Refactor febootstrap-supermin-helper code into separate files.

This is just code movement.  There is no change to the code.

7 files changed, 1013 insertions, 879 deletions

diff --git a/helper/Makefile.am b/helper/Makefile.am
index 66d5b49..1033837 100644
--- a/helper/Makefile.am
+++ b/helper/Makefile.am
@@ -20,7 +20,12 @@
 bin_PROGRAMS = \
 	febootstrap-supermin-helper
 
-febootstrap_supermin_helper_SOURCES = main.c
+febootstrap_supermin_helper_SOURCES = \
+	helper.h \
+	appliance.c \
+	kernel.c \
+	main.c \
+	utils.c
 febootstrap_supermin_helper_CFLAGS = -Wall -I../lib
 febootstrap_supermin_helper_LDADD = $(LTLIBINTL) -L../lib -lgnu
 
diff --git a/helper/README b/helper/README
new file mode 100644
index 0000000..2577b31
--- /dev/null
+++ b/helper/README
@@ -0,0 +1,11 @@
+This directory contains the febootstrap-supermin-helper
+reimplementation in C.
+
+This program builds the supermin appliance on the fly each time the
+appliance runs (or in recent versions of libguestfs, the appliance is
+cached as long as the host files don't change).
+
+*NOTE*: This program is designed to be very short-lived, and so we
+don't normally bother to free up any memory that we allocate.  That's
+not completely true - we free up stuff if it's obvious and easy to
+free up, and ignore the rest.
diff --git a/helper/appliance.c b/helper/appliance.c
new file mode 100644
index 0000000..c7200bd
--- /dev/null
+++ b/helper/appliance.c
@@ -0,0 +1,501 @@
+/* febootstrap-supermin-helper reimplementation in C.
+ * Copyright (C) 2009-2010 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <limits.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <dirent.h>
+#include <fnmatch.h>
+#include <sys/stat.h>
+#include <assert.h>
+
+#include "error.h"
+#include "fts_.h"
+#include "full-write.h"
+#include "xalloc.h"
+#include "xvasprintf.h"
+
+#include "helper.h"
+
+/* Buffer size used in copy operations throughout.  Large for
+ * greatest efficiency.
+ */
+#define BUFFER_SIZE 65536
+
+static void iterate_inputs (char **inputs, int nr_inputs);
+static void iterate_input_directory (const char *dirname, int dirfd);
+static void write_kernel_modules (const char *whitelist, const char *modpath);
+static void write_hostfiles (const char *hostfiles_file);
+static void write_to_fd (const void *buffer, size_t len);
+static void write_file_to_fd (const char *filename);
+static void write_file_len_to_fd (const char *filename, size_t len);
+static void write_padding (size_t len);
+static void cpio_append_fts_entry (FTSENT *entry);
+static void cpio_append_stat (const char *filename, struct stat *);
+static void cpio_append (const char *filename);
+static void cpio_append_trailer (void);
+
+static int out_fd = -1;
+static off_t out_offset = 0;
+
+/* Create the appliance.
+ *
+ * The initrd consists of these components concatenated together:
+ *
+ * (1) The base skeleton appliance that we constructed at build time.
+ *     format = plain cpio
+ * (2) The host files which match wildcards in *.supermin.hostfiles.
+ *     input format = plain text, output format = plain cpio
+ * (3) The modules from modpath which are on the module whitelist.
+ *     output format = plain cpio
+ *
+ * The original shell script used the external cpio program to create
+ * parts (2) and (3), but we have decided it's going to be faster if
+ * we just write out the data outselves.  The reasons are that
+ * external cpio is slow (particularly when used with SELinux because
+ * it does 512 byte reads), and the format that we're writing is
+ * narrow and well understood, because we only care that the Linux
+ * kernel can read it.
+ *
+ * This version contains some improvements over the C version written
+ * for libguestfs, in that we can have multiple base images (or
+ * hostfiles) or use a directory to store these files.
+ */
+void
+create_appliance (char **inputs, int nr_inputs,
+                  const char *whitelist,
+                  const char *modpath,
+                  const char *initrd)
+{
+  out_fd = open (initrd, O_WRONLY | O_CREAT | O_TRUNC | O_NOCTTY, 0644);
+  if (out_fd == -1)
+    error (EXIT_FAILURE, errno, "open: %s", initrd);
+  out_offset = 0;
+
+  iterate_inputs (inputs, nr_inputs);
+
+  /* Kernel modules (3). */
+  write_kernel_modules (whitelist, modpath);
+
+  cpio_append_trailer ();
+
+  /* Finish off and close output file. */
+  if (close (out_fd) == -1)
+    error (EXIT_FAILURE, errno, "close: %s", initrd);
+}
+
+/* Iterate over the inputs to find out what they are, visiting
+ * directories if specified.
+ */
+static void
+iterate_inputs (char **inputs, int nr_inputs)
+{
+  int i;
+  for (i = 0; i < nr_inputs; ++i) {
+    if (verbose)
+      print_timestamped_message ("visiting %s", inputs[i]);
+
+    int fd = open (inputs[i], O_RDONLY);
+    if (fd == -1)
+      error (EXIT_FAILURE, errno, "open: %s", inputs[i]);
+
+    struct stat statbuf;
+    if (fstat (fd, &statbuf) == -1)
+      error (EXIT_FAILURE, errno, "fstat: %s", inputs[i]);
+
+    /* Directory? */
+    if (S_ISDIR (statbuf.st_mode))
+      iterate_input_directory (inputs[i], fd);
+    else if (S_ISREG (statbuf.st_mode)) {
+      /* Is it a cpio file? */
+      char buf[6];
+      if (read (fd, buf, 6) == 6 && memcmp (buf, "070701", 6) == 0)
+        /* Yes, a cpio file.  This is a skeleton appliance, case (1). */
+        write_file_to_fd (inputs[i]);
+      else
+        /* No, must be hostfiles, case (2). */
+        write_hostfiles (inputs[i]);
+    }
+    else
+      error (EXIT_FAILURE, 0, "%s: input is not a regular file or directory",
+             inputs[i]);
+
+    close (fd);
+  }
+}
+
+static void
+iterate_input_directory (const char *dirname, int dirfd)
+{
+  char path[PATH_MAX];
+  strcpy (path, dirname);
+  size_t len = strlen (dirname);
+  path[len++] = '/';
+
+  char *inputs[] = { path };
+
+  DIR *dir = fdopendir (dirfd);
+  if (dir == NULL)
+    error (EXIT_FAILURE, errno, "fdopendir: %s", dirname);
+
+  struct dirent *d;
+  while ((errno = 0, d = readdir (dir)) != NULL) {
+    if (d->d_name[0] == '.') /* ignore ., .. and any hidden files. */
+      continue;
+
+    strcpy (&path[len], d->d_name);
+    iterate_inputs (inputs, 1);
+  }
+
+  if (errno != 0)
+    error (EXIT_FAILURE, errno, "readdir: %s", dirname);
+
+  if (closedir (dir) == -1)
+    error (EXIT_FAILURE, errno, "closedir: %s", dirname);
+}
+
+/* Copy kernel modules.
+ *
+ * Find every file under modpath.
+ *
+ * Exclude all *.ko files, *except* ones which match names in
+ * the whitelist (which may contain wildcards).  Include all
+ * other files.
+ *
+ * Add chosen files to the output.
+ *
+ * whitelist_file may be NULL, to include ALL kernel modules.
