> -----Original Message-----
> From: Christoph Hellwig [mailto:[email protected]]
> Sent: Monday, October 15, 2018 5:28 PM
> To: Daniel Verkamp <[email protected]>
> Cc: [email protected]; [email protected];
> Michael S. Tsirkin <[email protected]>; Jason Wang <[email protected]>;
> Jens Axboe <[email protected]>; Stefan Hajnoczi <[email protected]>; Liu,
> Changpeng <[email protected]>
> Subject: Re: [PATCH v8] virtio_blk: add discard and write zeroes support
>
> On Fri, Oct 12, 2018 at 02:06:28PM -0700, Daniel Verkamp wrote:
> > From: Changpeng Liu <[email protected]>
> >
> > In commit 88c85538, "virtio-blk: add discard and write zeroes features
> > to specification" (https://github.com/oasis-tcs/virtio-spec), the virtio
>
> There is some issues in this spec. For one using the multiple ranges
> also for write zeroes is rather inefficient. Write zeroes really should
> use the same format as read and write.
Because there is no length parameter for virtio block specification, adding the
two extra commands will not break the existing specification and driver
implementation.
Also existing Linux implementation for write zeroes will not use multiple
segment
at all so there is always one range in practice.
>
> Second the unmap flag isn't properly specified at all, as nothing
> says the device may not unmap without the unmap flag. Please take
> a look at the SCSI or NVMe Ń•pec for some guidance.
The unmap flag is only used for write zeroes command, as discard command will
not
guarantee the spaces will be zeroed, so adding this flag means (Discard + Write
Zeroes),
so this definitely is backend related, the backend implementation can use same
code
to implement discard and write zeroes commands.
>
> > +static inline int virtblk_setup_discard_write_zeroes(struct request *req,
> > + bool unmap)
>
> Why is this an inline function?
