ocaml: Fix thread safety of strings in bindings (RHBZ#604691).

There's a thread safety issue with the current OCaml bindings which
is well explained in the bug report:

https://bugzilla.redhat.com/show_bug.cgi?id=604691

This commit fixes the safety issue by copying strings temporarily
before releasing the thread lock.  Updated code looks like this:

  char *filename = guestfs_safe_strdup (g, String_val (filenamev));
  int r;

  caml_enter_blocking_section ();
  r = guestfs_add_drive_ro (g, filename);
  caml_leave_blocking_section ();
  free (filename);
  if (r == -1)
    ocaml_guestfs_raise_error (g, "add_drive_ro");

Also included is a regression test.

1 files changed, 72 insertions, 0 deletions

diff --git a/ocaml/t/guestfs_070_threads.ml b/ocaml/t/guestfs_070_threads.ml
new file mode 100644
index 00000000..e13ac7b6
--- /dev/null
+++ b/ocaml/t/guestfs_070_threads.ml
@@ -0,0 +1,72 @@
+(* libguestfs OCaml bindings
+ * Copyright (C) 2010 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *)
+
+open Unix
+
+(* Start a background thread which does lots of allocation and
+ * GC activity.
+ *)
+let thread = Thread.create (
+  fun () ->
+    while true do
+      Gc.compact ();
+      ignore (Array.init 1000 (fun i -> Thread.yield (); String.create (8*i)))
+    done
+) ()
+
+let () =
+  let g = Guestfs.create () in
+
+  let fd = openfile "test.img" [O_WRONLY;O_CREAT;O_NOCTTY;O_TRUNC] 0o666 in
+  ftruncate fd (500 * 1024 * 1024);
+  close fd;
+
+  (* Copy these strings so they're located on the heap and
+   * subject to garbage collection.
+   *)
+  let s = String.copy "test.img" in
+  Guestfs.add_drive_ro g s;
+  Guestfs.launch g;
+
+  let dev = String.copy "/dev/sda" in
+  Guestfs.pvcreate g dev;
+  let vg = String.copy "VG" in
+  Guestfs.vgcreate g vg [|dev|];
+  let s = String.copy "LV1" in
+  Guestfs.lvcreate g s vg 200;
+  let s = String.copy "LV2" in
+  Guestfs.lvcreate g s vg 200;
+
+  let lvs = Guestfs.lvs g in
+  if lvs <> [|"/dev/VG/LV1"; "/dev/VG/LV2"|] then
+    failwith "Guestfs.lvs returned incorrect result";
+
+  let s = String.copy "ext3" in
+  let lv = String.copy "/dev/VG/LV1" in
+  Guestfs.mkfs g s lv;
+  let s = String.copy "/" in
+  Guestfs.mount_options g "" lv s;
+  let s = String.copy "/test" in
+  Guestfs.touch g s;
+
+  Guestfs.umount_all g;
+  Guestfs.sync g;
+  Guestfs.close g;
+  unlink "test.img";
+  Gc.compact ();
+  exit 0