lib/libkvm: start adding basic tests for kvm(3)

- kvm_close: add a testcase to verify support for errno = EINVAL / -1
  (see D10065) when kd == NULL is provided to the libcall.
- kvm_geterr:
-- Add a negative testcase for kd == NULL returning "" (see D10022).
-- Add two positive testcases:
--- test the error case using kvm_write on a O_RDONLY descriptor.
--- test the "no error" case using kvm_read(3) and kvm_nlist(3) as
    helper routines and by injecting a bogus error message via
    _kvm_err (an internal API) _kvm_err was used as there isn't a
    formalized way to clear the error output, and because
    kvm_nlist always returns ENOENT with the NULL terminator today.
- kvm_open, kvm_open2:
-- Add some basic negative tests for kvm_open(3) and kvm_open2(3).
   Testing positive cases with a specific
   `corefile`/`execfile`/`resolver` requires more work and would require
   user intervention today in order to reliably test this out.

Reviewed by:	markj
MFC after:	2 months
Sponsored by:	Dell EMC Isilon
Differential Revision:	D10024

7 files changed, 527 insertions, 0 deletions

diff --git a/lib/libkvm/tests/Makefile b/lib/libkvm/tests/Makefile
new file mode 100644
index 000000000000..1f80d41ae580
--- /dev/null
+++ b/lib/libkvm/tests/Makefile
@@ -0,0 +1,22 @@
+# $FreeBSD$
+
+.include <bsd.own.mk>
+
+ATF_TESTS_C+=	kvm_close_test
+ATF_TESTS_C+=	kvm_geterr_test
+ATF_TESTS_C+=	kvm_open_test
+ATF_TESTS_C+=	kvm_open2_test
+
+CFLAGS.kvm_geterr_test+=	-I${.CURDIR:H}
+
+LIBADD+=	kvm
+
+WARNS?=		6
+
+BINDIR=		${TESTSDIR}
+
+.for t in kvm_geterr_test kvm_open_test kvm_open2_test
+SRCS.$t=	$t.c kvm_test_common.c
+.endfor
+
+.include <bsd.test.mk>
diff --git a/lib/libkvm/tests/kvm_close_test.c b/lib/libkvm/tests/kvm_close_test.c
new file mode 100644
index 000000000000..ab626df118a2
--- /dev/null
+++ b/lib/libkvm/tests/kvm_close_test.c
@@ -0,0 +1,57 @@
+/*-
+ * Copyright (c) 2017 Ngie Cooper <ngie@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <errno.h>
+#include <fcntl.h>
+#include <kvm.h>
+#include <signal.h>
+
+#include <atf-c.h>
+
+ATF_TC(kvm_close_negative_test_NULL);
+ATF_TC_HEAD(kvm_close_negative_test_NULL, tc)
+{
+
+	atf_tc_set_md_var(tc, "descr",
+	    "test that kvm_close(NULL) succeeds without error");
+}
+
+ATF_TC_BODY(kvm_close_negative_test_NULL, tc)
+{
+
+	ATF_REQUIRE_ERRNO(EINVAL, kvm_close(NULL) == -1);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, kvm_close_negative_test_NULL);
+
+	return (atf_no_error());
+}
diff --git a/lib/libkvm/tests/kvm_geterr_test.c b/lib/libkvm/tests/kvm_geterr_test.c
new file mode 100644
index 000000000000..dc589acbb689
--- /dev/null
+++ b/lib/libkvm/tests/kvm_geterr_test.c
@@ -0,0 +1,137 @@
+/*-
+ * Copyright (c) 2017 Ngie Cooper <ngie@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <kvm.h>
+#include <limits.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <atf-c.h>
+
+#include "kvm_private.h"
+
