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

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

This interface is already implemented in Linux >= 3.11.


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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