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? Stefan
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