+#include "kvm_test_common.h"
+
+ATF_TC(kvm_geterr_negative_test_NULL);
+ATF_TC_HEAD(kvm_geterr_negative_test_NULL, tc)
+{
+
+	atf_tc_set_md_var(tc, "descr",
+	    "test that kvm_geterr(NULL) returns NULL");
+}
+
+ATF_TC_BODY(kvm_geterr_negative_test_NULL, tc)
+{
+
+	ATF_REQUIRE(!errbuf_has_error(kvm_geterr(NULL)));
+}
+
+ATF_TC(kvm_geterr_positive_test_error);
+ATF_TC_HEAD(kvm_geterr_positive_test_error, tc)
+{
+
+	atf_tc_set_md_var(tc, "descr",
+	    "test that kvm_geterr(kd) when kd doesn't contain an error returns \"\"");
+	atf_tc_set_md_var(tc, "require.user", "root");
+}
+
+ATF_TC_BODY(kvm_geterr_positive_test_error, tc)
+{
+	kvm_t *kd;
+	char *error_msg;
+
+	errbuf_clear();
+	kd = kvm_open2(NULL, NULL, O_RDONLY, errbuf, NULL);
+	ATF_CHECK(!errbuf_has_error(errbuf));
+	ATF_REQUIRE_MSG(kd != NULL, "kvm_open2 failed: %s", errbuf);
+	ATF_REQUIRE_MSG(kvm_write(kd, 0, NULL, 0) == -1,
+	    "kvm_write succeeded unexpectedly on an O_RDONLY file descriptor");
+	error_msg = kvm_geterr(kd);
+	ATF_CHECK(errbuf_has_error(error_msg));
+	ATF_REQUIRE_MSG(kvm_close(kd) == 0, "kvm_close failed: %s",
+	    strerror(errno));
+}
+
+ATF_TC(kvm_geterr_positive_test_no_error);
+ATF_TC_HEAD(kvm_geterr_positive_test_no_error, tc)
+{
+
+	atf_tc_set_md_var(tc, "descr",
+	    "test that kvm_geterr(kd) when kd contains an error returns an error message");
+	atf_tc_set_md_var(tc, "require.user", "root");
+}
+
+ATF_TC_BODY(kvm_geterr_positive_test_no_error, tc)
+{
+#define	ALL_IS_WELL	"that ends well"
+	kvm_t *kd;
+	char *error_msg;
+	struct nlist nl[] = {
+#define	SYMNAME	"_mp_maxcpus"
+#define	X_MAXCPUS	0
+		{ SYMNAME, 0, 0, 0, 0 },
+		{ NULL, 0, 0, 0, 0 },
+	};
+	ssize_t rc;
+	int mp_maxcpus, retcode;
+
+	errbuf_clear();
+	kd = kvm_open2(NULL, NULL, O_RDONLY, errbuf, NULL);
+	ATF_CHECK(!errbuf_has_error(errbuf));
+	ATF_REQUIRE_MSG(kd != NULL, "kvm_open2 failed: %s", errbuf);
+	retcode = kvm_nlist(kd, nl);
+	ATF_REQUIRE_MSG(retcode != -1,
+	    "kvm_nlist failed (returned %d): %s", retcode, kvm_geterr(kd));
+	if (nl[X_MAXCPUS].n_type == 0)
+		atf_tc_skip("symbol (\"%s\") couldn't be found", SYMNAME);
+	_kvm_err(kd, NULL, "%s", ALL_IS_WELL); /* XXX: internal API */
+	rc = kvm_read(kd, nl[X_MAXCPUS].n_value, &mp_maxcpus,
+	    sizeof(mp_maxcpus));
+
+	ATF_REQUIRE_MSG(rc != -1, "kvm_read failed: %s", kvm_geterr(kd));
+	error_msg = kvm_geterr(kd);
+	ATF_REQUIRE_MSG(strcmp(error_msg, ALL_IS_WELL) == 0,
+	    "error message changed: %s", error_msg);
+	ATF_REQUIRE_MSG(kvm_close(kd) == 0, "kvm_close failed: %s",
+	    strerror(errno));
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, kvm_geterr_negative_test_NULL);
+	ATF_TP_ADD_TC(tp, kvm_geterr_positive_test_error);
+	ATF_TP_ADD_TC(tp, kvm_geterr_positive_test_no_error);
+
+	return (atf_no_error());
+}
diff --git a/lib/libkvm/tests/kvm_open2_test.c b/lib/libkvm/tests/kvm_open2_test.c
new file mode 100644
index 000000000000..77b9158d8581
