/* libguestfs - the guestfsd daemon
 * Copyright (C) 2009-2012 Red Hat Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <config.h>

#ifdef HAVE_WINDOWS_H
# include <windows.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <rpc/types.h>
#include <rpc/xdr.h>
#include <getopt.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <signal.h>
#include <netdb.h>
#include <sys/select.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <errno.h>

#ifdef HAVE_PRINTF_H
# include <printf.h>
#endif

#include "sockets.h"
#include "c-ctype.h"
#include "ignore-value.h"
#include "error.h"

#include "daemon.h"

static char *read_cmdline (void);

#ifndef MAX
# define MAX(a,b) ((a)>(b)?(a):(b))
#endif

/* Not the end of the world if this open flag is not defined. */
#ifndef O_CLOEXEC
# define O_CLOEXEC 0
#endif

/* If root device is an ext2 filesystem, this is the major and minor.
 * This is so we can ignore this device from the point of view of the
 * user, eg. in guestfs_list_devices and many other places.
 */
static dev_t root_device = 0;

int verbose = 0;

static int print_shell_quote (FILE *stream, const struct printf_info *info, const void *const *args);
static int print_sysroot_shell_quote (FILE *stream, const struct printf_info *info, const void *const *args);
#ifdef HAVE_REGISTER_PRINTF_SPECIFIER
static int print_arginfo (const struct printf_info *info, size_t n, int *argtypes, int *size);
#else
#ifdef HAVE_REGISTER_PRINTF_FUNCTION
static int print_arginfo (const struct printf_info *info, size_t n, int *argtypes);
#else
#error "HAVE_REGISTER_PRINTF_{SPECIFIER|FUNCTION} not defined"
#endif
#endif

#ifdef WIN32
static int
winsock_init (void)
{
  int r;

  /* http://msdn2.microsoft.com/en-us/library/ms742213.aspx */
  r = gl_sockets_startup (SOCKETS_2_2);
  return r == 0 ? 0 : -1;
}
#else /* !WIN32 */
static int
winsock_init (void)
{
  return 0;
}
#endif /* !WIN32 */

/* Location to mount root device. */
const char *sysroot = "/sysroot"; /* No trailing slash. */
size_t sysroot_len = 8;

/* If set (the default), do 'umount-all' when performing autosync. */
int autosync_umount = 1;

/* Not used explicitly, but required by the gnulib 'error' module. */
const char *program_name = "guestfsd";

/* Name of the virtio-serial channel. */
#define VIRTIO_SERIAL_CHANNEL "/dev/virtio-ports/org.libguestfs.channel.0"

static void
usage (void)
{
  fprintf (stderr,
    "guestfsd [-r] [-v|--verbose]\n");
}

int
main (int argc, char *argv[])
{
  static const char *options = "rv?";
  static const struct option long_options[] = {
    { "help", 0, 0, '?' },
    { "verbose", 0, 0, 'v' },
    { 0, 0, 0, 0 }
  };
  int c;
  char *cmdline;

  ignore_value (chdir ("/"));

  if (winsock_init () == -1)
    error (EXIT_FAILURE, 0, "winsock initialization failed");

#ifdef HAVE_REGISTER_PRINTF_SPECIFIER
  /* http://udrepper.livejournal.com/20948.html */
  register_printf_specifier ('Q', print_shell_quote, print_arginfo);
  register_printf_specifier ('R', print_sysroot_shell_quote, print_arginfo);
#else
#ifdef HAVE_REGISTER_PRINTF_FUNCTION
  register_printf_function ('Q', print_shell_quote, print_arginfo);
  register_printf_function ('R', print_sysroot_shell_quote, print_arginfo);
#else
#error "HAVE_REGISTER_PRINTF_{SPECIFIER|FUNCTION} not defined"
#endif
#endif

  struct stat statbuf;
  if (stat ("/", &statbuf) == 0)
    root_device = statbuf.st_dev;

  for (;;) {
    c = getopt_long (argc, argv, options, long_options, NULL);
    if (c == -1) break;

    switch (c) {
      /* The -r flag is used when running standalone.  It changes
       * several aspects of the daemon.
       */
    case 'r':
      sysroot = "";
      sysroot_len = 0;
      autosync_umount = 0;
      break;

    case 'v':
      verbose = 1;
      break;

    case '?':
      usage ();
      exit (EXIT_SUCCESS);

    default:
      fprintf (stderr, "guestfsd: unexpected command line option 0x%x\n", c);
      exit (EXIT_FAILURE);
    }
  }

  if (optind < argc) {
    usage ();
    exit (EXIT_FAILURE);
  }

  cmdline = read_cmdline ();

