cgrouprs: Enhance CgroupPid

Implement `From<u32>` and `From<i32>` for `CgroupPid` to allow conversion
from these types directly. Add `as_raw()` method to retrieve the raw PID
value, and add `set()` method to modify the PID value.

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

Author: justxuewei

src/lib.rs

@@ -34,7 +34,7 @@ pub enum FreezerState {
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy)]
 pub struct CgroupPid {
     /// The process identifier
-    pub pid: u64,
+    pid: u64,
 }
 
 impl From<u64> for CgroupPid {
@@ -49,6 +49,28 @@ impl From<&std::process::Child> for CgroupPid {
     }
 }
 
+impl From<u32> for CgroupPid {
+    fn from(u: u32) -> CgroupPid {
+        CgroupPid { pid: u as u64 }
+    }
+}
+
+impl From<i32> for CgroupPid {
+    fn from(u: i32) -> CgroupPid {
+        CgroupPid { pid: u as u64 }
+    }
+}
+
+impl CgroupPid {
+    pub fn set(&mut self, pid: u64) {
+        self.pid = pid;
+    }
+
+    pub fn as_raw(&self) -> u64 {
+        self.pid
+    }
+}
+
 #[cfg(test)]
 pub mod tests {
     use std::fs;