ostree-repo-checkout.c

/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
 *
 * Copyright (C) 2011,2013 Colin Walters <walters@verbum.org>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Author: Colin Walters <walters@verbum.org>
 */

#include "config.h"

#include <glib-unix.h>
#include <sys/xattr.h>
#include <gio/gfiledescriptorbased.h>
#include <gio/gunixoutputstream.h>
#include "otutil.h"

#include "ostree-repo-file.h"
#include "ostree-core-private.h"
#include "ostree-repo-private.h"

#define WHITEOUT_PREFIX ".wh."

static gboolean
checkout_object_for_uncompressed_cache (OstreeRepo      *self,
                                        const char      *loose_path,
                                        GFileInfo       *src_info,
                                        GInputStream    *content,
                                        GCancellable    *cancellable,
                                        GError         **error)
{
  gboolean ret = FALSE;
  g_autofree char *temp_filename = NULL;
  g_autoptr(GOutputStream) temp_out = NULL;
  glnx_fd_close int fd = -1;
  int res;
  guint32 file_mode;

  /* Don't make setuid files in uncompressed cache */
  file_mode = g_file_info_get_attribute_uint32 (src_info, "unix::mode");
  file_mode &= ~(S_ISUID|S_ISGID);

  if (!glnx_open_tmpfile_linkable_at (self->tmp_dir_fd, ".", O_WRONLY | O_CLOEXEC,
                                      &fd, &temp_filename,
                                      error))
    goto out;
  temp_out = g_unix_output_stream_new (fd, FALSE);

  if (g_output_stream_splice (temp_out, content, 0, cancellable, error) < 0)
    goto out;

  if (!g_output_stream_flush (temp_out, cancellable, error))
    goto out;

  if (!self->disable_fsync)
    {
      do
        res = fsync (fd);
      while (G_UNLIKELY (res == -1 && errno == EINTR));
      if (G_UNLIKELY (res == -1))
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }

  if (!g_output_stream_close (temp_out, cancellable, error))
    goto out;

  if (fchmod (fd, file_mode) < 0)
    {
      glnx_set_error_from_errno (error);
      goto out;
    }

  if (!_ostree_repo_ensure_loose_objdir_at (self->uncompressed_objects_dir_fd,
                                            loose_path,
                                            cancellable, error))
    goto out;

  if (!glnx_link_tmpfile_at (self->tmp_dir_fd, GLNX_LINK_TMPFILE_NOREPLACE_IGNORE_EXIST,
                             fd, temp_filename,
                             self->uncompressed_objects_dir_fd, loose_path,
                             error))
    goto out;

  ret = TRUE;
 out:
  return ret;
}

static gboolean
fsync_is_enabled (OstreeRepo   *self,
                  OstreeRepoCheckoutOptions *options)
{
  return !(self->disable_fsync || options->disable_fsync);
}

static gboolean
write_regular_file_content (OstreeRepo            *self,
                            OstreeRepoCheckoutOptions *options,
                            GOutputStream         *output,
                            GFileInfo             *file_info,
                            GVariant              *xattrs,
                            GInputStream          *input,
                            GCancellable          *cancellable,
                            GError               **error)
{
  gboolean ret = FALSE;
  const OstreeRepoCheckoutMode mode = options->mode;
  int fd;
  int res;

  if (g_output_stream_splice (output, input, 0,
                              cancellable, error) < 0)
    goto out;

  if (!g_output_stream_flush (output, cancellable, error))
    goto out;

  fd = g_file_descriptor_based_get_fd ((GFileDescriptorBased*)output);

  if (mode != OSTREE_REPO_CHECKOUT_MODE_USER)
    {
      do
        res = fchown (fd,
                      g_file_info_get_attribute_uint32 (file_info, "unix::uid"),
                      g_file_info_get_attribute_uint32 (file_info, "unix::gid"));
      while (G_UNLIKELY (res == -1 && errno == EINTR));
      if (G_UNLIKELY (res == -1))
        {
          glnx_set_error_from_errno (error);
          goto out;
        }

