[crac] RFR: Correct System.nanotime() value after restore [v4]

[Radim Vansa]

On Fri, 21 Apr 2023 14:52:49 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Set nanotime only if bootid changes
>
> src/hotspot/os/linux/os_linux.cpp line 6605:
> 
>> 6603: 
>> 6604: bool os::read_bootid(char *dest, size_t size) {
>> 6605:   int fd = ::open("/proc/sys/kernel/random/boot_id", O_RDONLY);
> 
> Bood_id looks interesting! But AFAICS it remains the same for each new container, and the boot time may have been adjusted for that container.
> 
> anton at mercury:~$ docker run -it ubuntu:20.04 cat /proc/sys/kernel/random/boot_id
> 9b913973-3082-471a-add5-6b802a04a9b2
> anton at mercury:~$ docker run -it ubuntu:20.04 cat /proc/sys/kernel/random/boot_id
> 9b913973-3082-471a-add5-6b802a04a9b2
> anton at mercury:~$ cat /proc/sys/kernel/random/boot_id
> 9b913973-3082-471a-add5-6b802a04a9b2
> 
> 
> Should not we mix something extra to boot_id, for example, a hostname (which is different for each container)?

The aim of this work is to prevent 'random' readings. New containers will keep the `boot_id` but their monotonic time *might* be adjusted, true. I agree with the comment above that in that case we should still ensure monotonicity, but since the readings are not 'random' I think that we can assume that the user did adjust monotonic time intentionally, and the application should observe that.

-------------

PR Review Comment: https://git.openjdk.org/crac/pull/53#discussion_r1173879844