  /* Set the verbose flag. */
  verbose = verbose ||
    (cmdline && strstr (cmdline, "guestfs_verbose=1") != NULL);
  if (verbose)
    printf ("verbose daemon enabled\n");

  if (verbose) {
    if (cmdline)
      printf ("linux commmand line: %s\n", cmdline);
    else
      printf ("could not read linux command line\n");
  }

  free (cmdline);

#ifndef WIN32
  /* Make sure SIGPIPE doesn't kill us. */
  struct sigaction sa;
  memset (&sa, 0, sizeof sa);
  sa.sa_handler = SIG_IGN;
  sa.sa_flags = 0;
  if (sigaction (SIGPIPE, &sa, NULL) == -1)
    perror ("sigaction SIGPIPE"); /* but try to continue anyway ... */
#endif

#ifdef WIN32
# define setenv(n,v,f) _putenv(n "=" v)
#endif
  /* Set up a basic environment.  After we are called by /init the
   * environment is essentially empty.
   * https://bugzilla.redhat.com/show_bug.cgi?id=502074#c5
   *
   * NOTE: if you change $PATH, you must also change 'prog_exists'
   * function below.
   */
  setenv ("PATH", "/sbin:/usr/sbin:/bin:/usr/bin", 1);
  setenv ("SHELL", "/bin/sh", 1);
  setenv ("LC_ALL", "C", 1);
  setenv ("TERM", "dumb", 1);

#ifndef WIN32
  /* We document that umask defaults to 022 (it should be this anyway). */
  umask (022);
#else
  /* This is the default for Windows anyway.  It's not even clear if
   * Windows ever uses this -- the MSDN documentation for the function
   * contains obvious errors.
   */
  _umask (0);
#endif

  /* Make a private copy of /etc/lvm so we can change the config (see
   * daemon/lvm-filter.c).
   */
  copy_lvm ();

  /* Connect to virtio-serial channel. */
  int sock = open (VIRTIO_SERIAL_CHANNEL, O_RDWR|O_CLOEXEC);
  if (sock == -1) {
    fprintf (stderr,
             "\n"
             "Failed to connect to virtio-serial channel.\n"
             "\n"
             "This is a fatal error and the appliance will now exit.\n"
             "\n"
             "Usually this error is caused by either QEMU or the appliance\n"
             "kernel not supporting the vmchannel method that the\n"
             "libguestfs library chose to use.  Please run\n"
             "'libguestfs-test-tool' and provide the complete, unedited\n"
             "output to the libguestfs developers, either in a bug report\n"
             "or on the libguestfs redhat com mailing list.\n"
             "\n");
    perror (VIRTIO_SERIAL_CHANNEL);
    exit (EXIT_FAILURE);
  }

  /* Send the magic length message which indicates that
   * userspace is up inside the guest.
   */
  char lenbuf[4];
  XDR xdr;
  uint32_t len = GUESTFS_LAUNCH_FLAG;
  xdrmem_create (&xdr, lenbuf, sizeof lenbuf, XDR_ENCODE);
  xdr_u_int (&xdr, &len);

  if (xwrite (sock, lenbuf, sizeof lenbuf) == -1) {
    perror ("xwrite");
    exit (EXIT_FAILURE);
  }

  xdr_destroy (&xdr);

  /* Enter the main loop, reading and performing actions. */
  main_loop (sock);

  exit (EXIT_SUCCESS);
}

/* Read /proc/cmdline. */
static char *
read_cmdline (void)
{
  int fd = open ("/proc/cmdline", O_RDONLY|O_CLOEXEC);
  if (fd == -1) {
    perror ("/proc/cmdline");
    return NULL;
  }

  size_t len = 0;
  ssize_t n;
  char buf[256];
  char *r = NULL;

  for (;;) {
    n = read (fd, buf, sizeof buf);
    if (n == -1) {
      perror ("read");
      free (r);
      close (fd);
      return NULL;
    }
    if (n == 0)
      break;
    char *newr = realloc (r, len + n + 1); /* + 1 is for terminating NUL */
    if (newr == NULL) {
      perror ("realloc");
      free (r);
      close (fd);
      return NULL;
    }
    r = newr;
    memcpy (&r[len], buf, n);
    len += n;
  }

