Re: [Qemu-devel] write_zeroes/trim on the whole disk

[Paolo Bonzini]

On 24/09/2016 14:27, Vladimir Sementsov-Ogievskiy wrote:
> On 24.09.2016 15:06, Vladimir Sementsov-Ogievskiy wrote:
>> On 24.09.2016 00:21, Wouter Verhelst wrote:
>>> On Fri, Sep 23, 2016 at 02:00:06PM -0500, Eric Blake wrote:
>>>> My preference would be a new flag to the existing commands, with
>>>> explicit documentation that 0 offset and 0 length must be used with
>>>> that
>>>> flag, when requesting a full-device wipe.
>>> Alternatively, what about a flag that says "if you use this flag, the
>>> size should be left-shifted by X bits before processing"? That allows
>>> you to do TRIM or WRITE_ZEROES on much larger chunks, without being
>>> limited to "whole disk" commands. We should probably make it an illegal
>>> flag for any command that actually sends data over the wire, though.
>>
>> Note: if disk size is not aligned to X we will have to send request
>> larger than the disk size to clear the whole disk.
> 
> Also, in this case, which realization of bdrv interface in qemu would be
> most appropriate? Similar flag (in this case X must be defined in some
> very transparent way, as a constant of 64k for example), or flag
> BDRV_REQ_WHOLE_DISK, or separate .bdrv_zero_all and .bdrv_discard_all ?

This makes nice sense.

It also matches the SANITIZE command from the SCSI command set.

Paolo