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Re: [Xen-devel] [PATCH 08/11] xen-blkfront: remove bio splitting.

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
Date: Fri, 21 Apr 2017 12:46:22 +0100
Cc: Jens Axboe <axboe@xxxxxxxxx>, NeilBrown <neilb@xxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
Delivery-date: Fri, 21 Apr 2017 11:46:40 +0000
List-id: Xen developer discussion <xen-devel.lists.xen.org>

On Fri, Apr 21, 2017 at 04:36:20AM -0700, Christoph Hellwig wrote:
> Btw, I really don't understand why this code even looks at bios over
> just requeueing the request.  Can someone explain that bit to me?

This was done because Linux could migrate from a host supporting indirect
descriptors to a host not supporting them, and so the maximum number of
segments per request could change, and the requests already on the queue might
need to be split.

Roger.

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References:
- [Xen-devel] [PATCH 00/10] block: assorted cleanup for bio splitting and cloning.
  - From: NeilBrown
- [Xen-devel] [PATCH 08/11] xen-blkfront: remove bio splitting.
  - From: NeilBrown
- Re: [Xen-devel] [PATCH 08/11] xen-blkfront: remove bio splitting.
  - From: Christoph Hellwig

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