  if (r)
    r[len] = '\0';

  if (close (fd) == -1) {
    perror ("close");
    free (r);
    return NULL;
  }

  return r;
}

/* Return true iff device is the root device (and therefore should be
 * ignored from the point of view of user calls).
 */
int
is_root_device (const char *device)
{
  struct stat statbuf;
  if (stat (device, &statbuf) == -1) {
    perror (device);
    return 0;
  }
  if (statbuf.st_rdev == root_device)
    return 1;
  return 0;
}

/* Turn "/path" into "/sysroot/path".
 *
 * Caller must check for NULL and call reply_with_perror ("malloc")
 * if it is.  Caller must also free the string.
 *
 * See also the custom %R printf formatter which does shell quoting too.
 */
char *
sysroot_path (const char *path)
{
  char *r;
  size_t len = strlen (path) + sysroot_len + 1;

  r = malloc (len);
  if (r == NULL)
    return NULL;

  snprintf (r, len, "%s%s", sysroot, path);
  return r;
}

int
xwrite (int sock, const void *v_buf, size_t len)
{
  ssize_t r;
  const char *buf = v_buf;

  while (len > 0) {
    r = write (sock, buf, len);
    if (r == -1) {
      perror ("write");
      return -1;
    }
    buf += r;
    len -= r;
  }

  return 0;
}

int
xread (int sock, void *v_buf, size_t len)
{
  int r;
  char *buf = v_buf;

  while (len > 0) {
    r = read (sock, buf, len);
    if (r == -1) {
      perror ("read");
      return -1;
    }
    if (r == 0) {
      fprintf (stderr, "read: unexpected end of file on fd %d\n", sock);
      return -1;
    }
    buf += r;
    len -= r;
  }

  return 0;
}

int
add_string_nodup (struct stringsbuf *sb, char *str)
{
  char **new_argv;

  if (sb->size >= sb->alloc) {
    sb->alloc += 64;
    new_argv = realloc (sb->argv, sb->alloc * sizeof (char *));
    if (new_argv == NULL) {
      reply_with_perror ("realloc");
      free_stringslen (sb->argv, sb->size);
      sb->argv = NULL;
      return -1;
    }
    sb->argv = new_argv;
  }

  sb->argv[sb->size] = str;
  sb->size++;

  return 0;
}

int
add_string (struct stringsbuf *sb, const char *str)
{
  char *new_str = NULL;

  if (str) {
    new_str = strdup (str);
    if (new_str == NULL) {
      reply_with_perror ("strdup");
      free_stringslen (sb->argv, sb->size);
      sb->argv = NULL;
      return -1;
    }
  }

  return add_string_nodup (sb, new_str);
}

int
end_stringsbuf (struct stringsbuf *sb)
{
  return add_string_nodup (sb, NULL);
}

size_t
count_strings (char *const *argv)
{
  size_t argc;

  for (argc = 0; argv[argc] != NULL; ++argc)
    ;
  return argc;
}

/* http://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2 */
int
is_power_of_2 (unsigned long v)
{
  return v && ((v & (v - 1)) == 0);
}

static int
compare (const void *vp1, const void *vp2)
{
  char * const *p1 = (char * const *) vp1;
  char * const *p2 = (char * const *) vp2;
  return strcmp (*p1, *p2);
}

void
sort_strings (char **argv, size_t len)
{
  qsort (argv, len, sizeof (char *), compare);
}

void
free_strings (char **argv)
{
  size_t argc;

  for (argc = 0; argv[argc] != NULL; ++argc)
    free (argv[argc]);
  free (argv);
}

void
free_stringslen (char **argv, size_t len)
{
  size_t i;

  for (i = 0; i < len; ++i)
    free (argv[i]);
  free (argv);
}

/* Easy ways to run external commands.  For full documentation, see
 * 'commandrvf' below.
 */
int
commandf (char **stdoutput, char **stderror, int flags, const char *name, ...)
{
  va_list args;
  const char **argv;
  char *s;
  size_t i;
  int r;

