ostree export: Add --prefix option

This lets you set a prefix for the resulting archive patsh.
Especially useful in combination with --subpath, for instance
--subpath=subdir --prefix=subdir to extract just subdir.

Closes: #265
Approved by: cgwalters

src/libostree/ostree-repo-libarchive.c

@@ -480,6 +480,12 @@ file_to_archive_entry_common (GFile         *root,
   g_autoptr(GVariant) xattrs = NULL;
   time_t ts = (time_t) opts->timestamp_secs;
 
+  if (opts->path_prefix && opts->path_prefix[0])
+    {
+      g_autofree char *old_pathstr = pathstr;
+      pathstr = g_strconcat (opts->path_prefix, old_pathstr, NULL);
+    }
+
   if (pathstr == NULL || !pathstr[0])
     {
       g_free (pathstr);

src/libostree/ostree-repo.h

@@ -610,7 +610,10 @@ typedef struct {
   guint64 timestamp_secs;
 
   guint unused_uint[8];
-  gpointer unused_ptrs[8];
+
+  char *path_prefix;
+
+  gpointer unused_ptrs[7];
 } OstreeRepoExportArchiveOptions;
 
 _OSTREE_PUBLIC

src/ostree/ot-builtin-export.c

@@ -33,11 +33,13 @@
 
 static char *opt_output_path;
 static char *opt_subpath;
+static char *opt_prefix;
 static gboolean opt_no_xattrs;
 
 static GOptionEntry options[] = {
   { "no-xattrs", 0, 0, G_OPTION_ARG_NONE, &opt_no_xattrs, "Skip output of extended attributes", NULL },
   { "subpath", 0, 0, G_OPTION_ARG_STRING, &opt_subpath, "Checkout sub-directory PATH", "PATH" },
+  { "prefix", 0, 0, G_OPTION_ARG_STRING, &opt_prefix, "Add PATH as prefix to archive pathnames", "PATH" },
   { "output", 'o', 0, G_OPTION_ARG_STRING, &opt_output_path, "Output to PATH ", "PATH" },
   { NULL }
 };
@@ -132,6 +134,8 @@ ostree_builtin_export (int argc, char **argv, GCancellable *cancellable, GError
   else
     subtree = g_object_ref (root);
 
+  opts.path_prefix = opt_prefix;
+
   if (!ostree_repo_export_tree_to_archive (repo, &opts, (OstreeRepoFile*)subtree, a,
                                            cancellable, error))
     goto out;