Time namespace

Two things (for now) we want to solve with this:

1. Shift timer's offsets
2. Make start-time remain "unchanged" after C/R
3. Continuous flow of monotonic time (CLOCK_MONOTONIC).

What about other kinds of counters like perf events and trace events?

TODO

Required in RFC

• selftests to test all we've added
• TIME_NS iffdefery everywhere

Maybe later

• CLONE_NEWTIME reuses the last free flag from sys_clone() - any way to still keep extensibility for the syscall?
• arm64/arm32/s390/power64 - add archs vvar support (nit: big/little-endianess for timespec::nsec)
• REALTIME-related:
  • REALTIME offsets
  • vvar offsets will need synchronization (like gtod_read_begin()/gtod_read_retry())
  • vfs modification/creation time should work
  • starttime in /proc/pid/stat
  • btime in /proc/stat
  • utime()/utimes()/futimesat() (with times == NULL)
  • utimensat()/futimens() - with UTIME_NOW
  • mq_timedsend()/mq_timedreceive()
  • semtimedop()
  • timerfd
  • timer_create()
  • COARSE times
  • clock_nanosleep()
• Adjtime (too complicated for PoC)
• Cpu time for thread/pid/pgid (times())
• /proc/stat ticks? (top uses them e.g.)
• pid creation time (probably different unrelated API)
• clock_tai - if we care about isolation from host's time

Git

• https://github.com/0x7f454c46/linux/tree/wip/time-ns

Links

• 09/2018 LWN: Time namespaces
• 09/2018 RFC 00/20 ns: Introduce Time Namespace
• 06/2018 The progress of Time namespace
• 04/2017 Two Objects not Namespaced by the Linux Kernel
• 04/2006 LWN: Virtual time
• 08/2015 What's missing from upstream kernel containers?
• 09/2009 LPC2009
• 00/2006 Multiple Instances of the Global Linux Namespaces
• 00/2017 VirtualTimeKernel
• 00/2016 Article about usage of time namespace in VirtualTimeKernel