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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 12-12-2007, 11:53 AM
James Bottomley
 
Default blk_end_request: add new request completion interface (take 4)

On Tue, 2007-12-11 at 17:40 -0500, Kiyoshi Ueda wrote:
> This patch adds 2 new interfaces for request completion:
> o blk_end_request() : called without queue lock
> o __blk_end_request() : called with queue lock held
>
> blk_end_request takes 'error' as an argument instead of 'uptodate',
> which current end_that_request_* take.
> The meanings of values are below and the value is used when bio is
> completed.
> 0 : success
> < 0 : error
>
> Some device drivers call some generic functions below between
> end_that_request_{first/chunk} and end_that_request_last().
> o add_disk_randomness()
> o blk_queue_end_tag()
> o blkdev_dequeue_request()

If we can roll the whole thing together, that would be nice. However,
the way you're doing it with this patch, we now have an asymmetrical
interface: The request routine must explicitly start the tag, but now
doesn't have to end it.

We really need symmetry. Either go back to start tag/end tag, or absorb
the whole lot into the block infrastructure.

The original reason for the explicit start/end is that there are some
requests on a tagged device that aren't able to be tagged by the block
layer (some devices reserve tag numbers for specific meanings).
However, I don't think there's any driver that actually implemented this
feature.

James


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