From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55384) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fEd8Q-0003XW-OL for qemu-devel@nongnu.org; Fri, 04 May 2018 12:00:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fEd8P-00021n-Bc for qemu-devel@nongnu.org; Fri, 04 May 2018 12:00:38 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:36222 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fEd8P-00021E-5H for qemu-devel@nongnu.org; Fri, 04 May 2018 12:00:37 -0400 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Fri, 4 May 2018 17:00:26 +0100 Message-Id: <20180504160026.14017-4-berrange@redhat.com> In-Reply-To: <20180504160026.14017-1-berrange@redhat.com> References: <20180504160026.14017-1-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: [Qemu-devel] [PATCH 3/3] glib: enforce the minimum required version and warn about old APIs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Peter Maydell , Markus Armbruster , Paolo Bonzini , Thomas Huth , Olaf Hering , Stefan Hajnoczi , Michael Roth , Eric Blake , Stefan Berger , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= There are two useful macros that can be defined before including glib.h that are related to the min required glib version - GLIB_VERSION_MIN_REQUIRED When this is defined, if code uses an API that was deprecated in this version, or older, a compiler warning will be emitted. This alerts maintainers to update their code to whatever new replacement API is now recommended best practice. - GLIB_VERSION_MAX_ALLOWED When this is defined, if code uses an API that was introduced in a version that is newer than the declared version, a compiler warning will be emitted. This alerts maintainers if new code accidentally uses functionality that won't be available on some supported platforms. The GLIB_VERSION_MAX_ALLOWED constant makes it a bit harder to opt in to using specific new APIs with a GLIB_CHECK_VERSION conditional. To workaround this Pragmas can be used to temporarily turn off the -Wdeprecated-declarations compiler warning, while a static inline compat function is implemented. Nothing needs that at this time, so just illustrate it in a comment for benefit of future changes. Signed-off-by: Daniel P. Berrang=C3=A9 --- include/glib-compat.h | 49 +++++++++++++++++++++++++++++++++++++++++++++= ++++ 1 file changed, 49 insertions(+) diff --git a/include/glib-compat.h b/include/glib-compat.h index 3b340ab33c..d066f6d257 100644 --- a/include/glib-compat.h +++ b/include/glib-compat.h @@ -16,8 +16,57 @@ #ifndef QEMU_GLIB_COMPAT_H #define QEMU_GLIB_COMPAT_H =20 +/* Ask for warnings for anything that was marked deprecated in + * the defined version, or before. It is a candidate for rewrite. + */ +#define GLIB_VERSION_MIN_REQUIRED GLIB_VERSION_2_42 + +/* Ask for warnings if code tries to use function that did not + * exist in the defined version. These risk breaking builds + */ +#define GLIB_VERSION_MAX_ALLOWED GLIB_VERSION_2_42 + #include =20 +/* + * Note that because of the GLIB_VERSION_MAX_ALLOWED constant + * above, allowing use of functions from newer GLib via this + * compat header needs a little trickery to prevent warnings + * being emitted. + * + * Consider a function from newer glib-X.Y that we want to use + * + * int g_foo(const char *wibble) + * + * We must define a static inline function with the same + * signature that does what we need, but with a "_qemu" + * suffix eg + * + * _Pragma("GCC diagnostic push") + * _Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"") + * static inline void g_foo_qemu(const char *wibble) + * { + * #if GLIB_CHECK_VERSION(X, Y, 0) + * g_foo(wibble) + * #else + * g_something_equivalent_in_older_glib(wibble); + * #endif + * } + * _Pragma("GCC diagnostic pop") + * + * The Pragma calls turn off -Wdeprecated-declarations, + * ensuring this wrapper function impl doesn't trigger the + * compiler warning about using too new glib APIs. Finally + * we can do + * + * #define g_foo(a) g_foo_qemu(a) + * + * So now the code elsewhere in QEMU, which *does* have the + * -Wdeprecated-declarations warning active, can call + * g_foo(...) as normal, without generating warnings. + */ + + #if defined(_WIN32) && !GLIB_CHECK_VERSION(2, 50, 0) /* * g_poll has a problem on Windows when using --=20 2.14.3