Merge branch 'PR/nsenter-pidfd' of https://github.com/karelzak/util-l…

…inux-work

* 'PR/nsenter-pidfd' of https://github.com/karelzak/util-linux-work:
  nsenter: Rewrite --user-parent to use pidfd
  include/pidfd-utils: add namespaces ioctls
  nsenter: reuse pidfd for --net-socket
  nsenter: use macros to access the nsfiles array
  nsenter: use pidfd to enter target namespaces
  nsenter: use separate function to enter namespaces
  nsenter: add functions to enable/disable namespaces

include/pidfd-utils.h

@@ -8,14 +8,35 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 
+#ifdef HAVE_SYS_PIDFD_H
+# include <sys/pidfd.h>
+#endif
+
+/*
+ * pidfd ioctls
+ *
+ * All added by commit to kernel 6.11, commit 5b08bd408534bfb3a7cf5778da5b27d4e4fffe12.
+ */
+#ifndef PIDFS_IOCTL_MAGIC
+# define PIDFS_IOCTL_MAGIC 0xFF
+# define PIDFD_GET_CGROUP_NAMESPACE            _IO(PIDFS_IOCTL_MAGIC, 1)
+# define PIDFD_GET_IPC_NAMESPACE               _IO(PIDFS_IOCTL_MAGIC, 2)
+# define PIDFD_GET_MNT_NAMESPACE               _IO(PIDFS_IOCTL_MAGIC, 3)
+# define PIDFD_GET_NET_NAMESPACE               _IO(PIDFS_IOCTL_MAGIC, 4)
+# define PIDFD_GET_PID_NAMESPACE               _IO(PIDFS_IOCTL_MAGIC, 5)
+# define PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE  _IO(PIDFS_IOCTL_MAGIC, 6)
+# define PIDFD_GET_TIME_NAMESPACE              _IO(PIDFS_IOCTL_MAGIC, 7)
+# define PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 8)
+# define PIDFD_GET_USER_NAMESPACE              _IO(PIDFS_IOCTL_MAGIC, 9)
+# define PIDFD_GET_UTS_NAMESPACE               _IO(PIDFS_IOCTL_MAGIC, 10)
+#endif
+
+
 #ifdef HAVE_SYS_SYSCALL_H
 # include <sys/syscall.h>
 # include <unistd.h>
 
 # if defined(SYS_pidfd_send_signal) && defined(SYS_pidfd_open)
-#  ifdef HAVE_SYS_PIDFD_H
-#   include <sys/pidfd.h>
-#  endif
 #  ifndef HAVE_PIDFD_SEND_SIGNAL
 static inline int pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
 				    unsigned int flags)