util: add transactions.c

Add simple transaction API to use in further update of block graph
operations.

Supposed usage is:

- "prepare" is main function of the action and it should make the main
  effect of the action to be visible for the following actions, keeping
  possibility of roll-back, saving necessary things in action state,
  which is prepended to the action list (to do that, prepare func
  should call tran_add()). So, driver struct doesn't include "prepare"
  field, as it is supposed to be called directly.

- commit/rollback is supposed to be called for the list of action
  states, to commit/rollback all the actions in reverse order

- When possible "commit" should not make visible effect for other
  actions, which make possible transparent logical interaction between
  actions.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210428151804.439460-9-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 97 insertions, 0 deletions

diff --git a/util/meson.build b/util/meson.build
index 510765c..97fad44 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -41,6 +41,7 @@ util_ss.add(files('qsp.c'))
 util_ss.add(files('range.c'))
 util_ss.add(files('stats64.c'))
 util_ss.add(files('systemd.c'))
+util_ss.add(files('transactions.c'))
 util_ss.add(when: 'CONFIG_POSIX', if_true: files('drm.c'))
 util_ss.add(files('guest-random.c'))
 util_ss.add(files('yank.c'))
diff --git a/util/transactions.c b/util/transactions.c
new file mode 100644
index 0000000..d0bc9a3
--- /dev/null
+++ b/util/transactions.c
@@ -0,0 +1,96 @@
+/*
+ * Simple transactions API
+ *
+ * Copyright (c) 2021 Virtuozzo International GmbH.
+ *
+ * Author:
+ *  Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+
+#include "qemu/transactions.h"
+#include "qemu/queue.h"
+
+typedef struct TransactionAction {
+    TransactionActionDrv *drv;
+    void *opaque;
+    QSLIST_ENTRY(TransactionAction) entry;
+} TransactionAction;
+
+struct Transaction {
+    QSLIST_HEAD(, TransactionAction) actions;
+};
+
+Transaction *tran_new(void)
+{
+    Transaction *tran = g_new(Transaction, 1);
+
+    QSLIST_INIT(&tran->actions);
+
+    return tran;
+}
+
+void tran_add(Transaction *tran, TransactionActionDrv *drv, void *opaque)
+{
+    TransactionAction *act;
+
+    act = g_new(TransactionAction, 1);
+    *act = (TransactionAction) {
+        .drv = drv,
+        .opaque = opaque
+    };
+
+    QSLIST_INSERT_HEAD(&tran->actions, act, entry);
+}
+
+void tran_abort(Transaction *tran)
+{
+    TransactionAction *act, *next;
+
+    QSLIST_FOREACH_SAFE(act, &tran->actions, entry, next) {
+        if (act->drv->abort) {
+            act->drv->abort(act->opaque);
+        }
+
+        if (act->drv->clean) {
+            act->drv->clean(act->opaque);
+        }
+
+        g_free(act);
+    }
+
+    g_free(tran);
+}
+
+void tran_commit(Transaction *tran)
+{
+    TransactionAction *act, *next;
+
+    QSLIST_FOREACH_SAFE(act, &tran->actions, entry, next) {
+        if (act->drv->commit) {
+            act->drv->commit(act->opaque);
+        }
+
+        if (act->drv->clean) {
+            act->drv->clean(act->opaque);
+        }
+
+        g_free(act);
+    }
+
+    g_free(tran);
+}