hw/xen: Implement XenStore transactions
Given that the whole thing supported copy on write from the beginning,
transactions end up being fairly simple. On starting a transaction, just
take a ref of the existing root; swap it back in on a successful commit.
The main tree has a transaction ID too, and we keep a record of the last
transaction ID given out. if the main tree is ever modified when it isn't
the latest, it gets a new transaction ID.
A commit can only succeed if the main tree hasn't moved on since it was
forked. Strictly speaking, the XenStore protocol allows a transaction to
succeed as long as nothing *it* read or wrote has changed in the interim,
but no implementations do that; *any* change is sufficient to abort a
transaction.
This does not yet fire watches on the changed nodes on a commit. That bit
is more fun and will come in a follow-on commit.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
diff --git a/tests/unit/test-xs-node.c b/tests/unit/test-xs-node.c
index 19000b6..3c36545 100644
--- a/tests/unit/test-xs-node.c
+++ b/tests/unit/test-xs-node.c
@@ -42,6 +42,7 @@
g_assert(s->nr_nodes == 1);
g_hash_table_unref(s->watches);
+ g_hash_table_unref(s->transactions);
xs_node_unref(s->root);
g_free(s);
@@ -271,12 +272,129 @@
}
+static void do_test_xs_node_tx(bool fail, bool commit)
+{
+ XenstoreImplState *s = setup();
+ GString *watches = g_string_new(NULL);
+ GByteArray *data = g_byte_array_new();
+ unsigned int tx_id = XBT_NULL;
+ int err;
+
+ g_assert(s);
+
+ /* Set a watch */
+ err = xs_impl_watch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+ g_assert(watches->len == strlen("somewatch"));
+ g_assert(!strcmp(watches->str, "somewatch"));
+ g_string_truncate(watches, 0);
+
+ /* Write something */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/relative/path",
+ "something");
+ g_assert(s->nr_nodes == 7);
+ g_assert(!err);
+ g_assert(!strcmp(watches->str,
+ "some/relative/pathwatch"));
+ g_string_truncate(watches, 0);
+
+ /* Create a transaction */
+ err = xs_impl_transaction_start(s, DOMID_GUEST, &tx_id);
+ g_assert(!err);
+
+ if (fail) {
+ /* Write something else in the root */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/relative/path",
+ "another thing");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 7);
+ g_assert(!strcmp(watches->str,
+ "some/relative/pathwatch"));
+ g_string_truncate(watches, 0);
+ }
+
+ g_assert(!watches->len);
+
+ /* Perform a write in the transaction */
+ err = write_str(s, DOMID_GUEST, tx_id, "some/relative/path",
+ "something else");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 7);
+ g_assert(!watches->len);
+
+ err = xs_impl_read(s, DOMID_GUEST, XBT_NULL, "some/relative/path", data);
+ g_assert(!err);
+ if (fail) {
+ g_assert(data->len == strlen("another thing"));
+ g_assert(!memcmp(data->data, "another thing", data->len));
+ } else {
+ g_assert(data->len == strlen("something"));
+ g_assert(!memcmp(data->data, "something", data->len));
+ }
+ g_byte_array_set_size(data, 0);
+
+ err = xs_impl_read(s, DOMID_GUEST, tx_id, "some/relative/path", data);
+ g_assert(!err);
+ g_assert(data->len == strlen("something else"));
+ g_assert(!memcmp(data->data, "something else", data->len));
+ g_byte_array_set_size(data, 0);
+
+ /* Attempt to commit the transaction */
+ err = xs_impl_transaction_end(s, DOMID_GUEST, tx_id, commit);
+ if (commit && fail) {
+ g_assert(err == EAGAIN);
+ } else {
+ g_assert(!err);
+ }
+ g_assert(!watches->len);
+ g_assert(s->nr_nodes == 7);
+
+ err = xs_impl_unwatch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+
+ err = xs_impl_read(s, DOMID_GUEST, XBT_NULL, "some/relative/path", data);
+ g_assert(!err);
+ if (fail) {
+ g_assert(data->len == strlen("another thing"));
+ g_assert(!memcmp(data->data, "another thing", data->len));
+ } else if (commit) {
+ g_assert(data->len == strlen("something else"));
+ g_assert(!memcmp(data->data, "something else", data->len));
+ } else {
+ g_assert(data->len == strlen("something"));
+ g_assert(!memcmp(data->data, "something", data->len));
+ }
+ g_byte_array_unref(data);
+ g_string_free(watches, true);
+ xs_impl_delete(s);
+}
+
+static void test_xs_node_tx_fail(void)
+{
+ do_test_xs_node_tx(true, true);
+}
+
+static void test_xs_node_tx_abort(void)
+{
+ do_test_xs_node_tx(false, false);
+ do_test_xs_node_tx(true, false);
+}
+static void test_xs_node_tx_succeed(void)
+{
+ do_test_xs_node_tx(false, true);
+}
+
int main(int argc, char **argv)
{
g_test_init(&argc, &argv, NULL);
module_call_init(MODULE_INIT_QOM);
g_test_add_func("/xs_node/simple", test_xs_node_simple);
+ g_test_add_func("/xs_node/tx_abort", test_xs_node_tx_abort);
+ g_test_add_func("/xs_node/tx_fail", test_xs_node_tx_fail);
+ g_test_add_func("/xs_node/tx_succeed", test_xs_node_tx_succeed);
return g_test_run();
}
