Pidfd store

Pidfd store increases the reliability of pid reuse detection during pre-dumps/dumps using task pidfd instead of task creation time.

It is only supported for RPC and the C library.

Usage

A connectionless unix socket is passed to CRIU during each pre-dump/dump through the RPC option pidfd_store_sk or criu_set_pidfd_store_sk routine in the the library.

NOTE: This is targeted at migration tools like P.Haul, because the passed socket must be kept alive throughout all pre-dump/dump iterations.

Feature check

This feature requires pidfd_open and pidfd_getfd syscalls. Support could be checked with:

CLI: criu check --feature pidfd_store.

RPC: CRIU_REQ_TYPE__FEATURE_CHECK and set pidfd_store to true in the "features" field of the request

How it works

The pidfd_store_sk is used as a queue for task pidfds. CRIU sends tasks pidfds to this socket and receives them in the next pre-dump/dump iteration. Those pidfds could then be used to check whether the task is still alive, otherwise it is a case of pid reuse and CRIU should make a full page dump.