[PATCH v2 2/4] tests/qtest/migration: Add infrastructure to skip tests on older QEMUs

[Fabiano Rosas <farosas@suse.de>]

We can run the migration tests with two different QEMU binaries to
test migration compatibility between QEMU versions. This means we'll
be running the tests with an older QEMU in either source or
destination.

We need to avoid trying to test functionality that is unknown to the
older QEMU. This could mean new features, bug fixes, error message
changes, QEMU command line changes, migration API changes, etc.

Add a 'since' argument to the tests that inform when the functionality
that is being test has been added to QEMU so we can skip the test on
older versions.

Also add a version comparison function so we can adapt test code
depending on the QEMU binary version being used.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 tests/qtest/migration-helpers.c | 11 +++++++++++
 tests/qtest/migration-helpers.h |  1 +
 tests/qtest/migration-test.c    | 29 +++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/tests/qtest/migration-helpers.c b/tests/qtest/migration-helpers.c
index 24fb7b3525..20220bfda0 100644
--- a/tests/qtest/migration-helpers.c
+++ b/tests/qtest/migration-helpers.c
@@ -292,3 +292,14 @@ char *resolve_machine_version(const char *alias, const char *var1,
 
     return find_common_machine_version(machine_name, var1, var2);
 }
+
+int migration_vercmp(QTestState *who, const char *tgt_version)
+{
+    int major, minor, micro;
+    g_autofree char *version = NULL;
+
+    qtest_query_version(who, &major, &minor, &micro);
+    version = g_strdup_printf("%d.%d", major, minor + !!micro);
+
+    return strcmp(version, tgt_version);
+}
diff --git a/tests/qtest/migration-helpers.h b/tests/qtest/migration-helpers.h
index e31dc85cc7..7b4f8e851e 100644
--- a/tests/qtest/migration-helpers.h
+++ b/tests/qtest/migration-helpers.h
@@ -47,4 +47,5 @@ char *find_common_machine_version(const char *mtype, const char *var1,
                                   const char *var2);
 char *resolve_machine_version(const char *alias, const char *var1,
                               const char *var2);
+int migration_vercmp(QTestState *who, const char *tgt_version);
 #endif /* MIGRATION_HELPERS_H */
diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
index d520c587f7..001470238b 100644
--- a/tests/qtest/migration-test.c
+++ b/tests/qtest/migration-test.c
@@ -637,6 +637,12 @@ typedef struct {
     bool use_dirty_ring;
     const char *opts_source;
     const char *opts_target;
+    /*
+     * If a test checks against new functionality that might not be
+     * present in older QEMUs this needs to be set so we can skip
+     * running it when doing compatibility testing.
+     */
+    const char *since;
 } MigrateStart;
 
 /*
@@ -850,6 +856,17 @@ static int test_migrate_start(QTestState **from, QTestState **to,
         qtest_qmp_set_event_callback(*from,
                                      migrate_watch_for_stop,
                                      &got_src_stop);
+
+        if (args->since && migration_vercmp(*from, args->since) < 0) {
+            g_autofree char *msg = NULL;
+
+            msg = g_strdup_printf("Test requires at least QEMU version %s",
+                                  args->since);
+            g_test_skip(msg);
+            qtest_quit(*from);
+
+            return -1;
+        }
     }
 
     cmd_target = g_strdup_printf("-accel kvm%s -accel tcg "
@@ -872,6 +889,18 @@ static int test_migrate_start(QTestState **from, QTestState **to,
                                  migrate_watch_for_resume,
                                  &got_dst_resume);
 
+    if (args->since && migration_vercmp(*to, args->since) < 0) {
+        g_autofree char *msg = NULL;
+
+        msg = g_strdup_printf("Test requires at least QEMU version %s",
+                              args->since);
+        g_test_skip(msg);
+        qtest_quit(*to);
+        qtest_quit(*from);
+
+        return -1;
+    }
+
     /*
      * Remove shmem file immediately to avoid memory leak in test failed case.
      * It's valid because QEMU has already opened this file
-- 
2.35.3