8254001: [Metrics] Enhance parsing of cgroup interface files for version detection

Reviewed-by: sgehwolf
Backport-of: a50725db2ab621e1a17cb5505f78e4bc73972a27

Author: jmtd

jdk/src/linux/classes/jdk/internal/platform/CgroupInfo.java

@@ -26,36 +26,86 @@
 package jdk.internal.platform;
 
 /**
- * Data structure to hold info from /proc/self/cgroup
+ * Data structure to hold info from /proc/self/cgroup,
+ * /proc/cgroups and /proc/self/mountinfo
  *
  * man 7 cgroups
  *
  * @see CgroupSubsystemFactory
  */
-class CgroupInfo {
+public class CgroupInfo {
 
     private final String name;
     private final int hierarchyId;
     private final boolean enabled;
+    private String mountPoint;
+    private String mountRoot;
+    private String cgroupPath;
 
     private CgroupInfo(String name, int hierarchyId, boolean enabled) {
         this.name = name;
         this.hierarchyId = hierarchyId;
         this.enabled = enabled;
     }
 
-    String getName() {
+    public String getName() {
         return name;
     }
 
-    int getHierarchyId() {
+    public int getHierarchyId() {
         return hierarchyId;
     }
 
-    boolean isEnabled() {
+    public boolean isEnabled() {
         return enabled;
     }
 
+    public String getMountPoint() {
+        return mountPoint;
+    }
+
+    public void setMountPoint(String mountPoint) {
+        this.mountPoint = mountPoint;
+    }
+
+    public String getMountRoot() {
+        return mountRoot;
+    }
+
+    public void setMountRoot(String mountRoot) {
+        this.mountRoot = mountRoot;
+    }
+
+    public String getCgroupPath() {
+        return cgroupPath;
+    }
+
+    public void setCgroupPath(String cgroupPath) {
+        this.cgroupPath = cgroupPath;
+    }
+
+    /*
+     * Creates a CgroupInfo instance from a line in /proc/cgroups.
+     * Comment token (hash) is handled by the caller.
+     *
+     * Example (annotated):
+     *
+     * #subsys_name     hierarchy       num_cgroups     enabled
+     * cpuset           10              1               1         (a)
+     * cpu              7               8               1         (b)
+     * [...]
+     *
+     * Line (a) would yield:
+     *   info = new CgroupInfo("cpuset", 10, true);
+     *   return info;
+     * Line (b) results in:
+     *   info = new CgroupInfo("cpu", 7, true);
+     *   return info;
+     *
+     *
+     * See CgroupSubsystemFactory.determineType()
+     *
+     */
     static CgroupInfo fromCgroupsLine(String line) {
         String[] tokens = line.split("\\s+");
         if (tokens.length != 4) {