linux-kernel - Re: [PATCH] scsi: virtio-scsi: Fix address translation failure of HighMem pages used by sg list

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Date:	Fri, 27 Jul 2012 08:50:12 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wang Sen <kelvin.xupt@...il.com>
CC:	Boaz Harrosh <bharrosh@...asas.com>,
	Wang Sen <senwang@...ux.vnet.ibm.com>,
	linux-scsi@...r.kernel.org, JBottomley@...allels.com,
	stefanha@...ux.vnet.ibm.com, mc@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: virtio-scsi: Fix address translation failure of
 HighMem pages used by sg list

Il 27/07/2012 05:12, Wang Sen ha scritto:
>> > No this code is correct, though you will need to make sure to properly
>> > terminate the destination sg_list.
> Yes, the terminate marker in the destination list is set when initialization.
> sg_set_page would not break this marker because it saved both the two
> maker bits at sg_asign_page.
> 
> Also, the allocation of destination sg list considered the total number of
> the source sg_list. So, sg_set_page can work correctly.
> 
> The value assignment method also can also work correctly, because the
> termination marker in source sg_list has been set in blk_rq_map_sg(), as
> the last entry of source sg_list is just copied to the the last entry
> in destination
> list.
> 
> Uh, Paolo, Boaz, have  you reached agreement on which method to use?

Let's use the value assignment, and document it in the commit message as
follows:

Value assignment creates a well-formed scatterlist, because the
termination marker in source sg_list has been set in blk_rq_map_sg().
The last entry of the source sg_list is just copied to the the last
entry in destination list.  Note that, for now, virtio_ring does not
care about the form of the scatterlist and simply processes the first
out_num + in_num consecutive elements of the sg[] array.

Paolo
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