+ */
+static void
+write_kernel_modules (const char *whitelist_file, const char *modpath)
+{
+  char **whitelist = NULL;
+  if (whitelist_file != NULL)
+    whitelist = load_file (whitelist_file);
+
+  char *paths[2] = { (char *) modpath, NULL };
+  FTS *fts = fts_open (paths, FTS_COMFOLLOW|FTS_PHYSICAL, NULL);
+  if (fts == NULL)
+    error (EXIT_FAILURE, errno, "write_kernel_modules: fts_open: %s", modpath);
+
+  for (;;) {
+    errno = 0;
+    FTSENT *entry = fts_read (fts);
+    if (entry == NULL && errno != 0)
+      error (EXIT_FAILURE, errno, "write_kernel_modules: fts_read: %s", modpath);
+    if (entry == NULL)
+      break;
+
+    /* Ignore directories being visited in post-order. */
+    if (entry->fts_info & FTS_DP)
+      continue;
+
+    /* Is it a *.ko file? */
+    if (entry->fts_namelen >= 3 &&
+        entry->fts_name[entry->fts_namelen-3] == '.' &&
+        entry->fts_name[entry->fts_namelen-2] == 'k' &&
+        entry->fts_name[entry->fts_namelen-1] == 'o') {
+      if (whitelist) {
+        /* Is it a *.ko file which is on the whitelist? */
+        size_t j;
+        for (j = 0; whitelist[j] != NULL; ++j) {
+          int r;
+          r = fnmatch (whitelist[j], entry->fts_name, 0);
+          if (r == 0) {
+            /* It's on the whitelist, so include it. */
+            if (verbose >= 2)
+              fprintf (stderr, "including kernel module %s (matches whitelist entry %s)\n",
+                       entry->fts_name, whitelist[j]);
+            cpio_append_fts_entry (entry);
+            break;
+          } else if (r != FNM_NOMATCH)
+            error (EXIT_FAILURE, 0, "internal error: fnmatch ('%s', '%s', %d) returned unexpected non-zero value %d\n",
+                   whitelist[j], entry->fts_name, 0, r);
+        } /* for (j) */
+      } else { /* whitelist == NULL, always include */
+        if (verbose >= 2)
+          fprintf (stderr, "including kernel module %s\n", entry->fts_name);
+        cpio_append_fts_entry (entry);
+      }
+    } else
+      /* It's some other sort of file, or a directory, always include. */
+      cpio_append_fts_entry (entry);
+  }
+
+  if (fts_close (fts) == -1)
+    error (EXIT_FAILURE, errno, "write_kernel_modules: fts_close: %s", modpath);
+}
+
+/* Copy the host files.
+ *
+ * Read the list of entries in hostfiles (which may contain
+ * wildcards).  Look them up in the filesystem, and add those files
+ * that exist.  Ignore any files that don't exist or are not readable.
+ */
+static void
+write_hostfiles (const char *hostfiles_file)
+{
+  char **hostfiles = load_file (hostfiles_file);
+
+  /* Hostfiles list can contain "." before each path - ignore it.
+   * It also contains each directory name before we enter it.  But
+   * we don't read that until we see a wildcard for that directory.
+   */
+  size_t i, j;
+  for (i = 0; hostfiles[i] != NULL; ++i) {
+    char *hostfile = hostfiles[i];
+    if (hostfile[0] == '.')
+      hostfile++;
+
+    struct stat statbuf;
+
+    /* Is it a wildcard? */
+    if (strchr (hostfile, '*') || strchr (hostfile, '?')) {
+      char *dirname = xstrdup (hostfile);
+      char *patt = strrchr (dirname, '/');
+      assert (patt);
+      *patt++ = '\0';
+
+      char **files = read_dir (dirname);
+      files = filter_fnmatch (files, patt, FNM_NOESCAPE);
+
+      /* Add matching files. */
+      for (j = 0; files[j] != NULL; ++j) {
+        char *tmp = xasprintf ("%s/%s", dirname, files[j]);
+
+        if (verbose >= 2)
+          fprintf (stderr, "including host file %s (matches %s)\n", tmp, patt);
+
+        cpio_append (tmp);
+
+        free (tmp);
+      }
+    }
+    /* Else does this file/directory/whatever exist? */
+    else if (lstat (hostfile, &statbuf) == 0) {
+      if (verbose >= 2)
+        fprintf (stderr, "including host file %s (directly referenced)\n",
+                 hostfile);
+
+      cpio_append_stat (hostfile, &statbuf);
+    } /* Ignore files that don't exist. */
+  }
+}
+
+/* Copy contents of buffer to out_fd and keep out_offset correct. */
+static void
+write_to_fd (const void *buffer, size_t len)
+{
+  if (full_write (out_fd, buffer, len) != len)
+    error (EXIT_FAILURE, errno, "write");
+  out_offset += len;
+}
+
+/* Copy contents of file to out_fd. */
+static void
+write_file_to_fd (const char *filename)
+{
+  char buffer[BUFFER_SIZE];
+  int fd2;
+  ssize_t r;
+
+  if (verbose >= 2)
+    fprintf (stderr, "write_file_to_fd %s -> %d\n", filename, out_fd);
+
+  fd2 = open (filename, O_RDONLY);
+  if (fd2 == -1)
+    error (EXIT_FAILURE, errno, "open: %s", filename);
+  for (;;) {
+    r = read (fd2, buffer, sizeof buffer);
+    if (r == 0)
+      break;
+    if (r == -1) {
+      if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
+        continue;
+      error (EXIT_FAILURE, errno, "read: %s", filename);
+    }
+    write_to_fd (buffer, r);
+  }
+
+  if (close (fd2) == -1)
+    error (EXIT_FAILURE, errno, "close: %s", filename);
+}
+
+/* Copy file of given length to output, and fail if the file has
+ * changed size.
+ */
+static void
+write_file_len_to_fd (const char *filename, size_t len)
+{
+  char buffer[BUFFER_SIZE];
+  size_t count = 0;
+
+  if (verbose >= 2)
+    fprintf (stderr, "write_file_to_fd %s -> %d\n", filename, out_fd);
+
+  int fd2 = open (filename, O_RDONLY);
+  if (fd2 == -1)
+    error (EXIT_FAILURE, errno, "open: %s", filename);
+  for (;;) {
+    ssize_t r = read (fd2, buffer, sizeof buffer);
+    if (r == 0)
+      break;
+    if (r == -1) {
+      if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
+        continue;
+      error (EXIT_FAILURE, errno, "read: %s", filename);
+    }
+    write_to_fd (buffer, r);
+    count += r;
+    if (count > len)
+      error (EXIT_FAILURE, 0, "write_file_len_to_fd: %s: file has increased in size\n", filename);
+  }
+
+  if (close (fd2) == -1)
+    error (EXIT_FAILURE, errno, "close: %s", filename);
+
+  if (count != len)
+    error (EXIT_FAILURE, 0, "febootstrap-supermin-helper: write_file_len_to_fd: %s: file has changed size\n", filename);
+}
+
+/* Append the file pointed to by FTSENT to the cpio output. */
+static void
+cpio_append_fts_entry (FTSENT *entry)
+{
+  if (entry->fts_info & FTS_NS || entry->fts_info & FTS_NSOK)
+    cpio_append (entry->fts_path);
+  else
+    cpio_append_stat (entry->fts_path, entry->fts_statp);
+}
+
+/* Append the file named 'filename' to the cpio output. */
+static void
+cpio_append (const char *filename)
+{
+  struct stat statbuf;
+
+  if (lstat (filename, &statbuf) == -1)
+    error (EXIT_FAILURE, errno, "lstat: %s", filename);
+  cpio_append_stat (filename, &statbuf);
+}
+
+/* Append the file to the cpio output. */
+#define PADDING(len) ((((len) + 3) & ~3) - (len))
+
+#define CPIO_HEADER_LEN (6 + 13*8)
+
+static void
+cpio_append_stat (const char *filename, struct stat *statbuf)
+{
+  const char *orig_filename = filename;
+
+  if (*filename == '/')
+    filename++;
+  if (*filename == '\0')
+    filename = ".";
+
+  if (verbose >= 2)
+    fprintf (stderr, "cpio_append_stat %s 0%o -> %d\n",
+             orig_filename, statbuf->st_mode, out_fd);
+
+  /* Regular files and symlinks are the only ones that have a "body"
+   * in this cpio entry.
