Il 19/12/2012 11:47, Stefan Hajnoczi ha scritto: > On Tue, Dec 18, 2012 at 01:32:48PM +0100, Paolo Bonzini wrote: >> +/** >> + * virtqueue_start_buf - start building buffer for the other end >> + * @vq: the struct virtqueue we're talking about. >> + * @buf: a struct keeping the state of the buffer >> + * @data: the token identifying the buffer. >> + * @count: the number of buffers that will be added > > Perhaps count should be named count_bufs or num_bufs. Ok. >> + * @count_sg: the number of sg lists that will be added > > What is the purpose of count_sg? It is needed to decide whether to use an indirect or a direct buffer. The idea is to avoid a memory allocation if the driver is providing us with separate sg elements (under the assumption that they will be few). Originally I wanted to use a mix of direct and indirect buffer (direct if add_buf received a one-element scatterlist, otherwise indirect). It would have had the same effect, without having to specify count_sg in advance. The spec is not clear if that is allowed or not, but in the end they do not work with either QEMU or vhost, so I chose this alternative instead. Paolo > Stefan > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
