X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/5e9787f914dd1a2f762ae7a653fe8dda36f8f555..e9f7d73dc0d84ee7127b8f83a4955521e8091708:/lib/crunchrun/cgroup.go

diff --git a/lib/crunchrun/cgroup.go b/lib/crunchrun/cgroup.go
index 48ec93b876..a722e5f142 100644
--- a/lib/crunchrun/cgroup.go
+++ b/lib/crunchrun/cgroup.go
@@ -7,13 +7,16 @@ package crunchrun
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io/fs"
 )
 
 // Return the current process's cgroup for the given subsystem.
-func findCgroup(subsystem string) (string, error) {
+//
+// If the host has cgroups v2 and not v1 (i.e., unified mode), return
+// the current process's cgroup.
+func findCgroup(fsys fs.FS, subsystem string) (string, error) {
 	subsys := []byte(subsystem)
-	cgroups, err := ioutil.ReadFile("/proc/self/cgroup")
+	cgroups, err := fs.ReadFile(fsys, "proc/self/cgroup")
 	if err != nil {
 		return "", err
 	}
@@ -22,7 +25,20 @@ func findCgroup(subsystem string) (string, error) {
 		if len(toks) < 3 {
 			continue
 		}
+		if len(toks[1]) == 0 && string(toks[0]) == "0" {
+			// cgroups v2: "0::$PATH"
+			//
+			// In "hybrid" mode, this entry is last, so we
+			// use it when the specified subsystem doesn't
+			// match a cgroups v1 entry.
+			//
+			// In "unified" mode, this is the only entry,
+			// so we use it regardless of which subsystem
+			// was specified.
+			return string(toks[2]), nil
+		}
 		for _, s := range bytes.Split(toks[1], []byte(",")) {
+			// cgroups v1: "7:cpu,cpuacct:/user.slice"
 			if bytes.Compare(s, subsys) == 0 {
 				return string(toks[2]), nil
 			}