--- /dev/null
+++ b/lib/libkvm/tests/kvm_open2_test.c
@@ -0,0 +1,117 @@
+/*-
+ * Copyright (c) 2017 Ngie Cooper <ngie@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <kvm.h>
+#include <limits.h>
+#include <paths.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <atf-c.h>
+
+#include "kvm_test_common.h"
+
+ATF_TC_WITHOUT_HEAD(kvm_open2_negative_test_nonexistent_corefile);
+ATF_TC_BODY(kvm_open2_negative_test_nonexistent_corefile, tc)
+{
+
+	errbuf_clear();
+	ATF_CHECK(kvm_open2(NULL, "/nonexistent", O_RDONLY, NULL, NULL) == NULL);
+	ATF_CHECK(!errbuf_has_error(errbuf));
+	errbuf_clear();
+	ATF_CHECK(kvm_open2(NULL, "/nonexistent", O_RDONLY,
+	    errbuf, NULL) == NULL);
+	ATF_CHECK(errbuf_has_error(errbuf));
+}
+
+ATF_TC_WITHOUT_HEAD(kvm_open2_negative_test_nonexistent_execfile);
+ATF_TC_BODY(kvm_open2_negative_test_nonexistent_execfile, tc)
+{
+
+	errbuf_clear();
+	ATF_CHECK(kvm_open2("/nonexistent", _PATH_DEVZERO, O_RDONLY,
+	    NULL, NULL) == NULL);
+	ATF_CHECK(strlen(errbuf) == 0);
+	errbuf_clear();
+	ATF_CHECK(kvm_open2("/nonexistent", _PATH_DEVZERO, O_RDONLY,
+	    errbuf, NULL) == NULL);
+	ATF_CHECK(errbuf_has_error(errbuf));
+}
+
+ATF_TC(kvm_open2_negative_test_invalid_corefile);
+ATF_TC_HEAD(kvm_open2_negative_test_invalid_corefile, tc)
+{
+
+	atf_tc_set_md_var(tc, "require.user", "root");
+}
+
+ATF_TC_BODY(kvm_open2_negative_test_invalid_corefile, tc)
+{
+	kvm_t *kd;
+
+	errbuf_clear();
+	atf_utils_create_file("some-file", "this is a text file");
+	kd = kvm_open2(NULL, "some-file", O_RDONLY, errbuf, NULL);
+	ATF_CHECK(errbuf_has_error(errbuf));
+	ATF_REQUIRE_MSG(kd == NULL, "kvm_open2 succeeded");
+}
+
+ATF_TC(kvm_open2_negative_test_invalid_execfile);
+ATF_TC_HEAD(kvm_open2_negative_test_invalid_execfile, tc)
+{
+
+	atf_tc_set_md_var(tc, "require.user", "root");
+}
+
+ATF_TC_BODY(kvm_open2_negative_test_invalid_execfile, tc)
+{
+	kvm_t *kd;
+
+	errbuf_clear();
+	atf_utils_create_file("some-file", "this is a text file");
+	kd = kvm_open2("some-file", "/bin/sh", O_RDONLY, errbuf, NULL);
+	ATF_CHECK(errbuf_has_error(errbuf));
+	ATF_REQUIRE_MSG(kd == NULL, "kvm_open2 succeeded unexpectedly");
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, kvm_open2_negative_test_invalid_corefile);
+	ATF_TP_ADD_TC(tp, kvm_open2_negative_test_invalid_execfile);
+	ATF_TP_ADD_TC(tp, kvm_open2_negative_test_nonexistent_corefile);
+	ATF_TP_ADD_TC(tp, kvm_open2_negative_test_nonexistent_execfile);
+
+	return (atf_no_error());
+}
diff --git a/lib/libkvm/tests/kvm_open_test.c b/lib/libkvm/tests/kvm_open_test.c
new file mode 100644
index 000000000000..995993bb783f
--- /dev/null
+++ b/lib/libkvm/tests/kvm_open_test.c
@@ -0,0 +1,105 @@
+/*-
+ * Copyright (c) 2017 Ngie Cooper <ngie@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <kvm.h>
+#include <limits.h>
+#include <paths.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <atf-c.h>
+
+#include "kvm_test_common.h"