  /* Collect the command line arguments into an array. */
  i = 2;
  argv = malloc (sizeof (char *) * i);
  if (argv == NULL) {
    perror ("malloc");
    return -1;
  }
  argv[0] = (char *) name;
  argv[1] = NULL;

  va_start (args, name);

  while ((s = va_arg (args, char *)) != NULL) {
    const char **p = realloc (argv, sizeof (char *) * (++i));
    if (p == NULL) {
      perror ("realloc");
      free (argv);
      va_end (args);
      return -1;
    }
    argv = p;
    argv[i-2] = s;
    argv[i-1] = NULL;
  }

  va_end (args);

  r = commandvf (stdoutput, stderror, flags, (const char * const*) argv);

  /* NB: Mustn't free the strings which are on the stack. */
  free (argv);

  return r;
}

/* Same as 'command', but we allow the status code from the
 * subcommand to be non-zero, and return that status code.
 * We still return -1 if there was some other error.
 */
int
commandrf (char **stdoutput, char **stderror, int flags, const char *name, ...)
{
  va_list args;
  const char **argv;
  char *s;
  int i, r;

  /* Collect the command line arguments into an array. */
  i = 2;
  argv = malloc (sizeof (char *) * i);
  if (argv == NULL) {
    perror ("malloc");
    return -1;
  }
  argv[0] = (char *) name;
  argv[1] = NULL;

  va_start (args, name);

  while ((s = va_arg (args, char *)) != NULL) {
    const char **p = realloc (argv, sizeof (char *) * (++i));
    if (p == NULL) {
      perror ("realloc");
      free (argv);
      va_end (args);
      return -1;
    }
    argv = p;
    argv[i-2] = s;
    argv[i-1] = NULL;
  }

  va_end (args);

  r = commandrvf (stdoutput, stderror, flags, argv);

  /* NB: Mustn't free the strings which are on the stack. */
  free (argv);

  return r;
}

/* Same as 'command', but passing an argv. */
int
commandvf (char **stdoutput, char **stderror, int flags,
           char const *const *argv)
{
  int r;

  r = commandrvf (stdoutput, stderror, flags, (void *) argv);
  if (r == 0)
    return 0;
  else
    return -1;
}

/* This is a more sane version of 'system(3)' for running external
 * commands.  It uses fork/execvp, so we don't need to worry about
 * quoting of parameters, and it allows us to capture any error
 * messages in a buffer.
 *
 * If stdoutput is not NULL, then *stdoutput will return the stdout
 * of the command.
 *
 * If stderror is not NULL, then *stderror will return the stderr
 * of the command.  If there is a final \n character, it is removed
 * so you can use the error string directly in a call to
 * reply_with_error.
 *
 * Flags:
 *
 * COMMAND_FLAG_FOLD_STDOUT_ON_STDERR: For broken external commands
 * that send error messages to stdout (hello, parted) but that don't
 * have any useful stdout information, use this flag to capture the
 * error messages in the *stderror buffer.  If using this flag,
 * you should pass stdoutput as NULL because nothing could ever be
 * captured in that buffer.
 *
 * COMMAND_FLAG_CHROOT_COPY_FILE_TO_STDIN: For running external
 * commands on chrooted files correctly (see RHBZ#579608) specifying
 * this flag causes another process to be forked which chroots into
 * sysroot and just copies the input file to stdin of the specified
 * command.  The file descriptor is ORed with the flags, and that file
 * descriptor is always closed by this function.  See hexdump.c for an
 * example of usage.
 */
int
commandrvf (char **stdoutput, char **stderror, int flags,
            char const* const *argv)
{
  size_t so_size = 0, se_size = 0;
  int so_fd[2], se_fd[2];
  int flag_copy_stdin = flags & COMMAND_FLAG_CHROOT_COPY_FILE_TO_STDIN;
  int stdin_fd[2] = { -1, -1 };
  pid_t pid, stdin_pid = -1;
  int r, quit, i;
  fd_set rset, rset2;
  char buf[256];
  char *p;

  if (stdoutput) *stdoutput = NULL;
  if (stderror) *stderror = NULL;

  if (verbose) {
    printf ("%s", argv[0]);
    for (i = 1; argv[i] != NULL; ++i)
      printf (" %s", argv[i]);
    printf ("\n");
  }

