Support for RHEL 4.18 kernels

[rafaelroquetto]

Relax the minimum supported version and tweak a few tests to allow Beyla to run on RHEL 4.8 kernel series.

From the package description:

"This is the package which provides the Linux kernel for Red Hat Enterprise
Linux. It is based on upstream Linux at version 4.18.0 and maintains kABI
compatibility of a set of approved symbols, however it is heavily modified with
backports and fixes pulled from newer upstream Linux kernel releases. This means
this is not a 4.18.0 kernel anymore: it includes several components which come
from newer upstream linux versions, while maintaining a well tested and stable
core. Some of the components/backports that may be pulled in are: changes like
updates to the core kernel (eg.: scheduler, cgroups, memory management, security
fixes and features), updates to block layer, supported filesystems, major driver
updates for supported hardware in Red Hat Enterprise Linux, enhancements for
enterprise customers, etc."

(source)

These are the kernels whose version is analogous to 4.18.0-xxx.el8 and they feature the functionality required by Beyla, included but not limited to:

• BTF support
• BPF ring buffers

Early RHEL 4.18 kernels (such as 4.18.0-240.el8) do not yet feature BPF ring buffers and are not supported.
These kernels do not support BEYLA_BPF_TRACK_REQUEST_HEADERS=1.

Tested on:

• CentOS 8 (4.18.0-348.7.1.el8_5.x86_64)
• AlmaLinux 8 (4.18.0-553.16.1.el8_10.x86_64)

Resolves #1146

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 81.13%. Comparing base (5c8c8c2) to head (6af03dd).

Files with missing lines	Patch %	Lines
pkg/internal/ebpf/instrumenter.go	0.00%	3 Missing ⚠️
pkg/beyla/os.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1175      +/-   ##
==========================================
- Coverage   81.16%   81.13%   -0.03%     
==========================================
  Files         136      136              
  Lines       11447    11451       +4     
==========================================
  Hits         9291     9291              
- Misses       1630     1634       +4     
  Partials      526      526              

Flag	Coverage Δ
integration-test	56.94% <16.66%> (-0.02%)	⬇️
k8s-integration-test	58.83% <16.66%> (-0.01%)	⬇️
oats-test	35.79% <16.66%> (-0.02%)	⬇️
unittests	53.51% <0.00%> (-0.05%)	⬇️

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[mariomac]

Amazing job!

[marctc]

Amazing, few lines you fixed this!

[grcevski]

LGTM! Great stuff @rafaelroquetto!