      do
        res = fchmod (fd, g_file_info_get_attribute_uint32 (file_info, "unix::mode"));
      while (G_UNLIKELY (res == -1 && errno == EINTR));
      if (G_UNLIKELY (res == -1))
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
              
      if (xattrs)
        {
          if (!glnx_fd_set_all_xattrs (fd, xattrs, cancellable, error))
            goto out;
        }
    }
          
  if (fsync_is_enabled (self, options))
    {
      if (fsync (fd) == -1)
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }
          
  if (!g_output_stream_close (output, cancellable, error))
    goto out;

  ret = TRUE;
 out:
  return ret;
}

static gboolean
checkout_file_from_input_at (OstreeRepo     *self,
                             OstreeRepoCheckoutOptions *options,
                             GFileInfo      *file_info,
                             GVariant       *xattrs,
                             GInputStream   *input,
                             int             destination_dfd,
                             const char     *destination_name,
                             GCancellable   *cancellable,
                             GError        **error)
{
  gboolean ret = FALSE;
  int res;

  if (g_file_info_get_file_type (file_info) == G_FILE_TYPE_SYMBOLIC_LINK)
    {
      do
        res = symlinkat (g_file_info_get_symlink_target (file_info),
                         destination_dfd, destination_name);
      while (G_UNLIKELY (res == -1 && errno == EINTR));
      if (res == -1)
        {
          glnx_set_error_from_errno (error);
          goto out;
        }

      if (options->mode != OSTREE_REPO_CHECKOUT_MODE_USER)
        {
          if (G_UNLIKELY (fchownat (destination_dfd, destination_name,
                                    g_file_info_get_attribute_uint32 (file_info, "unix::uid"),
                                    g_file_info_get_attribute_uint32 (file_info, "unix::gid"),
                                    AT_SYMLINK_NOFOLLOW) == -1))
            {
              glnx_set_error_from_errno (error);
              goto out;
            }

          if (xattrs)
            {
              if (!glnx_dfd_name_set_all_xattrs (destination_dfd, destination_name,
                                                   xattrs, cancellable, error))
                goto out;
            }
        }
    }
  else if (g_file_info_get_file_type (file_info) == G_FILE_TYPE_REGULAR)
    {
      g_autoptr(GOutputStream) temp_out = NULL;
      int fd;
      guint32 file_mode;

      file_mode = g_file_info_get_attribute_uint32 (file_info, "unix::mode");
      /* Don't make setuid files on checkout when we're doing --user */
      if (options->mode == OSTREE_REPO_CHECKOUT_MODE_USER)
        file_mode &= ~(S_ISUID|S_ISGID);

      do
        fd = openat (destination_dfd, destination_name, O_WRONLY | O_CREAT | O_EXCL, file_mode);
      while (G_UNLIKELY (fd == -1 && errno == EINTR));
      if (fd == -1)
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
      temp_out = g_unix_output_stream_new (fd, TRUE);
      fd = -1; /* Transfer ownership */

      if (!write_regular_file_content (self, options, temp_out, file_info, xattrs, input,
                                       cancellable, error))
        goto out;
    }
  else
    g_assert_not_reached ();
  
  ret = TRUE;
 out:
  return ret;
}

/*
 * This function creates a file under a temporary name, then rename()s
 * it into place.  This implements union-like behavior.
 */
static gboolean
checkout_file_unioning_from_input_at (OstreeRepo     *repo,
                                      OstreeRepoCheckoutOptions  *options,
                                      GFileInfo      *file_info,
                                      GVariant       *xattrs,
                                      GInputStream   *input,
                                      int             destination_dfd,
                                      const char     *destination_name,
                                      GCancellable   *cancellable,
                                      GError        **error)
{
  gboolean ret = FALSE;
  g_autofree char *temp_filename = NULL;

