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Re: [dm-devel] [PATCH] dm_crypt: Issue all previous bios before remapping barrier bio



On Mon, 1 Feb 2010, Milan Broz wrote:

> On 02/01/2010 04:19 PM, Nikanth Karthikesan wrote:
> > Before remapping a barrier bio, make sure that there are no un-issued
> > pending I/O in the workqueue. Otherwise a dm_flush would simply add
> > a barrier request to the underlying device, without issuing the bio's
> > queued in the dm_crypt device.
> 
> This should not be needed. Core dm code waits for all bios submitted before
> barrier requests.
> 
> Mikulas, could you verify it?
> 
> Milan

Yes, you are right, the patch is not needed.

When the target receives an empty barrier request, there are no other data 
requests in flight.

BTW. The target may receive more empty barrier requests simultaneously, if 
it asked for it by setting ti->num_flush_requests to more than one. But 
barrier and non-barrier requests are never mixed.

Mikulas


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