Re: [Qemu-devel] [PATCH v4 21/23] block: Align block status requests

[Eric Blake <eblake@redhat.com>]

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On 09/13/2017 11:03 AM, Eric Blake wrote:
> Any device that has request_alignment greater than 512 should be
> unable to report status at a finer granularity; it may also be
> simpler for such devices to be guaranteed that the block layer
> has rounded things out to the granularity boundary (the way the
> block layer already rounds all other I/O out).  Besides, getting
> the code correct for super-sector alignment also benefits us
> for the fact that our public interface now has byte granularity,
> even though none of our drivers have byte-level callbacks.
> 
> Add an assertion in blkdebug that proves that the block layer
> never requests status of unaligned sections, similar to what it
> does on other requests (while still keeping the generic helper
> in place for when future patches add a throttle driver).  Note
> that iotest 177 already covers this (it would fail if you use
> just the blkdebug.c hunk without the io.c changes).  Meanwhile,
> we can drop assertions in callers that no longer have to pass
> in sector-aligned addresses.

Bummer - 'git bisect' says this patch causes iotests 190 to hang.  I'm
investigating root cause, but I'll have to post a fixup once I figure it
out.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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