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

[Vladimir Sementsov-Ogievskiy]

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 ?

--
Best regards,
Vladimir