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

[Vladimir Sementsov-Ogievskiy]

On 24.09.2016 23:14, Carl-Daniel Hailfinger wrote:
> On 24.09.2016 19:33, Vladimir Sementsov-Ogievskiy wrote:
> > On 24.09.2016 20:13, Vladimir Sementsov-Ogievskiy wrote:
> > > I agree that requests larger than disk size are ugly.. But splitting
> > > request brings me again to idea of having separate command or flag
> > > for clearing the whole disk without that dance. Server may report
> > > availability of this/flag command only if target driver supports fast
> > > write_zeroes (qcow2 in our case).
> > Also, such flag may be used to satisfy all needs:
> >
> > flag BIG_REQUEST is set and length = 0    ->    request on the whole
> > disk, offset must be 0
> > flag BIG_REQUEST is set and length > 0    ->    request on
> > (offset*block_size, length*block_size), length*block_size must be <=
> > disk_size
> What happens if length*block_size<=disk_size, but
> offset*block_size+length*block_size>disk_size? Wraparound?

Personally, for me main scenario for is length=0, to clear the whole 
disk. In general allowing requests larger than disk size may not be very 
good idea.. Also:

On 24.09.2016 19:49, Alex Bligh wrote:
> > >May be, additional option, specifying the shift would be better. With 
> > convention that if offset+length exceeds disk size, length should be recalculated 
> > as disk_size-offset.
> I don't think we should do that. We already have clear semantics that prevent 
> operations beyond the end of the disk. Again, just break the command up into 
> multipl commands. No great hardship.

So, most possible answer on your question: it should be an error.

> Regards,
> Carl-Daniel


--
Best regards,
Vladimir