On Tue, 7 Apr 2015 17:01:31 +0200
Cornelia Huck <cornelia.huck@xxxxxxxxxx> wrote:
> On Tue, 07 Apr 2015 14:19:31 +0200
> Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx> wrote:
>
> > This patch brings cross-endian support to vhost when used to implement
> > legacy virtio devices. Since it is a relatively rare situation, the
> > feature availability is controlled by a kernel config option (not set
> > by default).
> >
> > The ioctls introduced by this patch are for legacy only: virtio 1.0
> > devices are returned EPERM.
> >
> > Signed-off-by: Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/vhost/Kconfig | 10 ++++++++
> > drivers/vhost/vhost.c | 55 ++++++++++++++++++++++++++++++++++++++++++++
> > drivers/vhost/vhost.h | 17 +++++++++++++-
> > include/uapi/linux/vhost.h | 5 ++++
> > 4 files changed, 86 insertions(+), 1 deletion(-)
>
> > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
> > +static long vhost_set_vring_endian_legacy(struct vhost_virtqueue *vq,
> > + void __user *argp)
> > +{
> > + struct vhost_vring_state s;
> > +
> > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> > + return -EPERM;
> > +
> > + if (copy_from_user(&s, argp, sizeof(s)))
> > + return -EFAULT;
> > +
> > + vq->legacy_is_little_endian = !!s.num;
> > + return 0;
> > +}
> > +
> > +static long vhost_get_vring_endian_legacy(struct vhost_virtqueue *vq,
> > + u32 idx,
> > + void __user *argp)
> > +{
> > + struct vhost_vring_state s = {
> > + .index = idx,
> > + .num = vq->legacy_is_little_endian
> > + };
> > +
> > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> > + return -EPERM;
> > +
> > + if (copy_to_user(argp, &s, sizeof(s)))
> > + return -EFAULT;
> > +
> > + return 0;
> > +}
> > +#else
> > +static long vhost_set_vring_endian_legacy(struct vhost_virtqueue *vq,
> > + void __user *argp)
> > +{
> > + return 0;
>
> I'm wondering whether this handler should return an error if the
> feature is not configured for the kernel? How can the userspace caller
> find out whether it has successfully prompted the kernel to handle the
> endianness correctly?
>
Yes you're right. I think -ENOIOCTLCMD as suggested by Michael is a good
candidate.
Thanks.
> > +}
> > +
> > +static long vhost_get_vring_endian_legacy(struct vhost_virtqueue *vq,
> > + u32 idx,
> > + void __user *argp)
> > +{
> > + return 0;
> > +}
> > +#endif /* CONFIG_VHOST_SET_ENDIAN_LEGACY */
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