[libgsystem] fileutils: Add gs_file_open_dir_fd_at()

[Colin Walters <walters src gnome org>]

commit 681eef7fbb5b13fd747ad074eea216c72e673940
Author: Colin Walters <walters verbum org>
Date:   Thu Feb 27 11:46:49 2014 -0500

    fileutils: Add gs_file_open_dir_fd_at()
    
    This will be used in the OSTree checkout code, where we want to
    mkdir() and then open it.

 src/gsystem-file-utils.c |   28 ++++++++++++++++++++++++++++
 src/gsystem-file-utils.h |    6 ++++++
 2 files changed, 34 insertions(+), 0 deletions(-)
---
diff --git a/src/gsystem-file-utils.c b/src/gsystem-file-utils.c
index 27e0e2d..545fb30 100644
--- a/src/gsystem-file-utils.c
+++ b/src/gsystem-file-utils.c
@@ -464,6 +464,34 @@ gs_file_open_dir_fd (GFile         *path,
 }
 
 /**
+ * gs_file_open_dir_fd_at:
+ * @parent_dfd: Parent directory file descriptor
+ * @name: Directory name
+ * @out_fd: (out): File descriptor for directory
+ * @cancellable: Cancellable
+ * @error: Error
+ *
+ * On success, sets @out_fd to a file descriptor for the directory
+ * that can be used with UNIX functions such as openat().
+ */
+gboolean
+gs_file_open_dir_fd_at (int            parent_dfd,
+                        const char    *name,
+                        int           *out_fd,
+                        GCancellable  *cancellable,
+                        GError       **error)
+{
+  /* Linux specific probably */
+  *out_fd = openat (parent_dfd, name, O_RDONLY | O_NONBLOCK | O_DIRECTORY | O_CLOEXEC);
+  if (*out_fd == -1)
+    {
+      _set_error_from_errno (error);
+      return FALSE;
+    }
+  return TRUE;
+}
+
+/**
  * gs_file_open_in_tmpdir_at:
  * @tmpdir_fd: Directory to place temporary file
  * @mode: Default mode (will be affected by umask)
diff --git a/src/gsystem-file-utils.h b/src/gsystem-file-utils.h
index 2da6646..85ef9ad 100644
--- a/src/gsystem-file-utils.h
+++ b/src/gsystem-file-utils.h
@@ -75,6 +75,12 @@ gboolean gs_file_open_dir_fd (GFile         *path,
                               GCancellable  *cancellable,
                               GError       **error);
 
+gboolean gs_file_open_dir_fd_at (int            parent_dfd,
+                                 const char    *name,
+                                 int           *out_fd,
+                                 GCancellable  *cancellable,
+                                 GError       **error);
+
 gboolean gs_file_open_in_tmpdir_at (int                tmpdir_fd,
                                     int                mode,
                                     char             **out_name,