libcontainer: cgroups: deal with unlimited case for pids.max

Make sure we don't error out collecting statistics for cases where
pids.max == "max". In that case, we can use a limit of 0 which means
"unlimited".

In addition, change the name of the stats attribute (Max) to mirror the
name of the resources attribute in the spec (Limit) so that it's
consistent internally.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

libcontainer/cgroups/fs/pids.go

@@ -4,6 +4,7 @@ package fs
 
 import (
 	"fmt"
+	"path/filepath"
 	"strconv"
 
 	"github.com/opencontainers/runc/libcontainer/cgroups"
@@ -52,12 +53,21 @@ func (s *PidsGroup) GetStats(path string, stats *cgroups.Stats) error {
 		return fmt.Errorf("failed to parse pids.current - %s", err)
 	}
 
-	max, err := getCgroupParamUint(path, "pids.max")
+	maxString, err := getCgroupParamString(path, "pids.max")
 	if err != nil {
 		return fmt.Errorf("failed to parse pids.max - %s", err)
 	}
 
+	// Default if pids.max == "max" is 0 -- which represents "no limit".
+	var max uint64
+	if maxString != "max" {
+		max, err = parseUint(maxString, 10, 64)
+		if err != nil {
+			return fmt.Errorf("failed to parse pids.max - unable to parse %q as a uint from Cgroup file %q", maxString, filepath.Join(path, "pids.max"))
+		}
+	}
+
 	stats.PidsStats.Current = current
-	stats.PidsStats.Max = max
+	stats.PidsStats.Limit = max
 	return nil
 }

libcontainer/cgroups/stats.go

@@ -55,7 +55,7 @@ type PidsStats struct {
 	// number of pids in the cgroup
 	Current uint64 `json:"current,omitempty"`
 	// active pids hard limit
-	Max uint64 `json:"max,omitempty"`
+	Limit uint64 `json:"limit,omitempty"`
 }
 
 type BlkioStatEntry struct {