+   */
+  int has_body = S_ISREG (statbuf->st_mode) || S_ISLNK (statbuf->st_mode);
+
+  size_t len = strlen (filename) + 1;
+
+  char header[CPIO_HEADER_LEN + 1];
+  snprintf (header, sizeof header,
+            "070701"            /* magic */
+            "%08X"              /* inode */
+            "%08X"              /* mode */
+            "%08X" "%08X"       /* uid, gid */
+            "%08X"              /* nlink */
+            "%08X"              /* mtime */
+            "%08X"              /* file length */
+            "%08X" "%08X"       /* device holding file major, minor */
+            "%08X" "%08X"       /* for specials, device major, minor */
+            "%08X"              /* name length (including \0 byte) */
+            "%08X",             /* checksum (not used by the kernel) */
+            (unsigned) statbuf->st_ino, statbuf->st_mode,
+            statbuf->st_uid, statbuf->st_gid,
+            (unsigned) statbuf->st_nlink, (unsigned) statbuf->st_mtime,
+            has_body ? (unsigned) statbuf->st_size : 0,
+            major (statbuf->st_dev), minor (statbuf->st_dev),
+            major (statbuf->st_rdev), minor (statbuf->st_rdev),
+            (unsigned) len, 0);
+
+  /* Write the header. */
+  write_to_fd (header, CPIO_HEADER_LEN);
+
+  /* Follow with the filename, and pad it. */
+  write_to_fd (filename, len);
+  size_t padding_len = PADDING (CPIO_HEADER_LEN + len);
+  write_padding (padding_len);
+
+  /* Follow with the file or symlink content, and pad it. */
+  if (has_body) {
+    if (S_ISREG (statbuf->st_mode))
+      write_file_len_to_fd (orig_filename, statbuf->st_size);
+    else if (S_ISLNK (statbuf->st_mode)) {
+      char tmp[PATH_MAX];
+      if (readlink (orig_filename, tmp, sizeof tmp) == -1)
+        error (EXIT_FAILURE, errno, "readlink: %s", orig_filename);
+      write_to_fd (tmp, statbuf->st_size);
+    }
+
+    padding_len = PADDING (statbuf->st_size);
+    write_padding (padding_len);
+  }
+}
+
+/* CPIO voodoo. */
+static void
+cpio_append_trailer (void)
+{
+  struct stat statbuf;
+  memset (&statbuf, 0, sizeof statbuf);
+  statbuf.st_nlink = 1;
+  cpio_append_stat ("TRAILER!!!", &statbuf);
+
+  /* CPIO seems to pad up to the next block boundary, ie. up to
+   * the next 512 bytes.
+   */
+  write_padding (((out_offset + 511) & ~511) - out_offset);
+  assert ((out_offset & 511) == 0);
+}
+
+/* Write 'len' bytes of zeroes out. */
+static void
+write_padding (size_t len)
+{
+  static const char buffer[512] = { 0 };
+
+  while (len > 0) {
+    size_t n = len < sizeof buffer ? len : sizeof buffer;
+    write_to_fd (buffer, n);
+    len -= n;
+  }
+}
diff --git a/helper/helper.h b/helper/helper.h
new file mode 100644
index 0000000..42bf824
--- /dev/null
+++ b/helper/helper.h
@@ -0,0 +1,46 @@
+/* febootstrap-supermin-helper reimplementation in C.
+ * Copyright (C) 2009-2010 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef FEBOOTSTRAP_SUPERMIN_HELPER_H
+#define FEBOOTSTRAP_SUPERMIN_HELPER_H
+
+/* main.c */
+extern struct timeval start_t;
+extern int verbose;
+
+/* appliance.c */
+extern void create_appliance (char **inputs, int nr_inputs, const char *whitelist, const char *modpath, const char *initrd);
+
+/* kernel.c */
+extern const char *create_kernel (const char *hostcpu, const char *kernel);
+
+/* utils.c */
+extern void print_timestamped_message (const char *fs, ...);
+extern int64_t timeval_diff (const struct timeval *x, const struct timeval *y);
+extern int reverse_filevercmp (const void *p1, const void *p2);
+extern void add_string (char ***argv, size_t *n_used, size_t *n_alloc, const char *str);
+extern size_t count_strings (char *const *argv);
+extern char **read_dir (const char *name);
+extern char **filter (char **strings, int (*)(const char *));
+extern char **filter_fnmatch (char **strings, const char *patt, int flags);
+extern char **filter_notmatching_substring (char **strings, const char *sub);
+extern void sort (char **strings, int (*compare) (const void *, const void *));
+extern int isdir (const char *path);
+extern char **load_file (const char *filename);
+
+#endif /* FEBOOTSTRAP_SUPERMIN_HELPER_H */
diff --git a/helper/kernel.c b/helper/kernel.c
new file mode 100644
index 0000000..3301826
--- /dev/null
+++ b/helper/kernel.c
@@ -0,0 +1,148 @@
+/* febootstrap-supermin-helper reimplementation in C.
+ * Copyright (C) 2009-2010 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <fnmatch.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "error.h"
+#include "xvasprintf.h"
+
+#include "helper.h"
+
+/* Directory containing candidate kernels.  We could make this
+ * configurable at some point.
+ */
+#define KERNELDIR "/boot"
+#define MODULESDIR "/lib/modules"
+
+static char *
+get_modpath (const char *kernel_name)
+{
+  /* Ignore "vmlinuz-" at the beginning of the kernel name. */
+  const char *version = &kernel_name[8];
+
+  /* /lib/modules/<version> */
+  char *modpath = xasprintf (MODULESDIR "/%s", version);
+  if (!modpath) {
+    perror ("xasprintf");
+    exit (EXIT_FAILURE);
+  }
+
+  return modpath;
+}
+
+/* kernel_name is "vmlinuz-*".  Check if there is a corresponding
+ * module path in /lib/modules.
+ */
+static int
+has_modpath (const char *kernel_name)
+{
+  char *modpath = get_modpath (kernel_name);
+
+  if (verbose)
+    fprintf (stderr, "checking modpath %s is a directory\n", modpath);
+
+  int r = isdir (modpath);
+
+  if (r) {
+    if (verbose)
+      fprintf (stderr, "picked %s because modpath %s exists\n",
+               kernel_name, modpath);
+    free (modpath);
+    return 1;
+  }
+  else {
+    free (modpath);
+    return 0;
+  }
+}
+
+/* Create the kernel.  This chooses an appropriate kernel and makes a
+ * symlink to it.
+ *
+ * Look for the most recent kernel named vmlinuz-*.<arch>* which has a
+ * corresponding directory in /lib/modules/. If the architecture is
+ * x86, look for any x86 kernel.
+ *
+ * RHEL 5 didn't append the arch to the kernel name, so look for
+ * kernels without arch second.
+ *
+ * If no suitable kernel can be found, exit with an error.
+ *
+ * This function returns the module path (ie. /lib/modules/<version>).