  if (g_file_info_get_file_type (file_info) == G_FILE_TYPE_SYMBOLIC_LINK)
    {
      if (!_ostree_make_temporary_symlink_at (destination_dfd,
                                              g_file_info_get_symlink_target (file_info),
                                              &temp_filename,
                                              cancellable, error))
        goto out;
          
      if (xattrs)
        {
          if (!glnx_dfd_name_set_all_xattrs (destination_dfd, temp_filename,
                                               xattrs, cancellable, error))
            goto out;
        }
      if (G_UNLIKELY (renameat (destination_dfd, temp_filename,
                                destination_dfd, destination_name) == -1))
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }
  else if (g_file_info_get_file_type (file_info) == G_FILE_TYPE_REGULAR)
    {
      glnx_fd_close int temp_fd = -1;
      g_autoptr(GOutputStream) temp_out = NULL;
      guint32 file_mode;

      file_mode = g_file_info_get_attribute_uint32 (file_info, "unix::mode");
      /* Don't make setuid files on checkout when we're doing --user */
      if (options->mode == OSTREE_REPO_CHECKOUT_MODE_USER)
        file_mode &= ~(S_ISUID|S_ISGID);

      if (!glnx_open_tmpfile_linkable_at (destination_dfd, ".", O_WRONLY | O_CLOEXEC,
                                          &temp_fd, &temp_filename,
                                          error))
        goto out;
      temp_out = g_unix_output_stream_new (temp_fd, FALSE);

      if (!write_regular_file_content (repo, options, temp_out, file_info, xattrs, input,
                                       cancellable, error))
        goto out;

      if (!glnx_link_tmpfile_at (destination_dfd, GLNX_LINK_TMPFILE_REPLACE,
                                 temp_fd, temp_filename, destination_dfd,
                                 destination_name,
                                 error))
        goto out;
    }
  else
    g_assert_not_reached ();

  ret = TRUE;
 out:
  return ret;
}

static gboolean
checkout_file_hardlink (OstreeRepo                          *self,
                        OstreeRepoCheckoutOptions           *options,
                        const char                          *loose_path,
                        int                                  destination_dfd,
                        const char                          *destination_name,
                        gboolean                             allow_noent,
                        gboolean                            *out_was_supported,
                        GCancellable                        *cancellable,
                        GError                             **error)
{
  gboolean ret = FALSE;
  gboolean ret_was_supported = FALSE;
  int srcfd = (self->mode == OSTREE_REPO_MODE_BARE || self->mode == OSTREE_REPO_MODE_BARE_USER) ?
    self->objects_dir_fd : self->uncompressed_objects_dir_fd;

 again:
  if (linkat (srcfd, loose_path, destination_dfd, destination_name, 0) != -1)
    ret_was_supported = TRUE;
  else if (!options->no_copy_fallback && (errno == EMLINK || errno == EXDEV || errno == EPERM))
    {
      /* EMLINK, EXDEV and EPERM shouldn't be fatal; we just can't do the
       * optimization of hardlinking instead of copying.
       */
      ret_was_supported = FALSE;
    }
  else if (allow_noent && errno == ENOENT)
    {
      ret_was_supported = FALSE;
    }
  else if (errno == EEXIST && options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES)
    { 
      /* Idiocy, from man rename(2)
       *
       * "If oldpath and newpath are existing hard links referring to
       * the same file, then rename() does nothing, and returns a
       * success status."
       *
       * So we can't make this atomic.  
       */
      (void) unlinkat (destination_dfd, destination_name, 0);
      goto again;
    }
  else
    {
      g_prefix_error (error, "Hardlinking %s to %s: ", loose_path, destination_name);
      glnx_set_error_from_errno (error);
      goto out;
    }

  ret = TRUE;
  if (out_was_supported)
    *out_was_supported = ret_was_supported;
 out:
  return ret;
}

