libcgroups v2 manager stats failed when no hugetlb releated files

[Sherlock-Holo]

if a cgroup doesn't contain hugetlb releated files, the v2 manager will fail with

Caused by:
0: io error: failed to read /sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/prctl-ttt/hugetlb.2MB.events: No such file or directory (os error 2)
1: failed to read /sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/prctl-ttt/hugetlb.2MB.events: No such file or directory (os error 2)

[YJDoc2]

Hey, thanks for reporting this. Can you also add your system information / setup and how you were running this, so we can try to reproduce?

[Sherlock-Holo]

I am using archlinux

uname -a

Linux sherlock 6.5.9-arch2-1 #1 SMP PREEMPT_DYNAMIC Thu, 26 Oct 2023 00:52:20 +0000 x86_64 GNU/Linux

pub fn show_cgroup_info<M>(manager: &M, name: &str) -> anyhow::Result<CgroupInfo>
where
    M: CgroupManager,
    M::Error: Error + Send + Sync + 'static,
{
    let stats = manager
        .stats()
        .with_context(|| format!("get cgroup {name} info failed"))?;
    let memory = (stats.memory.memory.limit != u64::MAX)
        .then(|| Byte::from_bytes(stats.memory.memory.limit as _));

    Ok(CgroupInfo {
        cpu: CpuInfo {
            cpu: MaxOrInt::Int(0),
        },
        memory: MemoryInfo { limit: memory },
    })
}

and when I call this function, I use the v2 manager implement

[xiaoyang-sde]

The stats method of libcgroups::v2::Manager assumes that all types of controller listed in CONTROLLER_TYPES are enabled in the cgroup it manages. Therefore, it will attempt to read the hugetlb.2MB.events file even if the hugetlb controller is not enabled.

https://github.com/containers/youki/blob/7b5e8f238e45497fe041c9f622a9a4e0b3f0e7e4/crates/libcgroups/src/v2/manager.rs#L216-L233

I think a potential solution is to implement a method similar to util::get_available_controllers, which reads the enabled controllers of the current cgroup, and then generate stats for these enabled controllers. (I'm willing to submit a pull request if this issue needs to be addressed.)