Am 06.02.2015 um 11:42 schrieb Stefan Hajnoczi: > On Thu, Feb 05, 2015 at 03:29:17PM +0100, Peter Lieven wrote: >> Am 05.02.2015 um 15:00 schrieb Stefan Hajnoczi: >>> On Fri, Jan 30, 2015 at 10:08:02PM +0100, Peter Lieven wrote: >>>> Just wondering if VIRTQUEUE_MAX_SIZE in include/hw/virtio/virtio.h should >>>> not be equal to IOV_MAX instead of the hardcoded 1024? >>> The vring queue size is guest-visible to some extent (e.g. vring memory >>> layout). Tying it to a constant that is defined by the host operating >>> system could lead to problems (e.g. live migration between different >>> hosts). >>> >>> Anyway, all of the virtio devices have a queue size that is less than or >>> equal to VIRTQUEUE_MAX_SIZE (and there is an assertion to check this in >>> virtio_add_queue()). >>> >>> Guests are supposed to honor the vring queue size, although indirect >>> descriptors seem to be able to use up to VIRTQUEUE_MAX_SIZE according to >>> my understanding of QEMU's virtio.c code. >>> >>> Why would you like to use IOV_MAX? >> The idea was that IOV_MAX is the limit in case of at least virtio-blk. The >> host >> will not support more than IOV_MAX iovecs passed to a block request. > Is there an issue in practice?
If there is no platform where IOV_MAX is less than 1024 then not. Peter
