builder: add simple OCaml osinfo-db reader

Add a simple OCaml-based implementation of reader of the osinfo-db:
the only interface is an iterator that invokes an user-supplied
function with each XML file found.

This implementation behaves like the current C implementation, and
still supports the old libosinfo db.

[RWMJ: Fixed trailing whitespace]

.gitignore

@@ -93,6 +93,7 @@ Makefile.in
 /builder/index-scan.c
 /builder/libguestfs.conf
 /builder/opensuse.conf
+/builder/osinfo_config.ml
 /builder/oUnit-*
 /builder/*.out
 /builder/*.qcow2

builder/Makefile.am

@@ -214,6 +214,10 @@ CLEANFILES += *.qcow2 *.xz
 
 check_DATA = $(disk_images)
 
+osinfo_config.ml: Makefile
+	echo 'let libosinfo_db_path = "$(datadir)/libosinfo/db"' > $@-t
+	mv $@-t $@
+
 fedora.qcow2: ../test-data/phony-guests/fedora.img
 	rm -f $@ $@-t
 	qemu-img convert -f raw -O qcow2 $< $@-t

builder/osinfo.ml

@@ -0,0 +1,76 @@
+(* virt-builder
+ * Copyright (C) 2017 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.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *)
+
+open Std_utils
+open Tools_utils
+open Osinfo_config
+
+let rec fold fn base =
+  let locations =
+    (* (1) Try the shared osinfo directory, using either the
+     * $OSINFO_SYSTEM_DIR envvar or its default value.
+     *)
+    let dir =
+      try Sys.getenv "OSINFO_SYSTEM_DIR"
+      with Not_found -> "/usr/share/osinfo" in
+    ((dir // "os"), read_osinfo_db_three_levels) ::
+
+      (* (2) Try the libosinfo directory, using the newer three-directory
+       * layout ($LIBOSINFO_DB_PATH / "os" / $group-ID / [file.xml]).
+       *)
+      let path = Osinfo_config.libosinfo_db_path // "os" in
+      (path, read_osinfo_db_three_levels) ::
+
+        (* (3) Try the libosinfo directory, using the old flat directory
+         * layout ($LIBOSINFO_DB_PATH / "oses" / [file.xml]).
+         *)
+        let path = Osinfo_config.libosinfo_db_path // "oses" in
+        (path, read_osinfo_db_flat) :: [] in
+
+
+  let files =
+    List.flatten (
+      filter_map (
+          fun (path, f) ->
+            if is_directory path then Some (f path)
+            (* This is not an error: RHBZ#948324. *)
+            else None
+      ) locations
+  ) in
+
+  List.fold_left fn base files
+
+and read_osinfo_db_three_levels path =
+  debug "osinfo: loading 3-level-directories database from %s" path;
+  let entries = Array.to_list (Sys.readdir path) in
+  let entries = List.map ((//) path) entries in
+  (* Iterate only on directories. *)
+  let entries = List.filter is_directory entries in
+  List.flatten (List.map read_osinfo_db_directory entries)
+
+and read_osinfo_db_flat path =
+  debug "osinfo: loading flat database from %s" path;
+  read_osinfo_db_directory path
+
+and read_osinfo_db_directory path =
+  let entries = Sys.readdir path in
+  let entries = Array.to_list entries in
+  let entries = List.filter (fun x -> Filename.check_suffix x ".xml") entries in
+  let entries = List.map ((//) path) entries in
+  let entries = List.filter is_regular_file entries in
+  entries

builder/osinfo.mli

@@ -0,0 +1,22 @@
+(* virt-builder
+ * Copyright (C) 2017 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.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *)
+
+val fold : ('a -> string -> 'a) -> 'a -> 'a
+(** [fold f base] folds function [f] over every file in the
+    osinfo-db/libosinfo database of OS definitions.
+  *)