static gboolean
checkout_one_file_at (OstreeRepo                        *repo,
                      OstreeRepoCheckoutOptions         *options,
                      GFile                             *source,
                      GFileInfo                         *source_info,
                      int                                destination_dfd,
                      const char                        *destination_name,
                      GCancellable                      *cancellable,
                      GError                           **error)
{
  gboolean ret = FALSE;
  const char *checksum;
  gboolean is_symlink;
  gboolean can_cache;
  gboolean need_copy = TRUE;
  char loose_path_buf[_OSTREE_LOOSE_PATH_MAX];
  g_autoptr(GInputStream) input = NULL;
  g_autoptr(GVariant) xattrs = NULL;
  gboolean is_whiteout;

  is_symlink = g_file_info_get_file_type (source_info) == G_FILE_TYPE_SYMBOLIC_LINK;

  checksum = ostree_repo_file_get_checksum ((OstreeRepoFile*)source);

  is_whiteout = !is_symlink && options->process_whiteouts &&
    g_str_has_prefix (destination_name, WHITEOUT_PREFIX);

  /* First, see if it's a Docker whiteout,
   * https://github.com/docker/docker/blob/1a714e76a2cb9008cd19609059e9988ff1660b78/pkg/archive/whiteouts.go
   */
  if (is_whiteout)
    {
      const char *name = destination_name + (sizeof (WHITEOUT_PREFIX) - 1);

      if (!name[0])
        {
          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
                       "Invalid empty whiteout '%s'", name);
          goto out;
        }

      g_assert (name[0] != '/'); /* Sanity */

      if (!glnx_shutil_rm_rf_at (destination_dfd, name, cancellable, error))
        goto out;

      need_copy = FALSE;
    }
  else if (!is_symlink)
    {
      gboolean did_hardlink = FALSE;
      /* Try to do a hardlink first, if it's a regular file.  This also
       * traverses all parent repos.
       */
      OstreeRepo *current_repo = repo;

      while (current_repo)
        {
          gboolean is_bare = ((current_repo->mode == OSTREE_REPO_MODE_BARE
                               && options->mode == OSTREE_REPO_CHECKOUT_MODE_NONE) ||
                              (current_repo->mode == OSTREE_REPO_MODE_BARE_USER
                               && options->mode == OSTREE_REPO_CHECKOUT_MODE_USER));
          gboolean current_can_cache = (options->enable_uncompressed_cache
                                        && current_repo->enable_uncompressed_cache);
          gboolean is_archive_z2_with_cache = (current_repo->mode == OSTREE_REPO_MODE_ARCHIVE_Z2
                                               && options->mode == OSTREE_REPO_CHECKOUT_MODE_USER
                                               && current_can_cache);

          /* But only under these conditions */
          if (is_bare || is_archive_z2_with_cache)
            {
              /* Override repo mode; for archive-z2 we're looking in
                 the cache, which is in "bare" form */
              _ostree_loose_path (loose_path_buf, checksum, OSTREE_OBJECT_TYPE_FILE, OSTREE_REPO_MODE_BARE);
              if (!checkout_file_hardlink (current_repo,
                                           options,
                                           loose_path_buf,
                                           destination_dfd, destination_name,
                                           TRUE, &did_hardlink,
                                           cancellable, error))
                goto out;

              if (did_hardlink && options->devino_to_csum_cache)
                {
                  struct stat stbuf;
                  OstreeDevIno *key;
                  
                  if (TEMP_FAILURE_RETRY (fstatat (destination_dfd, destination_name, &stbuf, AT_SYMLINK_NOFOLLOW)) != 0)
                    {
                      glnx_set_error_from_errno (error);
                      goto out;
                    }
                  
                  key = g_new (OstreeDevIno, 1);
                  key->dev = stbuf.st_dev;
                  key->ino = stbuf.st_ino;
                  memcpy (key->checksum, checksum, OSTREE_SHA256_STRING_LEN+1);
                  
                  g_hash_table_add ((GHashTable*)options->devino_to_csum_cache, key);
                }

              if (did_hardlink)
                break;
            }
          current_repo = current_repo->parent_repo;
        }

      need_copy = !did_hardlink;
    }

  can_cache = (options->enable_uncompressed_cache
               && repo->enable_uncompressed_cache);

