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

From: Marcin Dziegielewski
Date: Mon Mar 18 2019 - 09:32:49 EST

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>
 drivers/nvme/host/core.c | 3 ++-
 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 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);


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:

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.



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.