+ */
+const char *
+create_kernel (const char *hostcpu, const char *kernel)
+{
+  char **all_files = read_dir (KERNELDIR);
+
+  /* In original: ls -1dvr /boot/vmlinuz-*.$arch* 2>/dev/null | grep -v xen */
+  const char *patt;
+  if (hostcpu[0] == 'i' && hostcpu[2] == '8' && hostcpu[3] == '6' &&
+      hostcpu[4] == '\0')
+    patt = "vmlinuz-*.i?86*";
+  else
+    patt = xasprintf ("vmlinuz-*.%s*", hostcpu);
+
+  char **candidates;
+  candidates = filter_fnmatch (all_files, patt, FNM_NOESCAPE);
+  candidates = filter_notmatching_substring (candidates, "xen");
+  candidates = filter (candidates, has_modpath);
+
+  if (candidates[0] == NULL) {
+    /* In original: ls -1dvr /boot/vmlinuz-* 2>/dev/null | grep -v xen */
+    patt = "vmlinuz-*";
+    candidates = filter_fnmatch (all_files, patt, FNM_NOESCAPE);
+    candidates = filter_notmatching_substring (candidates, "xen");
+    candidates = filter (candidates, has_modpath);
+
+    if (candidates[0] == NULL)
+      goto no_kernels;
+  }
+
+  sort (candidates, reverse_filevercmp);
+
+  /* Choose the first candidate. */
+  char *tmp = xasprintf (KERNELDIR "/%s", candidates[0]);
+
+  if (verbose)
+    fprintf (stderr, "creating symlink %s -> %s\n", kernel, tmp);
+
+  if (symlink (tmp, kernel) == -1)
+    error (EXIT_FAILURE, errno, "symlink kernel");
+
+  free (tmp);
+
+  return get_modpath (candidates[0]);
+
+  /* Print more diagnostics here than the old script did. */
+ no_kernels:
+  fprintf (stderr,
+           "febootstrap-supermin-helper: failed to find a suitable kernel.\n"
+           "I looked for kernels in " KERNELDIR " and modules in " MODULESDIR
+           ".\n"
+           "If this is a Xen guest, and you only have Xen domU kernels\n"
+           "installed, try installing a fullvirt kernel (only for\n"
+           "febootstrap use, you shouldn't boot the Xen guest with it).\n");
+  exit (EXIT_FAILURE);
+}
diff --git a/helper/main.c b/helper/main.c
index a81cf61..a30e02c 100644
--- a/helper/main.c
+++ b/helper/main.c
@@ -16,61 +16,25 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
-/* This script builds the supermin appliance on the fly each
- * time the appliance runs.
- *
- * *NOTE*: This program is designed to be very short-lived, and so we
- * don't normally bother to free up any memory that we allocate.
- * That's not completely true - we free up stuff if it's obvious and
- * easy to free up, and ignore the rest.
- */
-
 #include <config.h>
 
 #include <stdio.h>
 #include <stdlib.h>
-#include <stdarg.h>
-#include <stdint.h>
 #include <string.h>
 #include <errno.h>
-#include <fcntl.h>
-#include <inttypes.h>
 #include <unistd.h>
 #include <getopt.h>
 #include <limits.h>
-#include <fnmatch.h>
-#include <dirent.h>
 #include <sys/types.h>
 #include <sys/time.h>
-#include <sys/stat.h>
 #include <assert.h>
 
 #include "error.h"
-#include "filevercmp.h"
-#include "fts_.h"
-#include "full-write.h"
-#include "hash.h"
-#include "hash-pjw.h"
-#include "xalloc.h"
-#include "xvasprintf.h"
 
-/* Directory containing candidate kernels.  We could make this
- * configurable at some point.
- */
-#define KERNELDIR "/boot"
-#define MODULESDIR "/lib/modules"
+#include "helper.h"
 
-/* Buffer size used in copy operations throughout.  Large for
- * greatest efficiency.
- */
-#define BUFFER_SIZE 65536
-
-static struct timeval start_t;
-static int verbose = 0;
-
-static void print_timestamped_message (const char *fs, ...);
-static const char *create_kernel (const char *hostcpu, const char *kernel);
-static void create_appliance (char **inputs, int nr_inputs, const char *whitelist, const char *modpath, const char *initrd);
+struct timeval start_t;
+int verbose = 0;
 
 enum { HELP_OPTION = CHAR_MAX + 1 };
 
@@ -195,842 +159,3 @@ main (int argc, char *argv[])
 
   exit (EXIT_SUCCESS);
 }
-
-/* Compute Y - X and return the result in milliseconds.
- * Approximately the same as this code:
- * http://www.mpp.mpg.de/~huber/util/timevaldiff.c
- */
-static int64_t
-timeval_diff (const struct timeval *x, const struct timeval *y)
-{
-  int64_t msec;
-
-  msec = (y->tv_sec - x->tv_sec) * 1000;
-  msec += (y->tv_usec - x->tv_usec) / 1000;
-  return msec;
-}
-
-static void
-print_timestamped_message (const char *fs, ...)
-{
-  struct timeval tv;
-  gettimeofday (&tv, NULL);
-
-  va_list args;
-  char *msg;
-  int err;
-
-  va_start (args, fs);
-  err = vasprintf (&msg, fs, args);
-  va_end (args);
-
-  if (err < 0) return;
-
-  fprintf (stderr, "supermin helper [%05" PRIi64 "ms] %s\n",
-           timeval_diff (&start_t, &tv), msg);
-
-  free (msg);
-}
-
-static char **read_dir (const char *dir);
-static char **filter (char **strings, int (*)(const char *));
-static char **filter_fnmatch (char **strings, const char *patt, int flags);
-static char **filter_notmatching_substring (char **strings, const char *sub);
-static void sort (char **strings, int (*compare) (const void *, const void *));
-static int isdir (const char *path);
-
-static int
-reverse_filevercmp (const void *p1, const void *p2)
-{
-  const char *s1 = * (char * const *) p1;
-  const char *s2 = * (char * const *) p2;
-
-  /* Note, arguments are reversed to achieve a reverse sort. */
-  return filevercmp (s2, s1);
-}
-
-static char *
-get_modpath (const char *kernel_name)
-{
-  /* Ignore "vmlinuz-" at the beginning of the kernel name. */
-  const char *version = &kernel_name[8];
-
-  /* /lib/modules/<version> */
-  char *modpath = xasprintf (MODULESDIR "/%s", version);
-  if (!modpath) {
-    perror ("xasprintf");
-    exit (EXIT_FAILURE);
-  }
-
-  return modpath;
-}
-
-/* kernel_name is "vmlinuz-*".  Check if there is a corresponding
- * module path in /lib/modules.
- */
-static int
-has_modpath (const char *kernel_name)
-{
-  char *modpath = get_modpath (kernel_name);
-
-  if (verbose)
-    fprintf (stderr, "checking modpath %s is a directory\n", modpath);
-
-  int r = isdir (modpath);
-
-  if (r) {
-    if (verbose)
-      fprintf (stderr, "picked %s because modpath %s exists\n",
-               kernel_name, modpath);
-    free (modpath);
-    return 1;
-  }
-  else {
-    free (modpath);
-    return 0;
-  }
-}
-
-/* Create the kernel.  This chooses an appropriate kernel and makes a
- * symlink to it.
- *
- * Look for the most recent kernel named vmlinuz-*.<arch>* which has a
- * corresponding directory in /lib/modules/. If the architecture is
- * x86, look for any x86 kernel.
- *
- * RHEL 5 didn't append the arch to the kernel name, so look for
- * kernels without arch second.
- *
- * If no suitable kernel can be found, exit with an error.
- *
- * This function returns the module path (ie. /lib/modules/<version>).
