feat(inputs.cgroup): Support more cgroup v2 formats

[psnszsn]

Summary

Add support for the following cgroup v2 formats:

• PSI format used by cpu.pressure, io.pressure and memory.pressure
• "max" as value
• space separated KEY=VAL used by hugetlb.*.numa_stat

Checklist

• No AI generated code was used in this PR

Related issues

resolves #16473

[telegraf-tiger]

Thanks so much for the pull request!
🤝 ✒️ Just a reminder that the CLA has not yet been signed, and we'll need it before merging. Please sign the CLA when you get a chance, then post a comment here saying !signed-cla

[srebhan]

Thanks for your contribution @psnszsn! Just one concern regarding potential type conflicts in the code.

[srebhan]

To be honest, this concerns me a bit as this calls for type conflicts. Imagine you get

MY_KEY=4

in a first gather cycle but

MY_KEY=3.14

in a second cycle. The very same field will be an integer in the first cycle but a float in the second cycle! This cases all sorts of issues on the output side. We've been there in the past...
I'm not sure if the issue exists for cgroups as the problem could be avoided if floats always contain a decimal separator but if that's not guaranteed I suggest to either have a named list of fields being float or to add a flag to always force fields into float (and not int).

[psnszsn]

As far as I understand the only files that have numbers with a fractional part are {cpu, io, memory}.pressure that use the PSI format.

They always have the decimal separator so in that case they will always be parsed as floats:

$ cat /sys/fs/cgroup/cpu.pressure
some avg10=0.00 avg60=0.00 avg300=0.00 total=397576165
full avg10=0.00 avg60=0.00 avg300=0.00 total=376593821

However, the issue you are describing could also happen for values that have "max" as the default but are otherwise ints... In that case what would be a good alternative to the "max" string? Maybe math.MaxInt64?

[srebhan]

Are fields with the max string always of the integer type? If so, math.MaxInt64 would be the best way to go. For the PSI/float metrics, it seems like they always contain the decimal separator (e.g. 0.00) so this should be good. Maybe add a comment to the code for the next one stumbling upon this?

[telegraf-tiger]

Download PR build artifacts for linux_amd64.tar.gz, darwin_arm64.tar.gz, and windows_amd64.zip.
Downloads for additional architectures and packages are available below.

🥳 This pull request decreases the Telegraf binary size by -1.62 % for linux amd64 (new size: 284.0 MB, nightly size 288.6 MB)

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Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz

[srebhan]

Awesome @psnszsn! Thanks for the quick updates and your contribution!

[DStrand1]

Thanks for the PR!