shrinking.
	F_SEAL_GROW   = 0x0004 // Prevent file from growing.
	F_SEAL_WRITE  = 0x0008 // Prevent writes.
)

// Constants related to fallocate(2). Source: include/uapi/linux/falloc.h
const (
	FALLOC_FL_KEEP_SIZE      = 0x01
	FALLOC_FL_PUNCH_HOLE     = 0x02
	FALLOC_FL_NO_HIDE_STALE  = 0x04
	FALLOC_FL_COLLAPSE_RANGE = 0x08
	FALLOC_FL_ZERO_RANGE     = 0x10
	FALLOC_FL_INSERT_RANGE   = 0x20
	FALLOC_FL_UNSHARE_RANGE  = 0x40
)