On Wed, Dec 19, 2012 at 06:51:30PM +0200, Michael S. Tsirkin wrote: > On Wed, Dec 19, 2012 at 01:04:08PM +0100, Paolo Bonzini wrote: > > 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 > > Hmm it should work with vhost. BTW passing in num_in + num_out would be nicer than explicit direction: closer to the current add_buf. > > > > > Stefan > > > -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
