Re: [PATCH] nvme: lightnvm: expose OC devices as zero size to OS

[Matias BjÃrling]

On 3/18/19 2:32 PM, Marcin Dziegielewski wrote:
> On 3/14/19 2:56 PM, Matias BjÃrling wrote:
> > On 3/14/19 6:41 AM, Marcin Dziegielewski wrote:
> > > Open channel devices are not able to handle traditional
> > > IO requests addressed by LBA, so following current
> > > approach to exposing special nvme devices as zero size
> > > (e.g. with namespace formatted to use metadata) also
> > > open channel devices should be exposed as zero size
> > > to OS.
> > >
> > > Signed-off-by: Marcin Dziegielewski <marcin.dziegielewski@xxxxxxxxx>
> > > ---
> > > Â drivers/nvme/host/core.c | 3 ++-
> > > Â 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > > index 07bf2bf..52cd5c8 100644
> > > --- a/drivers/nvme/host/core.c
> > > +++ b/drivers/nvme/host/core.c
> > > @@ -1606,7 +1606,8 @@ static void nvme_update_disk_info(struct 
> > > gendisk *disk,
> > > ÂÂÂÂÂ if (ns->ms && !ns->ext &&
> > > ÂÂÂÂÂÂÂÂÂ (ns->ctrl->ops->flags & NVME_F_METADATA_SUPPORTED))
> > > ÂÂÂÂÂÂÂÂÂ nvme_init_integrity(disk, ns->ms, ns->pi_type);
> > > -ÂÂÂ if (ns->ms && !nvme_ns_has_pi(ns) && !blk_get_integrity(disk))
> > > +ÂÂÂ if ((ns->ms && !nvme_ns_has_pi(ns) && !blk_get_integrity(disk)) ||
> > > +ÂÂÂÂÂÂÂ ns->ndev)
> > > ÂÂÂÂÂÂÂÂÂ capacity = 0;
> > > ÂÂÂÂÂ set_capacity(disk, capacity);
> >
> > Marcin,
> >
> > The read/write as traditional I/Os feature is supported in OCSSD 2.0. 
> > For example, one can hook support up through the zone device support 
> > in the kernel. There is a patch here that enables it here:
> >
> > https://github.com/OpenChannelSSD/linux/commit/e79e747601a315784e505d51a9265e82a3e7613c 
> >
> >
> > With that, an OCSSD device can be used as a traditional zoned block 
> > device, and use the existing infrastructure. Which is really neat.
> >
> > It is not upstream, since it depends on some features that we 
> > introduce with zoned namespaces, but in general, tools can read/write 
> > from a block device as any other, just honoring the special write 
> > rules that are for OCSSD/zoned block devices.
> >
> > -Matias
>
> Matias,
>
> If zone related changes will be in upstream soon, I agree that this 
> patch is not needed.
>
> But, I can not agree that tools can use OCSSD device as normal block 
> device - for example in current implementation I don't see way to send 
> erase request and of course without it we can not send write. Because of 
> that, it was my intention to block normal IO to OCSSD device by default.
>
> Marcin

It is implemented the same way as "Zone reset" is implemented in 
ZAC/ZBC. The kernel converts the trim to a vector erase and issues that 
instead.