  /* Ok, if we're archive-z2 and we didn't find an object, uncompress
   * it now, stick it in the cache, and then hardlink to that.
   */
  if (can_cache
      && !is_whiteout
      && !is_symlink
      && need_copy
      && repo->mode == OSTREE_REPO_MODE_ARCHIVE_Z2
      && options->mode == OSTREE_REPO_CHECKOUT_MODE_USER)
    {
      gboolean did_hardlink;
      
      if (!ostree_repo_load_file (repo, checksum, &input, NULL, NULL,
                                  cancellable, error))
        goto out;

      /* Overwrite any parent repo from earlier */
      _ostree_loose_path (loose_path_buf, checksum, OSTREE_OBJECT_TYPE_FILE, OSTREE_REPO_MODE_BARE);

      if (!checkout_object_for_uncompressed_cache (repo, loose_path_buf,
                                                   source_info, input,
                                                   cancellable, error))
        {
          g_prefix_error (error, "Unpacking loose object %s: ", checksum);
          goto out;
        }
      
      g_clear_object (&input);

      /* Store the 2-byte objdir prefix (e.g. e3) in a set.  The basic
       * idea here is that if we had to unpack an object, it's very
       * likely we're replacing some other object, so we may need a GC.
       *
       * This model ensures that we do work roughly proportional to
       * the size of the changes.  For example, we don't scan any
       * directories if we didn't modify anything, meaning you can
       * checkout the same tree multiple times very quickly.
       *
       * This is also scale independent; we don't hardcode e.g. looking
       * at 1000 objects.
       *
       * The downside is that if we're unlucky, we may not free
       * an object for quite some time.
       */
      g_mutex_lock (&repo->cache_lock);
      {
        gpointer key = GUINT_TO_POINTER ((g_ascii_xdigit_value (checksum[0]) << 4) + 
                                         g_ascii_xdigit_value (checksum[1]));
        if (repo->updated_uncompressed_dirs == NULL)
          repo->updated_uncompressed_dirs = g_hash_table_new (NULL, NULL);
        g_hash_table_insert (repo->updated_uncompressed_dirs, key, key);
      }
      g_mutex_unlock (&repo->cache_lock);

      if (!checkout_file_hardlink (repo, options, loose_path_buf,
                                   destination_dfd, destination_name,
                                   FALSE, &did_hardlink,
                                   cancellable, error))
        {
          g_prefix_error (error, "Using new cached uncompressed hardlink of %s to %s: ", checksum, destination_name);
          goto out;
        }

      need_copy = !did_hardlink;
    }

  /* Fall back to copy if we couldn't hardlink */
  if (need_copy)
    {
      if (!ostree_repo_load_file (repo, checksum, &input, NULL, &xattrs,
                                  cancellable, error))
        goto out;

      if (options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES)
        {
          if (!checkout_file_unioning_from_input_at (repo, options, source_info, xattrs, input,
                                                     destination_dfd,
                                                     destination_name,
                                                     cancellable, error)) 
            {
              g_prefix_error (error, "Union checkout of %s to %s: ", checksum, destination_name);
              goto out;
            }
        }
      else
        {
          if (!checkout_file_from_input_at (repo, options, source_info, xattrs, input,
                                            destination_dfd,
                                            destination_name,
                                            cancellable, error))
            {
              g_prefix_error (error, "Checkout of %s to %s: ", checksum, destination_name);
              goto out;
            }
        }

      if (input)
        {
          if (!g_input_stream_close (input, cancellable, error))
            goto out;
        }
    }

