sheepdog: cancel aio requests if possible

This patch tries to cancel aio requests in pending queue and failed
queue.  When the sheepdog driver cannot cancel the requests, it waits
for them to be completed.
Signed-off-by: NMORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Tested-by: NLiu Yuan <namei.unix@gmail.com>
Reviewed-by: NLiu Yuan <namei.unix@gmail.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/sheepdog.c

@@ -299,7 +299,8 @@ struct SheepdogAIOCB {
     Coroutine *coroutine;
     void (*aio_done_func)(SheepdogAIOCB *);
 
-    bool canceled;
+    bool cancelable;
+    bool *finished;
     int nr_pending;
 };
 
@@ -418,6 +419,7 @@ static inline void free_aio_req(BDRVSheepdogState *s, AIOReq *aio_req)
 {
     SheepdogAIOCB *acb = aio_req->aiocb;
 
+    acb->cancelable = false;
     QLIST_REMOVE(aio_req, aio_siblings);
     g_free(aio_req);
 
@@ -426,23 +428,68 @@ static inline void free_aio_req(BDRVSheepdogState *s, AIOReq *aio_req)
 
 static void coroutine_fn sd_finish_aiocb(SheepdogAIOCB *acb)
 {
-    if (!acb->canceled) {
-        qemu_coroutine_enter(acb->coroutine, NULL);
+    qemu_coroutine_enter(acb->coroutine, NULL);
+    if (acb->finished) {
+        *acb->finished = true;
     }
     qemu_aio_release(acb);
 }
 
+/*
+ * Check whether the specified acb can be canceled
+ *
+ * We can cancel aio when any request belonging to the acb is:
+ *  - Not processed by the sheepdog server.
+ *  - Not linked to the inflight queue.
+ */
+static bool sd_acb_cancelable(const SheepdogAIOCB *acb)
+{
+    BDRVSheepdogState *s = acb->common.bs->opaque;
+    AIOReq *aioreq;
+
+    if (!acb->cancelable) {
+        return false;
+    }
+
+    QLIST_FOREACH(aioreq, &s->inflight_aio_head, aio_siblings) {
+        if (aioreq->aiocb == acb) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
 static void sd_aio_cancel(BlockDriverAIOCB *blockacb)
 {
     SheepdogAIOCB *acb = (SheepdogAIOCB *)blockacb;
+    BDRVSheepdogState *s = acb->common.bs->opaque;
+    AIOReq *aioreq, *next;
+    bool finished = false;
+
+    acb->finished = &finished;
+    while (!finished) {
+        if (sd_acb_cancelable(acb)) {
+            /* Remove outstanding requests from pending and failed queues.  */
+            QLIST_FOREACH_SAFE(aioreq, &s->pending_aio_head, aio_siblings,
+                               next) {
+                if (aioreq->aiocb == acb) {
+                    free_aio_req(s, aioreq);
+                }
+            }
+            QLIST_FOREACH_SAFE(aioreq, &s->failed_aio_head, aio_siblings,
+                               next) {
+                if (aioreq->aiocb == acb) {
+                    free_aio_req(s, aioreq);
+                }
+            }
 
-    /*
-     * Sheepdog cannot cancel the requests which are already sent to
-     * the servers, so we just complete the request with -EIO here.
-     */
-    acb->ret = -EIO;
-    qemu_coroutine_enter(acb->coroutine, NULL);
-    acb->canceled = true;
+            assert(acb->nr_pending == 0);
+            sd_finish_aiocb(acb);
+            return;
+        }
+        qemu_aio_wait();
+    }
 }
 
 static const AIOCBInfo sd_aiocb_info = {
@@ -463,7 +510,8 @@ static SheepdogAIOCB *sd_aio_setup(BlockDriverState *bs, QEMUIOVector *qiov,
     acb->nb_sectors = nb_sectors;
 
     acb->aio_done_func = NULL;
-    acb->canceled = false;
+    acb->cancelable = true;
+    acb->finished = NULL;
     acb->coroutine = qemu_coroutine_self();
     acb->ret = 0;
     acb->nr_pending = 0;