On 19/09/2018 22:50, Dmitry Safonov wrote: > From: Andrei Vagin <avagin@xxxxxxxxxx> > > Time Namespace isolates clock values. > > The kernel provides access to several clocks CLOCK_REALTIME, > CLOCK_MONOTONIC, CLOCK_BOOTTIME, etc. > > CLOCK_REALTIME > System-wide clock that measures real (i.e., wall-clock) time. > > CLOCK_MONOTONIC > Clock that cannot be set and represents monotonic time since > some unspecified starting point. > > CLOCK_BOOTTIME > Identical to CLOCK_MONOTONIC, except it also includes any time > that the system is suspended. > > For many users, the time namespace means the ability to changes time in > a container (CLOCK_REALTIME). > > But in a context of the checkpoint/restore functionality, monotonic and > bootime clocks become interesting. Both clocks are monotonic with > unspecified staring points. These clocks are widely used to measure time > slices, set timers. After restoring or migrating processes, we have to > guarantee that they never go backward. In an ideal case, the behavior of > these clocks should be the same as for a case when a whole system is > suspended. All this means that we need to be able to set CLOCK_MONOTONIC > and CLOCK_BOOTTIME clocks, what can be done by adding per-namespace > offsets for clocks. > > Link: https://criu.org/Time_namespace > Link: https://lists.openvz.org/pipermail/criu/2018-June/041504.html > Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx> > Co-developed-by: Dmitry Safonov <dima@xxxxxxxxxx> > Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx> > --- > fs/proc/namespaces.c | 3 + > include/linux/nsproxy.h | 1 + > include/linux/proc_ns.h | 1 + > include/linux/time_namespace.h | 59 ++++++++++++++ > include/linux/user_namespace.h | 1 + > include/uapi/linux/sched.h | 1 + > init/Kconfig | 7 ++ > kernel/Makefile | 1 + > kernel/fork.c | 3 +- > kernel/nsproxy.c | 19 ++++- > kernel/time_namespace.c | 169 +++++++++++++++++++++++++++++++++++++++++ > 11 files changed, 262 insertions(+), 3 deletions(-) > create mode 100644 include/linux/time_namespace.h > create mode 100644 kernel/time_namespace.c > ... > diff --git a/kernel/time_namespace.c b/kernel/time_namespace.c > new file mode 100644 > index 000000000000..902cd9c22159 > --- /dev/null > +++ b/kernel/time_namespace.c ... > + > +struct time_namespace init_time_ns = { > + .kref = KREF_INIT(2), > + .user_ns = &init_user_ns, > + .ns.inum = PROC_UTS_INIT_INO, Do you mean PROC_TIME_INIT_INO? > +#ifdef CONFIG_UTS_NS > + .ns.ops = &timens_operations, > +#endif Do you mean CONFIG_TIME_NS? Thanks, Laurent