  /* Note: abort is used in a few places along the error paths early
   * in this function.  This is because (a) cleaning up correctly is
   * very complex at these places and (b) abort is used when a
   * resource problems is indicated which would be due to much more
   * serious issues - eg. memory or file descriptor leaks.  We
   * wouldn't expect fork(2) or pipe(2) to fail in normal
   * circumstances.
   */

  if (pipe (so_fd) == -1 || pipe (se_fd) == -1) {
    error (0, errno, "pipe");
    abort ();
  }

  if (flag_copy_stdin) {
    if (pipe (stdin_fd) == -1) {
      error (0, errno, "pipe");
      abort ();
    }
  }

  pid = fork ();
  if (pid == -1) {
    error (0, errno, "fork");
    abort ();
  }

  if (pid == 0) {		/* Child process running the command. */
    signal (SIGALRM, SIG_DFL);
    signal (SIGPIPE, SIG_DFL);
    close (0);
    if (flag_copy_stdin) {
      dup2 (stdin_fd[0], 0);
      close (stdin_fd[0]);
      close (stdin_fd[1]);
    } else {
      /* Set stdin to /dev/null (ignore failure) */
      ignore_value (open ("/dev/null", O_RDONLY|O_CLOEXEC));
    }
    close (so_fd[0]);
    close (se_fd[0]);
    if (!(flags & COMMAND_FLAG_FOLD_STDOUT_ON_STDERR))
      dup2 (so_fd[1], 1);
    else
      dup2 (se_fd[1], 1);
    dup2 (se_fd[1], 2);
    close (so_fd[1]);
    close (se_fd[1]);

    execvp (argv[0], (void *) argv);
    perror (argv[0]);
    _exit (EXIT_FAILURE);
  }

  if (flag_copy_stdin) {
    int fd = flags & COMMAND_FLAG_FD_MASK;

    stdin_pid = fork ();
    if (stdin_pid == -1) {
      error (0, errno, "fork");
      abort ();
    }

    if (stdin_pid == 0) {       /* Child process copying stdin. */
      close (so_fd[0]);
      close (so_fd[1]);
      close (se_fd[0]);
      close (se_fd[1]);

      close (1);
      dup2 (stdin_fd[1], 1);
      close (stdin_fd[0]);
      close (stdin_fd[1]);

      if (chroot (sysroot) == -1) {
        perror ("chroot");
        _exit (EXIT_FAILURE);
      }

      ssize_t n;
      char buffer[BUFSIZ];
      while ((n = read (fd, buffer, sizeof buffer)) > 0) {
        if (xwrite (1, buffer, n) == -1)
          /* EPIPE error indicates the command process has exited
           * early.  If the command process fails that will be caught
           * by the daemon, and if not, then it's not an error.
           */
          _exit (errno == EPIPE ? EXIT_SUCCESS : EXIT_FAILURE);
      }

      if (n == -1) {
        perror ("read");
        _exit (EXIT_FAILURE);
      }

      if (close (fd) == -1) {
        perror ("close");
        _exit (EXIT_FAILURE);
      }

      _exit (EXIT_SUCCESS);
    }

    close (fd);
    close (stdin_fd[0]);
    close (stdin_fd[1]);
  }

  /* Parent process. */
  close (so_fd[1]);
  close (se_fd[1]);

  FD_ZERO (&rset);
  FD_SET (so_fd[0], &rset);
  FD_SET (se_fd[0], &rset);

  quit = 0;
  while (quit < 2) {
  again:
    rset2 = rset;
    r = select (MAX (so_fd[0], se_fd[0]) + 1, &rset2, NULL, NULL, NULL);
    if (r == -1) {
      if (errno == EINTR)
        goto again;

      perror ("select");
    quit:
      if (stdoutput) {
        free (*stdoutput);
        *stdoutput = NULL;
      }
      if (stderror) {
        free (*stderror);
        /* Need to return non-NULL *stderror here since most callers
         * will try to print and then free the err string.
         * Unfortunately recovery from strdup failure here is not
         * possible.
         */
        *stderror = strdup ("error running external command, "
                            "see debug output for details");
      }
      close (so_fd[0]);
      close (se_fd[0]);
      waitpid (pid, NULL, 0);
      if (stdin_pid >= 0) waitpid (stdin_pid, NULL, 0);
      return -1;
    }

    if (FD_ISSET (so_fd[0], &rset2)) { /* something on stdout */
      r = read (so_fd[0], buf, sizeof buf);
      if (r == -1) {
        perror ("read");
        goto quit;
      }
      if (r == 0) { FD_CLR (so_fd[0], &rset); quit++; }

