Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: > Il 02/01/2013 06:03, Rusty Russell ha scritto: >> Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: >>> 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. > > Unfortunately, that cannot work because not all architectures support > chained scatterlists. WHAT? I can't figure out what an arch needs to do to support this? Why is it an option for archs? Why is sg_chain() even defined for non-ARCH_HAS_SG_CHAIN? Jens, help!! All archs we care about support them, though, so I think we can ignore this issue for now. > (Also, as you mention chained scatterlists are horrible. They'd happen > to work for virtio-scsi, but not for virtio-blk where the response > status is part of the footer, not the header). We lost that debate 5 years ago, so we hack around it as needed. We can add helpers to append if we need. Thanks, Rusty. -- 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
