Simplified version of ostree mount setup, which causes an invisible/unmountable /sysroot mount after switch_root

gistfile1.c

#include <sys/mount.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

int main(void)
{
  /* For some reason the kernel refuses switching root if any file systems
   * are mounted MS_SHARED. */
  if (mount (NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
    {
      perror ("Failed to make \"/\" private mount");
      exit (1);
    }

  /* Make /fs a bind mount, so we can move it later */
  if (mount ("/sysroot/fs", "/sysroot/fs", NULL, MS_BIND, NULL) < 0)
    {
      perror ("failed to initial bind mount");
      exit (1);
    }

  if (mount ("/sysroot/fs", "/sysroot", NULL, MS_MOVE, NULL) < 0)
    {
      perror ("failed to MS_MOVE");
      exit (1);
    }
  exit (0);
}