+
+ATF_TC_WITHOUT_HEAD(kvm_open_negative_test_nonexistent_corefile);
+ATF_TC_BODY(kvm_open_negative_test_nonexistent_corefile, tc)
+{
+
+	ATF_CHECK(kvm_open(NULL, "/nonexistent", NULL, O_RDONLY, NULL) == NULL);
+	ATF_CHECK(kvm_open(NULL, "/nonexistent", NULL, O_RDONLY,
+	    getprogname()) == NULL);
+}
+
+ATF_TC_WITHOUT_HEAD(kvm_open_negative_test_nonexistent_execfile);
+ATF_TC_BODY(kvm_open_negative_test_nonexistent_execfile, tc)
+{
+
+	ATF_CHECK(kvm_open("/nonexistent", _PATH_DEVZERO, NULL, O_RDONLY,
+	    NULL) == NULL);
+	ATF_CHECK(kvm_open("/nonexistent", _PATH_DEVZERO, NULL, O_RDONLY,
+	    getprogname()) == NULL);
+}
+
+ATF_TC(kvm_open_negative_test_invalid_corefile);
+ATF_TC_HEAD(kvm_open_negative_test_invalid_corefile, tc)
+{
+
+	atf_tc_set_md_var(tc, "require.user", "root");
+}
+
+ATF_TC_BODY(kvm_open_negative_test_invalid_corefile, tc)
+{
+	kvm_t *kd;
+
+	atf_utils_create_file("some-file", "this is a text file");
+	kd = kvm_open(NULL, "some-file", NULL, O_RDONLY, getprogname());
+	ATF_REQUIRE_MSG(kd == NULL, "kvm_open didn't return NULL on failure");
+}
+
+ATF_TC(kvm_open_negative_test_invalid_execfile);
+ATF_TC_HEAD(kvm_open_negative_test_invalid_execfile, tc)
+{
+
+	atf_tc_set_md_var(tc, "require.user", "root");
+}
+
+ATF_TC_BODY(kvm_open_negative_test_invalid_execfile, tc)
+{
+	kvm_t *kd;
+
+	atf_utils_create_file("some-file", "this is a text file");
+	kd = kvm_open("some-file", "/bin/sh", NULL, O_RDONLY, getprogname());
+	ATF_REQUIRE_MSG(kd == NULL, "kvm_open succeeded unexpectedly");
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, kvm_open_negative_test_invalid_corefile);
+	ATF_TP_ADD_TC(tp, kvm_open_negative_test_invalid_execfile);
+	ATF_TP_ADD_TC(tp, kvm_open_negative_test_nonexistent_corefile);
+	ATF_TP_ADD_TC(tp, kvm_open_negative_test_nonexistent_execfile);
+
+	return (atf_no_error());
+}
diff --git a/lib/libkvm/tests/kvm_test_common.c b/lib/libkvm/tests/kvm_test_common.c
new file mode 100644
index 000000000000..ae9f081bdfd2
--- /dev/null
+++ b/lib/libkvm/tests/kvm_test_common.c
@@ -0,0 +1,49 @@
+/*-
+ * Copyright (c) 2017 Ngie Cooper <ngie@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <string.h>
+
+#include "kvm_test_common.h"
+
+char	errbuf[_POSIX2_LINE_MAX];
+
+void
+errbuf_clear(void)
+{
+
+	strcpy(errbuf, "");
+}
+
+bool
+errbuf_has_error(const char *_errbuf)
+{
+
+	return (strcmp(_errbuf, ""));
+}
diff --git a/lib/libkvm/tests/kvm_test_common.h b/lib/libkvm/tests/kvm_test_common.h
new file mode 100644
index 000000000000..1540a080f221
--- /dev/null
+++ b/lib/libkvm/tests/kvm_test_common.h
@@ -0,0 +1,40 @@
+/*-
+ * Copyright (c) 2017 Ngie Cooper <ngie@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef	__KVM_TEST_COMMON_H__
+
+#include <sys/types.h>
+#include <limits.h>
+#include <stdbool.h>
+
+extern char	errbuf[_POSIX2_LINE_MAX];
+
+void	errbuf_clear(void);
+bool	errbuf_has_error(const char *);
+
+#endif