      if (r > 0 && stdoutput) {
        so_size += r;
        p = realloc (*stdoutput, so_size);
        if (p == NULL) {
          perror ("realloc");
          goto quit;
        }
        *stdoutput = p;
        memcpy (*stdoutput + so_size - r, buf, r);
      }
    }

    if (FD_ISSET (se_fd[0], &rset2)) { /* something on stderr */
      r = read (se_fd[0], buf, sizeof buf);
      if (r == -1) {
        perror ("read");
        goto quit;
      }
      if (r == 0) { FD_CLR (se_fd[0], &rset); quit++; }

      if (r > 0) {
        if (verbose)
          ignore_value (write (2, buf, r));

        if (stderror) {
          se_size += r;
          p = realloc (*stderror, se_size);
          if (p == NULL) {
            perror ("realloc");
            goto quit;
          }
          *stderror = p;
          memcpy (*stderror + se_size - r, buf, r);
        }
      }
    }
  }

  close (so_fd[0]);
  close (se_fd[0]);

  /* Make sure the output buffers are \0-terminated.  Also remove any
   * trailing \n characters from the error buffer (not from stdout).
   */
  if (stdoutput) {
    void *q = realloc (*stdoutput, so_size+1);
    if (q == NULL) {
      perror ("realloc");
      free (*stdoutput);
    }
    *stdoutput = q;
    if (*stdoutput)
      (*stdoutput)[so_size] = '\0';
  }
  if (stderror) {
    void *q = realloc (*stderror, se_size+1);
    if (q == NULL) {
      perror ("realloc");
      free (*stderror);
    }
    *stderror = q;
    if (*stderror) {
      (*stderror)[se_size] = '\0';
      while (se_size > 0 && (*stderror)[se_size-1] == '\n') {
        se_size--;
        (*stderror)[se_size] = '\0';
      }
    }
  }

  if (flag_copy_stdin) {
    /* Check copy process didn't fail. */
    if (waitpid (stdin_pid, &r, 0) != stdin_pid) {
      perror ("waitpid");
      kill (pid, 9);
      waitpid (pid, NULL, 0);
      return -1;
    }

    if (!WIFEXITED (r) || WEXITSTATUS (r) != 0) {
      fprintf (stderr, "failed copying from input file, see earlier messages (r = %d)\n", r);
      kill (pid, 9);
      waitpid (pid, NULL, 0);
      return -1;
    }
  }

  /* Get the exit status of the command. */
  if (waitpid (pid, &r, 0) != pid) {
    perror ("waitpid");
    return -1;
  }

  if (WIFEXITED (r)) {
    return WEXITSTATUS (r);
  } else
    return -1;
}

/* Split an output string into a NULL-terminated list of lines.
 * Typically this is used where we have run an external command
 * which has printed out a list of things, and we want to return
 * an actual list.
 *
 * The corner cases here are quite tricky.  Note in particular:
 *
 *   "" -> []
 *   "\n" -> [""]
 *   "a\nb" -> ["a"; "b"]
 *   "a\nb\n" -> ["a"; "b"]
 *   "a\nb\n\n" -> ["a"; "b"; ""]
 *
 * The original string is written over and destroyed by this
 * function (which is usually OK because it's the 'out' string
 * from command()).  You can free the original string, because
 * add_string() strdups the strings.
 */
char **
split_lines (char *str)
{
  DECLARE_STRINGSBUF (lines);
  char *p, *pend;

  if (STREQ (str, ""))
    goto empty_list;

  p = str;
  while (p) {
    /* Empty last line? */
    if (p[0] == '\0')
      break;

    pend = strchr (p, '\n');
    if (pend) {
      *pend = '\0';
      pend++;
    }

    if (add_string (&lines, p) == -1) {
      return NULL;
    }

    p = pend;
  }

 empty_list:
  if (end_stringsbuf (&lines) == -1)
    return NULL;

  return lines.argv;
}

/* Skip leading and trailing whitespace, updating the original string
 * in-place.
 */
void
trim (char *str)
{
  size_t len = strlen (str);

  while (len > 0 && c_isspace (str[len-1])) {
    str[len-1] = '\0';
    len--;
  }

