On Wed, 13 Jan 2016 18:09:41 +0100 Greg Kurz <gk...@linux.vnet.ibm.com> wrote:
> The default use case for vhost is when the host and the vring have the > same endianness (default native endianness). But there are cases where > they differ and vhost should byteswap when accessing the vring: > - the host is big endian and the vring comes from a virtio 1.0 device > which is always little endian > - the architecture is bi-endian and the vring comes from a legacy virtio > device with a different endianness than the endianness of the host (aka > legacy cross-endian) > > These cases are handled by the vq->is_le and the optional vq->user_be, > with the following logic: > - if none of the fields is enabled, vhost access the vring without byteswap > - if the vring is virtio 1.0 and the host is big endian, vq->is_le is > enabled to enforce little endian access to the vring > - if the vring is legacy cross-endian, userspace enables vq->user_be > to inform vhost about the vring endianness. This endianness is then > enforced for vring accesses through vq->is_le again > > The logic is unclear in the current code. > > This patch introduces helpers with explicit enable and disable semantics, > for better clarity. > > No behaviour change. > > Signed-off-by: Greg Kurz <gk...@linux.vnet.ibm.com> > --- > drivers/vhost/vhost.c | 28 +++++++++++++++++++--------- > 1 file changed, 19 insertions(+), 9 deletions(-) Reviewed-by: Cornelia Huck <cornelia.h...@de.ibm.com>
