Re: [Xen-devel] [PATCH] blkif: add indirect descriptors interface to public headers

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/29/2013 10:28 AM, Ian Campbell wrote:
> On Fri, 2013-11-29 at 10:14 +0000, Jan Beulich wrote:
> > > > > On 28.11.13 at 18:02, Roger Pau MonnÃ<roger.pau@xxxxxxxxxx> wrote:
> > > On 12/11/13 11:36, Roger Pau Monne wrote:
> > > > Indirect descriptors introduce a new block operation
> > > > (BLKIF_OP_INDIRECT) that passes grant references instead of segments
> > > > in the request. This grant references are filled with arrays of
> > > > blkif_request_segment_aligned, this way we can send more segments in a
> > > > request.
> > > >
> > > > This interface is already implemented in Linux >= 3.11.
> > > Ping?
> > >
> > > I think all comments regarding this patch have been resolved.
> > So do I; I continue to have this in my to-be-applied list, pending
> > the necessary ack from Keir.
> I also had it in my queue and was thinking of applying it.
>
>
> There are some implicit holes in the struct on 64-bit though (e.g.
> between nr_segments and id). Perhaps you could add to your list making
> these more explicit as a general clean up, at least with a doc comment,
> if not an actual pad field? (Might be worth waiting for dissenting
> opinions on that though)
>
> Julien, IIRC you found an issue with the blk struct alignments on ARM
> (not related to this patch -- it just reminded me). That was a Linux
> side thing, right? Did you send a fix?
Yes, on ARM (32 and 64 bits), the structure are aligned on 64 bits. 
Linux headers use packed attribute. So the header on the Xen and Linux 
doesn't provide the same structure.
I didn't yet send a fix yet, because we only support Linux for now and 
we will likely broke compatibility with older Linux. Do we want the fix now?
--
Julien Grall

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