Re: [PATCH for-next 2/5] IB/core: Add support for extended query device caps

[Eli Cohen <eli-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On Tue, Nov 04, 2014 at 02:35:09PM +0200, Haggai Eran wrote:
> On 03/11/2014 10:02, Eli Cohen wrote:
> > +
> > +	if (ucore->outlen < sizeof(resp))
> > +		return -ENOSPC;
> 
> This check may cause compatibility problems when running a newer kernel
> with old userspace. The userspace code will have a smaller
> ib_uverbs_ex_query_device_resp struct, so the verb will always fail. A
> possible solution is to drop this check, and modify ib_copy_to_udata so
> that it only copies up to ucore->outlen bytes.
> 
Makes sense. Will fix that in V1.

> > +
> > +	if (cmd.comp_mask)
> > +		return -EINVAL;
> 
> This check may make it difficult for userspace to use this verb. If
> running an older kernel with a newer userspace, the userspace will need
> to run the verb multiple times to find out which combination of
> comp_mask bits is actually supported. I think a better way would be to
> drop this check, and let userspace rely on the returned comp_mask in the
> ib_uverbs_ex_query_device_resp struct to determine which features are
> supported by the current kernel.
>
Agree - this should hold true for any extended query. Will fix in v1.
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