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.
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.
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.
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 Syscalls affected by the above types:
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
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.
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]
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)
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. The year 2038 problem
User space interfaces
System calls
struct msqid_ds struct ppp_idle
struct semid_ds
struct timespec
struct timeval
struct scm_timestamping struct som_hdr struct itimerspec struct v4l2_event
struct snd_pcm_status
struct snd_pcm_mmap_status
struct snd_rawmidi_status
struct snd_timer_status
struct snd_timer_tread struct snd_ctl_elem_value
struct utimbuf
PPGETTIME PPSETTIME struct rusage struct itimerval struct timex struct v4l2_buffer File systems
Tasks
Small tasks
Medium tasks
Advanced tasks