cleanup: simplify some extract logic in sinsp_filtercheck_fd.cpp

[Andreagit97]

What type of PR is this?

/kind cleanup

Any specific area of the project related to this PR?

/area libsinsp

Does this PR require a change in the driver versions?

No

What this PR does / why we need it:

This PR cleans up some extraction logic. extract_from_null_fd was a too complex method for no reason.

I suggest reviewing it commit by commit.

This like other PRs I will open in the future should simplify this initiative #2068

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[github-actions]

Perf diff from master - unit tests

     5.18%     -1.24%  [.] sinsp_parser::process_event
     6.51%     +0.92%  [.] sinsp::next
     1.50%     -0.70%  [.] libsinsp::sinsp_suppress::process_event
     1.71%     -0.64%  [.] sinsp_parser::parse_context_switch
    10.10%     -0.60%  [.] sinsp_parser::reset
     2.08%     +0.48%  [.] scap_event_decode_params
     0.53%     +0.44%  [.] sinsp_evt::get_ts
     0.43%     +0.43%  [.] sinsp_threadinfo::sinsp_threadinfo
     0.32%     +0.40%  [.] sinsp_container_info::sinsp_container_info
     2.03%     -0.40%  [.] std::_Hashtable<long, std::pair<long const, std::shared_ptr<sinsp_threadinfo> >, std::allocator<std::pair<long const, std::shared_ptr<sinsp_threadinfo> > >, std::__detail::_Select1st, std::equal_to<long>, std::hash<long>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, false, true> >::_M_find_before_node

Heap diff from master - unit tests

peak heap memory consumption: 0B
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

Heap diff from master - scap file

peak heap memory consumption: 0B
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

Benchmarks diff from master

Comparing gbench_data.json to /root/actions-runner/_work/libs/libs/build/gbench_data.json
Benchmark                                                         Time             CPU      Time Old      Time New       CPU Old       CPU New
----------------------------------------------------------------------------------------------------------------------------------------------
BM_sinsp_split_mean                                            +0.0312         +0.0312           147           152           147           152
BM_sinsp_split_median                                          +0.0344         +0.0344           147           152           147           152
BM_sinsp_split_stddev                                          -0.3322         -0.3326             2             1             2             1
BM_sinsp_split_cv                                              -0.3524         -0.3527             0             0             0             0
BM_sinsp_concatenate_paths_relative_path_mean                  +0.0115         +0.0115            57            57            57            57
BM_sinsp_concatenate_paths_relative_path_median                +0.0047         +0.0047            57            57            57            57
BM_sinsp_concatenate_paths_relative_path_stddev                +3.7902         +3.8037             0             1             0             1
BM_sinsp_concatenate_paths_relative_path_cv                    +3.7357         +3.7490             0             0             0             0
BM_sinsp_concatenate_paths_empty_path_mean                     -0.0449         -0.0449            25            24            25            24
BM_sinsp_concatenate_paths_empty_path_median                   -0.0422         -0.0422            25            24            25            24
BM_sinsp_concatenate_paths_empty_path_stddev                   -0.7969         -0.7968             0             0             0             0
BM_sinsp_concatenate_paths_empty_path_cv                       -0.7873         -0.7872             0             0             0             0
BM_sinsp_concatenate_paths_absolute_path_mean                  +0.0141         +0.0141            56            57            56            57
BM_sinsp_concatenate_paths_absolute_path_median                +0.0129         +0.0129            56            57            56            57
BM_sinsp_concatenate_paths_absolute_path_stddev                +2.4904         +2.4884             0             1             0             1
BM_sinsp_concatenate_paths_absolute_path_cv                    +2.4418         +2.4398             0             0             0             0
BM_sinsp_split_container_image_mean                            -0.0119         -0.0119           396           391           396           391
BM_sinsp_split_container_image_median                          -0.0134         -0.0134           396           391           396           391
BM_sinsp_split_container_image_stddev                          +0.4117         +0.4095             1             2             1             2
BM_sinsp_split_container_image_cv                              +0.4287         +0.4264             0             0             0             0

[codecov]

Codecov Report

Attention: Patch coverage is 31.11111% with 31 lines in your changes missing coverage. Please review.

Project coverage is 74.55%. Comparing base (0ec8bac) to head (2c5dad8).
Report is 33 commits behind head on master.

Files with missing lines	Patch %	Lines
userspace/libsinsp/event.h	0.00%	25 Missing ⚠️
userspace/libsinsp/sinsp_filtercheck_fd.cpp	70.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2137      +/-   ##
==========================================
+ Coverage   74.46%   74.55%   +0.09%     
==========================================
  Files         254      254              
  Lines       33333    33293      -40     
  Branches     5721     5715       -6     
==========================================
+ Hits        24820    24822       +2     
+ Misses       8490     8450      -40     
+ Partials       23       21       -2     

Flag	Coverage Δ
libsinsp	74.55% <31.11%> (+0.09%)	⬆️

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[poiana]

LGTM label has been added.

Git tree hash: 3248a2cd3ecc8cd8b20d2932f93984a5b320eec0

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Andreagit97, FedeDP

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