Discussions around time virtualization are there for a long time. The first attempt to implement time namespace was in 2006 by Jeff Dike. >From that time, the topic appears on and off in various discussions. There are two main use cases for time namespaces: 1. change date and time inside a container; 2. adjust clocks for a container restored from a checkpoint. “It seems like this might be one of the last major obstacles keeping migration from being used in production systems, given that not all containers and connections can be migrated as long as a time dependency is capable of messing it up.” (by github.com/dav-ell) The kernel provides access to several clocks: CLOCK_REALTIME, CLOCK_MONOTONIC, CLOCK_BOOTTIME. Last two clocks are monotonous, but the start points for them are not defined and are different for each running system. When a container is migrated from one node to another, all clocks have to be restored into consistent states; in other words, they have to continue running from the same points where they have been dumped. The main idea behind this patch set is adding per-namespace offsets for system clocks. When a process in a non-root time namespace requests time of a clock, a namespace offset is added to the current value of this clock on a host and the sum is returned. All offsets are placed on a separate page, this allows up to map it as part of vvar into user processes and use offsets from vdso calls. Now offsets are implemented for CLOCK_MONOTONIC and CLOCK_BOOTTIME clocks. Questions to discuss: * Clone flags exhaustion. Currently there is only one unused clone flag bit left, and it may be worth to use it to extend arguments of the clone system call. * Realtime clock implementation details: Is having a simple offset enough? What to do when date and time is changed on the host? Is there a need to adjust vfs modification and creation times? Implementation for adjtime() syscall. Cc: Dmitry Safonov <0x7f454c46@xxxxxxxxx> Cc: Adrian Reber <adrian@xxxxxxxx> Cc: Andrei Vagin <avagin@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Christian Brauner <christian.brauner@xxxxxxxxxx> Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jeff Dike <jdike@xxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Cc: Shuah Khan <shuah@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: containers@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: criu@xxxxxxxxxx Cc: linux-api@xxxxxxxxxxxxxxx Cc: x86@xxxxxxxxxx Andrei Vagin (12): ns: Introduce Time Namespace timens: Add timens_offsets timens: Introduce CLOCK_MONOTONIC offsets timens: Introduce CLOCK_BOOTTIME offset timerfd/timens: Take into account ns clock offsets kernel: Take into account timens clock offsets in clock_nanosleep x86/vdso/timens: Add offsets page in vvar x86/vdso: Use set_normalized_timespec() to avoid 32 bit overflow posix-timers/timens: Take into account clock offsets selftest/timens: Add test for timerfd selftest/timens: Add test for clock_nanosleep timens/selftest: Add timer offsets test Dmitry Safonov (8): timens: Shift /proc/uptime x86/vdso: Restrict splitting vvar vma x86/vdso: Purge timens page on setns()/unshare()/clone() x86/vdso: Look for vvar vma to purge timens page timens: Add align for timens_offsets timens: Optimize zero-offsets selftest: Add Time Namespace test for supported clocks timens/selftest: Add procfs selftest arch/Kconfig | 5 + arch/x86/Kconfig | 1 + arch/x86/entry/vdso/vclock_gettime.c | 52 +++++ arch/x86/entry/vdso/vdso-layout.lds.S | 9 +- arch/x86/entry/vdso/vdso2c.c | 3 + arch/x86/entry/vdso/vma.c | 67 +++++++ arch/x86/include/asm/vdso.h | 2 + fs/proc/namespaces.c | 3 + fs/proc/uptime.c | 3 + fs/timerfd.c | 16 +- include/linux/nsproxy.h | 1 + include/linux/proc_ns.h | 1 + include/linux/time_namespace.h | 72 +++++++ include/linux/timens_offsets.h | 25 +++ include/linux/user_namespace.h | 1 + include/uapi/linux/sched.h | 1 + init/Kconfig | 8 + kernel/Makefile | 1 + kernel/fork.c | 3 +- kernel/nsproxy.c | 19 +- kernel/time/hrtimer.c | 8 + kernel/time/posix-timers.c | 89 ++++++++- kernel/time/posix-timers.h | 2 + kernel/time_namespace.c | 230 +++++++++++++++++++++++ tools/testing/selftests/timens/.gitignore | 5 + tools/testing/selftests/timens/Makefile | 6 + tools/testing/selftests/timens/clock_nanosleep.c | 98 ++++++++++ tools/testing/selftests/timens/config | 1 + tools/testing/selftests/timens/log.h | 21 +++ tools/testing/selftests/timens/procfs.c | 145 ++++++++++++++ tools/testing/selftests/timens/timens.c | 196 +++++++++++++++++++ tools/testing/selftests/timens/timer.c | 95 ++++++++++ tools/testing/selftests/timens/timerfd.c | 96 ++++++++++ 33 files changed, 1272 insertions(+), 13 deletions(-) create mode 100644 include/linux/time_namespace.h create mode 100644 include/linux/timens_offsets.h create mode 100644 kernel/time_namespace.c create mode 100644 tools/testing/selftests/timens/.gitignore create mode 100644 tools/testing/selftests/timens/Makefile create mode 100644 tools/testing/selftests/timens/clock_nanosleep.c create mode 100644 tools/testing/selftests/timens/config create mode 100644 tools/testing/selftests/timens/log.h create mode 100644 tools/testing/selftests/timens/procfs.c create mode 100644 tools/testing/selftests/timens/timens.c create mode 100644 tools/testing/selftests/timens/timer.c create mode 100644 tools/testing/selftests/timens/timerfd.c -- 2.13.6
