''unfortunately this page got deleted by accident, this version is restored from [https://web.archive.org/web/20150318062024/http://kernelnewbies.org/y2038], but most of the formatting is still missing.
== 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.
Audit of include/uapi for time_t impact
Structure and IOCTL dependency:
time_t
struct msqid64_ds (has 2038 padding!)
struct semid64_ds (has 2038 padding!)
struct cyclades_idle_stats
struct video_event
VIDEO_GET_EVENT
struct msqid_ds
struct ppp_idle
PPPIOCGIDLE
struct semid_ds
union semun
struct timespec
SIOCGSTAMPNS
struct coda_vattr
...
struct scm_timestamping
struct som_hdr
struct itimerspec
struct v4l2_event
VIDIOC_DQEVENT
struct snd_pcm_status
SNDRV_PCM_IOCTL_STATUS
struct snd_pcm_mmap_status
struct snd_pcm_sync_ptr
SNDRV_PCM_IOCTL_SYNC_PTR
struct snd_rawmidi_status
SNDRV_RAWMIDI_IOCTL_STATUS
struct snd_timer_status
SNDRV_TIMER_IOCTL_STATUS
struct snd_timer_tread
struct snd_ctl_elem_value
SNDRV_CTL_IOCTL_ELEM_READ
SNDRV_CTL_IOCTL_ELEM_WRITE
struct timeval
SIOCGSTAMP
struct zatm_t_hist
struct bcm_msg_head
struct elf_prstatus
struct input_event
struct omap3isp_stat_data
VIDIOC_OMAP3ISP_STAT_REQ
PPGETTIME
PPSETTIME
struct rusage
struct itimerval
struct timex
struct v4l2_buffer
VIDIOC_QUERYBUF
VIDIOC_QBUF
VIDIOC_DQBUF
VIDIOC_PREPARE_BUF
struct utimbuf
Syscalls affected by the above types:
sys_time
sys_stime
sys_nanosleep
sys_clock_settime
sys_clock_gettime
sys_clock_getres
sys_clock_nanosleep
sys_sched_rr_get_interval
sys_futex
sys_rt_sigtimedwait
sys_io_getevents
sys_recvmmsg
sys_semtimedop
sys_mq_timedsend
sys_mq_timedreceive
sys_utimensat
sys_pselect6
sys_ppoll
sys_gettimeofday
sys_settimeofday
sys_utimes
sys_select
sys_futimesat
sys_utime
sys_timer_gettime
sys_timer_settime
sys_timerfd_settime
sys_timerfd_gettime
sys_wait4
sys_waitid
sys_getrusage
sys_getitimer
sys_setitimer
sys_adjtimex
sys_clock_adjtime
=== 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
=== Tasks ===
The task list is for people that want to get involved, there will be many more tasks over time, so this is just a starting point. In the end, we should remove all instances of 'time_t', 'timespec' and 'timeval' from the kernel.
==== Small tasks ====
Find a driver using time_t/timespec/timeval internally and convert it to ktime_t/timespec64, examples:
drivers/staging/media/lirc/lirc_imon.c (timeval, trivial)
drivers/staging/ft1000/ (time_t and timeval)
drivers/staging/android/sync_debug.c (timeval, very easy)
drivers/staging/android/timed_gpio.c (timeval, easy)
drivers/staging/bcm/LeakyBucket.c (timeval, slightly tricky)
drivers/staging/bcm/Bcmchar.c (timeval, very easy)
drivers/staging/comedi/drivers/comedi_test.c (timeval)
drivers/staging/comedi/drivers/serial2002.c (timeval, easy)
drivers/staging/dgnc/dgnc_tty.c (timeval, very easy)
drivers/staging/gdm72xx/ (timeval, easy)
drivers/staging/media/lirc/lirc_igorplugusb.c (timeval)
drivers/staging/media/lirc/lirc_parallel.c (timeval, easy)
drivers/staging/media/lirc/lirc_sasem.c (timeval, very easy)
drivers/staging/media/lirc/lirc_serial.c (timeval, easy)
drivers/staging/media/lirc/lirc_sir.c (timeval)
drivers/staging/rts5208/rtsx.h (timeval)
drivers/staging/olpc_dcon/olpc_dcon.c (timespec, rather broken)
drivers/staging/ozwpan/ozhcd.c (timespec)
drivers/staging/ozwpan/ozproto.c (timespec)
kernel/cpuset.c (time_t) [Status: Completed, Heena Sirwani]
fs/reiserfs/journal.c (time_t)
drivers/scsi/ips.c (time_t)
sound/pci/es1968.c (timeval) [Status: Completed, Tina Ruchandani]
kernel/power/hibernate.c (timeval) [Status: Completed, Tina Ruchandani]
drivers/s390/net/ctcm_fsms.c (timespec) [Status: Completed, Aya Mahfouz]
drivers/power/ab8500_fg.c (timespec) [Status: Completed, Ebru Akagunduz]
==== Medium tasks ====
Modify an ioctl interface in a driver to support both 32- and 64-bit time interfaces, examples:
drivers/staging/comedi/comedi_fops.c (INSN_GTOD, timeval)
drivers/staging/android/alarm-dev.c (timespec)
include/uapi/linux/atm_zatm.h (zatm_t_hist/timeval)
include/uapi/linux/videodev2.h (v4l2_buffer/timespec)
Fix the android logger time format (drivers/staging/android/logger.c)
Convert the internal timekeeping in fs/nfsd
Convert all 'ptp' users in the kernel
Convert all 'struct key' users (time_t)
Introduce known unsafe types (possibly like kernel_time32_t, kernel_compat_time_t etc) so we can annotate interfaces that are known to use a fixed size and cannot be changed to new types.
Fix all time issues in drivers/staging/lustre (maybe advanced task)
==== Advanced tasks ====
Introduce a new system call family to replace one or more of the problematic calls listed above.
Change the on-disk layout of a broken file system to optionally support longer time stamps
Port a small C library (uClibc, newlib, ...) to optionally use 64-bit time_t and build an embedded distribution (openembedded, openwrt, buildroot, ...) with this.
Tasks later in the project
Hook up all 32-bit architectures to use the new system calls
Introduce a Kconfig symbol to disable all code that has not yet been converted at compile time.