unix: add listns syscall introduced in Linux 6.19

unix/linux/types.go

@@ -150,6 +150,7 @@ struct termios2 {
 #include <linux/nexthop.h>
 #include <linux/nfc.h>
 #include <linux/nl80211.h>
+#include <linux/nsfs.h>
 #include <linux/openat2.h>
 #include <linux/perf_event.h>
 #include <linux/pps.h>
@@ -537,6 +538,16 @@ struct my_ptp_perout_request {
 	unsigned int flags;
 	struct ptp_clock_time on;
 };
+
+// the one defined in linux/nsfs.h has anonymous nested struct
+struct my_ns_id_req {
+	__u32 size;
+	__u32 spare;
+	__u64 ns_id;
+	__u32 ns_type;
+	__u32 spare2;
+	__u64 user_ns_id;
+};
 */
 import "C"
 
@@ -1090,6 +1101,22 @@ type OpenHow C.struct_open_how
 
 const SizeofOpenHow = C.sizeof_struct_open_how
 
+type NsIdReq C.struct_my_ns_id_req
+
+const (
+	NS_ID_REQ_SIZE_VER0 = C.NS_ID_REQ_SIZE_VER0
+	LISTNS_CURRENT_USER = C.LISTNS_CURRENT_USER
+
+	TIME_NS   = C.TIME_NS
+	MNT_NS    = C.MNT_NS
+	CGROUP_NS = C.CGROUP_NS
+	UTS_NS    = C.UTS_NS
+	IPC_NS    = C.IPC_NS
+	USER_NS   = C.USER_NS
+	PID_NS    = C.PID_NS
+	NET_NS    = C.NET_NS
+)
+
 const (
 	RESOLVE_BENEATH       = C.RESOLVE_BENEATH
 	RESOLVE_IN_ROOT       = C.RESOLVE_IN_ROOT

unix/syscall_linux.go

@@ -2032,6 +2032,7 @@ func Getrandom(buf []byte, flags int) (n int, err error) {
 //sysnb	Kill(pid int, sig syscall.Signal) (err error)
 //sys	Klogctl(typ int, buf []byte) (n int, err error) = SYS_SYSLOG
 //sys	Lgetxattr(path string, attr string, dest []byte) (sz int, err error)
+//sys	Listns(req *NsIdReq, nsIds []uint64, flags uint) (n int, err error)
 //sys	Listxattr(path string, dest []byte) (sz int, err error)
 //sys	Llistxattr(path string, dest []byte) (sz int, err error)
 //sys	Lremovexattr(path string, attr string) (err error)

unix/syscall_linux_test.go

@@ -141,6 +141,108 @@ func TestIoctlRetInt(t *testing.T) {
 	}
 }
 
+func TestListns(t *testing.T) {
+	callListns := func(tb testing.TB, req *unix.NsIdReq, nsIDs []uint64, flags uint, context string) int {
+		tb.Helper()
+		n, err := unix.Listns(req, nsIDs, flags)
+		if err != nil {
+			if errors.Is(err, unix.ENOSYS) {
+				tb.Skipf("listns syscall is not available (need Linux >= 6.19), skipping test: %v", err)
+			}
+			if errors.Is(err, unix.EPERM) || errors.Is(err, unix.EACCES) {
+				tb.Skipf("listns requires additional privileges in this environment, skipping test: %v", err)
+			}
+			tb.Fatalf("%s: Listns failed: %v", context, err)
+		}
+		if n < 0 || n > len(nsIDs) {
+			tb.Fatalf("%s: Listns returned unexpected count %d, want [0, %d]", context, n, len(nsIDs))
+		}
+		return n
+	}
+
+	t.Run("all namespaces", func(t *testing.T) {
+		req := &unix.NsIdReq{
+			Size:       unix.NS_ID_REQ_SIZE_VER0,
+			Ns_id:      0,
+			Ns_type:    0,
+			User_ns_id: 0,
+		}
+		ids := make([]uint64, 64)
+		callListns(t, req, ids, 0, "all namespaces")
+	})
+
+	t.Run("network namespaces only", func(t *testing.T) {
+		req := &unix.NsIdReq{
+			Size:       unix.NS_ID_REQ_SIZE_VER0,
+			Ns_id:      0,
+			Ns_type:    uint32(unix.NET_NS),
+			User_ns_id: 0,
+		}
+		ids := make([]uint64, 64)
+		callListns(t, req, ids, 0, "network namespaces only")
+	})
+
+	t.Run("current user namespace owner", func(t *testing.T) {
+		req := &unix.NsIdReq{
+			Size:       unix.NS_ID_REQ_SIZE_VER0,
+			Ns_id:      0,
+			Ns_type:    0,
+			User_ns_id: unix.LISTNS_CURRENT_USER,
+		}
+		ids := make([]uint64, 64)
+		callListns(t, req, ids, 0, "current user namespace owner")
+	})
+
+	t.Run("network and mount namespaces", func(t *testing.T) {
+		req := &unix.NsIdReq{
+			Size:       unix.NS_ID_REQ_SIZE_VER0,
+			Ns_id:      0,
+			Ns_type:    uint32(unix.NET_NS | unix.MNT_NS),
+			User_ns_id: 0,
+		}
+		ids := make([]uint64, 64)
+		callListns(t, req, ids, 0, "network and mount namespaces")
+	})
+
+	t.Run("pagination via ns_id", func(t *testing.T) {
+		const pageSize = 10
+		req := &unix.NsIdReq{
+			Size:       unix.NS_ID_REQ_SIZE_VER0,
+			Ns_id:      0,
+			Ns_type:    0,
+			User_ns_id: 0,
+		}
+		ids := make([]uint64, pageSize)
+
+		total := 0
+		for {
+			n := callListns(t, req, ids, 0, "pagination")
+			if n == 0 {
+				break
+			}
+
+			// Continue from the last seen namespace ID.
+			last := ids[n-1]
+			if last == req.Ns_id {
+				t.Fatalf("pagination did not advance: last=%d", last)
+			}
+			total += n
+			req.Ns_id = last
+
+			// Partial batch means we've exhausted all results.
+			if n < pageSize {
+				break
+			}
+		}
+
+		t.Logf("total ns: %d", total)
+		if total == 0 {
+			t.Fatalf("pagination should return at least one namespace")
+		}
+	})
+
+}
+
 func TestIoctlGetRTCTime(t *testing.T) {
 	f, err := os.Open("/dev/rtc0")
 	if err != nil {