Re: [PATCH 09/18] xen/xenbus: add xenbus_setup_ring() service function

[Juergen Gross <jgross@xxxxxxxx>]

On 20.04.22 20:44, Boris Ostrovsky wrote:
> On 4/20/22 11:09 AM, Juergen Gross wrote:
> > +/*
> > + * xenbus_setup_ring
> > + * @dev: xenbus device
> > + * @vaddr: pointer to starting virtual address of the ring
> > + * @nr_pages: number of pages to be granted
> > + * @grefs: grant reference array to be filled in
> > + *
> > + * Allocate physically contiguous pages for a shared ring buffer and grant it
> > + * to the peer of the given device. The ring buffer is initially filled with
> > + * zeroes. The virtual address of the ring is stored at @vaddr and the
> > + * grant references are stored in the @grefs array. In case of error @vaddr
> > + * will be set to NULL and @grefs will be filled with INVALID_GRANT_REF.
> > + */
> > +int xenbus_setup_ring(struct xenbus_device *dev, gfp_t gfp, void **vaddr,
> > +              unsigned int nr_pages, grant_ref_t *grefs)
> > +{
> > +    unsigned long ring_size = nr_pages * XEN_PAGE_SIZE;
> > +    unsigned int i;
> > +    int ret;
> > +
> > +    *vaddr = alloc_pages_exact(ring_size, gfp | __GFP_ZERO);
> > +    if (!*vaddr) {
> > +        ret = -ENOMEM;
> > +        goto err;
> > +    }
> > +
> > +    ret = xenbus_grant_ring(dev, *vaddr, nr_pages, grefs);
> > +    if (ret)
> > +        goto err;
> > +
> > +    return 0;
> > +
> > + err:
> > +    if (*vaddr)
> > +        free_pages_exact(*vaddr, ring_size);
> > +    for (i = 0; i < nr_pages; i++)
> > +        grefs[i] = INVALID_GRANT_REF;
> > +    *vaddr = NULL;
> > +
> > +    return ret;
> > +}
>
> We can create a wrapper around this function that will also call 
> SHARED_RING_INIT() and FRONT_RING_INIT(). A bunch of drivers do that.
This wrapper would need to be a macro, so I decided not to do that.

It would make sense to merge the call of SHARED_RING_INIT() into
FRONT_RING_INIT() (or better, have a new macro combining the two),
though, as there is no use case of FRONT_RING_INIT() without a
call of SHARED_RING_INIT() directly before it.


Juergen

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