  ret = TRUE;
 out:
  return ret;
}

/*
 * checkout_tree_at:
 * @self: Repo
 * @mode: Options controlling all files
 * @overwrite_mode: Whether or not to overwrite files
 * @destination_parent_fd: Place tree here
 * @destination_name: Use this name for tree
 * @source: Source tree
 * @source_info: Source info
 * @cancellable: Cancellable
 * @error: Error
 *
 * Like ostree_repo_checkout_tree(), but check out @source into the
 * relative @destination_name, located by @destination_parent_fd.
 */
static gboolean
checkout_tree_at (OstreeRepo                        *self,
                  OstreeRepoCheckoutOptions         *options,
                  int                                destination_parent_fd,
                  const char                        *destination_name,
                  OstreeRepoFile                    *source,
                  GFileInfo                         *source_info,
                  GCancellable                      *cancellable,
                  GError                           **error)
{
  gboolean ret = FALSE;
  gboolean did_exist = FALSE;
  glnx_fd_close int destination_dfd = -1;
  int res;
  g_autoptr(GVariant) xattrs = NULL;
  g_autoptr(GFileEnumerator) dir_enum = NULL;

  /* Create initially with mode 0700, then chown/chmod only when we're
   * done.  This avoids anyone else being able to operate on partially
   * constructed dirs.
   */
  do
    res = mkdirat (destination_parent_fd, destination_name, 0700);
  while (G_UNLIKELY (res == -1 && errno == EINTR));
  if (res == -1)
    {
      if (errno == EEXIST && options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES)
        did_exist = TRUE;
      else
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }

  if (!glnx_opendirat (destination_parent_fd, destination_name, TRUE,
                       &destination_dfd, error))
    goto out;

  /* Set the xattrs now, so any derived labeling works */
  if (!did_exist && options->mode != OSTREE_REPO_CHECKOUT_MODE_USER)
    {
      if (!ostree_repo_file_get_xattrs (source, &xattrs, NULL, error))
        goto out;

      if (xattrs)
        {
          if (!glnx_fd_set_all_xattrs (destination_dfd, xattrs, cancellable, error))
            goto out;
        }
    }

  if (g_file_info_get_file_type (source_info) != G_FILE_TYPE_DIRECTORY)
    {
      ret = checkout_one_file_at (self, options,
                                  (GFile *) source,
                                  source_info,
                                  destination_dfd,
                                  g_file_info_get_name (source_info),
                                  cancellable, error);
      goto out;
    }
  dir_enum = g_file_enumerate_children ((GFile*)source,
                                        OSTREE_GIO_FAST_QUERYINFO, 
                                        G_FILE_QUERY_INFO_NOFOLLOW_SYMLINKS,
                                        cancellable, 
                                        error);
  if (!dir_enum)
    goto out;

  while (TRUE)
    {
      GFileInfo *file_info;
      GFile *src_child;
      const char *name;

      if (!g_file_enumerator_iterate (dir_enum, &file_info, &src_child,
                                      cancellable, error))
        goto out;
      if (file_info == NULL)
        break;

      name = g_file_info_get_name (file_info);

      if (g_file_info_get_file_type (file_info) == G_FILE_TYPE_DIRECTORY)
        {
          if (!checkout_tree_at (self, options,
                                 destination_dfd, name,
                                 (OstreeRepoFile*)src_child, file_info,
                                 cancellable, error))
            goto out;
        }
      else
        {
          if (!checkout_one_file_at (self, options,
                                     src_child, file_info,
                                     destination_dfd, name,
                                     cancellable, error))
            goto out;
        }
    }

  /* We do fchmod/fchown last so that no one else could access the
   * partially created directory and change content we're laying out.
   */
  if (!did_exist)
    {
      do
        res = fchmod (destination_dfd,
                      g_file_info_get_attribute_uint32 (source_info, "unix::mode"));
      while (G_UNLIKELY (res == -1 && errno == EINTR));
      if (G_UNLIKELY (res == -1))
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }

  if (!did_exist && options->mode != OSTREE_REPO_CHECKOUT_MODE_USER)
    {
      do
        res = fchown (destination_dfd,
                      g_file_info_get_attribute_uint32 (source_info, "unix::uid"),
                      g_file_info_get_attribute_uint32 (source_info, "unix::gid"));
      while (G_UNLIKELY (res == -1 && errno == EINTR));
      if (G_UNLIKELY (res == -1))
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }

