Re: [Qemu-devel] [PATCHv2 07/11] iscsi: let bdrv_create conditionally zero out the device

[Paolo Bonzini]

Il 02/07/2013 12:56, Peter Lieven ha scritto:
> 
> Am 02.07.2013 um 12:49 schrieb Paolo Bonzini <address@hidden>:
> 
>> Il 02/07/2013 12:36, Peter Lieven ha scritto:
>>>>>> Perhaps we can have a new "discard_zeroes" field in bdrv_get_info, and
>>>>>> the unmap functionality can be moved up to qemu-img convert?
>>>>>
>>>>> Is there any other storage protocol out there that could benefit from it?
>>>>
>>>> Definitely LVM.  Perhaps in the future gluster too, though right now it
>>>> only supports discard on files, not block devices.
>>>
>>> Is discards on LVM sth that is already implemented in qemu?
>>
>> Yes, it supports BLKDISCARD (see handle_aiocb_discard in
>> block/raw-posix.c).  Of course there is no way to query the host
>> discard_zeroes setting yet.
> 
> No way in qemu or no way at all?

No way in QEMU.  Linux has the BLKDISCARDZEROES ioctl, it takes an int*
as the third argument and puts 0/1 in it.

Paolo