criu: Add pidfd support

[h0lyalg0rithm]

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[codecov-commenter]

Codecov Report

Patch coverage: 8.16% and project coverage change: -0.17% :warning:

Comparison is base (82bfb67) 70.67% compared to head (07b717f) 70.50%.

:exclamation: Current head 07b717f differs from pull request most recent head 9b0a7ce. Consider uploading reports for the commit 9b0a7ce to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##           criu-dev    #2259      +/-   ##
============================================
- Coverage     70.67%   70.50%   -0.17%     
============================================
  Files           133      135       +2     
  Lines         33330    33379      +49     
============================================
- Hits          23556    23534      -22     
- Misses         9774     9845      +71     

Files Changed	Coverage Δ
criu/cr-restore.c	67.38% <ø> (-0.19%)	:arrow_down:
criu/files.c	80.45% <0.00%> (-0.39%)	:arrow_down:
criu/include/pidfd.h	0.00% <0.00%> (ø)
criu/pidfd.c	0.00% <0.00%> (ø)
criu/proc_parse.c	67.96% <7.14%> (-0.58%)	:arrow_down:
criu/image.c	71.58% <100.00%> (+0.15%)	:arrow_up:

... and 6 files with indirect coverage changes

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[warusadura]

@h0lyalg0rithm Is it ok, if I write the zdtm test for this?

[h0lyalg0rithm]

@warusadura There is one bug that is to be fixed.Currently the patch lets you dump pidfd for processes which are not part of the current process tree.

I have the test prepared where I fork the test and have pidfd on the child process. But once you try to restore the process it fails as the child process is not created yet. One way to get around this is to wait until all the whole process tree is restored and then restore the pidfd.

I cannot think about any thing which doesnt sound hacky. What do you think?

[warusadura]

I cannot think about any thing which doesnt sound hacky. What do you think?

sorry @h0lyalg0rithm I'm not sure :)

[github-actions[bot]]

A friendly reminder that this PR had no activity for 30 days.

[rst0git]

closing in favour of https://github.com/checkpoint-restore/criu/pull/2449