[RFC PATCH 2/8] transactions: add tran_add_back

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

First change the transactions from a QLIST to QSIMPLEQ, then
use it to implement tran_add_tail, which allows adding elements
to the end of list transactions.

This is useful if we have some "preparation" transiction callbacks
that we want to run before the others but still only when invoking
finalize/commit/abort.

For example (A and B are lists transaction callbacks):

for (i=0; i < 3; i++) {
	tran_add(A[i]);
	tran_add_tail(B[i]);
}

tran_commit();

Will process transactions in this order: A2 - A1 - A0 - B0 - B1 - B2

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/qemu/transactions.h |  9 +++++++++
 util/transactions.c         | 29 +++++++++++++++++++++--------
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/include/qemu/transactions.h b/include/qemu/transactions.h
index 2f2060acd9..42783720b9 100644
--- a/include/qemu/transactions.h
+++ b/include/qemu/transactions.h
@@ -50,7 +50,16 @@ typedef struct TransactionActionDrv {
 typedef struct Transaction Transaction;
 
 Transaction *tran_new(void);
+/*
+ * Add transaction at the beginning of the transaction list.
+ * @tran will be the first transaction to be processed in finalize/commit/abort.
+ */
 void tran_add(Transaction *tran, TransactionActionDrv *drv, void *opaque);
+/*
+ * Add transaction at the end of the transaction list.
+ * @tran will be the last transaction to be processed in finalize/commit/abort.
+ */
+void tran_add_tail(Transaction *tran, TransactionActionDrv *drv, void *opaque);
 void tran_abort(Transaction *tran);
 void tran_commit(Transaction *tran);
 
diff --git a/util/transactions.c b/util/transactions.c
index 2dbdedce95..89e541c4a4 100644
--- a/util/transactions.c
+++ b/util/transactions.c
@@ -28,18 +28,18 @@
 typedef struct TransactionAction {
     TransactionActionDrv *drv;
     void *opaque;
-    QSLIST_ENTRY(TransactionAction) entry;
+    QSIMPLEQ_ENTRY(TransactionAction) entry;
 } TransactionAction;
 
 struct Transaction {
-    QSLIST_HEAD(, TransactionAction) actions;
+    QSIMPLEQ_HEAD(, TransactionAction) actions;
 };
 
 Transaction *tran_new(void)
 {
     Transaction *tran = g_new(Transaction, 1);
 
-    QSLIST_INIT(&tran->actions);
+    QSIMPLEQ_INIT(&tran->actions);
 
     return tran;
 }
@@ -54,20 +54,33 @@ void tran_add(Transaction *tran, TransactionActionDrv *drv, void *opaque)
         .opaque = opaque
     };
 
-    QSLIST_INSERT_HEAD(&tran->actions, act, entry);
+    QSIMPLEQ_INSERT_HEAD(&tran->actions, act, entry);
+}
+
+void tran_add_tail(Transaction *tran, TransactionActionDrv *drv, void *opaque)
+{
+    TransactionAction *act;
+
+    act = g_new(TransactionAction, 1);
+    *act = (TransactionAction) {
+        .drv = drv,
+        .opaque = opaque
+    };
+
+    QSIMPLEQ_INSERT_TAIL(&tran->actions, act, entry);
 }
 
 void tran_abort(Transaction *tran)
 {
     TransactionAction *act, *next;
 
-    QSLIST_FOREACH(act, &tran->actions, entry) {
+    QSIMPLEQ_FOREACH(act, &tran->actions, entry) {
         if (act->drv->abort) {
             act->drv->abort(act->opaque);
         }
     }
 
-    QSLIST_FOREACH_SAFE(act, &tran->actions, entry, next) {
+    QSIMPLEQ_FOREACH_SAFE(act, &tran->actions, entry, next) {
         if (act->drv->clean) {
             act->drv->clean(act->opaque);
         }
@@ -82,13 +95,13 @@ void tran_commit(Transaction *tran)
 {
     TransactionAction *act, *next;
 
-    QSLIST_FOREACH(act, &tran->actions, entry) {
+    QSIMPLEQ_FOREACH(act, &tran->actions, entry) {
         if (act->drv->commit) {
             act->drv->commit(act->opaque);
         }
     }
 
-    QSLIST_FOREACH_SAFE(act, &tran->actions, entry, next) {
+    QSIMPLEQ_FOREACH_SAFE(act, &tran->actions, entry, next) {
         if (act->drv->clean) {
             act->drv->clean(act->opaque);
         }
-- 
2.31.1