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y2038

The year 2038 problem

All 32-bit kernels to date use a signed 32-bit time_t type, which can only represent time until January 2038. Since embedded systems running 32-bit Linux are going to survive beyond that date, we have to change all current uses, in a backwards compatible way.

User space interfaces

We will likely keep the 32-bit time_t in all user space interfaces that currently use it, but add new interfaces with a 64-bit timespec or another type that can represent later times. Most importantly that impacts system calls, but also specific ioctl commands and a few other interfaces. User space programs have to be recompiled to use the new interfaces, and the policy whether to use the old or the time time is left to the C library. While that policy is a complex topic itself, we don't cover it here.

System calls

interfaces that uses relative time_t/timespec/timeval

These can stay compatible, but we'd have to use a different type if we change time_t.

  • nanosleep

  • select/pselect/poll/ppoll/epoll

  • getrusage (+ wait4?)

  • sched_rr_get_interval

  • sigtimedwait

  • alarm

  • Also: futex, recvmmsg, io_getevents?

interfaces that don't make sense for times in the past

Here, we are relatively free to change the start of the epoch in the kernel but convert to something else on the user space boundary. One possibility is to scale them to boot time and use ktime_t in the kernel.

[Does checkpoint/restore have any implications here wrt to how freely we can change the start of the epoch? E.g., when freezing/restoring processed from different systems that have timer_settime() timers?]

  • getitimer/setitimer

  • timer_settime/timer_gettime(+timerfd_settime, timerfd_gettime?)

  • gettimeofday/settimeofday

  • adjtimex

  • clock_gettime/clock_settime/clock_adjtime/clock_nanosleep(? what about clock_nanosleep TIMER_ABSTIME?)

  • time/stime

  • sysv ipc (msg, sem, shm)

  • sysinfo

interfaces that require absolute times

These absolutely have to use something better than time_t both in user space and in the kernel so we can deal with old files. A lot of file systems need to be fixed as well so we can actually store the times, regardless of whether we are running a 32 or 64 bit kernel.

  • stat/lstat/fstatat/

  • utime/utimes/futimesa/utimensat

ioctl

There are numerous ioctl commands using a time argument. This list is incomplete

  • audio time stamps

  • v4l time stamps

  • input event time stamps

  • socket time stamps

  • ...

memory mapped packet sockets

Socket timestamps are exported to user space using a memory mapped interface defined in include/uapi/linux/if_packet.h. There are currently three versions of this interface, all use a 32-bit time type. We will likely need a version 4 to solve this.

File systems

Each file system stores its file modification times in its own format on disk, and a lot of them have the same problem.

file system

time type

expiration year

9p (9P2000)

unsigned 32-bit seconds

2106

9p (9P2000.L)

signed 64-bit seconds, ns

never

adfs

40-bit cs since 1900

2248

affs

u32 days/mins/(secs/50)

11760870

afs

unsigned 32-bit seconds

2106

befs

unsigned 48-bit seconds

never

bfs

unsigned 32-bit seconds

2106

btrfs

signed 64-bit seconds, 32-bit ns

never

ceph

unsigned 32-bit second/ns

2106

cifs (smb)

7-bit years since 1980

2107

cifs (modern)

64-bit 100ns since 1601

30328

coda

timespec ioctl

2038

cramfs

fixed

1970

efs

unsigned 32-bit seconds

2106

exofs

signed 32-bit seconds

2038

ext2

signed 32-bit seconds

2038

ext3

signed 32-bit seconds

2038

ext4 (good old inodes)

signed 32-bit seconds

2038

ext4 (new inodes

34 bit seconds / 30-bit ns (but broken)

2038

f2fs

64-bit seconds / 32-bit ns

never

fat

7-bit years since 1980, 2s resolution

2107

freevxfs

unsigned 32-bit seconds/u32 microseconds

2106

fuse

64-bit second/32-bit ns

never

gfs2

u64 seconds/u32 ns

never

hfs

u32 seconds since 1904

2040

hfsplus

u32 seconds since 1904

2040

hostfs

timespec

2038

hpfs

unsigned 32-bit seconds

2106

isofs

'char' year since 1900 (fixable)

2028 (!)

jffs2

unsigned 32-bit seconds

2106

jfs

unsigned 32-bit seconds/ns

2106

logfs

signed 64-bit ns

2262

minix

unsigned 32-bit seconds

2106

ncpfs

7-bit year since 1980

2107

nfsv2,v3

unsigned 32-bit seconds/ns

2106

nfsv4

u64 seconds/u32 ns

never

nfsd

unsigned 32-bit seconds/ns

2106

nilfs2

u64 seconds/u32 ns

never

ntfs

64-bit 100ns since 1601

30828

ocfs2

34-bit seconds/30-bit ns

2514

omfs

64-bit milliseconds

never

pstore

ascii seconds

2106

qnx4

unsigned 32-bit seconds

2106

qnx6

unsigned 32-bit seconds

2106

reiserfs

unsigned 32-bit seconds

2106

romfs

fixed

1970

squashfs

unsigned 32-bit seconds

2106

sysv

unsigned 32-bit seconds

2106

ubifs

u64 second/u32 ns

never

udf

u16 year

2038

ufs1

unsigned 32-bit seconds

2106

ufs2

signed 64-bit seconds/u32 ns

never

xfs

signed 32-bit seconds/ns

2106

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last edited 2014-06-02 15:01:01 by arnd