manager: Introduce FsManager

`Manager` is a trait to unify the interface of cgroups. It is designed for
OCI containers. Its `set()` takes Linux resources of the OCI spec to set
cgroups.

The `FsManager`, the concrete implementation of `Manager`, manipulates
cgroups through cgroupfs, and supports both cgroups v1 and v2.

Signed-off-by: Xuewei Niu <niuxuewei.nxw@antgroup.com>

src/lib.rs

@@ -5,3 +5,45 @@
 //
 
 pub mod fs;
+#[cfg(feature = "oci")]
+pub mod manager;
+#[cfg(feature = "oci")]
+pub use manager::{FsManager, Manager};
+pub mod stats;
+pub use stats::CgroupStats;
+
+/// The maximum value for CPU shares in cgroups v1
+pub const CPU_SHARES_V1_MAX: u64 = 262144;
+/// The maximum value for CPU weight in cgroups v2
+pub const CPU_WEIGHT_V2_MAX: u64 = 10000;
+
+/// The current state of the control group
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+pub enum FreezerState {
+    /// The processes in the control group are _not_ frozen.
+    Thawed,
+    /// The processes in the control group are in the processes of being frozen.
+    Freezing,
+    /// The processes in the control group are frozen.
+    Frozen,
+}
+
+/// A structure representing a `pid`. Currently implementations exist for `u64` and
+/// `std::process::Child`.
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy)]
+pub struct CgroupPid {
+    /// The process identifier
+    pub pid: u64,
+}
+
+impl From<u64> for CgroupPid {
+    fn from(u: u64) -> CgroupPid {
+        CgroupPid { pid: u }
+    }
+}
+
+impl From<&std::process::Child> for CgroupPid {
+    fn from(u: &std::process::Child) -> CgroupPid {
+        CgroupPid { pid: u.id() as u64 }
+    }
+}