Re: [Qemu-devel] [PATCHv2 02/11] iscsi: read unmap info from block limits vpd page

[Peter Lieven]

Am 04.07.2013 um 14:37 schrieb Paolo Bonzini <address@hidden>:

> Il 03/07/2013 23:23, Peter Lieven ha scritto:
>> BDC is not used. I had an implementation that sent multiple descriptors out, 
>> but
>> at least for my storage the maximum unmap counts not for each descriptors, 
>> but for all
>> together. So in this case we do not need the field at all. I forgot to 
>> remove it.
>> 
>> discard and write_zeroes will both only send one request up to max_unmap in 
>> size.
>> 
>> apropos write_zeroes: do you know if UNMAP is guaranteed to unmap data if 
>> lbprz == 1?
> 
> Yes.  On the other hand note that WRITE_SAME should be guaranteed _not_
> to unmap if lbprz == 0 and you do WRITE_SAME with UNMAP and a zero
> payload, but I suspect there may be buggy targets here.
> 
>> I have read in the specs something that the target might unmap the blocks or 
>> not touch them at all.
>> Maybe you have more information.
> 
> That's even true of UNMAP itself, actually. :)
> 
> The storage can always "upgrade" a block from unmapped to anchored and
> from anchored to allocated, so UNMAP can be a no-op and still comply
> with the standard.

My concern was, if I UNMAP a block and lbprz == 1 is it guaranteed that it reads
as zero afterwards? Regardless if the target decides to "upgrade" the block or 
do
not unmap the block?

Peter