- */
-static const char *
-create_kernel (const char *hostcpu, const char *kernel)
-{
-  char **all_files = read_dir (KERNELDIR);
-
-  /* In original: ls -1dvr /boot/vmlinuz-*.$arch* 2>/dev/null | grep -v xen */
-  const char *patt;
-  if (hostcpu[0] == 'i' && hostcpu[2] == '8' && hostcpu[3] == '6' &&
-      hostcpu[4] == '\0')
-    patt = "vmlinuz-*.i?86*";
-  else
-    patt = xasprintf ("vmlinuz-*.%s*", hostcpu);
-
-  char **candidates;
-  candidates = filter_fnmatch (all_files, patt, FNM_NOESCAPE);
-  candidates = filter_notmatching_substring (candidates, "xen");
-  candidates = filter (candidates, has_modpath);
-
-  if (candidates[0] == NULL) {
-    /* In original: ls -1dvr /boot/vmlinuz-* 2>/dev/null | grep -v xen */
-    patt = "vmlinuz-*";
-    candidates = filter_fnmatch (all_files, patt, FNM_NOESCAPE);
-    candidates = filter_notmatching_substring (candidates, "xen");
-    candidates = filter (candidates, has_modpath);
-
-    if (candidates[0] == NULL)
-      goto no_kernels;
-  }
-
-  sort (candidates, reverse_filevercmp);
-
-  /* Choose the first candidate. */
-  char *tmp = xasprintf (KERNELDIR "/%s", candidates[0]);
-
-  if (verbose)
-    fprintf (stderr, "creating symlink %s -> %s\n", kernel, tmp);
-
-  if (symlink (tmp, kernel) == -1)
-    error (EXIT_FAILURE, errno, "symlink kernel");
-
-  free (tmp);
-
-  return get_modpath (candidates[0]);
-
-  /* Print more diagnostics here than the old script did. */
- no_kernels:
-  fprintf (stderr,
-           "febootstrap-supermin-helper: failed to find a suitable kernel.\n"
-           "I looked for kernels in " KERNELDIR " and modules in " MODULESDIR
-           ".\n"
-           "If this is a Xen guest, and you only have Xen domU kernels\n"
-           "installed, try installing a fullvirt kernel (only for\n"
-           "febootstrap use, you shouldn't boot the Xen guest with it).\n");
-  exit (EXIT_FAILURE);
-}
-
-static void iterate_inputs (char **inputs, int nr_inputs);
-static void iterate_input_directory (const char *dirname, int dirfd);
-static void write_kernel_modules (const char *whitelist, const char *modpath);
-static void write_hostfiles (const char *hostfiles_file);
-static void write_to_fd (const void *buffer, size_t len);
-static void write_file_to_fd (const char *filename);
-static void write_file_len_to_fd (const char *filename, size_t len);
-static void write_padding (size_t len);
-static char **load_file (const char *filename);
-static void cpio_append_fts_entry (FTSENT *entry);
-static void cpio_append_stat (const char *filename, struct stat *);
-static void cpio_append (const char *filename);
-static void cpio_append_trailer (void);
-
-static int out_fd = -1;
-static off_t out_offset = 0;
-
-/* Create the appliance.
- *
- * The initrd consists of these components concatenated together:
- *
- * (1) The base skeleton appliance that we constructed at build time.
- *     format = plain cpio
- * (2) The host files which match wildcards in *.supermin.hostfiles.
- *     input format = plain text, output format = plain cpio
- * (3) The modules from modpath which are on the module whitelist.
- *     output format = plain cpio
- *
- * The original shell script used the external cpio program to create
- * parts (2) and (3), but we have decided it's going to be faster if
- * we just write out the data outselves.  The reasons are that
- * external cpio is slow (particularly when used with SELinux because
- * it does 512 byte reads), and the format that we're writing is
- * narrow and well understood, because we only care that the Linux
- * kernel can read it.
- *
- * This version contains some improvements over the C version written
- * for libguestfs, in that we can have multiple base images (or
- * hostfiles) or use a directory to store these files.
- */
-static void
-create_appliance (char **inputs, int nr_inputs,
-                  const char *whitelist,
-                  const char *modpath,
-                  const char *initrd)
-{
-  out_fd = open (initrd, O_WRONLY | O_CREAT | O_TRUNC | O_NOCTTY, 0644);
-  if (out_fd == -1)
-    error (EXIT_FAILURE, errno, "open: %s", initrd);
-  out_offset = 0;
-
-  iterate_inputs (inputs, nr_inputs);
-
-  /* Kernel modules (3). */
-  write_kernel_modules (whitelist, modpath);
-
-  cpio_append_trailer ();
-
-  /* Finish off and close output file. */
-  if (close (out_fd) == -1)
-    error (EXIT_FAILURE, errno, "close: %s", initrd);
-}
-
-/* Iterate over the inputs to find out what they are, visiting
- * directories if specified.
- */
-static void
-iterate_inputs (char **inputs, int nr_inputs)
-{
-  int i;
-  for (i = 0; i < nr_inputs; ++i) {
-    if (verbose)
-      print_timestamped_message ("visiting %s", inputs[i]);
-
-    int fd = open (inputs[i], O_RDONLY);
-    if (fd == -1)
-      error (EXIT_FAILURE, errno, "open: %s", inputs[i]);
-
-    struct stat statbuf;
-    if (fstat (fd, &statbuf) == -1)
-      error (EXIT_FAILURE, errno, "fstat: %s", inputs[i]);
-
-    /* Directory? */
-    if (S_ISDIR (statbuf.st_mode))
-      iterate_input_directory (inputs[i], fd);
-    else if (S_ISREG (statbuf.st_mode)) {
-      /* Is it a cpio file? */
-      char buf[6];
-      if (read (fd, buf, 6) == 6 && memcmp (buf, "070701", 6) == 0)
-        /* Yes, a cpio file.  This is a skeleton appliance, case (1). */
-        write_file_to_fd (inputs[i]);
-      else
-        /* No, must be hostfiles, case (2). */
-        write_hostfiles (inputs[i]);
-    }
-    else
-      error (EXIT_FAILURE, 0, "%s: input is not a regular file or directory",
-             inputs[i]);
-
-    close (fd);
-  }
-}
-
-static void
-iterate_input_directory (const char *dirname, int dirfd)
-{
-  char path[PATH_MAX];
-  strcpy (path, dirname);
-  size_t len = strlen (dirname);
-  path[len++] = '/';
-
-  char *inputs[] = { path };
-
-  DIR *dir = fdopendir (dirfd);
-  if (dir == NULL)
-    error (EXIT_FAILURE, errno, "fdopendir: %s", dirname);
-
-  struct dirent *d;
-  while ((errno = 0, d = readdir (dir)) != NULL) {
-    if (d->d_name[0] == '.') /* ignore ., .. and any hidden files. */
-      continue;
-
-    strcpy (&path[len], d->d_name);
-    iterate_inputs (inputs, 1);
-  }
-
-  if (errno != 0)
-    error (EXIT_FAILURE, errno, "readdir: %s", dirname);
-
-  if (closedir (dir) == -1)
-    error (EXIT_FAILURE, errno, "closedir: %s", dirname);
-}
-
-/* Copy kernel modules.
- *
- * Find every file under modpath.
- *
- * Exclude all *.ko files, *except* ones which match names in
- * the whitelist (which may contain wildcards).  Include all
- * other files.
- *
- * Add chosen files to the output.
- *
- * whitelist_file may be NULL, to include ALL kernel modules.
- */
-static void
-write_kernel_modules (const char *whitelist_file, const char *modpath)
-{
-  char **whitelist = NULL;
-  if (whitelist_file != NULL)
-    whitelist = load_file (whitelist_file);
-
-  char *paths[2] = { (char *) modpath, NULL };
-  FTS *fts = fts_open (paths, FTS_COMFOLLOW|FTS_PHYSICAL, NULL);
-  if (fts == NULL)
-    error (EXIT_FAILURE, errno, "write_kernel_modules: fts_open: %s", modpath);
-
-  for (;;) {
-    errno = 0;
-    FTSENT *entry = fts_read (fts);
-    if (entry == NULL && errno != 0)
-      error (EXIT_FAILURE, errno, "write_kernel_modules: fts_read: %s", modpath);
-    if (entry == NULL)
-      break;
-
-    /* Ignore directories being visited in post-order. */
-    if (entry->fts_info & FTS_DP)
-      continue;
-
-    /* Is it a *.ko file? */
-    if (entry->fts_namelen >= 3 &&
-        entry->fts_name[entry->fts_namelen-3] == '.' &&
-        entry->fts_name[entry->fts_namelen-2] == 'k' &&
-        entry->fts_name[entry->fts_namelen-1] == 'o') {
-      if (whitelist) {
-        /* Is it a *.ko file which is on the whitelist? */
-        size_t j;
-        for (j = 0; whitelist[j] != NULL; ++j) {
-          int r;
-          r = fnmatch (whitelist[j], entry->fts_name, 0);
-          if (r == 0) {
-            /* It's on the whitelist, so include it. */
-            if (verbose >= 2)
-              fprintf (stderr, "including kernel module %s (matches whitelist entry %s)\n",
-                       entry->fts_name, whitelist[j]);
-            cpio_append_fts_entry (entry);
-            break;
-          } else if (r != FNM_NOMATCH)
-            error (EXIT_FAILURE, 0, "internal error: fnmatch ('%s', '%s', %d) returned unexpected non-zero value %d\n",
-                   whitelist[j], entry->fts_name, 0, r);
-        } /* for (j) */
-      } else { /* whitelist == NULL, always include */
-        if (verbose >= 2)
-          fprintf (stderr, "including kernel module %s\n", entry->fts_name);
-        cpio_append_fts_entry (entry);
-      }
-    } else
-      /* It's some other sort of file, or a directory, always include. */
-      cpio_append_fts_entry (entry);
-  }
-
-  if (fts_close (fts) == -1)
-    error (EXIT_FAILURE, errno, "write_kernel_modules: fts_close: %s", modpath);
-}
-
-/* Copy the host files.