  const char *p = str;
  while (*p && c_isspace (*p)) {
    p++;
    len--;
  }

  memmove (str, p, len+1);
}

/* printf helper function so we can use %Q ("quoted") and %R to print
 * shell-quoted strings.  See guestfs(3)/EXTENDING LIBGUESTFS for more
 * details.
 */
static int
print_shell_quote (FILE *stream,
                   const struct printf_info *info ATTRIBUTE_UNUSED,
                   const void *const *args)
{
#define SAFE(c) (c_isalnum((c)) ||					\
                 (c) == '/' || (c) == '-' || (c) == '_' || (c) == '.')
  int i, len;
  const char *str = *((const char **) (args[0]));

  for (i = len = 0; str[i]; ++i) {
    if (!SAFE(str[i])) {
      putc ('\\', stream);
      len ++;
    }
    putc (str[i], stream);
    len ++;
  }

  return len;
}

static int
print_sysroot_shell_quote (FILE *stream,
                           const struct printf_info *info,
                           const void *const *args)
{
  fputs (sysroot, stream);
  return sysroot_len + print_shell_quote (stream, info, args);
}

#ifdef HAVE_REGISTER_PRINTF_SPECIFIER
static int
print_arginfo (const struct printf_info *info ATTRIBUTE_UNUSED,
               size_t n, int *argtypes, int *size)
{
  if (n > 0) {
    argtypes[0] = PA_STRING;
    size[0] = sizeof (const char *);
  }
  return 1;
}
#else
#ifdef HAVE_REGISTER_PRINTF_FUNCTION
static int
print_arginfo (const struct printf_info *info, size_t n, int *argtypes)
{
  if (n > 0)
    argtypes[0] = PA_STRING;
  return 1;
}
#else
#error "HAVE_REGISTER_PRINTF_{SPECIFIER|FUNCTION} not defined"
#endif
#endif

/* Perform device name translation.  Don't call this directly -
 * use the RESOLVE_DEVICE macro.
 *
 * See guestfs(3) for the algorithm.
 *
 * We have to open the device and test for ENXIO, because
 * the device nodes themselves will exist in the appliance.
 */
int
device_name_translation (char *device)
{
  int fd;

  fd = open (device, O_RDONLY|O_CLOEXEC);
  if (fd >= 0) {
  close_ok:
    close (fd);
    return 0;
  }

  if (errno != ENXIO && errno != ENOENT)
    return -1;

  /* If the name begins with "/dev/sd" then try the alternatives. */
  if (STRNEQLEN (device, "/dev/sd", 7))
    return -1;

  device[5] = 'h';		/* /dev/hd (old IDE driver) */
  fd = open (device, O_RDONLY|O_CLOEXEC);
  if (fd >= 0)
    goto close_ok;

  device[5] = 'v';		/* /dev/vd (for virtio devices) */
  fd = open (device, O_RDONLY|O_CLOEXEC);
  if (fd >= 0)
    goto close_ok;

  device[5] = 's';		/* Restore original device name. */
  return -1;
}

/* Check program exists and is executable on $PATH.  Actually, we
 * just assume PATH contains the default entries (see main() above).
 */
int
prog_exists (const char *prog)
{
  static const char * const dirs[] =
    { "/sbin", "/usr/sbin", "/bin", "/usr/bin" };
  size_t i;
  char buf[1024];

  for (i = 0; i < sizeof dirs / sizeof dirs[0]; ++i) {
    snprintf (buf, sizeof buf, "%s/%s", dirs[i], prog);
    if (access (buf, X_OK) == 0)
      return 1;
  }
  return 0;
}

/* LVM and other commands aren't synchronous, especially when udev is
 * involved.  eg. You can create or remove some device, but the /dev
 * device node won't appear until some time later.  This means that
 * you get an error if you run one command followed by another.
 *
 * Use 'udevadm settle' after certain commands, but don't be too
 * fussed if it fails.
 *
 * 'udevsettle' was the old name for this command (RHEL 5).  This was
 * deprecated in favour of 'udevadm settle'.  The old 'udevsettle'
 * command was left as a symlink.  Then in Fedora 13 the old symlink
 * remained but it stopped working (RHBZ#548121), so we have to be
 * careful not to assume that we can use 'udevsettle' if it exists.
 */
void
udev_settle (void)
{
  (void) command (NULL, NULL, "udevadm", "settle", NULL);
  (void) command (NULL, NULL, "udevsettle", NULL);
}