qed: Implement .bdrv_co_readv/writev

Most of the qed code is now synchronous and matches the coroutine model.
One notable exception is the serialisation between requests which can
still schedule a callback. Before we can replace this with coroutine
locks, let's convert the driver's external interfaces to the coroutine
versions.

We need to be careful to handle both requests that call the completion
callback directly from the calling coroutine (i.e. fully synchronous
code) and requests that involve some callback, so that we need to yield
and wait for the completion callback coming from outside the coroutine.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Manos Pitsidianakis <el13635@mail.ntua.gr>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

block/qed.c

@@ -1322,16 +1322,32 @@ static void qed_aio_next_io(QEDAIOCB *acb)
     }
 }
 
-static BlockAIOCB *qed_aio_setup(BlockDriverState *bs,
-                                 int64_t sector_num,
-                                 QEMUIOVector *qiov, int nb_sectors,
-                                 BlockCompletionFunc *cb,
-                                 void *opaque, int flags)
+typedef struct QEDRequestCo {
+    Coroutine *co;
+    bool done;
+    int ret;
+} QEDRequestCo;
+
+static void qed_co_request_cb(void *opaque, int ret)
 {
-    QEDAIOCB *acb = qemu_aio_get(&qed_aiocb_info, bs, cb, opaque);
+    QEDRequestCo *co = opaque;
 
-    trace_qed_aio_setup(bs->opaque, acb, sector_num, nb_sectors,
-                        opaque, flags);
+    co->done = true;
+    co->ret = ret;
+    qemu_coroutine_enter_if_inactive(co->co);
+}
+
+static int coroutine_fn qed_co_request(BlockDriverState *bs, int64_t sector_num,
+                                       QEMUIOVector *qiov, int nb_sectors,
+                                       int flags)
+{
+    QEDRequestCo co = {
+        .co     = qemu_coroutine_self(),
+        .done   = false,
+    };
+    QEDAIOCB *acb = qemu_aio_get(&qed_aiocb_info, bs, qed_co_request_cb, &co);
+
+    trace_qed_aio_setup(bs->opaque, acb, sector_num, nb_sectors, &co, flags);
 
     acb->flags = flags;
     acb->qiov = qiov;
@@ -1344,53 +1360,34 @@ static BlockAIOCB *qed_aio_setup(BlockDriverState *bs,
 
     /* Start request */
     qed_aio_start_io(acb);
-    return &acb->common;
-}
 
-static BlockAIOCB *bdrv_qed_aio_readv(BlockDriverState *bs,
-                                      int64_t sector_num,
-                                      QEMUIOVector *qiov, int nb_sectors,
-                                      BlockCompletionFunc *cb,
-                                      void *opaque)
-{
-    return qed_aio_setup(bs, sector_num, qiov, nb_sectors, cb, opaque, 0);
+    if (!co.done) {
+        qemu_coroutine_yield();
+    }
+
+    return co.ret;
 }
 
-static BlockAIOCB *bdrv_qed_aio_writev(BlockDriverState *bs,
-                                       int64_t sector_num,
-                                       QEMUIOVector *qiov, int nb_sectors,
-                                       BlockCompletionFunc *cb,
-                                       void *opaque)
+static int coroutine_fn bdrv_qed_co_readv(BlockDriverState *bs,
+                                          int64_t sector_num, int nb_sectors,
+                                          QEMUIOVector *qiov)
 {
-    return qed_aio_setup(bs, sector_num, qiov, nb_sectors, cb,
-                         opaque, QED_AIOCB_WRITE);
+    return qed_co_request(bs, sector_num, qiov, nb_sectors, 0);
 }
 
-typedef struct {
-    Coroutine *co;
-    int ret;
-    bool done;
-} QEDWriteZeroesCB;
-
-static void coroutine_fn qed_co_pwrite_zeroes_cb(void *opaque, int ret)
+static int coroutine_fn bdrv_qed_co_writev(BlockDriverState *bs,
+                                           int64_t sector_num, int nb_sectors,
+                                           QEMUIOVector *qiov)
 {
-    QEDWriteZeroesCB *cb = opaque;
-
-    cb->done = true;
-    cb->ret = ret;
-    if (cb->co) {
-        aio_co_wake(cb->co);
-    }
+    return qed_co_request(bs, sector_num, qiov, nb_sectors, QED_AIOCB_WRITE);
 }
 
 static int coroutine_fn bdrv_qed_co_pwrite_zeroes(BlockDriverState *bs,
                                                   int64_t offset,
                                                   int count,
                                                   BdrvRequestFlags flags)
 {
-    BlockAIOCB *blockacb;
     BDRVQEDState *s = bs->opaque;
-    QEDWriteZeroesCB cb = { .done = false };
     QEMUIOVector qiov;
     struct iovec iov;
 
@@ -1407,19 +1404,9 @@ static int coroutine_fn bdrv_qed_co_pwrite_zeroes(BlockDriverState *bs,
     iov.iov_len = count;
 
     qemu_iovec_init_external(&qiov, &iov, 1);
-    blockacb = qed_aio_setup(bs, offset >> BDRV_SECTOR_BITS, &qiov,
-                             count >> BDRV_SECTOR_BITS,
-                             qed_co_pwrite_zeroes_cb, &cb,
-                             QED_AIOCB_WRITE | QED_AIOCB_ZERO);
-    if (!blockacb) {
-        return -EIO;
-    }
-    if (!cb.done) {
-        cb.co = qemu_coroutine_self();
-        qemu_coroutine_yield();
-    }
-    assert(cb.done);
-    return cb.ret;
+    return qed_co_request(bs, offset >> BDRV_SECTOR_BITS, &qiov,
+                          count >> BDRV_SECTOR_BITS,
+                          QED_AIOCB_WRITE | QED_AIOCB_ZERO);
 }
 
 static int bdrv_qed_truncate(BlockDriverState *bs, int64_t offset, Error **errp)
@@ -1615,8 +1602,8 @@ static BlockDriver bdrv_qed = {
     .bdrv_create              = bdrv_qed_create,
     .bdrv_has_zero_init       = bdrv_has_zero_init_1,
     .bdrv_co_get_block_status = bdrv_qed_co_get_block_status,
-    .bdrv_aio_readv           = bdrv_qed_aio_readv,
-    .bdrv_aio_writev          = bdrv_qed_aio_writev,
+    .bdrv_co_readv            = bdrv_qed_co_readv,
+    .bdrv_co_writev           = bdrv_qed_co_writev,
     .bdrv_co_pwrite_zeroes    = bdrv_qed_co_pwrite_zeroes,
     .bdrv_truncate            = bdrv_qed_truncate,
     .bdrv_getlength           = bdrv_qed_getlength,