RE: [PATCH v2 4/4] xen-blkback: support dynamic unbind/bind

Durrant, Paul
2019-12-11T14:46:29Z

> -----Original Message-----
> > > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-
> > blkback/xenbus.c
> > > index e8c5c54e1d26..13d09630b237 100644
> > > --- a/drivers/block/xen-blkback/xenbus.c
> > > +++ b/drivers/block/xen-blkback/xenbus.c
> > > @@ -181,6 +181,8 @@ static int xen_blkif_map(struct xen_blkif_ring
> > *ring, grant_ref_t *gref,
> > > {
> > > int err;
> > > struct xen_blkif *blkif = ring->blkif;
> > > + struct blkif_common_sring *sring_common;
> > > + RING_IDX rsp_prod, req_prod;
> > >
> > > /* Already connected through? */
> > > if (ring->irq)
> > > @@ -191,46 +193,66 @@ static int xen_blkif_map(struct xen_blkif_ring
> > *ring, grant_ref_t *gref,
> > > if (err < 0)
> > > return err;
> > >
> > > + sring_common = (struct blkif_common_sring *)ring->blk_ring;
> > > + rsp_prod = READ_ONCE(sring_common->rsp_prod);
> > > + req_prod = READ_ONCE(sring_common->req_prod);
> > > +
> > > switch (blkif->blk_protocol) {
> > > case BLKIF_PROTOCOL_NATIVE:
> > > {
> > > - struct blkif_sring *sring;
> > > - sring = (struct blkif_sring *)ring->blk_ring;
> > > - BACK_RING_INIT(&ring->blk_rings.native, sring,
> > > - XEN_PAGE_SIZE * nr_grefs);
> > > + struct blkif_sring *sring_native =
> > > + (struct blkif_sring *)ring->blk_ring;
> >
> > I think you can constify both sring_native and sring_common (and the
> > other instances below).
>
> Yes, I can do that. I don't think the macros would mind.
>

Spoke to soon. They do mind, of course, because the sring pointer in the front/back ring is not (and should not) be const. I can const sring_common but no others.

Paul