tests: qtest: add qtest_has_accel() to check if tested binary supports accelerator

Currently it is not possible to create tests that have KVM as a hard
requirement on a host that doesn't support KVM for tested target
binary (modulo going through the trouble of compiling out
the offending test case).

Following scenario makes test fail when it's run on non x86 host:
  qemu-system-x86_64 -enable-kvm -M q35,kernel-irqchip=on -smp 1,maxcpus=288

This patch introduces qtest_has_accel() to let users check if accel is
available in advance and avoid executing non run-able test-cases.

It implements detection of TCG and KVM only, the rest could be
added later on, when we actually start testing them in qtest.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20210902113551.461632-3-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

meson.build

@@ -75,6 +75,12 @@ else
   kvm_targets = []
 endif
 
+kvm_targets_c = ''
+if not get_option('kvm').disabled() and targetos == 'linux'
+  kvm_targets_c = '"' + '" ,"'.join(kvm_targets) + '"'
+endif
+config_host_data.set('CONFIG_KVM_TARGETS', kvm_targets_c)
+
 accelerator_targets = { 'CONFIG_KVM': kvm_targets }
 
 if cpu in ['aarch64']

tests/qtest/libqos/libqtest.h

@@ -588,6 +588,14 @@ bool qtest_big_endian(QTestState *s);
  */
 const char *qtest_get_arch(void);
 
+/**
+ * qtest_has_accel:
+ * @accel_name: Accelerator name to check for.
+ *
+ * Returns: true if the accelerator is built in.
+ */
+bool qtest_has_accel(const char *accel_name);
+
 /**
  * qtest_add_func:
  * @str: Test case path.

tests/qtest/libqtest.c

@@ -922,6 +922,33 @@ const char *qtest_get_arch(void)
     return end + 1;
 }
 
+bool qtest_has_accel(const char *accel_name)
+{
+    if (g_str_equal(accel_name, "tcg")) {
+#if defined(CONFIG_TCG)
+        return true;
+#else
+        return false;
+#endif
+    } else if (g_str_equal(accel_name, "kvm")) {
+        int i;
+        const char *arch = qtest_get_arch();
+        const char *targets[] = { CONFIG_KVM_TARGETS };
+
+        for (i = 0; i < ARRAY_SIZE(targets); i++) {
+            if (!strncmp(targets[i], arch, strlen(arch))) {
+                if (!access("/dev/kvm", R_OK | W_OK)) {
+                    return true;
+                }
+            }
+        }
+    } else {
+        /* not implemented */
+        g_assert_not_reached();
+    }
+    return false;
+}
+
 bool qtest_get_irq(QTestState *s, int num)
 {
     /* dummy operation in order to make sure irq is up to date */