- *
- * Read the list of entries in hostfiles (which may contain
- * wildcards).  Look them up in the filesystem, and add those files
- * that exist.  Ignore any files that don't exist or are not readable.
- */
-static void
-write_hostfiles (const char *hostfiles_file)
-{
-  char **hostfiles = load_file (hostfiles_file);
-
-  /* Hostfiles list can contain "." before each path - ignore it.
-   * It also contains each directory name before we enter it.  But
-   * we don't read that until we see a wildcard for that directory.
-   */
-  size_t i, j;
-  for (i = 0; hostfiles[i] != NULL; ++i) {
-    char *hostfile = hostfiles[i];
-    if (hostfile[0] == '.')
-      hostfile++;
-
-    struct stat statbuf;
-
-    /* Is it a wildcard? */
-    if (strchr (hostfile, '*') || strchr (hostfile, '?')) {
-      char *dirname = xstrdup (hostfile);
-      char *patt = strrchr (dirname, '/');
-      assert (patt);
-      *patt++ = '\0';
-
-      char **files = read_dir (dirname);
-      files = filter_fnmatch (files, patt, FNM_NOESCAPE);
-
-      /* Add matching files. */
-      for (j = 0; files[j] != NULL; ++j) {
-        char *tmp = xasprintf ("%s/%s", dirname, files[j]);
-
-        if (verbose >= 2)
-          fprintf (stderr, "including host file %s (matches %s)\n", tmp, patt);
-
-        cpio_append (tmp);
-
-        free (tmp);
-      }
-    }
-    /* Else does this file/directory/whatever exist? */
-    else if (lstat (hostfile, &statbuf) == 0) {
-      if (verbose >= 2)
-        fprintf (stderr, "including host file %s (directly referenced)\n",
-                 hostfile);
-
-      cpio_append_stat (hostfile, &statbuf);
-    } /* Ignore files that don't exist. */
-  }
-}
-
-/*----------*/
-/* Helper functions. */
-
-static void
-add_string (char ***argv, size_t *n_used, size_t *n_alloc, const char *str)
-{
-  char *new_str;
-
-  if (*n_used >= *n_alloc)
-    *argv = x2nrealloc (*argv, n_alloc, sizeof (char *));
-
-  if (str)
-    new_str = xstrdup (str);
-  else
-    new_str = NULL;
-
-  (*argv)[*n_used] = new_str;
-
-  (*n_used)++;
-}
-
-static size_t
-count_strings (char *const *argv)
-{
-  size_t argc;
-
-  for (argc = 0; argv[argc] != NULL; ++argc)
-    ;
-  return argc;
-}
-
-struct dir_cache {
-  char *path;
-  char **files;
-};
-
-static size_t
-dir_cache_hash (void const *x, size_t table_size)
-{
-  struct dir_cache const *p = x;
-  return hash_pjw (p->path, table_size);
-}
-
-static bool
-dir_cache_compare (void const *x, void const *y)
-{
-  struct dir_cache const *p = x;
-  struct dir_cache const *q = y;
-  return strcmp (p->path, q->path) == 0;
-}
-
-/* Read a directory into a list of strings.
- *
- * Previously looked up directories are cached and returned quickly,
- * saving some considerable amount of time compared to reading the
- * directory over again.  However this means you really must not
- * alter the array of strings that are returned.
- *
- * Returns an empty list if the directory cannot be opened.
- */
-static char **
-read_dir (const char *name)
-{
-  static Hash_table *ht = NULL;
-
-  if (!ht)
-    ht = hash_initialize (1024, NULL, dir_cache_hash, dir_cache_compare, NULL);
-
-  struct dir_cache key = { .path = (char *) name };
-  struct dir_cache *p = hash_lookup (ht, &key);
-  if (p)
-    return p->files;
-
-  char **files = NULL;
-  size_t n_used = 0, n_alloc = 0;
-
-  DIR *dir = opendir (name);
-  if (!dir) {
-    /* If it fails to open, that's OK, skip to the end. */
-    /*perror (name);*/
-    goto done;
-  }
-
-  for (;;) {
-    errno = 0;
-    struct dirent *d = readdir (dir);
-    if (d == NULL) {
-      if (errno != 0)
-        /* But if it fails here, after opening and potentially reading
-         * part of the directory, that's a proper failure - inform the
-         * user and exit.
-         */
-        error (EXIT_FAILURE, errno, "%s", name);
-      break;
-    }
-
-    add_string (&files, &n_used, &n_alloc, d->d_name);
-  }
-
-  if (closedir (dir) == -1)
-    error (EXIT_FAILURE, errno, "closedir: %s", name);
-
- done:
-  /* NULL-terminate the array. */
-  add_string (&files, &n_used, &n_alloc, NULL);
-
-  /* Add it to the hash for next time. */
-  p = xmalloc (sizeof *p);
-  p->path = (char *) name;
-  p->files = files;
-  p = hash_insert (ht, p);
-  assert (p != NULL);
-
-  return files;
-}
-
-/* Filter a list of strings, returning only those where f(s) != 0. */
-static char **
-filter (char **strings, int (*f) (const char *))
-{
-  char **out = NULL;
-  size_t n_used = 0, n_alloc = 0;
-
-  int i;
-  for (i = 0; strings[i] != NULL; ++i) {
-    if (f (strings[i]) != 0)
-      add_string (&out, &n_used, &n_alloc, strings[i]);
-  }
-
-  add_string (&out, &n_used, &n_alloc, NULL);
-  return out;
-}
-
-/* Filter a list of strings and return only those matching the wildcard. */
-static char **
-filter_fnmatch (char **strings, const char *patt, int flags)
-{
-  char **out = NULL;
-  size_t n_used = 0, n_alloc = 0;
-
-  int i, r;
-  for (i = 0; strings[i] != NULL; ++i) {
-    r = fnmatch (patt, strings[i], flags);
-    if (r == 0)
-      add_string (&out, &n_used, &n_alloc, strings[i]);
-    else if (r != FNM_NOMATCH)
-      error (EXIT_FAILURE, 0, "internal error: fnmatch ('%s', '%s', %d) returned unexpected non-zero value %d\n",
-             patt, strings[i], flags, r);
-  }
-
-  add_string (&out, &n_used, &n_alloc, NULL);
-  return out;
-}
-
-/* Filter a list of strings and return only those which DON'T contain sub. */
-static char **
-filter_notmatching_substring (char **strings, const char *sub)
-{
-  char **out = NULL;
-  size_t n_used = 0, n_alloc = 0;
-
-  int i;
-  for (i = 0; strings[i] != NULL; ++i) {
-    if (strstr (strings[i], sub) == NULL)
-      add_string (&out, &n_used, &n_alloc, strings[i]);
-  }
-
-  add_string (&out, &n_used, &n_alloc, NULL);
-  return out;
-}
-
-/* Sort a list of strings, in place, with the comparison function supplied. */
-static void
-sort (char **strings, int (*compare) (const void *, const void *))
-{
-  qsort (strings, count_strings (strings), sizeof (char *), compare);
-}
-
-/* Return true iff path exists and is a directory.  This version
- * follows symlinks.
