Implement chcpu

[alxndrv]

This PR implements pretty much the entirety of chcpu.

Some things still missing:

• Tests: I'm not entirely sure how to properly test something which is so tightly coupled to system internals.
• Exit codes: chcpu should return a non-zero exit code in some edge cases. This implementation does check for most such cases, but pretty much always returns a success exit-code. I'm guessing that uucore::error::UResult can be used to solve this somehow without having to manually call std::process::exit().

[sylvestre]

in general, to test such things, you either try to mock up
and you do your best to look at the error management

[alxndrv]

@sylvestre Thanks for the review, I'll implement your suggestions a bit later. Since we're on the topic of deduping: there's some code here that's copy-pasted from my work on lscpu (the parse_cpu_list() function). Should there be some kind of "lib" crate for common stuff like this? These kinds of CPU lists come up in a bunch of Linux utils and theres no sense in implementing it all over again every time. There's other similar examples: for example the mount-related utils all have to parse mount entries from /proc/<pid>/mountinfo and could benefit from having a shared lib.

[sylvestre]

Should there be some kind of "lib" crate for common stuff like this?

yes, we try to publish content in uucore
https://docs.rs/uucore/latest/uucore/

[Copilot]

PR Overview

This PR implements the new chcpu utility for managing CPU states via enabling, disabling, configuring, and dispatching mode management. Key changes include:

• Adding package configuration and build targets for chcpu.
• Implementing core CPU management functions with system file interaction and error handling placeholders.
• Providing documentation and updating the global Cargo.toml feature flags.

Reviewed Changes

File	Description
src/uu/chcpu/Cargo.toml	Defines package configuration for chcpu.
src/uu/chcpu/src/chcpu.rs	Implements CPU management functionality (enable, disable, etc.).
src/uu/chcpu/chcpu.md	Adds documentation for the chcpu command.
src/uu/chcpu/src/main.rs	Defines the main entry point for chcpu.
Cargo.toml	Updates feature flags to include chcpu.

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Comments suppressed due to low confidence (2)

src/uu/chcpu/src/chcpu.rs:186

• [nitpick] On failure to trigger a CPU rescan, handling the error with a proper exit code would improve reliability instead of only printing a message.

Err(e) => println!("Failed to trigger rescan of CPUs: {}", e.kind()),

src/uu/chcpu/src/chcpu.rs:230

• [nitpick] Consider returning an appropriate error with a non-zero exit code when the dispatching mode is unsupported, following the TODO guidance.

if !path.exists() {

[Copilot]

Calling panic! on an unexpected CPU online state can cause abrupt termination. Consider returning an error or handling the unexpected state more gracefully.

Suggested change

	fn is_online(&self) -> bool {
	fs::read_to_string(self.get_path().join("online"))
	.map(|content| match content.trim() {
	"0" => false,
	"1" => true,
	other => panic!("Unrecognized CPU online state: {}", other),
	})
	// Just in case the caller forgot to check `is_hotpluggable` first,
	// instead of panicing that the file doesn't exist, return true
	// This is because a non-hotpluggable CPU is assumed to be always online
	.unwrap_or(true)
	fn is_online(&self) -> Result<bool, String> {
	fs::read_to_string(self.get_path().join("online"))
	.map(|content| match content.trim() {
	"0" => Ok(false),
	"1" => Ok(true),
	other => Err(format!("Unrecognized CPU online state: {}", other)),
	})
	// Just in case the caller forgot to check `is_hotpluggable` first,
	// instead of panicing that the file doesn't exist, return Ok(true)
	// This is because a non-hotpluggable CPU is assumed to be always online
	.unwrap_or(Ok(true))

[Copilot]

Using unwrap here may cause an unexpected panic on I/O error. It would be better to propagate the error using Result to handle read failures gracefully.

Suggested change

	fn read_cpu_file(&self, file: &str) -> String {
	fs::read_to_string(self.get_path().join(file)).unwrap()
	fn read_cpu_file(&self, file: &str) -> std::io::Result<String> {
	fs::read_to_string(self.get_path().join(file))

[alxndrv]

Updated the implementation to make use of UResults in order to return correct non-zero exit codes in most failure scenarios. Also added some basic test scenarios and cleaned up the code a bit.

[alxndrv]

Should there be some kind of "lib" crate for common stuff like this?

yes, we try to publish content in uucore https://docs.rs/uucore/latest/uucore/

In regards to this, good to know. I can look into adding the shared CPU list parsing functionality to that later, and then replace the implementations present in util-linux in a separate PR. Does that sound fine?

[sylvestre]

I am really really sorry but I took this #234 instead. it was more complete :(

sorry again :(

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (f91b55d) to head (88131fa).
Report is 8 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #226   +/-   ##
===========================
===========================

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