Get the first pid of a namespace using bpf calls

[krishnacx]

Hi

As you are aware, Linux PID namespaces provide isolation of processes. Attached is the screenshot of list of processes running under a namespace and list of namespaces.

As shown in screenshot, there are 3 pid namespaces displaying its first pid and no of processes in current namespace.

I could figure out the namespace id of the any of the task running under a namespace from bpf_get_current_task() and subsequantly using BPF_CORE_READ APIs. I have referred the PR:#3647 for this. This was helpful. I want to figure out if there is mechanism to identify the first process(pid) of a given namespace using bpf APIs for any of the task.

Eg: For pidnsid of 4026532275, it should return 120.

Kindly assist.