Re: [libvirt] creating stream

On 04/05/2017 12:35 AM, Vasiliy Tolstov wrote: Not entirely true. We like all devs, but we just discourage people to use our RPC as it's internal. It doesn't offer the full set of features provided by libvirt APIs: for instance some drivers (e.g. ESX) don't use it and use curl instead to communicate with remote hypervisor. The second reason is that we might change the RPC suddenly without prior notice and thus your application would just stop working. The libvirt streams are a bit kind of magic. Esp. on RPC level. Basically, when client and server wants to transfer some data over a stream, both of them call virStreamNew() which creates a local object which so far is not tied to the other stream in any way. The point where these two streams start to be connected is the public API that involves the stream, for instance virStorageVolDownload(). The streams can be viewed as an UNIX socket or some other type of socket. virStreamSend() corresponds to write() and virStreamRecv() then corresponds to read(). So if one side sends some data to the stream, the other side can receive the data. On the code level, there's again a driver that implements the methods as there are several implementations available. Firstly, there's network implementation in our RPC code (this is responsible for transferring stream data to the other side), then there's local implementation for working with files (virFDStream), and finally ESX has its own implementation (it uses curl for fetching/uploading data onto ESX hypervisor). I'm currently working on sparse streams (so that files transferred through our streams stay sparse), and let me tell you - the code is pretty complicated. http://libvirt.org/internals/rpc.html Michal