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Re: [Xen-devel] [PATCH 5/9] drm/xen-front: Implement handling of shared display buffers

On 02/23/2018 04:36 PM, Boris Ostrovsky wrote:
On 02/23/2018 02:53 AM, Oleksandr Andrushchenko wrote:
On 02/23/2018 02:25 AM, Boris Ostrovsky wrote:
On 02/21/2018 03:03 AM, Oleksandr Andrushchenko wrote:
     static int __init xen_drv_init(void)
+    /* At the moment we only support case with XEN_PAGE_SIZE ==
Why BUILD_BUG_ON? This should simply not load if page sizes are

This is a compile time check, so if kernel/Xen is configured
to use page size combination which is not supported by the
driver it will fail during compilation. This seems correct to me,
because you shouldn't even try to load the driver which
cannot handle different page sizes to not make any harm.

This will prevent whole kernel from building. So, for example,
randconfig builds will fail.

makes a lot of sense, thank you
will rework so I reject to load if the requirement is not met

+    ret = gnttab_map_refs(map_ops, NULL, buf->pages, buf->num_pages);
+    BUG_ON(ret);
We should try not to BUG*(). There are a few in this patch (and possibly
others) that I think can be avoided.

I will rework BUG_* for map/unmap code to handle errors,
but will still leave
     /* either pages or sgt, not both */
     BUG_ON(cfg->pages && cfg->sgt);
which is a real driver bug and must not happen
Why not return an error?

In fact, AFAICS you only call it in patch 9 where both of these can be
tested, in which case something like -EINVAL would look reasonable.
ok, will remove BUG_ON as well

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