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

[Kevin Wolf <kwolf@redhat.com>]

Am 24.09.2016 um 14:27 hat Vladimir Sementsov-Ogievskiy geschrieben:
> 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 ?

Maybe the best would be to extend the existing discard/write_zeroes
functions to take a 64 bit byte count and then NBD can internally
check whether a request clears the whole disk.

Kevin