RFR: 8284330: jcmd may not be able to find processes in the container [v3]

[Thomas Stuefe]

On Fri, 8 Apr 2022 08:34:24 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> jcmd uses src/jdk.internal.jvmstat/linux/classes/sun/jvmstat/PlatformSupportImpl.java to scan temporary directories to find out processes in the container. It checks inode to ensure the temp directory is not conflicted. However inode maybe same value between the container and others. Thus we should check device id for that case.
>> 
>> For example I saw following case on [distroless cc-debian11](https://github.com/GoogleContainerTools/distroless/blob/main/cc/README.md) container. I started rescue:jdk19 container with sharing PID namespace. `/proc/1/root/tmp` is different from `/tmp` on rescue:jdk19, but they are same inode value. However we can see the differense in device id.
>> 
>> 
>> $ podman run -it --rm --entrypoint=sh --pid=container:fa39662f7352 rescue:jdk19
>> / #
>> / # stat /tmp
>>   File: /tmp
>>   Size: 29              Blocks: 0          IO Block: 4096   directory
>> Device: efh/239d        Inode: 135674931   Links: 1
>> Access: (1777/drwxrwxrwt)  Uid: (    0/    root)   Gid: (    0/    root)
>> Access: 2022-04-05 08:51:37.000000000
>> Modify: 2022-04-05 08:51:37.000000000
>> Change: 2022-04-05 08:51:37.000000000
>> 
>> / # stat /proc/1/root/tmp
>>   File: /proc/1/root/tmp
>>   Size: 29              Blocks: 0          IO Block: 4096   directory
>> Device: e1h/225d        Inode: 135674931   Links: 1
>> Access: (1777/drwxrwxrwt)  Uid: (    0/    root)   Gid: (    0/    root)
>> Access: 2022-04-05 08:51:37.000000000
>> Modify: 2022-04-05 08:50:42.000000000
>> Change: 2022-04-05 08:50:42.000000000
>
> Yasumasa Suenaga has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update the comment

still good

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PR: https://git.openjdk.java.net/jdk/pull/8103