Il 12/02/2013 16:43, Michael S. Tsirkin ha scritto: > On Tue, Feb 12, 2013 at 04:32:27PM +0100, Paolo Bonzini wrote: >> Il 12/02/2013 15:56, Michael S. Tsirkin ha scritto: >>>>> +/** >>>>> + * virtqueue_start_buf - start building buffer for the other end >>>>> + * @vq: the struct virtqueue we're talking about. >>>>> + * @data: the token identifying the buffer. >>>>> + * @nents: the number of buffers that will be added >>> This function starts building one buffer, number of buffers >>> is a bit weird here. >> >> Ok. >> >>>>> + * @nsg: the number of sg lists that will be added >>> This means number of calls to add_sg ? Not sure why this matters. >>> How about we pass in in_num/out_num - that is total # of sg, >>> same as add_buf? >> >> It is used to choose between direct and indirect. > > total number of in and out should be enough for this, no? Originally, I used nsg/nents because I wanted to use mixed direct and indirect buffers. nsg/nents let me choose between full direct (nsg == nents), mixed (num_free >= nsg), full indirect (num_free < nsg). Then I had to give up because QEMU does not support it, but I still would like to keep that open in the API. In this series, however, I am still using nsg to choose between direct and indirect. I would like to use dirtect for small scatterlists, even if they are surrounded by a request/response headers/footers. >>>>> +/** >>>>> + * virtqueue_add_sg - add sglist to buffer being built >>>>> + * @_vq: the virtqueue for which the buffer is being built >>>>> + * @sgl: the description of the buffer(s). >>>>> + * @nents: the number of items to process in sgl >>>>> + * @dir: whether the sgl is read or written (DMA_TO_DEVICE/DMA_FROM_DEVICE only) >>>>> + * >>>>> + * Note that, unlike virtqueue_add_buf, this function follows chained >>>>> + * scatterlists, and stops before the @nents-th item if a scatterlist item >>>>> + * has a marker. >>>>> + * >>>>> + * Caller must ensure we don't call this with other virtqueue operations >>>>> + * at the same time (except where noted). >>> Hmm so if you want to add in and out, need separate calls? >>> in_num/out_num would be nicer? >> >> If you want to add in and out just use virtqueue_add_buf... > > I thought the point of this one is maximum flexibility. Maximum flexibility does not include doing everything in one call (the other way round in fact: you already need to wrap with start/end, hence doing one or two extra add_sg calls is not important). Paolo -- 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
