Re: [Qemu-block] [Qemu-devel] [PATCH v2 03/15] block: Add flag to avoid wasted work in bdrv_is_allocated()

[Eric Blake]

On 07/05/2017 07:07 AM, Fam Zheng wrote:
>>>
>>> Sorry for bikeshedding.
>>
>> Not a problem, I also had some double-takes in writing my own code
>> trying to remember which way I wanted the 'allocation' boolean to be
>> set, so coming up with a more intuitive name/default state in order to
>> help legibility is worth it.  Do any of my above suggestions sound better?
>>
> 
> I'd vote for "mapping" because it has a close connection with offset (as in
> BDRV_BLOCK_OFFSET_VALID).
> 
> Or simply call it "offset" and if false, never return BDRV_BLOCK_OFFSET_VALID.

Well, there ARE drivers that WANT to return BDRV_BLOCK_OFFSET_VALID
regardless of the state of the boolean (namely, any driver that also
returns BDRV_BLOCK_RAW, to hint that this is a passthrough and the query
should be repeated at the next BDS in the chain).  So stating that
'offset' is false MUST preclude BDRV_BLOCK_OFFSET_VALID is a bit too
strong, but I can probably come up with appropriate wording that meets
in the middle ground (if 'offset' is true, then make all efforts to
include BDRV_BLOCK_OFFSET_VALID in the return if that is possible; if it
is false, then omitting the flag in order to get a larger pnum is
acceptable)).

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

signature.asc
Description: OpenPGP digital signature