block/nbd-client: refactor request send/receive

Add nbd_co_request, to remove code duplications in
nbd_client_co_{pwrite,pread,...} functions. Also this is
needed for further refactoring.
Signed-off-by: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20170804151440.320927-8-vsementsov@virtuozzo.com>
[eblake: make nbd_co_request a wrapper, rather than merging two
existing functions]
Signed-off-by: NEric Blake <eblake@redhat.com>

block/nbd-client.c

@@ -220,28 +220,40 @@ static void nbd_co_receive_reply(NBDClientSession *s,
     qemu_co_mutex_unlock(&s->send_mutex);
 }
 
+static int nbd_co_request(BlockDriverState *bs,
+                          NBDRequest *request,
+                          QEMUIOVector *qiov)
+{
+    NBDClientSession *client = nbd_get_client_session(bs);
+    NBDReply reply;
+    int ret;
+
+    assert(!qiov || request->type == NBD_CMD_WRITE ||
+           request->type == NBD_CMD_READ);
+    ret = nbd_co_send_request(bs, request,
+                              request->type == NBD_CMD_WRITE ? qiov : NULL);
+    if (ret < 0) {
+        reply.error = -ret;
+    } else {
+        nbd_co_receive_reply(client, request, &reply,
+                             request->type == NBD_CMD_READ ? qiov : NULL);
+    }
+    return -reply.error;
+}
+
 int nbd_client_co_preadv(BlockDriverState *bs, uint64_t offset,
                          uint64_t bytes, QEMUIOVector *qiov, int flags)
 {
-    NBDClientSession *client = nbd_get_client_session(bs);
     NBDRequest request = {
         .type = NBD_CMD_READ,
         .from = offset,
         .len = bytes,
     };
-    NBDReply reply;
-    int ret;
 
     assert(bytes <= NBD_MAX_BUFFER_SIZE);
     assert(!flags);
 
-    ret = nbd_co_send_request(bs, &request, NULL);
-    if (ret < 0) {
-        reply.error = -ret;
-    } else {
-        nbd_co_receive_reply(client, &request, &reply, qiov);
-    }
-    return -reply.error;
+    return nbd_co_request(bs, &request, qiov);
 }
 
 int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
@@ -253,8 +265,6 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
         .from = offset,
         .len = bytes,
     };
-    NBDReply reply;
-    int ret;
 
     if (flags & BDRV_REQ_FUA) {
         assert(client->info.flags & NBD_FLAG_SEND_FUA);
@@ -263,26 +273,18 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
 
     assert(bytes <= NBD_MAX_BUFFER_SIZE);
 
-    ret = nbd_co_send_request(bs, &request, qiov);
-    if (ret < 0) {
-        reply.error = -ret;
-    } else {
-        nbd_co_receive_reply(client, &request, &reply, NULL);
-    }
-    return -reply.error;
+    return nbd_co_request(bs, &request, qiov);
 }
 
 int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
                                 int bytes, BdrvRequestFlags flags)
 {
-    int ret;
     NBDClientSession *client = nbd_get_client_session(bs);
     NBDRequest request = {
         .type = NBD_CMD_WRITE_ZEROES,
         .from = offset,
         .len = bytes,
     };
-    NBDReply reply;
 
     if (!(client->info.flags & NBD_FLAG_SEND_WRITE_ZEROES)) {
         return -ENOTSUP;
@@ -296,21 +298,13 @@ int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
         request.flags |= NBD_CMD_FLAG_NO_HOLE;
     }
 
-    ret = nbd_co_send_request(bs, &request, NULL);
-    if (ret < 0) {
-        reply.error = -ret;
-    } else {
-        nbd_co_receive_reply(client, &request, &reply, NULL);
-    }
-    return -reply.error;
+    return nbd_co_request(bs, &request, NULL);
 }
 
 int nbd_client_co_flush(BlockDriverState *bs)
 {
     NBDClientSession *client = nbd_get_client_session(bs);
     NBDRequest request = { .type = NBD_CMD_FLUSH };
-    NBDReply reply;
-    int ret;
 
     if (!(client->info.flags & NBD_FLAG_SEND_FLUSH)) {
         return 0;
@@ -319,13 +313,7 @@ int nbd_client_co_flush(BlockDriverState *bs)
     request.from = 0;
     request.len = 0;
 
-    ret = nbd_co_send_request(bs, &request, NULL);
-    if (ret < 0) {
-        reply.error = -ret;
-    } else {
-        nbd_co_receive_reply(client, &request, &reply, NULL);
-    }
-    return -reply.error;
+    return nbd_co_request(bs, &request, NULL);
 }
 
 int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset, int bytes)
@@ -336,21 +324,12 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset, int bytes)
         .from = offset,
         .len = bytes,
     };
-    NBDReply reply;
-    int ret;
 
     if (!(client->info.flags & NBD_FLAG_SEND_TRIM)) {
         return 0;
     }
 
-    ret = nbd_co_send_request(bs, &request, NULL);
-    if (ret < 0) {
-        reply.error = -ret;
-    } else {
-        nbd_co_receive_reply(client, &request, &reply, NULL);
-    }
-    return -reply.error;
-
+    return nbd_co_request(bs, &request, NULL);
 }
 
 void nbd_client_detach_aio_context(BlockDriverState *bs)