  /* Set directory mtime to OSTREE_TIMESTAMP, so that it is constant for all checkouts.
   * Must be done after setting permissions and creating all children.
   */
  if (!did_exist)
    {
      const struct timespec times[2] = { { OSTREE_TIMESTAMP, UTIME_OMIT }, { OSTREE_TIMESTAMP, 0} };
      do
        res = futimens (destination_dfd, times);
      while (G_UNLIKELY (res == -1 && errno == EINTR));
      if (G_UNLIKELY (res == -1))
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }

  if (fsync_is_enabled (self, options))
    {
      if (fsync (destination_dfd) == -1)
        {
          glnx_set_error_from_errno (error);
          goto out;
        }
    }

  ret = TRUE;
 out:
  return ret;
}

/**
 * ostree_repo_checkout_tree:
 * @self: Repo
 * @mode: Options controlling all files
 * @overwrite_mode: Whether or not to overwrite files
 * @destination: Place tree here
 * @source: Source tree
 * @source_info: Source info
 * @cancellable: Cancellable
 * @error: Error
 *
 * Check out @source into @destination, which must live on the
 * physical filesystem.  @source may be any subdirectory of a given
 * commit.  The @mode and @overwrite_mode allow control over how the
 * files are checked out.
 */
gboolean
ostree_repo_checkout_tree (OstreeRepo               *self,
                           OstreeRepoCheckoutMode    mode,
                           OstreeRepoCheckoutOverwriteMode    overwrite_mode,
                           GFile                    *destination,
                           OstreeRepoFile           *source,
                           GFileInfo                *source_info,
                           GCancellable             *cancellable,
                           GError                  **error)
{
  OstreeRepoCheckoutOptions options = { 0, };

  options.mode = mode;
  options.overwrite_mode = overwrite_mode;
  /* Backwards compatibility */
  options.enable_uncompressed_cache = TRUE;

  return checkout_tree_at (self, &options,
                           AT_FDCWD, gs_file_get_path_cached (destination),
                           source, source_info,
                           cancellable, error);
}

/**
 * ostree_repo_checkout_tree_at:
 * @self: Repo
 * @options: (allow-none): Options
 * @destination_dfd: Directory FD for destination
 * @destination_path: Directory for destination
 * @commit: Checksum for commit
 * @cancellable: Cancellable
 * @error: Error
 *
 * Similar to ostree_repo_checkout_tree(), but uses directory-relative
 * paths for the destination, uses a new `OstreeRepoCheckoutOptions`,
 * and takes a commit checksum and optional subpath pair, rather than
 * requiring use of `GFile` APIs for the caller.
 *
 * Note in addition that unlike ostree_repo_checkout_tree(), the
 * default is not to use the repository-internal uncompressed objects
 * cache.
 */
gboolean
ostree_repo_checkout_tree_at (OstreeRepo                         *self,
                              OstreeRepoCheckoutOptions         *options,
                              int                                destination_dfd,
                              const char                        *destination_path,
                              const char                        *commit,
                              GCancellable                      *cancellable,
                              GError                           **error)
{
  gboolean ret = FALSE;
  g_autoptr(GFile) commit_root = NULL;
  g_autoptr(GFile) target_dir = NULL;
  g_autoptr(GFileInfo) target_info = NULL;
  OstreeRepoCheckoutOptions default_options = { 0, };

  if (!options)
    {
      default_options.subpath = NULL;
      options = &default_options;
    }

  commit_root = (GFile*) _ostree_repo_file_new_for_commit (self, commit, error);
  if (!commit_root)
    goto out;

  if (!ostree_repo_file_ensure_resolved ((OstreeRepoFile*)commit_root, error))
    goto out;

