Re: [PATCH] target: Pass through I/O topology for block backstores

[Andy Grover <agrover@redhat.com>]

On 10/11/2013 11:03 AM, Christoph Hellwig wrote:
> On Fri, Oct 11, 2013 at 10:40:06AM -0700, Andy Grover wrote:
>> In addition to block size (already implemented), passing through
>> alignment offset, logical-to-phys block exponent, I/O granularity and
>> optimal I/O length will allow initiators to properly handle layout on
>> LUNs with 4K block sizes.
>>
>> Tested with various weird values via scsi_debug module.
>>
>> One thing to look at with this patch is the new block limits values --
>> instead of granularity 1 optimal 8192, Lio will now be returning whatever
>> the block device says, which may affect performance.
>
> Wouldn't it be nicer to have a single method that takes a whole
> queue_limits structure?

It seemed better to me to keep the munging from queue_limits values to 
what the target core needed in the block backstore code, and not use a 
block-specific structure in the backstore<->core interface.

It looks like a few includes of blkdev.h slipped into target core, but 
these can be removed safely -- lio core doesn't depend on the block layer.

We could define a new struct to get the 4 values at once, but it didn't 
seem worth it, esp. since two are only needed by emulate_readcapacity16, 
and the other two only by emulate_evpd_b0.

-- Andy