Add APIs to get xattrs from disk

I'm aiming to do some more work on the Rust side around `fsck`
like functionality, and this is a useful primitive.  There isn't
a great Rust crate for xattrs, and I think it's better to share this
code.

src/libostree/libostree-devel.sym

@@ -20,7 +20,11 @@
    - uncomment the include in Makefile-libostree.am
 */
 
-
+LIBOSTREE_2022.4 {
+global:
+  ostree_fs_get_all_xattrs;
+  ostree_fs_get_all_xattrs_at;
+} LIBOSTREE_2021.5;
 
 /* Stub section for the stable release *after* this development one; don't
  * edit this other than to update the year.  This is just a copy/paste

src/libostree/ostree-core.c

@@ -836,6 +836,51 @@ gboolean ostree_break_hardlink (int               dfd,
   return TRUE;
 }
 
+/**
+ * ostree_fs_get_all_xattrs:
+ * @fd: File descriptor
+ * @cancellable: Cancellable
+ * @error: Error
+ *
+ * Retrieve all extended attributes in a canonical (sorted) order from
+ * the given file descriptor.
+ *
+ * Returns: (transfer full): A GVariant of type `a(ayay)`
+ */
+GVariant *
+ostree_fs_get_all_xattrs (int fd, GCancellable *cancellable, GError **error)
+{
+  GVariant *ret = NULL;
+  if (!glnx_fd_get_all_xattrs (fd, &ret, cancellable, error))
+    return NULL;
+  return ret;
+}
+
+/**
+ * ostree_fs_get_all_xattrs_at:
+ * @dfd: Directory file descriptor
+ * @path: Filesystem path
+ * @cancellable: Cancellable
+ * @error: Error
+ *
+ * Retrieve all extended attributes in a canonical (sorted) order from
+ * the given path, relative to the provided directory file descriptor.
+ * The target path will not be dereferenced.  Currently on Linux, this
+ * API must be used currently to retrieve extended attributes
+ * for symbolic links because while `O_PATH` exists, it cannot be used
+ * with `fgetxattr()`.
+ *
+ * Returns: (transfer full): A GVariant of type `a(ayay)`
+ */
+GVariant *
+ostree_fs_get_all_xattrs_at (int dfd, const char *path, GCancellable *cancellable, GError **error)
+{
+  GVariant *ret = NULL;
+  if (!glnx_dfd_name_get_all_xattrs (dfd, path, &ret, cancellable, error))
+    return NULL;
+  return ret;
+}
+
 /**
  * ostree_checksum_file_from_input:
  * @file_info: File information
@@ -928,8 +973,8 @@ ostree_checksum_file (GFile            *f,
   g_autoptr(GVariant) xattrs = NULL;
   if (objtype == OSTREE_OBJECT_TYPE_FILE)
     {
-      if (!glnx_dfd_name_get_all_xattrs (AT_FDCWD, gs_file_get_path_cached (f),
-                                         &xattrs, cancellable, error))
+      xattrs = ostree_fs_get_all_xattrs_at (AT_FDCWD, gs_file_get_path_cached (f), cancellable, error);
+      if (!xattrs)
         return FALSE;
     }
 

src/libostree/ostree-core.h

@@ -464,6 +464,12 @@ gboolean ostree_break_hardlink (int               dfd,
                                 GCancellable     *cancellable,
                                 GError          **error);
 
+_OSTREE_PUBLIC
+GVariant *ostree_fs_get_all_xattrs (int fd, GCancellable *cancellable, GError **error);
+
+_OSTREE_PUBLIC
+GVariant *ostree_fs_get_all_xattrs_at (int dfd, const char *path, GCancellable *cancellable, GError **error);
+
 /**
  * OstreeChecksumFlags:
  * @OSTREE_CHECKSUM_FLAGS_NONE: Default checksumming without tweaks.

src/libostree/ostree-repo-commit.c

@@ -3436,14 +3436,15 @@ get_final_xattrs (OstreeRepo                       *self,
       else if (dfd_subpath == NULL)
         {
           g_assert (dfd != -1);
-          if (!glnx_fd_get_all_xattrs (dfd, &original_xattrs, cancellable, error))
+          original_xattrs = ostree_fs_get_all_xattrs (dfd, cancellable, error);
+          if (!original_xattrs)
             return FALSE;
         }
       else
         {
           g_assert (dfd != -1);
-          if (!glnx_dfd_name_get_all_xattrs (dfd, dfd_subpath, &original_xattrs,
-                                             cancellable, error))
+          original_xattrs = ostree_fs_get_all_xattrs_at (dfd, dfd_subpath, cancellable, error);
+          if (!original_xattrs)
             return FALSE;
         }
 
@@ -4641,8 +4642,8 @@ import_one_object_direct (OstreeRepo    *dest_repo,
           if (src_repo->mode == OSTREE_REPO_MODE_BARE)
             {
               g_autoptr(GVariant) xattrs = NULL;
-              if (!glnx_fd_get_all_xattrs (src_fd, &xattrs,
-                                           cancellable, error))
+              xattrs = ostree_fs_get_all_xattrs (src_fd, cancellable, error);
+              if (!xattrs)
                 return FALSE;
               if (!glnx_fd_set_all_xattrs (tmp_dest.fd, xattrs,
                                            cancellable, error))

src/libostree/ostree-repo.c

@@ -28,6 +28,7 @@
 #include <gio/gunixoutputstream.h>
 #include <gio/gfiledescriptorbased.h>
 #include "libglnx.h"
+#include "ostree-core.h"
 #include "otutil.h"
 #include <glnx-console.h>
 #include <linux/magic.h>
@@ -4345,9 +4346,12 @@ _ostree_repo_load_file_bare (OstreeRepo         *self,
         {
           if (self->disable_xattrs)
             ret_xattrs = g_variant_ref_sink (g_variant_new_array (G_VARIANT_TYPE ("(ayay)"), NULL, 0));
-          else if (!glnx_fd_get_all_xattrs (fd, &ret_xattrs,
-                                            cancellable, error))
-            return FALSE;
+          else 
+            {
+              ret_xattrs = ostree_fs_get_all_xattrs (fd, cancellable, error);
+              if (!ret_xattrs)
+                return FALSE;
+            }
         }
       else if (S_ISLNK (stbuf.st_mode) && out_xattrs)
         {