- */
-static int
-isdir (const char *path)
-{
-  struct stat statbuf;
-
-  if (stat (path, &statbuf) == -1)
-    return 0;
-
-  return S_ISDIR (statbuf.st_mode);
-}
-
-/* Copy contents of buffer to out_fd and keep out_offset correct. */
-static void
-write_to_fd (const void *buffer, size_t len)
-{
-  if (full_write (out_fd, buffer, len) != len)
-    error (EXIT_FAILURE, errno, "write");
-  out_offset += len;
-}
-
-/* Copy contents of file to out_fd. */
-static void
-write_file_to_fd (const char *filename)
-{
-  char buffer[BUFFER_SIZE];
-  int fd2;
-  ssize_t r;
-
-  if (verbose >= 2)
-    fprintf (stderr, "write_file_to_fd %s -> %d\n", filename, out_fd);
-
-  fd2 = open (filename, O_RDONLY);
-  if (fd2 == -1)
-    error (EXIT_FAILURE, errno, "open: %s", filename);
-  for (;;) {
-    r = read (fd2, buffer, sizeof buffer);
-    if (r == 0)
-      break;
-    if (r == -1) {
-      if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
-        continue;
-      error (EXIT_FAILURE, errno, "read: %s", filename);
-    }
-    write_to_fd (buffer, r);
-  }
-
-  if (close (fd2) == -1)
-    error (EXIT_FAILURE, errno, "close: %s", filename);
-}
-
-/* Copy file of given length to output, and fail if the file has
- * changed size.
- */
-static void
-write_file_len_to_fd (const char *filename, size_t len)
-{
-  char buffer[BUFFER_SIZE];
-  size_t count = 0;
-
-  if (verbose >= 2)
-    fprintf (stderr, "write_file_to_fd %s -> %d\n", filename, out_fd);
-
-  int fd2 = open (filename, O_RDONLY);
-  if (fd2 == -1)
-    error (EXIT_FAILURE, errno, "open: %s", filename);
-  for (;;) {
-    ssize_t r = read (fd2, buffer, sizeof buffer);
-    if (r == 0)
-      break;
-    if (r == -1) {
-      if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
-        continue;
-      error (EXIT_FAILURE, errno, "read: %s", filename);
-    }
-    write_to_fd (buffer, r);
-    count += r;
-    if (count > len)
-      error (EXIT_FAILURE, 0, "write_file_len_to_fd: %s: file has increased in size\n", filename);
-  }
-
-  if (close (fd2) == -1)
-    error (EXIT_FAILURE, errno, "close: %s", filename);
-
-  if (count != len)
-    error (EXIT_FAILURE, 0, "febootstrap-supermin-helper: write_file_len_to_fd: %s: file has changed size\n", filename);
-}
-
-/* Load in a file, returning a list of lines. */
-static char **
-load_file (const char *filename)
-{
-  char **lines = 0;
-  size_t n_used = 0, n_alloc = 0;
-
-  FILE *fp;
-  fp = fopen (filename, "r");
-  if (fp == NULL)
-    error (EXIT_FAILURE, errno, "fopen: %s", filename);
-
-  char line[4096];
-  while (fgets (line, sizeof line, fp)) {
-    size_t len = strlen (line);
-    if (len > 0 && line[len-1] == '\n')
-      line[len-1] = '\0';
-    add_string (&lines, &n_used, &n_alloc, line);
-  }
-
-  add_string (&lines, &n_used, &n_alloc, NULL);
-  return lines;
-}
-
-/* Append the file pointed to by FTSENT to the cpio output. */
-static void
-cpio_append_fts_entry (FTSENT *entry)
-{
-  if (entry->fts_info & FTS_NS || entry->fts_info & FTS_NSOK)
-    cpio_append (entry->fts_path);
-  else
-    cpio_append_stat (entry->fts_path, entry->fts_statp);
-}
-
-/* Append the file named 'filename' to the cpio output. */
-static void
-cpio_append (const char *filename)
-{
-  struct stat statbuf;
-
-  if (lstat (filename, &statbuf) == -1)
-    error (EXIT_FAILURE, errno, "lstat: %s", filename);
-  cpio_append_stat (filename, &statbuf);
-}
-
-/* Append the file to the cpio output. */
-#define PADDING(len) ((((len) + 3) & ~3) - (len))
-
-#define CPIO_HEADER_LEN (6 + 13*8)
-
-static void
-cpio_append_stat (const char *filename, struct stat *statbuf)
-{
-  const char *orig_filename = filename;
-
-  if (*filename == '/')
-    filename++;
-  if (*filename == '\0')
-    filename = ".";
-
-  if (verbose >= 2)
-    fprintf (stderr, "cpio_append_stat %s 0%o -> %d\n",
-             orig_filename, statbuf->st_mode, out_fd);
-
-  /* Regular files and symlinks are the only ones that have a "body"
-   * in this cpio entry.
-   */
-  int has_body = S_ISREG (statbuf->st_mode) || S_ISLNK (statbuf->st_mode);
-
-  size_t len = strlen (filename) + 1;
-
-  char header[CPIO_HEADER_LEN + 1];
-  snprintf (header, sizeof header,
-            "070701"            /* magic */
-            "%08X"              /* inode */
-            "%08X"              /* mode */
-            "%08X" "%08X"       /* uid, gid */
-            "%08X"              /* nlink */
-            "%08X"              /* mtime */
-            "%08X"              /* file length */
-            "%08X" "%08X"       /* device holding file major, minor */
-            "%08X" "%08X"       /* for specials, device major, minor */
-            "%08X"              /* name length (including \0 byte) */
-            "%08X",             /* checksum (not used by the kernel) */
-            (unsigned) statbuf->st_ino, statbuf->st_mode,
-            statbuf->st_uid, statbuf->st_gid,
-            (unsigned) statbuf->st_nlink, (unsigned) statbuf->st_mtime,
-            has_body ? (unsigned) statbuf->st_size : 0,
-            major (statbuf->st_dev), minor (statbuf->st_dev),
-            major (statbuf->st_rdev), minor (statbuf->st_rdev),
-            (unsigned) len, 0);
-
-  /* Write the header. */
-  write_to_fd (header, CPIO_HEADER_LEN);
-
-  /* Follow with the filename, and pad it. */
-  write_to_fd (filename, len);
-  size_t padding_len = PADDING (CPIO_HEADER_LEN + len);
-  write_padding (padding_len);
-
-  /* Follow with the file or symlink content, and pad it. */
-  if (has_body) {
-    if (S_ISREG (statbuf->st_mode))
-      write_file_len_to_fd (orig_filename, statbuf->st_size);
-    else if (S_ISLNK (statbuf->st_mode)) {
-      char tmp[PATH_MAX];
-      if (readlink (orig_filename, tmp, sizeof tmp) == -1)
-        error (EXIT_FAILURE, errno, "readlink: %s", orig_filename);
-      write_to_fd (tmp, statbuf->st_size);
-    }
-
-    padding_len = PADDING (statbuf->st_size);
-    write_padding (padding_len);
-  }
-}
-
-/* CPIO voodoo. */
-static void
-cpio_append_trailer (void)
-{
-  struct stat statbuf;
-  memset (&statbuf, 0, sizeof statbuf);
-  statbuf.st_nlink = 1;
-  cpio_append_stat ("TRAILER!!!", &statbuf);
-
-  /* CPIO seems to pad up to the next block boundary, ie. up to
-   * the next 512 bytes.
-   */
-  write_padding (((out_offset + 511) & ~511) - out_offset);
-  assert ((out_offset & 511) == 0);
-}
-
-/* Write 'len' bytes of zeroes out. */
-static void
-write_padding (size_t len)
-{
-  static const char buffer[512] = { 0 };
-
-  while (len > 0) {
-    size_t n = len < sizeof buffer ? len : sizeof buffer;
-    write_to_fd (buffer, n);
-    len -= n;
-  }
-}
diff --git a/helper/utils.c b/helper/utils.c
new file mode 100644
index 0000000..4d54cc5
--- /dev/null
+++ b/helper/utils.c
@@ -0,0 +1,298 @@
+/* febootstrap-supermin-helper reimplementation in C.
