nbd: don't change socket block during negotiate

The caller might handle non-blocking using coroutine. Leave the choice
to the caller to use a blocking or non-blocking negotiate.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

block/nbd-client.c

@@ -348,6 +348,7 @@ int nbd_client_session_init(NbdClientSession *client,
     int ret;
 
     /* NBD handshake */
+    qemu_set_block(sock);
     ret = nbd_receive_negotiate(sock, client->export_name,
                                 &client->nbdflags, &client->size,
                                 &client->blocksize);

nbd.c

@@ -443,7 +443,6 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
 
     TRACE("Receiving negotiation.");
 
-    qemu_set_block(csock);
     rc = -EINVAL;
 
     if (read_sync(csock, buf, 8) != 8) {
@@ -558,7 +557,6 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
     rc = 0;
 
 fail:
-    qemu_set_nonblock(csock);
     return rc;
 }