libct/userns: implement RunningInUserNS with sync.OnceValue

Now that we dropped support for go < 1.21, we can use this; moving the sync.once out of the runningInUserNS() implementation would also allow for it to be more easily tested if we'd decide to. Signed-off-by: Sebastiaan van Stijn <[email protected]>
moby · Jul 24, 2024 · bc3a8a5 · bc3a8a5
1 parent bc0de32
commit bc3a8a5
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Showing 3 changed files with 18 additions and 27 deletions.
diff --git a/user/userns/userns.go b/user/userns/userns.go
@@ -4,5 +4,5 @@ package userns
 // user namespace and memoizes the result. It returns false on non-Linux
 // platforms.
 func RunningInUserNS() bool {
-	return runningInUserNS()
+	return inUserNS()
 }
diff --git a/user/userns/userns_linux.go b/user/userns/userns_linux.go
@@ -7,32 +7,26 @@ import (
 	"sync"
 )
 
-var (
-	inUserNS bool
-	nsOnce   sync.Once
-)
+var inUserNS = sync.OnceValue(runningInUserNS)
 
 // runningInUserNS detects whether we are currently running in a user namespace.
 //
 // Originally copied from https://github.com/lxc/incus/blob/e45085dd42f826b3c8c3228e9733c0b6f998eafe/shared/util.go#L678-L700.
 func runningInUserNS() bool {
-	nsOnce.Do(func() {
-		file, err := os.Open("/proc/self/uid_map")
-		if err != nil {
-			// This kernel-provided file only exists if user namespaces are supported.
-			return
-		}
-		defer file.Close()
-
-		buf := bufio.NewReader(file)
-		l, _, err := buf.ReadLine()
-		if err != nil {
-			return
-		}
-
-		inUserNS = uidMapInUserNS(string(l))
-	})
-	return inUserNS
+	file, err := os.Open("/proc/self/uid_map")
+	if err != nil {
+		// This kernel-provided file only exists if user namespaces are supported.
+		return false
+	}
+	defer file.Close()
+
+	buf := bufio.NewReader(file)
+	l, _, err := buf.ReadLine()
+	if err != nil {
+		return false
+	}
+
+	return uidMapInUserNS(string(l))
 }
 
 func uidMapInUserNS(uidMap string) bool {

diff --git a/user/userns/userns_unsupported.go b/user/userns/userns_unsupported.go
@@ -2,8 +2,5 @@
 
 package userns
 
-// runningInUserNS is a stub for non-Linux systems
-// Always returns false
-func runningInUserNS() bool {
-	return false
-}
+// inUserNS is a stub for non-Linux systems. Always returns false.
+func inUserNS() bool { return false }