+ * Copyright (C) 2009-2010 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fnmatch.h>
+#include <inttypes.h>
+#include <sys/time.h>
+#include <sys/stat.h>
+#include <assert.h>
+
+#include "error.h"
+#include "filevercmp.h"
+#include "hash.h"
+#include "hash-pjw.h"
+#include "xalloc.h"
+
+#include "helper.h"
+
+/* Compute Y - X and return the result in milliseconds.
+ * Approximately the same as this code:
+ * http://www.mpp.mpg.de/~huber/util/timevaldiff.c
+ */
+int64_t
+timeval_diff (const struct timeval *x, const struct timeval *y)
+{
+  int64_t msec;
+
+  msec = (y->tv_sec - x->tv_sec) * 1000;
+  msec += (y->tv_usec - x->tv_usec) / 1000;
+  return msec;
+}
+
+void
+print_timestamped_message (const char *fs, ...)
+{
+  struct timeval tv;
+  gettimeofday (&tv, NULL);
+
+  va_list args;
+  char *msg;
+  int err;
+
+  va_start (args, fs);
+  err = vasprintf (&msg, fs, args);
+  va_end (args);
+
+  if (err < 0) return;
+
+  fprintf (stderr, "supermin helper [%05" PRIi64 "ms] %s\n",
+           timeval_diff (&start_t, &tv), msg);
+
+  free (msg);
+}
+
+int
+reverse_filevercmp (const void *p1, const void *p2)
+{
+  const char *s1 = * (char * const *) p1;
+  const char *s2 = * (char * const *) p2;
+
+  /* Note, arguments are reversed to achieve a reverse sort. */
+  return filevercmp (s2, s1);
+}
+
+void
+add_string (char ***argv, size_t *n_used, size_t *n_alloc, const char *str)
+{
+  char *new_str;
+
+  if (*n_used >= *n_alloc)
+    *argv = x2nrealloc (*argv, n_alloc, sizeof (char *));
+
+  if (str)
+    new_str = xstrdup (str);
+  else
+    new_str = NULL;
+
+  (*argv)[*n_used] = new_str;
+
+  (*n_used)++;
+}
+
+size_t
+count_strings (char *const *argv)
+{
+  size_t argc;
+
+  for (argc = 0; argv[argc] != NULL; ++argc)
+    ;
+  return argc;
+}
+
+struct dir_cache {
+  char *path;
+  char **files;
+};
+
+static size_t
+dir_cache_hash (void const *x, size_t table_size)
+{
+  struct dir_cache const *p = x;
+  return hash_pjw (p->path, table_size);
+}
+
+static bool
+dir_cache_compare (void const *x, void const *y)
+{
+  struct dir_cache const *p = x;
+  struct dir_cache const *q = y;
+  return strcmp (p->path, q->path) == 0;
+}
+
+/* Read a directory into a list of strings.
+ *
+ * Previously looked up directories are cached and returned quickly,
+ * saving some considerable amount of time compared to reading the
+ * directory over again.  However this means you really must not
+ * alter the array of strings that are returned.
+ *
+ * Returns an empty list if the directory cannot be opened.
+ */
+char **
+read_dir (const char *name)
+{
+  static Hash_table *ht = NULL;
+
+  if (!ht)
+    ht = hash_initialize (1024, NULL, dir_cache_hash, dir_cache_compare, NULL);
+
+  struct dir_cache key = { .path = (char *) name };
+  struct dir_cache *p = hash_lookup (ht, &key);
+  if (p)
+    return p->files;
+
+  char **files = NULL;
+  size_t n_used = 0, n_alloc = 0;
+
+  DIR *dir = opendir (name);
+  if (!dir) {
+    /* If it fails to open, that's OK, skip to the end. */
+    /*perror (name);*/
+    goto done;
+  }
+
+  for (;;) {
+    errno = 0;
+    struct dirent *d = readdir (dir);
+    if (d == NULL) {
+      if (errno != 0)
+        /* But if it fails here, after opening and potentially reading
+         * part of the directory, that's a proper failure - inform the
+         * user and exit.
+         */
+        error (EXIT_FAILURE, errno, "%s", name);
+      break;
+    }
+
+    add_string (&files, &n_used, &n_alloc, d->d_name);
+  }
+
+  if (closedir (dir) == -1)
+    error (EXIT_FAILURE, errno, "closedir: %s", name);
+
+ done:
+  /* NULL-terminate the array. */
+  add_string (&files, &n_used, &n_alloc, NULL);
+
+  /* Add it to the hash for next time. */
+  p = xmalloc (sizeof *p);
+  p->path = (char *) name;
+  p->files = files;
+  p = hash_insert (ht, p);
+  assert (p != NULL);
+
+  return files;
+}
+
+/* Filter a list of strings, returning only those where f(s) != 0. */
+char **
+filter (char **strings, int (*f) (const char *))
+{
+  char **out = NULL;
+  size_t n_used = 0, n_alloc = 0;
+
+  int i;
+  for (i = 0; strings[i] != NULL; ++i) {
+    if (f (strings[i]) != 0)
+      add_string (&out, &n_used, &n_alloc, strings[i]);
+  }
+
+  add_string (&out, &n_used, &n_alloc, NULL);
+  return out;
+}
+
+/* Filter a list of strings and return only those matching the wildcard. */
+char **
+filter_fnmatch (char **strings, const char *patt, int flags)
+{
+  char **out = NULL;
+  size_t n_used = 0, n_alloc = 0;
+
+  int i, r;
+  for (i = 0; strings[i] != NULL; ++i) {
+    r = fnmatch (patt, strings[i], flags);
+    if (r == 0)
+      add_string (&out, &n_used, &n_alloc, strings[i]);
+    else if (r != FNM_NOMATCH)
+      error (EXIT_FAILURE, 0, "internal error: fnmatch ('%s', '%s', %d) returned unexpected non-zero value %d\n",
+             patt, strings[i], flags, r);
+  }
+
+  add_string (&out, &n_used, &n_alloc, NULL);
+  return out;
+}
+
+/* Filter a list of strings and return only those which DON'T contain sub. */
+char **
+filter_notmatching_substring (char **strings, const char *sub)
+{
+  char **out = NULL;
+  size_t n_used = 0, n_alloc = 0;
+
+  int i;
+  for (i = 0; strings[i] != NULL; ++i) {
+    if (strstr (strings[i], sub) == NULL)
+      add_string (&out, &n_used, &n_alloc, strings[i]);
+  }
+
+  add_string (&out, &n_used, &n_alloc, NULL);
+  return out;
+}
+
+/* Sort a list of strings, in place, with the comparison function supplied. */
+void
+sort (char **strings, int (*compare) (const void *, const void *))
+{
+  qsort (strings, count_strings (strings), sizeof (char *), compare);
+}
+
+/* Return true iff path exists and is a directory.  This version
+ * follows symlinks.
+ */
+int
+isdir (const char *path)
+{
+  struct stat statbuf;
+
+  if (stat (path, &statbuf) == -1)
+    return 0;
+
+  return S_ISDIR (statbuf.st_mode);
+}
+
+/* Load in a file, returning a list of lines. */
+char **
+load_file (const char *filename)
+{
+  char **lines = 0;
+  size_t n_used = 0, n_alloc = 0;
+
+  FILE *fp;
+  fp = fopen (filename, "r");
+  if (fp == NULL)
+    error (EXIT_FAILURE, errno, "fopen: %s", filename);
+
+  char line[4096];
+  while (fgets (line, sizeof line, fp)) {
+    size_t len = strlen (line);
+    if (len > 0 && line[len-1] == '\n')
+      line[len-1] = '\0';
+    add_string (&lines, &n_used, &n_alloc, line);
+  }
+
+  add_string (&lines, &n_used, &n_alloc, NULL);
+  return lines;
+}