From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58094) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1btaYs-000511-Cf for qemu-devel@nongnu.org; Mon, 10 Oct 2016 09:24:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1btaYp-0007Gt-SG for qemu-devel@nongnu.org; Mon, 10 Oct 2016 09:24:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54520) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1btaYp-0007GZ-K3 for qemu-devel@nongnu.org; Mon, 10 Oct 2016 09:24:07 -0400 From: Eric Blake Date: Mon, 10 Oct 2016 08:23:49 -0500 Message-Id: <1476105837-9861-8-git-send-email-eblake@redhat.com> In-Reply-To: <1476105837-9861-1-git-send-email-eblake@redhat.com> References: <1476105837-9861-1-git-send-email-eblake@redhat.com> Subject: [Qemu-devel] [PATCH v6 07/15] qstring: Add qstring_consume_str() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: armbru@redhat.com, "Dr. David Alan Gilbert" , =?UTF-8?q?Andreas=20F=C3=A4rber?= Similar to g_string_free(), there are cases where we want to destroy our reference to a QString while grabbing its contents, where we want to avoid use-after-free but also avoid a needless strdup(). But unlike g_string_free(), we are at least sensible enough to add this feature via a different function name, instead of trying to overload two completely separate concepts into a single function. Do this by introducing the new qstring_consume_str(), then use it where it makes sense. In the case of monitor.c, note that QString _always_ has a non-NULL embedded string with at least one byte allocated for a terminating NUL, so special-casing on length 0 was wasted code. Signed-off-by: Eric Blake --- v6: no change [no v5 due to series split] v4: new patch, suggested by Markus --- include/qapi/qmp/qstring.h | 1 + monitor.c | 6 +----- qobject/qstring.c | 23 +++++++++++++++++++++++ qom/object.c | 3 +-- tests/check-qstring.c | 31 +++++++++++++++++++++++++++---- 5 files changed, 53 insertions(+), 11 deletions(-) diff --git a/include/qapi/qmp/qstring.h b/include/qapi/qmp/qstring.h index a987f3b..2d55c87 100644 --- a/include/qapi/qmp/qstring.h +++ b/include/qapi/qmp/qstring.h @@ -27,6 +27,7 @@ QString *qstring_from_str(const char *str); QString *qstring_from_substr(const char *str, int start, int end); size_t qstring_get_length(const QString *qstring); const char *qstring_get_str(const QString *qstring); +char *qstring_consume_str(QString *qstring); void qstring_append(QString *qstring, const char *str); void qstring_append_chr(QString *qstring, int c); void qstring_append_printf(QString *qstring, const char *fmt, ...) diff --git a/monitor.c b/monitor.c index 4ff74b7..aed0d0b 100644 --- a/monitor.c +++ b/monitor.c @@ -624,11 +624,7 @@ char *qmp_human_monitor_command(const char *command_line, bool has_cpu_index, cur_mon = old_mon; qemu_mutex_lock(&hmp.out_lock); - if (qstring_get_length(hmp.outbuf) > 0) { - output = g_strdup(qstring_get_str(hmp.outbuf)); - } else { - output = g_strdup(""); - } + output = qstring_consume_str(hmp.outbuf); qemu_mutex_unlock(&hmp.out_lock); out: diff --git a/qobject/qstring.c b/qobject/qstring.c index fbfae27..7a438e9 100644 --- a/qobject/qstring.c +++ b/qobject/qstring.c @@ -145,6 +145,29 @@ const char *qstring_get_str(const QString *qstring) } /** + * qstring_consume_str(): Destructively convert a QString to string + * + * The reference count of @qstring is decremented by one, and the + * caller is responsible for calling g_free() on the result. In the + * common case where @qstring was not shared, this is faster than + * using strdup() on the result of qstring_get_str(); otherwise, the + * result is a copy and remaining users of @qstring are unaffected. + */ +char *qstring_consume_str(QString *qstring) +{ + char *result; + + if (qstring->base.refcnt == 1) { + result = qstring->string; + qstring->string = NULL; + } else { + result = g_strdup(qstring->string); + } + qobject_decref(&qstring->base); + return result; +} + +/** * qstring_destroy_obj(): Free all memory allocated by a QString * object */ diff --git a/qom/object.c b/qom/object.c index 8166b7d..1a3c83e 100644 --- a/qom/object.c +++ b/qom/object.c @@ -1112,10 +1112,9 @@ char *object_property_get_str(Object *obj, const char *name, error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name, "string"); retval = NULL; } else { - retval = g_strdup(qstring_get_str(qstring)); + retval = qstring_consume_str(qstring); } - QDECREF(qstring); return retval; } diff --git a/tests/check-qstring.c b/tests/check-qstring.c index 239e9d9..11823c2 100644 --- a/tests/check-qstring.c +++ b/tests/check-qstring.c @@ -1,7 +1,7 @@ /* * QString unit-tests. * - * Copyright (C) 2009 Red Hat Inc. + * Copyright (C) 2009-2016 Red Hat Inc. * * Authors: * Luiz Capitulino @@ -31,9 +31,7 @@ static void qstring_from_str_test(void) g_assert(strcmp(str, qstring->string) == 0); g_assert(qobject_type(QOBJECT(qstring)) == QTYPE_QSTRING); - // destroy doesn't exit yet - g_free(qstring->string); - g_free(qstring); + QDECREF(qstring); } static void qstring_destroy_test(void) @@ -55,6 +53,30 @@ static void qstring_get_str_test(void) QDECREF(qstring); } +static void qstring_consume_str_test(void) +{ + QString *qstring; + char *ret_str; + const char *str = "QEMU/KVM"; + char *ptr; + + qstring = qstring_from_str(str); + QINCREF(qstring); + g_assert_cmpint(qstring->base.refcnt, ==, 2); + ptr = qstring->string; + + ret_str = qstring_consume_str(qstring); + g_assert_cmpint(qstring->base.refcnt, ==, 1); + g_assert(ret_str != ptr); + g_assert_cmpstr(ret_str, ==, str); + g_free(ret_str); + + ret_str = qstring_consume_str(qstring); + g_assert(ret_str == ptr); + g_assert_cmpstr(ret_str, ==, str); + g_free(ret_str); +} + static void qstring_append_chr_test(void) { int i; @@ -102,6 +124,7 @@ int main(int argc, char **argv) g_test_add_func("/public/append_chr", qstring_append_chr_test); g_test_add_func("/public/from_substr", qstring_from_substr_test); g_test_add_func("/public/to_qstring", qobject_to_qstring_test); + g_test_add_func("/public/consume_str", qstring_consume_str_test); return g_test_run(); } -- 2.7.4