Wanlong Gao [off-list ref] writes:

On 01/02/2013 01:03 PM, Rusty Russell wrote:

quoted

Paolo Bonzini [off-list ref] writes:

quoted

The virtqueue_add_buf function has two limitations:

1) it requires the caller to provide all the buffers in a single call;

2) it does not support chained scatterlists: the buffers must be
provided as an array of struct scatterlist;

Chained scatterlists are a horrible interface, but that doesn't mean we
shouldn't support them if there's a need.

I think I once even had a patch which passed two chained sgs, rather
than a combo sg and two length numbers.  It's very old, but I've pasted
it below.

Duplicating the implementation by having another interface is pretty
nasty; I think I'd prefer the chained scatterlists, if that's optimal
for you.

I rebased against virtio-next and use it in virtio-scsi, and tested it with 4 targets
virtio-scsi devices and host cpu idle=poll. Saw a little performance regression here.

Sure, but now you should be able to eliminate virtscsi_map_sgl(), right?
You should be able to use scsi_out(sc) and scsi_in(sc) directly, which
is what Paulo wanted to do...

Right Paulo?

Thanks,
Rusty.