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

System calls have been moved out "y2038/syscalls", that page is rather outdated, newer information is available at https://lwn.net/Articles/643234/

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.

Plan

1.Plan for VFS

1.2 Cleanup

• 1.2.1 Replace current_time and current_time_sec

  1.2.2 Fill in right granularities

  1.2.3 Fill in right ranges

1.3 Test

• 1.3.1 Test time written on disk and in memory are same

  1.3.2 Test time ranges beyond y2038

  1.3.3 Test time granularities are what the fs needs

  1.3.4 Test time ranges supported are same as what fs reports

  1.3.5 Perf tests

  1.3.6 Test to check i_dirty_* flags are updating correctly

  1.3.7 Test to check with different mount options like lazy atime etc.

1.4 Kernel tasks to transition vfs to use 64 bit times

• 1.4.1 Infrastructure patches for vfs_time approach

  1.4.2 Infrastructure patch for vfs granularity fields

  1.4.3 Change each fs to use vfs time patches

  1.4.4 Change vfs to use timespec64

  1.4.5 Expose fs granularities

  1.4.6 Expose fs ranges

  1.4.7 Add vfs policy for handling wrong ranges and granularity

  1.4.8 Stat and utime api changes

1.5 Runtime library

• 1.5.1 Make changes in one library

  1.5.2 Make it part of some userspace and run it

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.

Trivial tasks

Find a driver using time_t/timespec/timeval internally and convert it to ktime_t/timespec64, examples:

• drivers/firewire/core-cdev.c
• drivers/firewire/nosy.c
• drivers/hv/hv_util.c
• drivers/infiniband/hw/nes/
• drivers/misc/ibmasm/ibmasm.h
• drivers/net/wireless/atmel.c
• drivers/ide/pdc202xx_new.c
• fs/fuse/dir.c
• drivers/scsi/pmcraid.c

Small tasks

Find a driver using time_t/timespec/timeval internally and convert it to ktime_t/timespec64, examples:

• drivers/block/sx8.c
• drivers/char/ipmi/ipmi_ssif.c
• drivers/char/mmtimer.c
• drivers/cpufreq/speedstep-lib.c
• drivers/hsi/clients/cmt_speech.c
• drivers/media/platform/vivid/
• drivers/net/hamradio/baycom_ser_fdx.c

Medium tasks

• Modify an ioctl interface in a driver to support both 32- and 64-bit time interfaces, examples:
  • drivers/usb/misc/usbtest.c
• Convert the internal timekeeping in fs/nfsd
• Convert all 'struct key' users (time_t)
• fix all uses of timeval in drivers/scsi/bfa

Advanced tasks

• 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.
• start migrating the times in 'struct inode' and 'struct 'kstat' to separate 64-bit second + 32-bit nanosecond fields.

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.