fixup! fix: cannot start container when IPv6 is disabled

Move ErrNotExist handling from procnet.ReadStatsFileData to
getUsedPorts, so that the caller expresses the intent to ignore
missing IPv6 stats files rather than the general-purpose helper.

Signed-off-by: Shouhei <shouhei.yamaguchi.be@gmail.com>

Author: shouhei

pkg/portutil/port_allocate_linux.go

@@ -17,7 +17,9 @@
 package portutil
 
 import (
+	"errors"
 	"fmt"
+	"os"
 
 	"github.com/containerd/nerdctl/v2/pkg/portutil/iptable"
 	"github.com/containerd/nerdctl/v2/pkg/portutil/procnet"
@@ -86,14 +88,14 @@ func getUsedPorts(ip string, protocol string) (map[uint64]bool, error) {
 	// So we need some trick to process this situation.
 	if protocol == "tcp" {
 		tempTCPV6Data, err := procnet.ReadStatsFileData("tcp6")
-		if err != nil {
+		if err != nil && !errors.Is(err, os.ErrNotExist) {
 			return nil, err
 		}
 		netprocItems = append(netprocItems, procnet.Parse(tempTCPV6Data)...)
 	}
 	if protocol == "udp" {
 		tempUDPV6Data, err := procnet.ReadStatsFileData("udp6")
-		if err != nil {
+		if err != nil && !errors.Is(err, os.ErrNotExist) {
 			return nil, err
 		}
 		netprocItems = append(netprocItems, procnet.Parse(tempUDPV6Data)...)

pkg/portutil/procnet/procnet_linux.go

@@ -18,7 +18,6 @@ package procnet
 
 import (
 	"bufio"
-	"errors"
 	"fmt"
 	"os"
 )
@@ -53,10 +52,6 @@ func ReadStatsFileData(protocol string) ([]string, error) {
 
 	fp, err := os.Open(fileAddress)
 	if err != nil {
-		// IPv6-disabled environments do not have these files.
-		if (fileAddress == netTCP6Stats || fileAddress == netUDP6Stats) && errors.Is(err, os.ErrNotExist) {
-			return nil, nil
-		}
 		return nil, err
 	}
 	defer fp.Close()