X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/dfb9598282b677ead60f91c14f5e96405735d42f..e9f7d73dc0d84ee7127b8f83a4955521e8091708:/lib/crunchrun/cgroup.go

diff --git a/lib/crunchrun/cgroup.go b/lib/crunchrun/cgroup.go
index 0b254f5bd7..a722e5f142 100644
--- a/lib/crunchrun/cgroup.go
+++ b/lib/crunchrun/cgroup.go
@@ -6,28 +6,43 @@ package crunchrun
 
 import (
 	"bytes"
-	"io/ioutil"
-	"log"
+	"fmt"
+	"io/fs"
 )
 
 // Return the current process's cgroup for the given subsystem.
-func findCgroup(subsystem string) string {
+//
+// 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 {
-		log.Fatal(err)
+		return "", err
 	}
 	for _, line := range bytes.Split(cgroups, []byte("\n")) {
 		toks := bytes.SplitN(line, []byte(":"), 4)
 		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])
+				return string(toks[2]), nil
 			}
 		}
 	}
-	log.Fatalf("subsystem %q not found in /proc/self/cgroup", subsystem)
-	return ""
+	return "", fmt.Errorf("subsystem %q not found in /proc/self/cgroup", subsystem)
 }