programs using kgio crash under memory pressure during init

[Petr Novodvorskiy <nidd@skytap.com>]

In rare cases when we run our unit tests we get following error:

/var/lib/gems/1.8/gems/kgio-2.7.4/lib/kgio_ext.so: [BUG] constant not a
symbol or string
ruby 1.8.7 (2011-06-30 patchlevel 352) [x86_64-linux]

Aborted (core dumped)
rake aborted!

I was able to run out unit tests in memory constrained environment and get
to reproduce it 4 out of 5 runs. I was able to reproduce it even after I
upgraded our kgio version.

After looking in the code, I think I was able to identify the problem. In
init_kgio_tryopen(), when rb_funcall is called to get list of errno
constants, it doesn't protect returned list from garbage collecting. I made
modification (below) that seemed to fix the problem (I wasn't able to
reproduce it anymore).

Thanks,
Petr.

diff --git a/ext/kgio/tryopen.c b/ext/kgio/tryopen.c
index 20f3f6d..d97a5fa 100644
--- a/ext/kgio/tryopen.c
+++ b/ext/kgio/tryopen.c
@@ -162,7 +162,13 @@ void init_kgio_tryopen(void)
                rb_define_alias(cFile, "to_path", "path");

        errno2sym = st_init_numtable();
-       tmp = rb_funcall(rb_mErrno, rb_intern("constants"), 0);
+
+        VALUE *get_err_constants(VALUE blah) {
+          return rb_funcall(rb_mErrno, rb_intern("constants"), 0);
+        }
+        int exception;
+        tmp = rb_protect(get_err_constants, (VALUE)NULL, &exception);
+
        len = RARRAY_LEN(tmp);
        for (i = 0; i < len; i++) {
                VALUE error;