  if (options->subpath && strcmp (options->subpath, "/") != 0)
    target_dir = g_file_get_child (commit_root, options->subpath);
  else
    target_dir = g_object_ref (commit_root);
  target_info = g_file_query_info (target_dir, OSTREE_GIO_FAST_QUERYINFO,
                                   G_FILE_QUERY_INFO_NOFOLLOW_SYMLINKS,
                                   cancellable, error);
  if (!target_info)
    goto out;

  if (!checkout_tree_at (self, options,
                         destination_dfd,
                         destination_path,
                         (OstreeRepoFile*)target_dir, target_info,
                         cancellable, error))
    goto out;

  ret = TRUE;
 out:
  return ret;
}

static guint
devino_hash (gconstpointer a)
{
  OstreeDevIno *a_i = (gpointer)a;
  return (guint) (a_i->dev + a_i->ino);
}

static int
devino_equal (gconstpointer   a,
              gconstpointer   b)
{
  OstreeDevIno *a_i = (gpointer)a;
  OstreeDevIno *b_i = (gpointer)b;
  return a_i->dev == b_i->dev
    && a_i->ino == b_i->ino;
}

/**
 * ostree_repo_devino_cache_new:
 * 
 * OSTree has support for pairing ostree_repo_checkout_tree_at() using
 * hardlinks in combination with a later
 * ostree_repo_write_directory_to_mtree() using a (normally modified)
 * directory.  In order for OSTree to optimally detect just the new
 * files, use this function and fill in the `devino_to_csum_cache`
 * member of `OstreeRepoCheckoutOptions`, then call
 * ostree_repo_commit_set_devino_cache().
 *
 * Returns: (transfer full): Newly allocated cache
 */
OstreeRepoDevInoCache *
ostree_repo_devino_cache_new (void)
{
  return (OstreeRepoDevInoCache*) g_hash_table_new_full (devino_hash, devino_equal, g_free, NULL);
}

/**
 * ostree_repo_checkout_gc:
 * @self: Repo
 * @cancellable: Cancellable
 * @error: Error
 *
 * Call this after finishing a succession of checkout operations; it
 * will delete any currently-unused uncompressed objects from the
 * cache.
 */
gboolean
ostree_repo_checkout_gc (OstreeRepo        *self,
                         GCancellable      *cancellable,
                         GError           **error)
{
  gboolean ret = FALSE;
  g_autoptr(GHashTable) to_clean_dirs = NULL;
  GHashTableIter iter;
  gpointer key, value;

  g_mutex_lock (&self->cache_lock);
  to_clean_dirs = self->updated_uncompressed_dirs;
  self->updated_uncompressed_dirs = g_hash_table_new (NULL, NULL);
  g_mutex_unlock (&self->cache_lock);

  if (to_clean_dirs)
    g_hash_table_iter_init (&iter, to_clean_dirs);
  while (to_clean_dirs && g_hash_table_iter_next (&iter, &key, &value))
    {
      g_autofree char *objdir_name = g_strdup_printf ("%02x", GPOINTER_TO_UINT (key));
      g_auto(GLnxDirFdIterator) dfd_iter = { 0, };

      if (!glnx_dirfd_iterator_init_at (self->uncompressed_objects_dir_fd, objdir_name, FALSE,
                                        &dfd_iter, error))
        goto out;

      while (TRUE)
        {
          struct dirent *dent;
          struct stat stbuf;

          if (!glnx_dirfd_iterator_next_dent (&dfd_iter, &dent, cancellable, error))
            goto out;
          if (dent == NULL)
            break;

          if (fstatat (dfd_iter.fd, dent->d_name, &stbuf, AT_SYMLINK_NOFOLLOW) != 0)
            {
              glnx_set_error_from_errno (error);
              goto out;
            }
          
          if (stbuf.st_nlink == 1)
            {
              if (unlinkat (dfd_iter.fd, dent->d_name, 0) != 0)
                {
                  glnx_set_error_from_errno (error);
                  goto out;
                }
            }
        }
    }

  ret = TRUE;
 out:
  return ret;
}