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glib: enforce the minimum required version and warn about old APIs

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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. This workaround is illustrated with the
implementation of the g_strv_contains method to satisfy the test suite.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrangé 2018-05-04 16:25:00 +01:00
parent e7b3af8159
commit e71e8cc035
2 changed files with 68 additions and 2 deletions
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68
include/glib-compat.h
View File

@ -16,8 +16,74 @@
#ifndef QEMU_GLIB_COMPAT_H
#define QEMU_GLIB_COMPAT_H
/* 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_40
/* 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_40
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
#include <glib.h>
/*
* 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 e.g.
*
* 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
* }
*
* The #pragma at the top of this file turns 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.
*/
static inline gboolean g_strv_contains_qemu(const gchar *const *strv,
const gchar *str)
{
#if GLIB_CHECK_VERSION(2, 44, 0)
return g_strv_contains(strv, str);
#else
g_return_val_if_fail(strv != NULL, FALSE);
g_return_val_if_fail(str != NULL, FALSE);
for (; *strv != NULL; strv++) {
if (g_str_equal(str, *strv)) {
return TRUE;
}
}
return FALSE;
#endif
}
#define g_strv_contains(a, b) g_strv_contains_qemu(a, b)
#if defined(_WIN32) && !GLIB_CHECK_VERSION(2, 50, 0)
/*
* g_poll has a problem on Windows when using
@ -45,4 +111,6 @@ gint g_poll_fixed(GPollFD *fds, guint nfds, gint timeout);
} while (0)
#endif
#pragma GCC diagnostic pop
#endif

2
tests/test-qga.c
View File

@ -744,12 +744,10 @@ static void test_qga_config(gconstpointer data)
strv = g_key_file_get_string_list(kf, "general", "blacklist", &n, &error);
g_assert_cmpint(n, ==, 2);
#if GLIB_CHECK_VERSION(2, 44, 0)
g_assert_true(g_strv_contains((const char * const *)strv,
"guest-ping"));
g_assert_true(g_strv_contains((const char * const *)strv,
"guest-get-time"));
#endif
g_assert_no_error(error);
g_strfreev(strv);